The main functions of bone are support, protection of internal organs, voluntary movement, blood cell production, and mineral storage.¹ Bones provide the supporting framework that keeps the body from collapsing and also allows the body to bear weight. Bones also protect underlying vital organs and tissues. For example, the skull encloses the brain, the vertebrae surround the spinal cord, and the rib cage contains the lungs and heart. Bones serve as a point of attachment for muscles, which are connected to bones by tendons. Bones act as a lever for muscles, and movement occurs as a result of muscle contractions applied to these levers. Bones contain hematopoietic tissue for the production of red and white blood cells. Bones also serve as a site for storage of inorganic minerals such as calcium and phosphorus.

Bone is a dynamic tissue that continuously changes form and composition. It contains both organic material (collagen) and inorganic material (calcium, phosphate). The internal and external growth and remodeling of bone are ongoing processes.

Microscopic Structure.

Bone is classified according to structure as cortical (compact and dense) or cancellous (spongy). In cortical bone, cylindric structural units called osteons (Haversian systems) fit closely together, creating a dense bone structure (Fig. 62-1, A). Within the systems, the Haversian canals run parallel to the bone’s long axis and contain the blood vessels that travel to the bone’s interior from the periosteum. Surrounding each osteon are concentric rings known as lamellae, which characterize mature bone. Smaller canals (canaliculi) extend from the Haversian canals to the lacunae, where mature bone cells are embedded.

FIG. 62-1 Bone structure. A, Cortical (compact) bone showing numerous structural units called osteons. B, Anatomy of a long bone (tibia) showing cancellous and compact bone.

Cancellous bone lacks the organized structure of cortical bone. The lamellae are not arranged in concentric rings but rather along the lines of maximum stress placed on the bone. Cancellous bone tissue is filled with red or yellow marrow, and blood reaches the bone cells by passing through spaces in the marrow.

The three types of bone cells are osteoblasts, osteocytes, and osteoclasts.² Osteoblasts synthesize organic bone matrix (collagen) and are the basic bone-forming cells. Osteocytes are the mature bone cells. Osteoclasts participate in bone remodeling by assisting in the breakdown of bone tissue. Bone remodeling is the removal of old bone by osteoclasts (resorption) and the deposition of new bone by osteoblasts (ossification). The inner layer of bone is composed primarily of osteoblasts with a few osteoclasts.

Gross Structure.

The anatomic structure of bone is best represented by a typical long bone such as the tibia (see Fig. 62-1, B). Each long bone consists of the epiphysis, diaphysis, and metaphysis. The epiphysis, the widened area found at each end of a long bone, is composed primarily of cancellous bone. The wide epiphysis allows for greater weight distribution and provides stability for the joint. The epiphysis is also the location of muscle attachment. Articular cartilage covers the ends of the epiphysis to provide a smooth surface for joint movement. The diaphysis is the main shaft of the bone. It provides structural support and is composed of compact bone. The tubular structure of the diaphysis allows it to more easily withstand bending and twisting forces. The metaphysis is the flared area between the epiphysis and the diaphysis. Like the epiphysis, it is composed of cancellous bone.

The epiphyseal plate, or growth zone, is the cartilaginous area between the epiphysis and metaphysis. It actively produces bone to allow longitudinal growth in children. Injury to the epiphyseal plate in a growing child can lead to a shorter extremity that can cause significant functional problems. In the adult, the metaphysis and the epiphysis become joined as this plate hardens to mature bone.

The periosteum is composed of fibrous connective tissue that covers the bone. Tiny blood vessels penetrate the periosteum to provide nutrition to underlying bone. Musculotendinous fibers anchor to the outer layer of the periosteum. The inner layer of the periosteum is attached to the bone by bundles of collagen. No periosteum exists on the articular surfaces of long bones. These bone ends are covered by articular cartilage.

The medullary (marrow) cavity is in the center of the diaphysis and contains either red or yellow bone marrow.³ In the growing child, red bone marrow is actively involved in blood cell production (hematopoiesis). In the adult, the medullary cavity of long bones contains yellow bone marrow, which is mainly adipose tissue. Yellow marrow is involved in hematopoiesis only in times of great blood cell need. In adults, red marrow is found mainly in the flat bones, such as the pelvis, skull, sternum, cranium, ribs, vertebrae, and scapulae, and in the cancellous (“spongy”) material at the epiphyseal ends of long bones such as the femur and the humerus.

