Table 17-1 lists some of the more common musculoskeletal disorders.

Diseases of the musculoskeletal system are divided into two categories: systemic and local. Patients with systemic disease, such as rheumatoid arthritis, systemic lupus erythematosus, or polymyositis, may appear chronically ill, with generalized weakness, pain, and episodic stiffness of the joints. Patients with local disease are basically healthy individuals who suffer restriction of motion and pain from a single area. Included in this group are patients suffering from back pain, tennis elbow, arthritis, or bursitis. Although these patients may have only local symptoms, their disability can greatly limit their work capacity, and the disease can have a severe effect on their quality of life.

Diseases of the musculoskeletal system rank first in cost to workers’ compensation insurance carriers. Nearly 100,000 workers receive disability payments annually, with a total cost to the carriers of more than $200 billion annually.

It has been estimated that musculoskeletal problems rank second (after cardiovascular disorders) in accounting for visits to internists and third for surgical procedures in hospitals (after gynecologic and abdominal surgery). According to a Gallup poll, nearly 75% of individuals older than 18 years complained of foot pain at some time. More than $300 million is spent annually on insoles, corn remedies, bunion removers, other foot care products, and over-the-counter medications for foot care. Despite this widespread problem, fewer than 50% of clinicians know how to examine a foot correctly.

Although not usually fatal disorders, musculoskeletal conditions affect the quality of life. Studies indicate that backache is experienced by more than 80% of all Americans at some time in their lives. Patients with backache for longer than 6 months constitute a large portion of permanently disabled individuals. More than 50% of these patients never return to work. More than 25 million Americans suffer from arthritis that necessitates medical attention. Arthritis ranks second to cardiac disease as a cause of limitation of activity. Table 17-2 lists the most common musculoskeletal disorders in adults aged 45 years or older with the disease prevalence in the United States.

In the United States at least 10% of the population experiences a bone fracture, dislocation, or sprain annually. Each year more than 1.2 million fractures are sustained by women older than 50 years. There are more than 200,000 hip fractures annually, and these are associated with prolonged disability. Osteoporosis² is the most common musculoskeletal disorder in the world and is second only to arthritis as a leading cause of morbidity in the geriatric population. Postmenopausal osteoporosis and age-related osteoporosis increase the risk of fractures in the older population. There are more than 40 million women in the United States older than 50 years, and more than 50% of them have evidence of spinal osteoporosis. Almost 90% of women older than 75 years have significant radiographic evidence of osteoporosis.

The high prevalence of musculoskeletal disease in older adult patients who require assistance has a significant effect on the American economy. The annual cost of nursing home care for patients with musculoskeletal disease is almost $75 billion. More than 10 million individuals in the United States have some form of inflammatory arthritis, the most prevalent being rheumatoid arthritis. It is estimated that more than 7 million patients have this form of arthritis.

Musculoskeletal problems have the most significant financial effect on the aged population. More than $1 billion is spent annually by Medicare for hospitalization of patients with these conditions. This represents 20% of all Medicare payments.

Structure and Physiology

The principal functions of the musculoskeletal system are to support and protect the body and to bring about movement of the extremities for locomotion and the performance of tasks.

The parts of the musculoskeletal system are composed of variable forms of dense connective tissue, which include the following:

For a time, a layer of cartilage exists between the diaphysis and the epiphysis. This cartilage is known as the growth plate or epiphyseal plate. The purpose of the growth plate is to determine the longitudinal growth of the bone. The parts of a long bone are illustrated in Figure 17-1.

Cells in the periosteum can develop into osteoblasts, which lay down new bone, or into osteoclasts, which resorb bone. Trauma, infection, and tumors stimulate the development of osteoblasts. Osteoblasts secrete the matrix that is refashioned into lamellae and arranged to endure the mechanical stresses to which the bone is subjected.

A pathologic process that interferes with the normal architecture of bone tends to weaken it. Paget’s disease is a disease of bone in which there is a disruption of the normal architecture. Patients with this condition are extremely susceptible to pathologic fractures.

Skeletal muscle is an organ, the contraction of which produces movement.

Ligaments attach bone to bone, and tendons attach muscle to bone. Both are dense connective tissues that offer great resistance to pulling forces.

Cartilage is a type of connective tissue with great resilience. It plays an important role in joint function and in determining bone length.

The basic functional unit of the musculoskeletal system is the joint. A joint is a union of two or more bones. There are several types of joints in the body:

A hinge joint permits movement in only one axis: namely, flexion or extension. The axis is transverse. An example of a hinge joint is the elbow. A pivot joint permits rotation in one axis. The axis is longitudinal along the shaft of the bone. One bone moves around a central axis without any displacement from that axis. An example of a pivot joint is the proximal radioulnar joint. A condyloid joint permits movement in two axes. The articular surfaces are oval; thus these joints have been described as “egg-in-spoon” joints. One axis is the long diameter of the oval, and the other axis is the short diameter of the oval. The wrist joint is an example of a condyloid joint. A saddle joint is also a biaxial joint. The articular surfaces are saddle-shaped, with movements similar to those of a condyloid joint. The carpometacarpal joint of the thumb is an example of a saddle joint. The ball-and-socket joint is an example of a polyaxial joint; motion is possible in many axes. In a ball-and-socket joint, the articular surfaces are reciprocal segments of a sphere. The hip and shoulder joints are examples of ball-and-socket joints. A plane joint is also a polyaxial joint. In the plane joint, the articular surfaces are flat, and one bone merely rides over the other in many directions. The patellofemoral joint is an example of a plane joint. These different types of movable joints are shown in Figure 17-2.

