Module 2: Anatomy & Physiology * Terms marked by an asterisk are defined in the Glossary 2.1 Introduction The structure of each part of the human body is directly related to its function. The structures that make up the body serve several important functions, such as support, protection and movement. When these structures are extended beyond their normal functions and subjected to risk factors such as repetitive motions, forceful exertions, awkward postures*, poor body mechanics and poor ergonomics*, the risk of injury increases. The purpose of Module 2 is to describe how the human body should be used and the risks and consequences of improper use. To fulfill this purpose, Module 2 achieves four goals. It: identifies the major structures of the back and shoulder, and describes their functions. Relating the body s structures to their functions allows you to understand how the body should be used. contrasts dynamic muscle action with static muscle action. Recognizing the differences between these two types of forces enables you to assess risk factors associated with static and dynamic muscle action. identifies and describes types of musculoskeletal injuries (MSIs), and discusses risk factors that may contribute to the development of these types of injuries. Understanding MSIs enables you to assess risk factors associated with the development of MSIs. outlines preventative and corrective actions that can be taken to manage MSIs. Knowing the desirable actions for dealing with MSIs helps you take positive, proactive steps toward reducing the impact and severity of these injuries. 2.2 Anatomy of the Spine and Shoulder In good posture*, the spine is curved in the shape of a gentle S (see figures in this module). Poor posture exaggerates this curve and alters the back s delicate suspension system, resulting in stress and strain on all the structures of the back. The spine keeps the body upright and balances the pelvis and trunk over the legs for standing and locomotion (walking). The position of the pelvis determines the ability to maintain the normal S curve of the spine and the body s centre of gravity. When abdominal muscles (the pelvic girdle) are tight and firm, the pelvis is tilted in a normal position and the gentle, normal lower back curve is achieved. When the abdomen sags and the body slouches, the pelvis tilts forward and the lower back arches too much. The shoulder is the most mobile joint in the human body. The ball and socket joint allows for flexibility and range of movement, which makes it more vulnerable to injury. The shoulder relies heavily upon cartilage, ligaments and muscles for support. - 5 - April 2011
The principles of good posture (see Section 3.3) should apply to all daily activities, but especially to moving tasks. Using good body mechanics (see Section 3.4) means maintaining the body in the best possible position to prevent gravity from causing stress and strain on the back. When lowering and raising the body, the worker who bends the knees, keeps the trunk upright (maintaining the three natural curves of the spine) and the feet approximately shoulder width apart is using good body mechanics. In this position, the pelvis is correctly tilted and the lower back well protected. The body is more stable as the line of balance and body weight falls inside a wide base of support*. The work of lowering and raising the body is done with the large, strong leg muscles. Using poor body mechanics, such as bending at the waist with the knees straight, causes the body to be poorly balanced. This forces the back muscles to work too hard to keep the body weight balanced, creating a high risk of back injury. It is common for a woman to work during pregnancy and return to work after the birth of a baby. Women must pay extra attention to all aspects of proper transferring, lifting and repositioning techniques, body mechanics and posture before and after childbirth. It is obviously difficult to keep the client/object being moved close to the body when pregnant. The primary worker* must assign an appropriate role to the pregnant worker when she is assisting in a team transfer, lift or reposition. In addition, hormones secreted during pregnancy soften the ligaments around joints in preparation for the delivery of the baby. The worker s muscles must be strong to compensate for this temporary decrease in joint support from the ligaments. The worker should also strengthen her abdominal muscles by exercise before returning to work after delivery. The pregnant worker and the worker who has returned to work after the birth of a baby must be informed about these additional risk factors in order to correctly conduct a self assessment when moving a client/object. - 6 - April 2011
Figure: Structure and function of the back Spine Vertebrae Structure The spine is divided into three segments: neck (cervical spine); trunk (thoracic spine); and, low back (lumbar and sacral spine). The spine consists of 33 bones termed vertebrae that connect the head to the pelvis. Twenty-four of the vertebrae are movable: seven in the neck; twelve in the trunk; and, five in the lower back. At the bottom of the spine, five bones are fused together to form the sacrum, and four bones below that are fused together to form the coccyx (or tailbone). From the side, the spine curves in a gentle S shape the cervical vertebrae curve forward, the thoracic vertebrae curve backward, and the lumbar vertebrae curve forward. Each vertebra is drum-shaped at the front. Attached to the back of the drumshaped portion is a ring of bone through which the spinal cord passes. This ring of bone has three projections one going straight back and one to each side. Muscles and ligaments attach to these projections. The vertebrae sit one on top of the other, with a disc between the drumshaped portions. Discs are only found in the cervical, thoracic and lumbar segments. No discs are found in the coccyx and sacral areas, except between the lowest lumbar vertebra and the first sacral vertebra. Function The spine houses and protects the spinal cord, keeps the trunk in an upright position and gives the body flexibility. The lower back curve balances the pelvis and spine over the legs when standing or walking. The vertebrae surround the spinal cord and protect it from injury. The strong drum-shaped portions of the vertebrae support the weight of the body. - 7 - April 2011