Types.

The skeleton consists of 206 bones, which are classified according to shape as long, short, flat, or irregular.

Long bones are characterized by a central shaft (diaphysis) and two widened ends (epiphyses) (see Fig. 62-1, B). Examples include the femur, humerus, and tibia. Short bones are composed of cancellous bone covered by a thin layer of compact bone. Examples include the carpals in the hand and the tarsals in the foot.

Flat bones have two layers of compact bone separated by a layer of cancellous bone. Examples include the ribs, skull, scapula, and sternum. The spaces in the cancellous bone contain bone marrow. Irregular bones appear in a variety of shapes and sizes. Examples include the sacrum, mandible, and ear ossicles.

Joints

A joint (articulation) is a place where the ends of two bones are in proximity and move in relation to each other. Joints are classified by the degree of movement that they allow (Fig. 62-2).

The most common joint is the freely movable diarthrodial (synovial) type. Each joint is enclosed in a capsule of fibrous connective tissue, which joins the two bones together to form a cavity (Fig. 62-3). The capsule is lined by a synovial membrane, which secretes a thick synovial fluid to lubricate the joint, reduce friction, and allow opposing surfaces to slide smoothly over each other. The end of each bone is covered with articular (hyaline) cartilage. Supporting structures (e.g., ligaments, tendons) reinforce the joint capsule and provide limits and stability to joint movement. Types of diarthrodial joints are shown in Fig. 62-4.

FIG. 62-3 Structure of diarthrodial (synovial) joint.

Cartilage

The three types of cartilage tissue are hyaline, elastic, and fibrous. Hyaline cartilage, the most common, contains a moderate amount of collagen fibers. It is found in the trachea, bronchi, nose, epiphyseal plate, and articular surfaces of bones. Elastic cartilage, which contains both collagen and elastic fibers, is more flexible than hyaline cartilage. It is found in the ear, epiglottis, and larynx. Fibrous cartilage (fibrocartilage) consists mostly of collagen fibers and is a tough tissue that often functions as a shock absorber. It is found between the vertebral discs and also forms a protective cushion between the bones of the pelvic girdle, knee, and shoulder.

Cartilage in synovial joints serves as a support for soft tissue and provides the articular surface for joint movement. It protects underlying tissues. The cartilage in the epiphyseal plate is also involved in the growth of long bones before physical maturity is reached. Because articular cartilage is considered to be avascular, it must receive nourishment by the diffusion of material from the synovial fluid. The lack of a direct blood supply contributes to the slow metabolism of cartilage cells and explains why healing and repair of cartilage tissue occur slowly.

Muscle

Bursae

Bursae are small sacs of connective tissue lined with synovial membrane and containing viscous synovial fluid. They are typically located at bony prominences or joints to relieve pressure and decrease friction between moving parts.⁵ For example, bursae are found between the patella and the skin (prepatellar bursae), between the olecranon process of the elbow and the skin (olecranon bursae), between the head of the humerus and the acromion process of the scapula (subacromial bursae), and between the greater trochanter of the proximal femur and the skin (trochanteric bursae). Bursitis is an inflammation of a bursa sac. The inflammation may be acute or chronic.

Gerontologic Considerations

Effects of Aging on Musculoskeletal System

Many of the functional problems experienced by the aging adult are related to changes of the musculoskeletal system. Although some changes begin in early adulthood, obvious signs of musculoskeletal impairment may not appear until later adult years. Alterations may affect the older adult’s ability to complete self-care tasks and pursue other customary activities. Effects of musculoskeletal changes may range from mild discomfort and decreased ability to perform activities of daily living to severe, chronic pain and immobility. The risk for falls also increases in the older adult due in part to a loss of strength. Aging can also bring changes in the patient’s balance, thus making the person unsteady, and proprioception (awareness of self in relation to the environment) may be altered.

The bone remodeling process is altered in the aging adult. Increased bone resorption and decreased bone formation cause a loss of bone density, contributing to the development of osteopenia and osteoporosis (see Chapter 64). Muscle mass and strength also decrease with aging. Almost 30% of muscle mass is lost by age 70. A loss of motor neurons can cause additional problems with skeletal muscle movement. Tendons and ligaments become less flexible, and movement becomes more rigid. Joints in the aging adult are also more likely to be affected by osteoarthritis⁶ (see Chapter 65).