The stability of a joint depends on the following:

It is necessary to be familiar with certain anatomic terms that refer to position (Table 17-3). The median plane bisects the body into right and left halves. A plane parallel to the median plane is a sagittal plane. The terms medial and lateral are used in reference to the sagittal plane. A position closer to the median plane is medial; farther from the median plane, it is lateral. In the upper limb, the term ulnar is often used to denote medial, and radial to denote lateral. In the lower limb, tibial is used to denote medial, and peroneal or fibular denotes lateral. These anatomic terms are illustrated in Figure 17-3.

The front of the body is the anterior, or ventral, surface, and the back of the body is the posterior, or dorsal, side. The palmar, or volar, aspect of the hand is the anterior surface. The dorsal aspect of the foot faces upward, and the plantar aspect is the sole. Proximal refers to the part of an extremity that is closest to its root; distal refers to the part farthest from the root.

The most important terms relating to deformities of the bone structure are valgus and varus. In a valgus deformity, the distal portion of the bone is displaced away from the midline, and angulation is toward the midline. In a varus deformity, the distal portion of the extremity is displaced toward the midline, and angulation is away from the midline. The name of the deformity is determined by the joint involved. A valgus deformity of the knees, knock-knee, is termed genu valgum. A varus deformity of the knee, bowleg, is termed genu varum.

In the evaluation of a joint, assess the range of motion. Each joint has a characteristic range of motion that can be measured passively and actively. Passive range of motion is the motion elicited when the examiner moves the patient’s body. Active range of motion is the motion the patient performs as a result of moving the musculature. The passive range of motion usually equals the active range of motion except in cases of paralyzed muscles or ruptured tendons. The range of motion of individual joints is discussed later in this chapter. Joint motion is measured in degrees of a circle, with the joint at the center. If a limb is extended with the bones in a straight line, the joint is at zero position. The zero position is the neutral position of the joint. As the joint is flexed, the angle increases. The concept of range of motion is illustrated in Figure 17-4.

The six basic types of joint motion are as follows:

The definitions of these motions and the joints at which they occur are summarized in Table 17-4.

The anatomy of the shoulder joint is illustrated in Figure 17-5. The joint movements at the shoulder are abduction and adduction, flexion and extension, and internal and external rotation. These motions are illustrated in Figure 17-6.

The anatomy of the elbow joint is shown in Figure 17-7. The joint movements at the elbow are flexion and extension and supination and pronation. These motions are illustrated in Figure 17-8.

The anatomy of the wrist and fingers is illustrated in Figure 17-9. The joint movements at the wrist are dorsiflexion (or extension) and palmar flexion and supination and pronation. These motions are illustrated in Figure 17-10. The joint movements at the fingers are abduction and adduction and flexion. These motions are illustrated in Figure 17-11. The joint movements of the thumb are flexion and extension and opposition. These motions are illustrated in Figure 17-12.

The anatomy of the hip is illustrated in Figure 17-13. The joint movements at the hip are flexion and extension, abduction and adduction, and internal and external rotation. These motions are illustrated in Figure 17-14.

The anatomy of the knee is shown in Figure 17-15. The joint movements at the knee are flexion and hyperextension. These motions are illustrated in Figure 17-16.

The anatomy of the ankle and foot is illustrated in Figure 17-17. There are 26 bones and 55 articulations in the foot. The bones can be divided into three regions: forefoot, midfoot, and rear foot. The forefoot is represented by the 14 bones of the toes and 5 metatarsals. The big toe (hallux) has two phalanges, two joints (interphalangeal [IP] joints), and two tiny, round sesamoid bones that enable it to move up and down. The sesamoid bones are about the size of a kernel of corn. These bones are embedded in the flexor hallucis brevis tendon, one of several tendons that exert pressure from the big toe against the ground and help initiate the act of walking: the propulsive phase of the gait cycle. The other four toes each have three bones and two joints. The phalanges are connected to the metatarsals by five metatarsophalangeal (MTP) joints at the ball of the foot. The forefoot bears half the body’s weight and balances pressure on the ball of the foot.

The midfoot consists of the three cuneiform bones, the cuboid, and the navicular. The midfoot has five irregularly shaped tarsal bones, forms the foot’s arch, and serves as a shock absorber. The bones of the midfoot are connected to the forefoot and the hindfoot by muscles and the plantar fascia (arch ligament).

The rear foot is composed of the talus and the calcaneus. The foot contains two arches: the longitudinal in the midpart and the transverse in the forepart. The midtarsal joint is formed by the articulations of the navicular to the talus and the calcaneus to the cuboid. The largest tarsal bone is the calcaneus, the bottom of which is cushioned by a layer of fat. The attachment of the foot to the leg occurs through the talus. The joint movements at the ankle are dorsiflexion and plantar flexion. The motion of the subtalar joint is inversion and eversion. These motions are illustrated in Figure 17-18.

The anatomy of the cervical spine is shown in Figure 17-19. The joint movements of the neck are flexion and extension, rotation, and lateral flexion. These motions are illustrated in Figure 17-20.

The anatomy of the lumbar spine is illustrated in Figure 17-21. The joint movements of the lumbar spine are flexion and extension, rotation, and lateral extension. These motions are illustrated in Figure 17-22.

A summary of normal joint ranges of motion is shown in Table 17-5.

Review of Specific Symptoms

The most common symptoms of musculoskeletal disease are as follows: