Industrial ERG

CHAPTER 13 WORK-RELATED MUSCULOSKELETAL DISORDERS

LEARNING OBJECTIVE

At the end of the module, the students will have a basic understanding of various musculoskeletal disorders that are caused by occupational exposure to physical workplace risk factors. Anatomy of the muscular and skeletal systems is covered as well as injury and disorder prevention techniques.

INTRODUCTION

Musculoskeletal disorders are a broad class of disorders involving damage to muscles, tendons, ligaments, peripheral nerves, joints, cartilage, vertebral discs, bones, and/or supporting blood vessels. Work-related musculoskeletal disorder (WMSD) is a subcategory; these are injuries and illnesses that are caused or aggravated by working conditions. MSDs are not typically caused by acute events but occur slowly over time due to repeated wear and tear or microtraumas.

WMSDs are also known as cumulative trauma disorders (CTDs), repetitive strain injuries (RSIs), repetitive motion trauma (RMT), or occupational overuse syndrome. Examples of WMSDs include herniated disc, epicondylitis (tennis elbow), tendinitis, de Quervain's disease (tenosynovitis of the thumb), trigger finger, and Reynaud's syndrome (vibration white finger).

Researchers have identified specific physical workplace risk factors for the development of WMSDs: force, posture, compression, repetition, duration, vibration, and temperature. Exposure to these risk factors can result in decreased blood flow, elongation, compression, tears or strains to muscles, tendons, ligaments and nerves as well as disc or joint damage. When present for sufficient duration, frequency, or magnitude, physical workplace risk factors may cause WMSDs. In addition, personal risk factors, such as physical conditioning, existing health problems, gender, age, work technique, hobbies and organizational factors (e.g., job autonomy, quotas, deadlines) contribute to, but do not cause, the development of WMSDs.

Applying ergonomics principles to reduce a worker's exposure to the physical workplace risk factors decreases the chance of injury.

This unit is not designed to impart skills in the diagnoses of WMSDs, only occupational healthcare providers do so. This unit is a background in some of the more common WMSDs and explores anatomic features that are affected by WMSDs. It is written from the view point of an ergonomist and not a healthcare provider. For convenience, this chapter is divided into four sections:

· The musculoskeletal system

· Disorders of the

· spine

· upper extremities

· lower extremities.

THE MUSCULOSKELETAL SYSTEM

The musculoskeletal system's primary functions include supporting the body, allowing motion, and protecting vital organs. The musculoskeletal system is an organ system that gives humans the ability to move using their muscular + skeletal systems (musculoskeletal). The musculoskeletal system provides form, support, stability, and movement to the body. It is made up of the bones of the skeleton, cartilage (framework), muscles (movement), tendons, ligaments, and other connective tissue (support–connectivity) that supports and binds tissues and organs together ( Figure 13.1 ).

Figure 13.1  Parts of the musculoskeletal system (Used with permission Clip Art LLC;  http://www.clipartof.com/cgi-bin/download_image.pl?q=1299636_SMJPG_7GN82358YB166203F.jpg )

The skeleton is the framework of the human anatomy ( Figure 13.2 ), supporting the body and protecting its internal organs. Two hundred and six bones compose the skeleton, about half of which are in the hands and feet. Most of the bones are connected to other bones at flexible joints, which lend the framework a high degree of flexibility (see  Figure 13.3 ). Only one bone, the hyoid, is not directly connected to another bone in such an articulation.

Figure 13.2  Skeleton (Adapted with permission from Ergonomics Image Gallery)

Figure 13.3  Types of joints (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Humans have over 650 muscles that differ in size according to the jobs they do. These muscles constitute 40% of body weight. The special function of muscle tissue is contraction, making the muscle shorter and thicker. There are three kinds of muscle tissue: striated muscle, smooth muscle, and cardiac muscle. Most of the body's muscle consists of striated muscle, which is the skeletal muscle. It is also called a voluntary muscle because it can be consciously controlled via the central nervous system, unlike the cardiac muscles.

Muscles are named according to their shape, location, or a combination (see Figure 13.4). They are further categorized according to functions such as flexion, extension, or rotation (see Figure 13.5). For example, the subscapularis is in interior scapula muscle, the biceps brachii is a branched (three-headed) biceps muscle. Muscles, tendons, and ligaments work together to support the body, hold it upright, and control movement during rest and activity. Skeletal muscles help move the skeleton. Skeletal muscles contract when stimulated by a nerve. They can pull on the skeleton in the direction of the contraction. Muscles can only pull so they need to be arranged in antagonistic (or opposing) pairs; that is, one muscle in the pair contracts, while the other relaxes. The two muscles work together to produce movement of a joint, to steady a joint, and to prevent movement. For example, the biceps muscles contract, and your forearm is pulled toward your upper arm (flexion). Then your triceps muscles contract to pull your forearm away from your upper arm (extension) (Figures 13.6 and 13.5). This is an example of an antagonistic pair, one causes flexion (angle gets smaller) and the other causes extension (angle gets larger). Tendons and ligaments bear a burden of forces during muscular contraction and, therefore, are common injury sites for WMSD when the physical workplace risk factors go uncontrolled.

Figure 13.4  Different muscle shapes (Adapted from Clip Art Explosion)

Figure 13.5  Biceps and triceps muscles (Adapted from Clip Art Explosion)

Figure 13.6  Muscles in motion (Adapted from http://navylive.dodlive.mil/2011/12/22/u-s-navy-seabees-building-bridges/)

Muscles are attached to bone either directly or indirectly (via tendons). The muscle + skeleton system can be thought of as a machine. The nerves provide the energy to power the muscles. Muscles shorten and pull on a tendon (a cable). The levers are the bones that results in movement around a joint. Ligaments typically, but not always, provide the tunnels for the tendons to pass under and stabilize bones by crossing joints (Figure 13.7).

Figure 13.7  Bones, tendons and muscles and levers, cables and pulleys (Adapted with permission from Lippincott Williams & Wilkins, Baltimore, MD; http://www.clipartof.com/download?txn=577e6995e66d8d9c7f0dc5d21e5f9aa2)

Tendons

Tendons are an integral part of the musculoskeletal system. These sturdy bands of fibrous tissue attach muscles to bones; they pretty much hold it all together. Tendons are like cables, their length and thickness depending on their function;  Figure 13.7 , for example, shows wide, thick tendons supporting the hip versus long, thin tendons for fast, repetitive finger movements. Tendons transfer forces for movement from the muscles to the skeletal system (bones) and are common sites for WMSD injury. Tendon disorders generally occur at or near the joint where, surrounded by synovial sheaths, the tendon rubs on adjacent ligaments or bones. Repetitive movements or awkward posture can cause friction between the tendon and the bone, resulting in heat or inflammation at that site as well as wear. Think of a wire cable rubbing against a seized pulley.

To understand how tendons become diseased, one must understand tendon function and repair mechanisms. As muscles contract, tendons are subjected to mechanical loading and viscoelastic deformation. Tendons must have both tensile resistance to loading (to move attached bones) and elastic properties (to enable bones to move around turns, as in the hand). When placed under tension, tendons first elongate without significant increase in stress. With increased tension, tendons become stiffer in response to this further loading. If the load on these structures exceeds the elastic limit of the tissue (its ability to recoil to its original configuration), permanent changes occur. During subsequent loading of the damaged tendon, less stiffness is observed (i.e., more creep). In addition, if recovery time between contractions is too short, deformation can result in pathologic changes that decrease the tendon's ultimate strength.

· Tensile strength is resistance of a material to forces tending to tear it apart.

· Shear stress results when a force tends to make part of the body or one side of a plane slide past another.

· Stress is the internal force exerted by one part of an elastic body upon the adjoining part.

· Strain is the deformation or change in dimension occasioned by stress.

· Stress causes strain.

Tendons and ligaments are elastic and will “creep” (i.e., stretch) in response to tensile loading. Creeping involves progressive fiber recruitment and loss of the natural waviness of collagen fibers. That is, when a tendon is subjected to prolonged elongation and loading, the magnitude of the tensile force will gradually decrease (relaxation) and the length of the tendon will gradually increase (creep) to a level of equilibrium. Picture an outstretched arm carrying a 5-lb paint bucket. During repetitive loading, the tendon exhibits these properties and then recovers if there is sufficient recovery time. If the time interval between loadings does not permit restoration, then recovery can be incomplete, even if the elastic limit is not exceeded. The natural recovery property of a tendon (ligament or muscle) can be maintained or enhanced through administrative controls such as job rotation or engineering controls, which make a physical change to the workplace to match it to the workers capabilities ( Figure 13.8 ).