Figure: Structure and function of the back (continued). Discs Facet Joints -Ligaments Back Muscles Abdominal Muscles Spinal Cord Nerves Structure Annulus The annulus is the outer part of the disc that surrounds the nucleus. It consists of strong, criss-crossing elastic fibres. When these fibres tear, the nucleus bulges into the spaces left by the tear, causing pain. Nucleus The centre of the disc is the nucleus. It consists of a jelly-like substance that contains about 88 per cent water when the discs are healthy and young. Facet joints are similar to all other joints in that they are covered with cartilage and encased in an elastic capsule that contains fluid. Facets are found on either side of a vertebra, and interlock with the facets of the vertebra above and below to form facet joints. They are approximately the size of a finger joint. Ligaments are tough elastic fibres found in front of, behind, at the side of, and between vertebrae. The back muscles are short and much less powerful than leg muscles. They are found in two layers: superficial and deep. The three sets of abdominal muscles run vertically, transversely and obliquely. They are broad, flat structures. The spinal cord has 31 pairs of spinal nerves, each containing thousands of nerve fibres. Function The main function of the discs is to act as shock absorbers. When the percentage of water decreases (due to factors such as chronic illness, age, medication and poor nutrition), the discs lose their ability to function effectively as shock absorbers. The discs also act as spacers between the vertebrae, and are attached firmly to the vertebrae above and below, holding them together very strongly. Facet joints, together with the discs, allow movement in the spine. Ligaments connect and stabilize the vertebrae as one continuous structure. When ligaments are healthy, they prevent excessive or abnormal movement of all joints. The main function of the back muscles is postural, or keeping the vertebrae aligned and balanced (in other words, keeping the trunk upright). They were never designed for lifting. The abdominal muscles support the abdominal contents and spine. They maintain the pelvic tilt and protect the lower back. The spinal cord nerves transfer sensory information from the skin, muscles and joints to the brain. Muscles react to messages sent from the brain. - 8 - April 2011
Figure: Structure and function of the shoulder. Shoulder Structure The shoulder is formed by three bones: scapula (shoulder blade); humerus (upper arm bone); and clavicle (collarbone). It consists of three joints; however, the main joint is the glenohumeral joint. This is where the shoulder blade and upper arm bone connect. The shoulder is a ball and socket joint. The top of the humerus is shaped like a ball and it sits in a socket at the end of the scapula. Function The ball and socket joint allows for flexibility and a great range of movement in exchange for stability. The shoulder is responsible for getting the hand in the right position for performing any activity we do. Scapula The scapula (shoulder blade) is a large, thin, triangular bone found on each side of the upper back. It has several bony ridges and processes to which muscles and ligaments attach. It also has the glenoid fossa or socket where the head of the humerus connects. The main function of the scapula is to provide points for attachment of muscles and ligaments. It also enables the arm to move freely. Humerus The humerus (upper arm bone) is the largest and longest bone of the upper extremities. The head or ball is large and rounded and joins with the scapula. The humerus provides sites for attachment of muscles and ligaments. Clavicle Rotator Cuff The clavicle (collarbone) is a slightly S- shaped bone that can be seen and palpated on the front of the body above the chest. It has grooves and ridges to which muscles and ligaments attach. The rotator cuff consists of four muscles: supraspinatus, infraspinatus, teres minor, and subscapularis (SITS). These muscles surround the front, back and top of the shoulder joint like a cuff. The main function of the clavicle is to serve as a strut (support) to stabilize the shoulder and suspend the scapula and arm to allow for maximum movement. It is one of the most frequently fractured bones in the body because it is so close to the surface and because people often reach out their arms to break a fall. The rotator cuff holds the head of the humerus (ball) in the glenoid fossa of the scapula (socket) during all movements of the shoulder joint. It also helps stabilize the shoulder when moving the elbow, wrist and hand. - 9 - April 2011