Figure 13.8  Worker in one neutral posture is likely to develop a WMSD of the upper extremities or spine

Tendons are also subject to perpendicularly oriented compressive loading. This is seen when tendons are loaded as they turn corners, around pulleys, or bony surfaces. Friction is generated at these locations as the tendon slides against adjacent surfaces, causing a shearing force. This friction is significant in the hand and wrist. Higher levels of muscle tension are required to achieve a specific level of strength at the fingertip during nonneutral wrist postures, and those tendons are subject to greater shear stress with nonneutral wrist postures. Tendon friction is proportional to the axial tension of the tendon, the coefficient of friction between the tendon and its adjacent surface, and the angle of the tendon as it turns about a pulley. This may be a cause of surface degeneration in tendons. Internal degeneration may be the result of friction-induced internal heat generation.

Tendons are surrounded by a protective slippery sheath called a synovial sheath. A synovial sheath is a tubular bursa surrounding a tendon. Tendon tissue slides or glides in the sheath due to synovial fluid within the sheath. Passage of blood vessels and nerves into the tendon tissue is through the sheath. Damage or compression of the sheath can reduce blood flow to the tendon and eventually contribute to degradation.

Initial symptoms of tendon MSD include impaired motion, tenderness, pain on resisted contraction or passive stretch, swelling, or crepitation. With time, swelling and thickening of the tendon may occur from fibril disruption, partial laceration, impairment of blood flow and diffusion of metabolites, and the localized repair process. Ultimately, this limits the normal smooth passage of the tendon through its fibro-osseous canal. These chronic tissue changes are recognized as triggering.

Ligaments

Ligaments are fibrous bands or sheets of connective tissue linking two or more bones, cartilages, or structures together. One or more ligaments provide stability to a joint. Excessive movements such as hyperextension or hyperflexion may be restricted or prevented by ligaments (Figure 13.9).

Figure 13.9  Knee ligaments in the knee are numerous and vary in direction to provide stability and support (Adapted with permission from Shutterstock)

Movement of the body occurs about joints and between adjacent bones. Ligaments connect and hold all bones together (bone to bone). The ligaments allow the bones to move in all directions. These ligaments meld together to form the joint capsule. A joint capsule is a watertight sack of tissue that surrounds the bones and holds them close tightly together; a joint capsule around ligaments is similar to a synovial sheath or bursa round tendons. The inside of the capsules are lined with synovial membrane, which secrete synovial fluid, a mucus-like fluid that provides lubrication and nutrition to the articulating surface of the bones. The articulating surfaces are covered with cartilage. Cartilage becomes very slippery when lubricated with synovial fluid so that the adjacent surfaces slide against each other with very little resistance.

The biomechanical properties of ligament damage parallel those of tendons and were discussed previously. Ligaments are subject to creep, compression, deformation, and strain. Blood flow to ligaments is very slow, therefore, hastens recovery. Muscles have good blood flow, therefore, heal faster than tendons and ligaments.

Cartilage

Articulating surfaces of bones are covered with a shiny, smooth, white connective tissue called cartilage. Cartilage contributes to the synovial capsule of a joint and protects the underlying bone. The function of articular cartilage is to absorb shock and provide an extremely smooth surface to make motion easier. Articular cartilage can be up to one-quarter of an inch thick in the large, weight-bearing joints such as a hip. It is a bit thinner in joints such as the elbow, which does not support as great of a weight.

When movement occurs, joint cartilage is subject to two types of stress: gravitational pressure, particularly from weight-bearing joints of the legs and feet, and friction from the movement itself (picture of body and weights). Cartilage is well adapted to these stresses being strong, resilient, and smooth. Thus, it can absorb shock and allow sliding of bones relative to each other. Cartilage can become damaged by either blunt trauma or excessive wear. Rheumatoid arthritis and osteoarthritis (OA) are two common diseases involving damage to joint cartilage accompanied by inflammation, pain, and stiffness of the joint and surrounding muscles.

Joint cartilage does not contain blood vessels. It receives nutrients from the synovial fluid. Damage to the joint capsule can lead to cartilage deterioration. Cartilage has poor regenerative capacity and is, therefore, reluctant to heal. In addition, cartilage serves as a shock-absorbing function to protect underlying bone; once it is worn down, more force is transferred to the bone. This cycle highlights the importance of reducing an accumulation of microtraumas by limiting exposure to the physical workplace risk factors (Table 13.1).

Table 13.1  Stages of WMSD

Stage 1 – Usually shows aches and fatigue during the working hours, but with rest at night and days off work these aches seem to settle. This stage: 1.  Shows no drop in performance 2.  May persist for weeks or months 3.  Can be reversed

Stage 2 – Same symptoms occur early in the work shift and sleep does not settle the pain, in fact, sleep may be disturbed. This stage: 1.  Shows performance of the task is reduced 2.  Usually persists over months 3.  Can be reversed

Stage 3 – Symptoms persist while resting. Pain occurs while performing nonrepetitive movements. This stage: 1.  The person is unable to perform even light tasks 2.  May last for months or years 3.  Usually not reversible

Nerves

The nerves that control our voluntary and involuntary movement exit the spinal column in different regions. Injury of any form to a specific vertebrae area of the spine can affect other areas of the body. For example, a neck problem can cause pain or reduced strength in the arms and hands (Figure 13.10).

Figure 13.10  Nerve paths in the body (With permission Lippincott Williams & Wilkins, Baltimore, MD)

Muscles

The exact number of muscles that are contained in the human body is unknown. There are all sizes of muscles, ranging from the larger skeletal muscles of your leg, down to muscles that are literally “fibers” found attached to your spine. Muscles of the human body can be broken down into three categories: cardiac, skeletal, and smooth muscles. These three categories can be broken up into two subcategories: voluntary and involuntary muscles. In general, muscles have only two functions. Either they contract or they relax. In the MS system, we are most concerned with the voluntary skeletal muscles.

Muscles are composed of thousands of tiny fibers all running in the same direction. They are red because they are filled with many blood vessels that supply them with oxygen and nutrients and carry away carbon dioxide and waste materials. Muscles can be injured in three ways. First, muscles fibers can be strained or irritated, causing temporary aching and swelling. Second, and more seriously, a small group of fibers can be torn apart. Third, a muscle may be subjected to a severe blow and crushed, breaking many of its blood vessels and causing blood to seep into a broader area.

Skeletal Muscles

Of the two major muscle groups, voluntary and involuntary, the skeletal are voluntary muscles. Over 600 skeletal muscles have been discovered and named. Again, it is important to remember that our muscles either contract or relax . It is how we sit up; in general, the muscles of our thigh contract as the muscles of our posterior leg relax. Muscles can work in an antagonistic way (a muscle that opposes the action of another muscle, as by relaxing while the other one contracts, thereby producing smooth, coordinated movement) or agonistic way (working with another muscle or group of muscles to perform a certain action). So, why are skeletal muscles classified under the subcategory of “voluntary”? Voluntary muscle movements mean that we have control over their actions. For example, if they decide they want to flex their bicep, or decide to walk up the stairs, or throw a right hook, they are voluntarily creating these actions through a series of signals you send and receive to and from the brain.

Skeletal muscles originate at a certain part of a bone, and insert at another part of the bone, either on the same bone or a different bone. When we contract and relax our skeletal muscles, we cause movement of our bones. It can be stated that the larger the muscle, the stronger it is; and generally, the larger the muscle, the greater range of motion. Vern Putz-Anderson (1998) summarizes of various WMSDs identified by profession. For example,

· Letter carriers are prone to shoulder problems and thoracic outlet syndrome from carrying heavy loads with a shoulder strap.

· Musicians are prone to carpal tunnel and epicondylitis from repetitive wrist movements and palmer-based pressure.

· Material handlers are prone to thoracic outlet and shoulder-tendinitis from carrying heavy loads.

· Workers who grind are at risk of tenosynovitis, thoracic outlet, and de Quervain's from repetitive wrist motions and prolonged flexed shoulder postures. Vibration and forceful ulnar deviations and repetitive forearm pronation.

INTRODUCTION TO THE SPINE

The spine is one of the most important, sophisticated, and complex structures in the body. The spine is affected by almost every movement made.

The following structures are critical to proper spine function. Injury to any of the components of the spine may provoke disease and pain. Some forms of back injuries can be caused by a single event such as a heavy awkward lift. Disc injury can also occur from wear and tear caused by repeated trauma over a period of months or years, for example, loading a delivery truck.

The Vertebral Column

The vertebral column comprises the posterior aspect of the trunk. A normal vertebral column is comprised of 33 irregular-shaped bones that are called vertebrae. The vertebral column, also called the spine, extends from the base of the neck to the pelvis. An inaccurate assumption is to think that the spine is a rigorous supporting rod. The vertebrae are connected in such a way that a movable “S”-curved structure is created. Its major functions are to distribute weight of the trunk evenly to the lower limbs while protecting the spinal cord and providing attachment points for the ribs and muscles of the neck and back as well as providing a pathway for nerves from the central nervous system of the brain to the distal regions of the body.

Spinal Regions

We can think of the vertebral column as a series of fixed segments (the vertebrae that are bones) having mobile connections (discs, tendons, and ligaments). Movement of individual vertebrae is compounded such that the entire structure has considerable mobility in three dimensions. The type and extent of mobility varies with different spinal regions, depending on size and shape of vertebrae, body, and other factors. Each vertebra is attached to its neighbor by three joints, the intervertebral disc (posterior) and two pair of facets. The bodies are joined by the fibrocartilaginous. Joints allow motion (articulation). The joints in the spine are commonly called facet joints (Figure 13.11).

Figure 13.11  Curves and sections of the spine (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Each vertebrae pair is limited in motion; however, each small movement over the length of the vertebral column allows a wide range of motion. Flexion (bending forward) and extension (bending backward) movements encompass a wider range of motion when compared to lateral flexion (bending sideways) and rotation of the spine.

The cervical spine beginning at the base of the skull has seven vertebrae with eight pairs of cervical nerves responsible for controlling the neck, arms, and upper body (reference Figure 13.11). This vertebral group is sturdy enabling it to support the weight of the head. The amount of stress placed on these vertebrae varies with movement and posture. This area of the spine is very movable.

Directly below  the cervical region the thoracic portion of the spine starts. There are 12 vertebrae and 12 pairs of ribs, as well as nerve roots that control the midsection of the body. The ribs form the chest wall and protect many internal organs. This section of the spine is fairly immovable (try to move this area without moving your neck or lower back).

The third part of the spine is the lumbar vertebrae. There are normally five lumbar bones. However, some people have one less or one more. These vertebrae are the largest and strongest of the three regions (cervical, thoracic, and lumbar) because these carry the bulk of the body's weight. Five pairs of lumbar nerves manipulate the movement and sensory functions of the lower extremities. The lumbar region is the segment of the spine under the most pressure because it is on the bottom of the spine. When a person bends over, the lumbar region is asked to bend but still maintain the strength to hold up the spine.

A mass of five smaller bones, which are naturally fused together, is after the last lumbar vertebra. This bone mass is named the sacrum. Below the sacrum is the coccyx or tailbone made up of four little bones fused together. The sacrum and coccyx do not look like the other vertebrae. The pairs of nerve roots originating from this area are responsible for the action of the pelvic organs and buttock muscles. The sacrum and tailbone could be considered the basement and sub-basement of the building.

Maintaining the Curves

There are several characteristics curvatures of the vertebral column (reference Figures 13.11 and 13.12).

· Sacrum, convent toward the back

· Concave lumbar region (the term lordosis can refer either to an exaggeration of this curvature or to the normal condition

· Convex thoracic region (kyphosis)

· Concave cervical region.

Figure 13.12  Neutral and awkward spinal postures (Adapted with permission from Ergonomic Image Gallery)

Exact form of these curvatures varies between people.

Reducing the biomechanical loading on the spine is a key element in prevention against spinal injury. This can be done by:

· practicing proper postural alignment or a neutral spine when sitting, standing, and moving;

· including aerobic and flexibility exercises;

· getting enough rest.

The word posture comes from the Latin verb ponere, which means “to put or place.” The general concept of human posture refers to “the carriage of the body as a whole, the attitude of the body, or the position of the limbs (the arms and legs).”

· Webster's New World Medical Dictionary defines neutral posture as the stance that is attained "when the joints are not bent and the spine is aligned and not twisted. Neutral posture has given rise to the idea of achieving “ideal posture”. Ideal posture indicates proper alignment of the body's segments such that the least amount of energy is required to maintain a desired position. The benefit of achieving this ideal position would be that the least amount of stress is placed on the body's tissues. In this position, a person is able to completely and optimally attain balance and proportion of his or her body mass and framework, based on his or her physical limitations. Good posture optimizes breathing and affects the circulation of bodily fluids.

Spinal Discs and Vertebra

Each vertebra consists of two main parts: the massive body and the vertebral arch (Figure 13.13). The arch in turn can be divided into many parts that are sites for ligament and tendon attachments. The opening between the body and the arch is called the vertebral foramen. As foramina of many vertebrae are lined up, they form the vertebral canal through which the spinal cord passes. The spaces between the pedicles of adjacent vertebra from a series of openings called intervertebral foramina. As spinal nerves branch off the spinal cord, they exit through these foramina (Figure 13.14).

Figure 13.13  Parts of the vertebral body (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Figure 13.14  Parts of the spinal disc (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Each vertebrae is attached to its neighbor by three joints, two facets and a disc. Each vertebrae has two sets of facet joints. Posteriorly, two facets of the top vertebra connect two superior facets of the bottom vertebra. The bodies of the vertebrae are joined by the fibrocartilaginous intervertebral. These discs are comprised of a nucleus pulposus (inside) and an annulus fibrosus (outer rim). The nucleus pulposus, or fluid-like substance, which occupies the center portion of the disc, acts as a cushion and a shock-absorbing apparatus during activities such as walking, running, and jumping. The pulpy nucleus flattens and the annulus, or outer sheath that encompasses the nucleus pulposus, bulges when weight is applied, as occurs during standing and more so during lifting. During flexion and extension movements, the nucleus pulposus serves as a fulcrum. The annulus is simultaneously placed under compression on one side and tension on the other (Figure 13.15).

Figure 13.15  Disk movement during bending (Adapted with permission from Ergonomics Image Gallery)

At birth, 80% of the disc is composed of water. In order for the disc to function properly, it must be well hydrated. The nucleus pulposus is the major carrier of the body's axial load and relies on its water-based contents to maintain strength and pliability.

Clinical evidence shows that occupational low-back injuries occur most often at the intervertebral disc between L5 and the sacrum S1. Damage to cartilaginous end place of the intervertebral disc may be one of the causes of these injuries. Cumulative damage to the cartilage end places hampers the flow of important nutrients to the disc and provides disc degeneration. As the disc degenerates, there is an increased risk of disc failure, subsequent alteration of the spinal geometry and eventually pain resulting from vertebral pressure on adjacent spinal nerves. Damage to the spinal discs can go undetected until significant degeneration occurs due to the lack of nerve fibers in the cartilage endplate.

The Core Muscles

The “core” is a group of muscles that surrounds the trunk. The main function of the core is to stabilize and protect the spine and pelvis when the body is in motion. Major muscles included are the pelvic floor muscles (PFM), transversus abdominis (TA), multifidus (MF), internal and external obliques, rectus abdominis, erector spinae (sacrospinalis) especially the longissimus thoracis, and the diaphragm. Minor core muscles include the latissimus dorsi, gluteus maximus, and trapezius (Figure 13.16).

Figure 13.16  Frontal view of the core muscles (Adapted from Clip Art LLC)

There are four main muscle groups that make up the core: transversus abdominus, multifidus, PFM, and the diaphragm. TA is the deepest abdominal muscle that wraps around your abdomen like a corset and is connected to tissue surrounding the spine. When TA contracts, it is similar to the corset being tightened, therefore, assisting in increasing the pressure inside the abdomen that provides increased stability to the spine. MF is a deep lower back muscle that makes up the back part of the core. It is an important postural muscle that helps keep the spine erect. The PFMs are the bottom part of the core or the bathroom muscles and help to stabilize the pelvis. The diaphragm makes up the top part of the core. When all of these muscles contract simultaneously, they help to maintain the pressure in the abdomen, which then provides the stability to the spine and pelvis. These muscles can best contract when the spine is in a neutral posture.

A common misconception is that “strong abdominals protect the spine.” In fact, as described above, the abdominal muscles make up only one part of the core. Furthermore, only the deep abdominal muscle, TA, is involved in protecting the spine. The famous “6-pack” or rectus abdominis muscle that many fitness fanatics train actually plays no role in protecting the spine.

Adequate core stability not only reduces strain on the spine but also helps maintain optimal postural alignment that will help reduce risk of injury. Core stability is also an important part of any Total Health, Safety, or Ergonomics program. A strong core means a strong foundation from which our limbs can move more safely, with more power and efficiency, and with less risk of injury.

Spinal WMSDS

Why do so many people experience back pain? Our core muscles are involved in every move we make.

· New use – starting up a new activity; muscles may not be used to the range of motion, force, or speed required. For example, the first time you snowboard, even if you are an avid skier.

· Misuse – cumulative effect of bad body use over a long period (e.g., poor postural alignment) or pushing the body too far too often.

· Overuse – repetitive use of one muscle group causing an imbalance. For example, carrying your child on the same hip.

· Disuse – lack of exercise may not cause a back problem but one can result when we attempt an activity requiring a certain degree of strength or flexibility. A certain percentage of people stop exercise or physical activity when they experience back pain.

Any of these causes can be found in an occupational setting.

Classifications of Spinal WMSDs

The following list is an excerpt from ergonomics in back pain:

· Discogenic: disc hernia (most common at L 4-5 and L 5-S1)

· Neurological: nerve irritation, compression and/or tumors involving nerve roots

· Muscular/ligamentous tension: resulting from stress and nerve or ligament tension

· Trauma: acute injury or cumulative type

· Strain: small tears within the muscle/tendon

· Postural imbalance: creates uneven stresses on the musculoskeletal system

· Spasm: muscle contraction that produces an uncontrolled contraction

· Weakness: poor muscle tone

· Myofascitis: inflammation and tenderness of the muscle and the sheaths that envelop the muscle known as the fascia

· Structural: spondylolysis – a defect of the bony segment joining the articulations above and below a given segment

· Scoliosis: abnormal curve of the spine

· Compression fractures

· Dislocation degenerative disease annular tears

· Osteoarthritis: degenerative disorder that affects the facet joints and disk

· Stenosis – narrowing of a channel.

Neck disorders are commonly associated with prolonged exposure to static and awkward postures, typically as a consequence of visual requirements of a task. There is evidence that flexion beyond 30° leads to more rapid onset of fatigue, whereas low-back disorders are typically caused by repeated loading or high forces.

Stages of Disc Degeneration

The intervertebral disc changes over time from misuse, overuse, lack of use and new use. Early in our development, the spinal disc is spongy and firm. The nucleus portion in the center of the disc contains water and is plump separating the spinal vertebrae. This gives the disc its ability to absorb shock and protect the spine from heavy and repeated forces (Figure 13.17).

Figure 13.17  Types of disc disorders (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

The first change that occurs is that the annulus around the nucleus weakens and begins to develop small cracks and tears. The body tries to heal the cracks with scar tissue, but scar tissue is not as strong as the tissue it replaces. The torn annulus can be a source of pain for two reasons. First, there are pain sensors in the outer rim of the annulus. They signal a painful response when the tear reaches the outer edge of the annulus. Second, like injuries to other tissues in the body, a tear in the annulus can cause pain due to inflammation.

Over time if the disc does not have a chance to heal, or if the condition that caused the cracks remains unchanged, the disc begins to lose water, causing it to lose some of its fullness and height. As a result, the vertebra begins to move closer together. Scar tissue does not allow recovery as readily as uninjured tissue.

As the disc continues to degenerate, the space between the vertebra shrinks (vertebra move closer together). This compresses the facet joints along the spinal column. As these joints are forced together, extra pressure builds on the articular cartilage on the surface of the facet joints. This extra pressure can damage the facet joints. Over time, this may lead to arthritis in the facet joints. These degenerative changes in the disc, facet joints, and ligaments cause the spinal segment to become loose and unstable. The extra movement causes even more wear and tear on the spine. As a result, more and larger tears occur in the annulus.

The nucleus may push through the torn annulus and into the spinal canal. This is called a herniated or ruptured disc. The disc material that squeezes out can press against the spinal nerves. The disc also emits enzymes and chemicals that produce inflammation. The combination of pressure on the nerves and inflammation caused by the chemicals released from the disc causes pain.

If the degeneration continues, bone spurs develop around the facet joints and around the disc. No one knows exactly why these bone spurs develop. Most doctors think that bone spurs are the body's attempt to stop the extra motion between the spinal segments. These bone spurs can cause problems by pressing on the nerves of the spine, where they pass through the neural foramina. This pressure around the irritated nerve roots can cause pain, numbness, and weakness in the low back, buttocks, and lower limbs and feet.

A collapsed spinal segment eventually becomes stiff and immobile. Thickened ligaments and facet joints, scarred and dried disc tissue, and protruding bone spurs prevent normal movement. Typically, a stiff joint does not cause as much pain as one that slides around too much. So this stage of degeneration may actually lead to pain relief for some people.

Back Pain Solutions

Prevention is the best health insurance. The first step to a healthy mind and body is the understanding about lifestyle choices that contribute to overall wellness. Correct posture, balanced diet, regular exercise, and stress reduction are all important factors. Stretching and strengthening can help maintain or regain range of motion. At the first sign of pain or discomfort that is not alleviated by rest, that wakes you up in the night or limits your after work or work activities, contact a healthcare professional.

A professional evaluation usually includes questions about symptoms, past health problems, family history of disease, work habits, daily activities, and sleeping positions. A physical examination is performed to analyze posture, spinal, and joint alignment. Muscles may be checked for trigger points in the areas of discomfort and radiographs (X-rays) and other tests may be recommended to aid in diagnosis. When the examination and evaluation are complete, the healthcare professional can discuss the condition and prescribe a treatment plan that will aid in recovery. Treatment options may include rest, core muscle stabilization, physical therapy, over-the-counter anti-inflammatory medicines, prescription medication, pain management therapy, steroidal injections, behavioral and lifestyle changes, and minor to major surgery. Other forms of recovery include nontraditional medicines such as acupuncture and yoga. Regardless of the treatment, if the cause of the disorder is not altered, the treatment may not be effective in the long term (Figure 13.18).

Figure 13.18  Posterior spinal between L5 and S1 to correct a structural failure between the segments

HAND, WRIST, ARM AND SHOULDER WMSDS

For a complete discussion of upper limb musculoskeletal disorders, refer “Cumulative Trauma Disorders – A Manual for Musculoskeletal Diseases of the Upper Limbs” edited by Vern Putz-Anderson and published by Taylor and Francis.

The structures of the upper extremities are particularly vulnerable to soft tissue injury. A main reason is that almost all work requires the constant and active use of the arms and hands and that long tendons attach the forearm muscles around the elbow to the fingers (Health, 1988).

Nerve Disorders

The nerves and blood vessels that run into the arm and hand exit the spinal column at C6, C7, and C8. The nerves travel between two muscles in the neck called scalene muscles, over the top of the rib cage, under the collar bone, through the arm pit, and down the arm into the hand. The area where the nerves and vessels leave the neck between the two scalene muscles and over the first rib is known as the thoracic outlet (reference Figure 13.10).

The radial nerve runs along the thumb-side edge of the forearm. It wraps around the end of the radius bone toward the back of the hand. It gives sensation to the back of the hand from the thumb to the third finger. It also supplies the back of the thumb and just beyond the main knuckle of the back surface of the ring and middle fingers.

The median nerve travels through a tunnel within the wrist called the carpal tunnel. This nerve gives sensation to the thumb, index finger, long finger, and half of the ring finger. It also sends a nerve branch to control the muscles of the thumb (thenar).

The ulnar nerve travels through a separate tunnel, called Guyon's canal. This tunnel is formed by two carpal bones – the pisiform and hamate – and the ligament that connects them. After passing through the canal, the ulnar nerve branches out to supply feeling to the little finger and half the ring finger. Branches of this nerve also supply the small muscles in the palm and the muscle that pulls the thumb toward the palm.

The nerves that travel to the hand are subject to problems. Constant bending and straightening of the wrist and fingers can lead to irritation or pressure on the nerves within their tunnels and cause problems such as pain, numbness, and weakness in the hand, fingers, and thumb.

Historically, the median nerve was called the musician's nerve due to problems associated with plucking motions (such as plucking a harp) it is responsible for pulling the hand back. The ulnar nerve was called the carpenters nerve due to problems associated with repeated hammering. The ulnar nerve runs along the outside of the elbow and can snap or slip with repetitive/forceful hammering type motions. We all know where our ulnar nerve is. It creates that pins and needles sensation when we strike our elbow.

Carpal tunnel syndrome is one of the most well-known nerve disorders because of its prevalence in the mid-1990s when computers with mice were becoming common place in work settings and homes.

Carpal Tunnel Syndrome

The term carpal tunnel is a medical term for the space in the wrist where nerves and tendons pass from the forearm into the hand. Carpus is a word derived from the Greek word “karpos” which means “wrist.”

The wrist is surrounded by a band of ligament tissue that normally functions as a support for the joint and creates a capsule. The tight space between this fibrous band and the wrist bone is called the carpal tunnel. Knowing the structure of the hand helps understand why keeping the wrist straight while performing tasks is important. Looking closely, you can see that the median nerve lies just under the transverse carpal ligament. The nerve can be easily compressed or strained because it is just below a soft structure and subject to direct pressure from contact stress and internal pressure from awkward postures. Figure 13.19 shows how the median nerve innervates the thumb and the first three fingers of the hand. The nerve transmits signals to and from the hand. If the median nerve is damaged, the sensation and strength of the hand is often compromised or lost.