Figure: Structure and function of the shoulder (continued). Labrum Ligaments Muscles The labrum is a unique type of fibrous tissue that attaches almost all the way around the edge or rim of the glenoid fossa. It tends to be a triangular o-ring, however, its shape, size and thickness can vary. Ligaments are fibrous bands of connective tissue that link two or more bones. There are seven ligaments that support the shoulder. They are the annular, coracoacromial, coracoclavicular, costoclavicular, glenohumeral, interclavicular and sternoclavicular ligaments. There are two types of muscles surrounding the shoulder which are described as extrinsic and intrinsic. Extrinsic muscles are those which partly attach to the trunk and partly to a limb. Intrinsic muscles are those that originate and insert entirely within a structure. The extrinsic muscles of the shoulder are: trapezius, levator scapula, rhomboid major, rhomboid minor, serratus anterior, pectoralis minor, and pectoralis major. The intrinsic muscles are: deltoid, teres major, rotator cuff, and latissimus dorsi. The main function of the labrum is to form a deeper socket so that the head (ball) of the humerus fits into it. It assists with stabilizing the shoulder. It also provides a point of attachment for ligaments and tendons. The ligaments give the shoulder stability. A group of ligaments form the joint capsule, connecting the humerus to the socket of the scapula. These help hold the shoulder in place. The shoulder muscles provide both stability and movement. While certain muscles move the shoulder, others stabilize it. - 10 - April 2011
2.3 Dynamic and Static Muscle Action Most muscles are arranged in groups around joints. In dynamic (with movement) muscle action, one group bends the joint while the other extends or stretches the joint out. Muscles on one side of the joint cause movement in the desired direction while those on the other side control the speed of the movement. For example: when bending the elbow joint, the biceps bend the forearm up and at the same time, the triceps keep the movement smooth and coordinated. When extending the elbow joint, these muscles assume the opposite role. Since the muscles contract and relax alternately, there is good blood flow through them and their related structures. Static (without movement) muscle action occurs when muscles on both sides of the joint contract at the same time to keep the joint stable and in a fixed position (e.g., when an arm is held up and away from the trunk). This is called an isometric contraction or static loading. Static muscle action compresses the blood vessels, restricting circulation. When muscles contract in this manner, they fatigue and cramp, and require more time to recover than in the case of dynamic muscle action. When you squeeze your fist it turns white due to the fact that static muscle contractions reduce blood supply to the muscle. This also leads to a decrease in oxygen and nutrients. Sitting is a static activity that reduces blood flow to the postural muscles of the spine and surrounding structures. The risk of injury increases with dynamic and static muscle action when overuse becomes a factor. Dynamic actions often tend to feel less tiring; however, performing the same movement repeatedly (numerous times) can be harmful to the joints involved. Static muscle action is exhausting and uncomfortable. It may interfere in the blood supply to the area or part of that area held in a static position. The risk of injury increases when the duration, frequency or intensity of performing a task significantly increases. In other words, too much, too often or too quickly, without adequate rest periods, can increase the potential for injury. 2.4 Musculoskeletal Injuries (MSIs) Work-related musculoskeletal injuries (MSIs) may be defined as injuries, illnesses or diseases of muscles and their tendons, ligaments, bursae, nerves, joints, cartilage (including intervertebral discs), bones and supporting blood vessels in either the upper or lower extremities or the back. They can result from a sudden single event (such as a fall) but, more often, they develop over a period of time from activities that involve repetitive movements, excessive force and awkward postures at work and at home. MSIs are also referred to as repetitive strain injuries (RSIs), repetitive motion disorders, cumulative trauma disorders and overuse syndromes. Clinical diagnoses of MSIs include, but are not limited to, low back pain, herniated intervertebral discs, sciatica, tendonitis, bursitis, tenosynovitis, epicondylitis (tennis elbow), rotator cuff tendonitis, dequervain s syndrome, nerve entrapments (carpal and tarsal tunnel syndromes), neurovascular syndrome (white finger disease), fractures and dislocations. - 11 - April 2011
Despite growing awareness, MSIs in health care continue to exist and even increase at times. This may be happening for the following reasons: Clients are cared for in their homes, which may lack space, adjustable beds and other ergonomically designed equipment. As a result, workers are likely to use increased force and awkward postures to care for these clients. Clients admitted to long-term care facilities may require high levels of care. They may remain at home longer and may be admitted to these facilities when their physical or behavioural problems can no longer be managed at home. Clients body mass index may be increasing. Employers and workers may not often recognize that MSIs can be work-related, particularly those affecting the upper extremities of the body. Workers may be reluctant to report problems due to a variety of reasons. Some workers work alone and may not understand their role in managing these risks. Refer to Section 35 of Saskatchewan s Occupational Health and Safety Regulations, 1996. MSIs are accepted and/or expected as part of the job. Back pain may affect most adults at some point in their lives which may be fairly brief and not incapacitating or may be the opposite. Many factors cause low back pain and many names are used to describe back conditions, such as lumbago, pinched nerve, slipped disc, degenerating discs and sciatica (which occurs when the pain extends down the leg). Most lifting and twisting injuries are strains and sprains to the muscles, ligaments and small joints of the lower back. Overuse injuries caused by factors such as standing for long periods of time and poor body mechanics also affect the structures of the back. There are various types of MSIs, including: herniated disc is sometimes referred to as a slipped disc. Discs do not slip out of place. Once the outer part of the disc (or the annulus) tears, the jelly-like nucleus may push through