Figure 13.19  Carpal tunnel and median nerve (Adapted with permission from Shutterstock)

Causes of Carpal Tunnel Syndrome

Carpel Tunnel Syndrome (CTS) may develop when the median nerve is compressed or squeezed at the wrist. CTS is often the result of a combination of factors that increase pressure on the median nerve and tendons in the carpal tunnel, rather than a problem with the nerve itself. For example, damage to the tendon sheath can reduce blood flow to the nerve and cause its function to be impaired. Contributing factors include trauma or injury to the wrist that causes swelling, such as a sprain or fracture, overactivity of the pituitary gland, hypothyroidism, rheumatoid arthritis, mechanical problems in the wrist joint, work stress, repeated use of vibrating hand tools, fluid retention during pregnancy or menopause, or the development of a cyst or tumor in the canal.

There is no one cause of CTS but one or more of the following work activities may lead to CTS:

· Using a “pinch grip” with your fingers

· Extreme force involving the fingers, hand, and wrist

· Pressure on your hand, especially into the palm for long periods

· Repeated, rapid movements of the hand and wrist

· Tasks done while the hand or wrist is held in a bent or awkward position

· Low-frequency vibration to the hand

· Wearing gloves that do not fit

· Exposing the hands to cold temperatures for long periods

· Using tools that do not fit the hand requiring extreme pinch or oblique grips.

Jobs requiring highly repetitive and forceful motions are prime targets. The risk of developing CTS is not confined to people in a single industry or job; it is especially common in manufacturing, sewing, finishing, cleaning, and meat, poultry, or fish packing, and maintenance.

Symptoms of Carpal Tunnel Syndrome

Symptoms usually start gradually, with frequent burning, tingling, or itching and numbness in the palm of the hand and the fingers, especially the thumb and the index and middle fingers. Some carpal tunnel sufferers say their fingers feel useless and swollen, even though little or no swelling is apparent. The symptoms often first appear in one or both hands during the night, since many people sleep with flexed wrists. A person with CTS may wake up feeling the need to “shake out” the hand or wrist. As symptoms worsen, tingling is felt during the day. Decreased nerve conduction will impact strength may make it difficult to form a fist, grasp small objects, or perform other manual tasks.

Tendinitis

Tendinitis (or tendonitis) is a tendon inflammation that is associated with a muscle/tendon, which is repeatedly tensed, moved, bent, vibrated, or in contact with a hard surface. Tendons themselves are cords of tough, fibrous connective tissue that attach muscles to bones and are found throughout the entire human body. Tendinitis is the inflammation and irritation of a tendon. If the normal smooth gliding motion of a tendon is impaired, the tendon will become inflamed and tendinitis will start to occur. Tendinitis occurs largely in the arms, hands, and wrist because of the length of the tendons operating the fingers, and the exposure to repetitive motions, but tendinitis can occur in any tendon group.

Symptoms of Tendinitis

· When the tendon is under pressure, pain is the first tendinitis symptom to develop. This pressure could come from lifting objects, playing sports, long-term hyperextension of the arm, repeated work with the hands or any type of manual job. In the first stages of tendinitis, pain usually only occurs when the tendons are under pressure. As the tendinitis develops, pain will start to occur throughout the day whether the tendon is under pressure or not. The pain will occur when you touch the tendon and move the joint.

· Movement is restricted, for example, if the tendinitis has developed in the bicep the individual may not be able to extend the arm fully.

· Burning sensation is felt mostly after exercise or manual labor and in the morning or late at night.

· Affected area is swollen, red, warm, or lumpy. The tendon sheaths may be visibly swollen from the accumulation of fluid and inflammation. This is a sign that tendinitis has advanced.

Recovery from Tendon and Ligament Damage

Tendon and ligaments do not heal as quickly as muscles. Because of this, an injured worker may return to work after the initial pain or inflammation subsides but with a tendon/ligament that is not fully repaired, the repeated trauma from returning to unrestricted work too early can cause further damage.

Tendon/ligament repair is hastened due to oxygen supply. The body recovers through cell regeneration and cell energy is due to adenosine triphosphate (ATP). The more ATP cells make, the more energy cells have, and the faster they can reproduce to fill in the voided tissue. ATP is produced in the cell through processes such as glycolysis, the citric acid cycle, and the electron transport chain. Glycolysis and the citric acid cycle can only produce a few ATP (2 each), while the electron transport chain can produce many more (32–36). Without getting into physiology, the key to making the most energy possible is oxygen.

If one can introduce oxygen to a cell, cells can undergo what is called “aerobic respiration.” Basically, this means that cells can perform all three processes (glycolysis, citric acid cycle, and electron transport chain). Without oxygen, cells can only perform two of those processes (glycolysis and the citric acid cycle). This is less than ideal for recovery. Without oxygen, the cells produce about 1/8 the energy that would have been produced with oxygen in the cell. Ligaments and tendons do not receive a lot of oxygen. Blood is how oxygen is transported throughout the body, but since the fibrous structures do not have much vasculature, they do not see very much oxygen. The skin, by comparison, has tiny blood vessels throughout that constantly provide oxygen to the cells. This is why a tendon/ligament injury will heal much slower than a superficial cut on the skin.

It is not uncommon for tendinitis to develop as a result of another tendon or joint injury. For example, shoulder tendinitis is often developed after a rotator cuff injury and knee tendinitis can be developed after having knee surgery. In these cases, tendinitis usually develops because the injury has not completely healed.

de Quervain's Tendinitis

de Quervain's is a condition brought on by irritation or inflammation of the wrist tendons at the base of the thumb. The inflammation causes the compartment (a tunnel or a sheath) around the tendon to swell and enlarge, making thumb and wrist movement painful. Making a fist and grasping or holding objects are common painful movements with de Quervain's tendinitis.

What Causes de Quervain's Tendinitis

Repeatedly performing hand and thumb motions such as grasping, pinching, squeezing, or wringing may lead to inflammation. This inflammation can lead to swelling, which hampers the smooth gliding action of the tendons within the tunnel.

New mothers are especially prone to this type of tendinitis. Caring for an infant often creates awkward hand positioning and hormonal fluctuations associated with pregnancy and nursing further contribute to its occurrence. A wrist fracture can also predispose a patient to de Quervain's tendinitis, because of increased stresses across the tendons.

Tenosynovitis

This disorder occurs inside the tendon synovial sheath. Tenosynovitis develops when the inner (synovial) lining of the tendon sheath becomes injured or inflamed. It occurs most often in the hands, wrists, and elbows again due to the length of the tendons and many tunnels in which they pass though. The inner synovial lining is separate from the fibrous outer sheath covering the tendon, impacting nourishment and lubrication to the tendon. Irritation to the synovial lining can be caused by injury, overuse, repetitive strain, trauma, rheumatoid arthritis, gout, or infection. This condition is typically a precursor to CTS. Tenosynovitis can also occur when direct pressure is placed on a tendon and, yet the tendon is required to repeatedly move.

Again even though we are discussing the upper limbs, these conditions can occur in the lower limbs as well.

Trigger Finger

“Trigger finger” or “trigger thumb” are the common names for stenosing tenosynovitis. Trigger finger involves the pulleys and tendons in the hands and fingers that work together to bend the fingers. The tendons work like long ropes connecting the muscles of the forearm with the bones of the fingers and thumb. In the finger, the pulleys are a series of rings that form a tunnel through which the tendons must glide, much like the guides on a fishing rod through which the line (or tendon) must pass. These pulleys hold the tendons close against the bone. The tendons and the tunnel have a slick lining that allows easy gliding of the tendon through the pulleys. Trigger finger occurs when the pulley at the base of the finger becomes too thick and constricting around the tendon, making it hard for the tendon to move freely through the pulley. Sometimes, the tendon develops a nodule (knot) or swelling of its lining. Because of the increased resistance to the gliding of the tendon through the pulley, you may feel pain, popping, or a catching feeling in the finger or thumb (triggering). When the tendon catches, it produces inflammation and more swelling. This causes a vicious cycle of triggering, inflammation, and swelling.

Signs and Symptoms

Trigger finger may start with discomfort felt at the base of the finger or thumb, where they join the palm. This area is often tender to local pressure. A nodule may be found in this area and the finger or thumb becomes stuck or locked, and is hard to straighten or bend.

Figure 13.20 shows the area that becomes damaged from tools and, then the tendon does not slide through the opening as well. Once this condition occurs, the tendon is pretty much damaged for life. If our tendons did not have this arrangement, we could not curl our fingers (see Figure 13.21).