the outer wall of the disc and apply pressure on nerves, muscles, ligaments and joints. This may cause tingling, numbness and pain in the back and/or leg. The jelly-like fluid can also trigger an irritating inflammatory process that compounds the pain and degenerative process. The severity of the symptoms depends on the structures involved and the degree of involvement. back sprains and strains are the most common injuries affecting the back. Strains and sprains occur when the ligaments and muscles of the back are overused and over-extended. This can happen during client-handling activities, especially when risk factors such as forceful exertions and repetitive awkward postures occur in combination. This can also happen at home during activities such as gardening and painting when care is not taken to regularly interrupt the task at hand and stretch in the opposite direction. tendonitis occurs when repetitive movements and awkward postures cause tears in tendons. Because tendons have almost no blood supply, they heal very slowly. Tendonitis is very common in the hand, wrist, forearm and shoulder. The injured tendons become inflamed and swollen, and can be very painful. Tennis elbow, also called epicondylitis, is an injury to the tendon attaching a muscle to the bone around the elbow joint. - 12 - April 2011
ligament sprain results when ligaments are over-extended and the fibres tear. Like tendons, their blood supply is poor and, as a result, they take a long time to heal. Ligament sprains are often quite painful. ligament strain occurs when muscles and tendons are overused and tired, and the ligaments are left to support the joints. This can cause tears in a few or many fibres, resulting in a strain. Both strains and sprains may develop quickly or as a result of repeated small injuries accumulated over time. Sometimes when muscles cramp or go into spasms, there may be nothing wrong with the muscle itself. Rather, the muscle may be attempting to protect an underlying injury to a joint, ligament or disc. carpal tunnel syndrome includes symptoms such as numbness and tingling of the hands, especially at night. It occurs when the median nerve becomes pinched as a result of swollen tendon sheaths in the cramped carpal tunnel (the tendons for flexing the fingers, the median nerve and blood vessels pass through the carpal tunnel at wrist-level under the carpal ligament from the forearm to the hand). bursitis is an inflammation of the bursa (sac) found around some joints, such as the hips and shoulders. The inflammation leads to increased fluid within the bursa and swelling at the site, causing pain in the affected area when the joint is moved. Using proper posture and body mechanics in a combination of work and home activities decreases the likelihood of injury. By eliminating or managing the risk factors that may cause MSIs during the performance of a moving task, workers reduce the risk of injury to themselves and/or a client (see Module 5: Assessment). 2.5 Preventative/Corrective Actions Once an MSI is identified, it must be understood that continuing to aggravate the injury can potentially increase its severity and significantly delay the healing process. When signs and symptoms first appear, the worker must document and report these concerns to their immediate supervisor. The supervisor will advise the worker to consult an appropriate health care provider. The supervisor will also promptly investigate and review the worker s activities in order to take corrective measures to manage the risks involved. Refer to Section 81 of Saskatchewan s Occupational Health and Safety Regulations, 1996, for detailed regulations regarding workplace MSIs. - 13 - April 2011
There is a growing public awareness of the need to integrate and reintegrate people with disabilities into the workplace. As the average age of Canada s working population increases, we can anticipate increasing incidents of chronic disabling conditions and more cumulative trauma claims. This, in turn, means increased costs to society in lost time, Workers Compensation Board (WCB) premiums, health care, disability benefits, administration costs and public sector program costs. There is a strong and growing need within the health sector to help employees who are disabled return to work in a timely and appropriate manner that benefits both the employee and employer. Establishing a win-win climate for all workplace partners to assist disabled employees in regaining their physical well being, dignity and sense of self-worth is the next essential step we all need to take. The best practises are those that are easy to administer, treat all employees in a non-discriminatory manner and achieve results. Success in this endeavour will reduce the human, economic and social costs of disability to employees, employers and society. Adapted from the Disability Management Manual Saskatchewan Association of Health Organizations, 1998 2.6 Summary Module 2 introduced the following key points for anatomy and physiology: using the human body properly by applying principles of good posture, body mechanics and ergonomics helps to maintain the structure and function of the back, and reduces the risk of injury when moving a client/object the pregnant worker and the worker who has returned to work after the birth of a baby must be informed about additional risk factors in order to conduct a self assessment when performing a moving task static and dynamic muscles actions are potential risk factors that may affect the safety of a moving task by increasing the risk of injury to muscles and their related structures risk factors such as repetitive movements, forceful exertions, awkward postures, poor body mechanics and poor ergonomics at work and home can contribute to the development of MSIs preventative and corrective actions to manage MSIs should be taken as soon as MSIs are identified - 14 - April 2011