Figure 13.20  Pully's and damager in the finger (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Figure 13.21  Activity that can cause trigger finger

Nerve Disorders in the Elbow

The end of the humerus (arm bone) has two epicondyle, a lateral and a medial. Ligaments and tendons of the elbow joint are attached at the epicondyle and the nerves of the arm run over, beneath or between the elbows joint. Epicondylitis is inflammation at this attachment point of a tendon.

As you can see from Figure 13.22, all of the nerves that travel down the arm pass across the elbow. Three main nerves begin together at the shoulder: the radial nerve, the ulnar nerve, and the median nerve. These nerves carry signals from the brain to the muscles that move the arm. The nerves also carry signals back to the brain about sensations such as touch, pain, and temperature.

Figure 13.22  Median, radial, and ulnar never funneling through the elbow (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD; http://www.clipartof.com/download?txn=577e6995e66d8d9c7f0dc5d21e5f9aa2)

Some of the more common disorders of the elbow are problems of the nerves. Each nerve travels through its own tunnel as it crosses the elbow. Because the elbow must bend and rotate, the nerves must bend as well. Constant bending and straightening can lead to irritation as a nerve slides across a bone or pressure on the ligaments within their tunnels. For example, the cubital tunnel is a channel that allows the ulnar nerve to travel over the elbow and cubital tunnel syndrome is inflammation of the nerve within the tunnel or inflammation of the tunnel itself. Radial tunnel syndrome is caused by increased pressure on the radial nerve, which runs by the bones and muscles of the forearm and elbow.

Epicondylitis (Tennis-Elbow/Golfers Elbow)

There are several important tendons around the elbow. The biceps tendon attaches the large biceps muscle on the front of the arm to the radius. It allows the elbow to bend with force. One can feel this tendon crossing the front crease of the elbow when they tighten the biceps muscle.

The triceps tendon is the large tendon that connects the large triceps muscle on the back of the arm with the ulna. It allows the elbow to straighten with force, such as when you perform a push-up.

The muscles of the forearm cross the elbow and attach to the humerus. The outside, or lateral, bump just above the elbow is called the lateral epicondyle. Most of the muscles that straighten the fingers and wrist all come together in one tendon to attach in this area. The inside, or medial, bump just above the elbow is called the medial epicondyle. Most of the muscles that bend the fingers and wrist all come together in one tendon to attach in this area. These two tendons are important to understand because they are a common location of tendonitis.

Lateral epicondylitis, commonly known as “tennis elbow,” is an inflammation of the tendon fibers that attach the forearm extensor muscles to the outside of the elbow. These muscles lift the wrist and hand. Tennis elbow was first recognized by doctors more than 100 years ago. The name comes from a common cause; that is the back hand in tennis uses forceful wrist extension and rotation. Medial epicondylitis, known as “golfers elbow,” is an inflammation of the tendon fibers that attach the forearm flexor muscles on the inside of the elbow. Medial epicondylitis or “golfers elbow” is a similar condition that occurs on the inside of the elbow. The name comes from the common cause, due to forceful rotations and flexion of the forearm.

Pain may be felt where these fibers attach to the bone on the outside/inside of the elbow or along the muscles in the forearm. Pain is usually more noticeable during or after stressful use of the arm. In severe cases, lifting and grasping even light things may be painful.

Causes of Epicondylitis

Routine use of the arm or an injury to this area may stress or damage the muscle attachment and cause symptoms. Generally, people who develop this problem may be involved in activities with rotation of the forearm combined with forceful extension or flexion; for example, during painting. The condition is quite common in our late 30s and early 40s.

Signs and Symptoms of Epicondylitis

The area of most pain is usually found near the bone on the outer or inner side of the elbow. This area is usually tender when touched and may be uncomfortable when gripping. In severe cases, almost any elbow movement can be uncomfortable.

Ganglion Cysts

Ganglion cysts, also known as Bible bumps, are more common in women, and 70% occur in people between the ages of 20 and 40. Ganglion cysts most commonly occur on the back of the hand (60–70%), at the wrist joint, and can also develop on the palm side of the wrist. When found on the back of the wrist, they become more prominent when the wrist is flexed forward. Other places, although less common, include these (Figure 13.26):

· The base of the fingers on the palm, where they appear as small pea-sized bumps

· The fingertip, just below the cuticle, where they are called mucous cysts

· The outside of the knee and ankle

· The top of the foot.

What Causes Ganglion Cysts

The cause of ganglion cysts is not known. One theory suggests that trauma causes the tissue of the joint to break down forming small cysts, which then join into a larger, more obvious mass. The most likely theory involves a flaw in the joint capsule or tendon sheath that allows the joint tissue to bulge out.

Signs and Symptoms of Ganglion Cysts

The ganglion cyst usually appears as a bump (mass) that changes size. It is usually soft, anywhere from 1 to 3 cm in diameter (about 0.4–1.2 in.) and does not move. The swelling may appear over time or appear suddenly, may get smaller in size, and may even go away, only to come back at another time. Most ganglion cysts cause some degree of pain, usually following acute or repetitive trauma, but up to 35% are without symptoms, except for appearance. The pain is usually nonstop, aching, and made worse by joint motion. When the cyst is connected to a tendon, one may feel a sense of weakness in the affected finger.

Thoracic Outlet Syndrome (TOS) – Neuro-Vascular Disorder

Thoracic outlet syndrome is a combination of pain in the neck and shoulder, numbness and tingling of the fingers, and a weak grip. The thoracic outlet is the area between the rib cage and collarbone.

What Causes TOS

TOS is a rare condition. Blood vessels and nerves coming from the spine or major blood vessels of the body pass through a narrow space near the shoulder and armpit on their way to the arms. As they pass by or through the collarbone (clavicle) and upper ribs, they may not have enough space. Pressure (compression) on these blood vessels or nerves can cause symptoms in the arms or hands. Problems with the nerves account for almost all cases of thoracic outlet syndrome.

Compression can be caused by an extra cervical rib (above the first rib) or an abnormal tight fibrous band connecting the spinal vertebra to the rib. People who suffer from TOS often have a history of injury to the area or overuse of the shoulder. TOS can be a repetitive stress injury. People with long necks and droopy shoulders may be more likely to develop this condition because of extra pressure on their nerves and blood vessels.

Signs and Symptoms of TOS

Often symptoms are reproduced when the arm is positioned above the shoulder or extended. Individuals can have a wide range of symptoms from mild and intermittent, to severe and constant. Pains can extend to the fingers and hands, causing weakness. Symptoms of TOS may include the following:

· Pain, numbness, and tingling in the last three fingers and inner forearm

· Pain and tingling in the neck and shoulders (carrying something heavy may make the pain worse)

· Signs of poor circulation in the hand or forearm

· Weakness of the muscles in the hand.

Types of activities that can lead to TOS are those such as painting, sheet rocking, or overhead repairs on aircraft or vehicles.

LOWER LIMB

Lower limb WMSDs are currently a problem in many industries. “The epidemiology of these WMSDs has received until now modest awareness, despite this there is appreciable evidence that some activities (e.g., kneeling/squatting, climbing stairs or ladders, heavy lifting, walking/standing) are causal risk factors for their development.” Other causes for acute lower limb WMSDs are related with slip and trip hazards (Laboratory, 2009). Despite the short awareness given to this type of WMSD they deserve significant concern, since they are often sources of high degrees of immobility and thereby can substantially degrade the quality of life (Laboratory, 2009). The most common lower limb WMSDs are (Laboratory, 2009) as follows:

· Hip and thigh conditions – osteoarthritis (most frequent), piriformis syndrome

· Trochanteritis, hamstring strains, sacroiliac joint pain

· Knee/lower leg – osteoarthritis, bursitis, beat knee/hyperkeratosis, meniscal lesions, patellofemoral pain syndrome, prepatellar tendonitis, shin splints, infrapatellar tendonitis, stress fractures

· Ankle/foot – achilles tendonitis, blisters, foot corns, hallux valgus (bunions), hammer toes, pes traverse planus, plantar fasciitis, sprained ankle, stress fractures, varicose veins, venous disorders.

Hip, Knees, Foot, and Ankle

Patellofemoral Pain Syndrome

Patellofemoral syndrome is irritation to the underside of the patella where it meets the femur. Patellofemoral pain syndrome (PFPS) is a musculoskeletal disorder that has both work-related and nonwork-related origins. It is one of the least understood WMSDs and is often misdiagnosed.

The condition is generally caused by overuse and misuse of the knee joint, and risk increases with obesity or if the kneecap is not properly aligned. Women are more susceptible to PFPS, possibly due to the greater angle of the iliotibial band caused by the wider hips and shorter femur of the female anatomy. Kneecap alignment can be affected by unbalanced development of the quadriceps and iliotibial band muscle groups as well as tendon and ligament imbalances. These can be caused by performing repetitive work tasks that work or use the quadriceps and/or the iliotibial bands to a greater extent than the hamstrings. Forces put on the knee in sudden stopping and change of direction motions or change of direction motions while carrying weight, commonly seen in sports, also contribute to the condition. Changes in the cartilage under the kneecap, wearing down or becoming soft or rough can change the alignment between the kneecap and the tendons and bones of the upper and lower leg. The symptoms of the disorder include knee pain associated with extended sitting, squatting, jumping, and stair use (especially descending). The knee may at times “give out” and fail to support the body's weight and there may also be “popping” noises or a “grinding” feeling associated with movement of the joint.

Manual laborers experience the disorder due to overuse and misuse of the knee joint, namely, carrying loads and changing directions. Miners, construction workers, and carpenters, in general, report higher levels of all types of knee pain than people in other occupations. These types of professions involve frequent knee bending and heavy lifting and can also involve prolonged squatting and kneeling positions. People working at desk jobs may also experience the disorder (it is sometimes referred to as “theater-goers knee”) because sitting for long periods of time with the knees hyperflexed causes the quadriceps muscles to pull on the kneecap, which can move it out of proper alignment over time. The hyperflexed knee seated position is an awkward posture. It involves placing the feet farther back than the knees nearly under the thighs, which puts the thighs at a downward angle from the torso and stretches the quadriceps, thus pulling the kneecap up toward the waist.

Treatment methods can sometimes cause PFPS to worsen, discouraging patients. Physical therapy can be effective, but relief is not always attributed to the therapy. Sometimes, it is the body's ability to heal that brings relief. NSAIDS can be a short-term relief but do nothing to get at the real cause of the pain. Figure 13.23 provides an explanation of the etiology of an ankle sprain.

Figure 13.23  Ankle sprain (Adapted with permission by Lippincott Williams & Wilkins, Baltimore, MD; http://www.clipartof.com/download?txn=577e6995e66d8d9c7f0dc5d21e5f9aa2)

Hip Bursitis

Hip bursitis is a condition that causes pain over the outer part of the upper thigh. Bursitis occurs when the bursa, which is a small jelly-like sac that contains a small amount of fluid, becomes inflamed. There are a total of 160 bursae in the human body located around the major joints. Most bursae are found near the tendons around the large joints such as the shoulder joint, elbow joint, and hip and knee joint.

Bursae are fluid-filled sacs that cushion the joints of the body and allow joints, tendons, and muscles to glide over each other. They reduce friction and allow the human body to move without resistance. Bursae are generally healthy, but they can become inflamed and cause pain. When this occurs, it is known as bursitis. If the inflammation is not reduced, localized soft tissue trauma follows due to the increased stress between the tissues due to the added friction (Figure 13.24).

Figure 13.24  The hip joint (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Bursitis is caused by the overuse of or direct trauma to the joint. Putting constant pressure on the hips can help contribute to this condition. This happens when workers are exposed to long durations of standing or sitting on hard surfaces. Awkward standing postures increase the risk to the worker, especially if the worker begins to favor one hip over the other. Receiving a direct, hard hit to a worker's hip can also higher the possibility of developing this WMSD. This can occur if an employee falls on their hip in the workplace. Repetitive motion of the hip joint is also a risk factor. An example of this is constantly climbing stairs or ladders. If a worker must climb a ladder while carrying a load, then there is a combination of risk factors; therefore, the risk of injury increases.

Knees

The knee is one of the most important joints of our body. It plays an essential role in movement related to carrying the body weight in horizontal (running and walking) and vertical (jumps) directions.

The knee joins the upper leg or the femur to the knee cap (patella), which is then joined to the lower leg or the tibia and fibula. Tendons connect the patella to the leg muscles, and ligaments stabilize the knee (Figure 13.25).

Figure 13.25  The complex knee (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

The anterior cruciate ligament (ACL) prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur).

Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia, and numerous bursae help the knee move smoothly.

Knee disorders, like other cumulative disorders of the body, build up over time through cumulative exposures. Knee disorders primarily consist of bursitis, meniscal lesions or tears, and osteoarthritis. Though kneeling and squatting are considered to be 2 of the primary risk factors correlated to these knee disorders, 12 other risk factors should also be contemplated. These 14 contributing risk factors include both occupational (extrinsic) and personal (intrinsic) variables that affect primarily the labor industries. Example industries include mining, construction, manufacturing, and custodial services where knee bending postural activities exist as a commonality. The risks are described in Table 13.2 (Reid, 2010).

Table 13.2  Risk Factors for Knee Disorders

Risk	Extrinsic Risk	Intrinsic Risk	OA	Meniscal Disorders	Knee Bursitis
Kneeling	X		X	X	X
Squatting	X		X	X
Crawling	X		X	X
Stair/laddering climbing	X		X	X
Lifting/carrying/moving	X		X	X
Walking	X		X
Standing up form a kneel/squat/crawl	X		X	X
Chair sitting (while driving)	X			X
BMI		X	X
Past knee injury/surgery		X	X
Age		X	X
Using the knee as a hammer	X				X
Prolonged contact stress against the patella other than when kneeling	X				X
Physical intensive habits/hobbies that could affect the knee		X	X	X

Source: Adapted from Reid (2010).

ACL and MCL Injuries

The knee is primarily stabilized by a pair of cruciate ligaments. The ACL stretches from the lateral condyle of femur to the anterior intercondylar area. The ACL is critically important because it prevents the tibia from being pushed too far forward relative to the femur. It is often torn during twisting or bending of the knee. The posterior cruciate ligament (PCL) stretches from medial (middle) condyle of femur to the posterior intercondylar area. Injury to this ligament is uncommon but can occur as a direct result of forced trauma to the ligament. This ligament prevents posterior (backward) displacement of the tibia relative to the femur.

Tears of the ACL and medial collateral ligament (MCL) are two of the common knee injuries.

Anterior Cruciate Ligament (ACL)

The ACL is one of four ligaments critical to the stability of the knee joint. A ligament is made of tough fibrous material and functions to control excessive motion by limiting joint mobility. Of the four major ligaments of the knee, the ACL is the most frequently injured.

The ACL is the primary restraint to forward motion of the shinbone (tibia). The anatomy of the knee is critical to understanding this relationship. The femur (thighbone) sits on top of the tibia (shinbone), and the knee joint allows movement at the junction of these bones. Without ligaments to stabilize the knee, the joint would be unstable and prone to dislocation.

Medial Collateral Ligament

The MCL is also one of four ligaments that are critical to the stability of the knee joint. The MCL spans the distance from the end of the femur (thighbone) to the top of the tibia (shinbone) and is on the inside of the knee joint. The MCL resists widening of the inside of the joint or prevents “opening-up” of the knee.

Because the MCL resists widening of the inside of the knee joint, the MCL is usually injured when the outside of the knee joint is struck. This action causes the outside of the knee to buckle and the inside to widen. When the MCL is stretched too far, it is susceptible to tearing and injury. This is the injury seen by the action of “clipping” in a football game.

Ligament Injury Symptoms

The most common symptom following a ligament injury is pain directly over the ligament. Swelling over the torn ligament may appear, and bruising, and generalized joint swelling is common 1–2 days after the injury. In more severe injuries, patients may complain that the knee is unstable, or feel as though their knee may “give out” or buckle.

Knee Osteoarthritis

One of the most debilitating occupational knee disorders is knee osteoarthritis. This degenerative disease causes inflammation within the knee joint and is accompanied by cartilage rigidity and atrophy. The deformation and damage is exacerbated during movement and weight-bearing periods, which in turn affects additional joint structures within the knee. Inflammation, bone spurs, cartilage wear, narrowed joint space between the femur and tibia, and bone-to-bone contact are all signs of knee OA.

Osteoarthritis is the most common form of arthritis. It occurs when the protective cartilage on the ends of joint bones, most commonly in the hands, knees, hips, and/or spine, wears down over time. There is currently no cure for the disease; however, staying active, maintaining a healthy weight, and some medical treatments may slow progression of the disease and help improve pain and joint function. Obesity is acknowledged by several studies as having an influence toward the development of knee OA.

Individuals that stand on their feet or work on hard surfaces seem to be more susceptible to both hip and knee OA. For example, janitors who are on their feet or bending frequently, road construction workers, carpet layers, and sheet metal workers all have an increased rate of OA. The constant standing on an unforgiving surface such as pavement or concrete seems to take a toll on their knees.

Knee Bursitis

Although there are 11 bursae in the knee, according the Mayo Clinic Family Health Book, bursitis in the knee “most commonly occurs over the kneecap or on the inner side of the knee below the joint” (Litin, 2009).

Bursitis is the inflammation of a bursa sac accompanied by swelling (through fluid retention in the bursa sac) and thickening of the bursa walls. What is distinctive for knee bursitis is that its incidence is so common to certain industries that nicknames from those industries have been given. For example, in the coal mining industry, knee bursitis has come to be known as either “miner's knee” or “beat knee.” In the carpet and floor laying industries, “carpet-layer's knee” is found in the literature. For house cleaning or custodial businesses, “housemaid's knee” is commonly spoken.

Two primary types of risk factors related to knee bursitis are using the knee as a hammer (sudden impact stress) and kneeling on or leaning against the knee (prolonged contact stress). Both types of stresses involve distributing forces through the knee to the knee bursae. Personal hygiene is considered to be intrinsic to individuals. Moore et al. (as cited in Reid, 2010) found that hair follicles on the skin of the knee that become infected can also possibly lead to knee bursitis. Proper hygiene by workers (such as cleaning and disinfecting knee pads as well as replacing worn ones) is a plausible mitigation strategy (Reid, 2010).

When bursa becomes inflamed due to trauma, symptoms can include swelling or tenderness around the knee when pressure is put on it. This can cause pain when moving or at rest and even cause mobility issues.

Foot and Ankle

Jobs that necessitate prolonged standing and walking activities are commonly associated with worker's complaints of foot and ankle pain. The foot and ankle are flexible structures of bones, joints, muscles, and soft tissues that let us stand upright and perform activities like walking, running, and jumping. The feet are divided into three sections:

· The forefoot contains the five toes (phalanges) and the five longer bones (metatarsals).

· The mid-foot is a pyramid-shaped collection of bones that form the arches of the feet. These include the three cuneiform bones, the cuboid bone, and the navicular bone.

· The hind-foot forms the heel and ankle. The talus bone supports the leg bones (tibia and fibula), forming the ankle. The calcaneus (heel bone) is the largest bone in the foot.

Muscles, tendons, and ligaments run along the surfaces of the feet, allowing the complex movements needed for motion and balance. The Achilles tendon connects the heel to the calf muscle and is essential for running, jumping, and standing on the toes. The Achilles tendon is the thickest and strongest tendon in the body. It is about 6 in. long.

The talus bone has a shiny joint surface covering that allows the ankle to glide effortlessly across the shiny undersurface of the tibia. When these two bones meet, they form the ankle joint. On the outside of the ankle, there is a smaller thin bone called the fibula. This bone helps prevent the ankle bone from shifting outward.

The stability of their ankle joint is dependent upon the ability of these bones to keep the central bone in place while the ankle moves back and forth. The joint is more stable when your foot is flat on the floor. The ankle is more rigidly held in place by the bony stabilizers of the fibula and malleolus because they are closer to the talus. However, when the toes are pointed, the ankle becomes unstable because the distance between the bony stabilizers of your ankle becomes larger. Thus, the ankle then relies more and more on the soft tissues including the ligaments to continue to provide stability (Figure 13.26). When an ankle twists, it is usually when the toes are pointed.

Figure 13.26  The structure of the foot is laden with crossing ligaments (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

Injuries and Disorders of the Foot and Ankle

Many foot and ankle disorders/injuries have common causes, which include the following:

· The feet roll inward too much when walking or standing (excessive pronation).

· The arch is high or flat.

· Walking, standing, or running for long periods of time, especially on hard surfaces.

· Wearing shoes with inadequate arch support.

· Being overweight.

· Placing high loads on the foot, for example, when jumping.

Plantar Fasciitis

Plantar fasciitis is a common cause of heel pain. The plantar fascia is a flat ligament that connects the heel bone to the toes. Plantar fasciitis is caused by straining the ligament that supports the arch, which can lead to pain and swelling.

Bunion

Bunion is an enlargement on the side of the foot near the base of the big toe (hallux). The enlargement is made up of a bursa (fluid-filled sac) under the skin. Bunions can be painful and can be aggravated by activity and wearing tight shoes.

Neuroma

In the foot, a neuroma is a nerve that becomes irritated and swells up. If the nerve stays irritated, it can become thickened, which makes the nerve larger and causes more irritation. Pain from a neuroma is usually felt on the ball of the foot.

Corns

Corns and callouses are areas of thick, hard skin. They usually develop due to rubbing or irritation over a boney prominence. The hard, thick skin is called a corn if it is on their toe and it is called a callous if it is somewhere else on the foot.

Toenail Fungus

Fungi like a warm, moist, and dark environment (like inside a shoe). A fungal infection in your toenails may cause the nails to become discolored, thickened, crumbly, or loose. There are different causes and it is difficult to treat due to the hardness of the toenail.

Ingrown Toenail

An ingrown toenail can occur for various reasons. The sides or corners of the toenail usually curve down and put pressure on the skin. Sometimes, the toenail pierces the skin and then continues to grow into the skin. This may cause redness, swelling, pain, and sometimes infection.

Hammer Toes

A hammer toe is also sometimes referred to as a claw toe or mallet toe. It involves a deformity of the toe where there is an imbalance in the pull of the tendons. Either the tendon on top of the toe pulls harder or the tendon on the bottom of the toe pulls harder. This results in a curling up of the toe.

Plantar Warts

Plantar warts are caused by a virus. Plantar means bottom of the foot, but warts can occur other places on the foot and toes as well. Plantar warts can be painful depending on where they are located. Sometimes, they are mistaken for calluses because layers of hard skin can build up on top of the wart.

Athlete's Foot

Athlete's foot is a common skin condition that can affect everyone not just athletes. It is caused by a fungus. It may cause redness, itchiness, tiny bumps filled with fluid, or peeling skin. It is most commonly located between the toes or on the bottom of the feet.

Achilles Tendonitis

Achilles tendonitis involves inflammation of the Achilles tendon. If the tendon stays inflamed long enough, it can lead to thickening of the tendon. Sometimes nodules or bumps can form in the tendon. Achilles tendonitis can become a long-term problem or can lead to rupture of the tendon.

SUMMARY

WMSDs are the unnecessary consequence of not fitting the task to the capabilities of the person. WMSDs currently account for more than one-third of all occupational injuries and illnesses, making them the largest job-related injury and illness problem in the United States today. WMSDs are injuries and disorders of the muscles, nerves, tendons, ligaments, joints, cartilage, and spinal discs that result from physically stressful activities and working conditions. WMSDs include carpal tunnel syndrome, sciatica, tendinitis, herniated spinal disc, and low-back strain.

WMSDs may result from the following:

· The physical demands of work, for example, including doing the same motion over and over again, maintaining the same position or posture while performing tasks, or sitting for a long time.

· The layout and condition of the workplace or workstation, for example, tasks that involve long reaches, working surfaces that are too high or too low, workstation edges or objects pressing into muscles or tendons, or equipment located in places that force the worker to assume awkward positions.

· Characteristics of objects handled, for example, the weight, size, center of gravity, and the equipment used to move heavy objects.

· Environmental conditions, for example, excessive exposure to cold temperatures while performing work tasks.

Ergonomics, as the science of fitting jobs to workers, seeks practical solutions that help prevent WMSDs in the workplace. The goal of ergonomics is to design office and industrial workstations, facilities, furniture, equipment, tools, and job tasks that are compatible with human dimensions, capabilities, and expectations with the ultimate goals of improved productivity, satisfaction, and decreased injuries and illnesses.

WMSDs are preventable if the warning signs and symptoms are acted upon and the physical workplace risk factors are changed (Figure 13.27).

Figure 13.27  Stretching for improved blood flow and flexibility (Adapted with permission Lippincott Williams & Wilkins, Baltimore, MD)

KEY POINTS

WMSDs occur slowly over time and therefore can be reduced in frequency or severity with ergonomic improvements.

WMSDs can occur in any area of the body to any person.

Increased blood flow helps the body heal.

REVIEW QUESTIONS

1. Is pain a WMSD?

2. What is one method for avoiding carpal tunnel syndrome?

3. Which soft tissue heals the fastest and why?

EXERCISE

1. Assign students a body region, for example, upper limb or spine. Have them research different WMSDs and discuss how working conditions can be casual. They can each provide a brief oral presentation to the rest of the class.

REFERENCES

1. Litin, S. (2009). Mayo Clinic Family Health Book 4th edn. Time Inc.

2. Reid, C. (2010). A Review of Occupational Knee Disorders. Journal of Rehabilitation, 489–501.

3. Vern Putz-Anderson. (1998) Cumulative Trauma Disorders., Taylor & Francis.

ADDITIONAL SOURCES

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