Perform a musculoskeletal assessment with a particular emphasis on exercise practices. Obtain information on the type of exercise performed, including frequency and warm-up activities. Determine the impact of age-related changes of the musculoskeletal system on the older adult’s functional status. Specifically inquire about changes in self-care habits and ability to be self-sufficient in the home environment. Identify any musculoskeletal changes that increase the patient’s risk for falls, and discuss fall prevention strategies. Functional limitations that are accepted by older adults as a normal part of aging can often be halted or reversed with appropriate preventive strategies (see Table 63-1).

Diseases such as osteoarthritis and osteoporosis are not a normal part of growing older for many people. These metabolic bone diseases involve the deterioration of bone tissue (osteoporosis) and the destruction of cartilage (osteoarthritis). Carefully differentiate between expected changes and the effects of disease in the aging adult. Symptoms of disease can be treated in many cases, helping the older adult to return to a higher functional level. Age-related changes in the musculoskeletal system and differences in assessment findings are presented in Table 62-1.

TABLE 62-1

GERONTOLOGIC ASSESSMENT DIFFERENCES
Musculoskeletal System

Changes	Differences in Assessment Findings
Muscle
• Decreased number and diameter of muscle cells. Replacement of muscle cells by fibrous connective tissue. • Loss of elasticity in ligaments, tendons, and cartilage. • Reduced ability to store glycogen. Decreased ability to release glycogen as quick energy during stress. • Decreased basal metabolic rate.	• Decreased muscle strength and mass. Abdominal protrusion. Flabby muscles. • Increased rigidity in neck, shoulders, back, hips, and knees. • Decreased fine motor dexterity, decreased agility. • Slowed reaction times and reflexes as a result of slowing of impulse conduction along motor units. Earlier fatigue with activity.
Joints
• Increased risk for cartilage erosion that contributes to direct contact between bone ends and overgrowth of bone around joint margins. • Loss of water from discs between vertebrae, decreased height of intervertebral spaces.	• Joint stiffness, decreased mobility, limited ROM, possible crepitation on movement. Pain with motion and/or weight bearing. • Loss of height and shortening of trunk from disc compression. Posture change.
Bone
• Decreased bone density and strength, brittleness. • Slowed remodeling process.	• Loss of height and deformity such as dowager’s hump (kyphosis) from vertebral compression and degeneration. • Back pain, stiffness. • Bony prominences more pronounced. • Increased risk of osteopenia and osteoporosis.

Patient Introduction

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T.K. is a 78-yr-old white man brought to the emergency department by ambulance after falling on a patch of ice outside his home. He lay outside in the cold for 2 hr before neighbors found him. He is pale, diaphoretic, and complaining of excruciating pain in his left hip. The paramedics applied O₂ at 2 L via nasal cannula.

Critical Thinking

As you read through this assessment chapter, think about T.K.’s symptoms with the following questions in mind:

1. What is the most likely cause for T.K.’s acute hip pain?

2. What type of assessment would be most appropriate for T.K.: comprehensive, focused, or emergency? What would be your priority assessment(s)?

3. What questions would you ask T.K.?

4. What should be included in the physical assessment? What would you be looking for?

5. What diagnostic studies might you expect to be ordered?

Past Health History.

Because certain illnesses are known to affect the musculoskeletal system either directly or indirectly, question the patient about past medical problems, including tuberculosis, poliomyelitis, diabetes mellitus, parathyroid problems, hemophilia, rickets, soft tissue infection, and neuromuscular disabilities. In addition, past or developing musculoskeletal problems can affect the patient’s overall health. Trauma to the musculoskeletal system is a common reason for seeking medical evaluation. Questions should also focus on symptoms of arthritic and connective tissue diseases (e.g., gout, psoriatic arthritis, systemic lupus erythematosus), osteomalacia, osteomyelitis, and fungal infection of bones or joints. Ask the patient about possible sources of a secondary bacterial infection, such as ears, tonsils, teeth, sinuses, lungs, or genitourinary tract. These infections can enter the bones, resulting in osteomyelitis or joint destruction. Obtain a detailed account of the course and treatment of any of these problems.

Medications.

Question the patient regarding prescription and over-the-counter drugs and herbal products and nutritional supplements (see the Complementary & Alternative Therapies box in Chapter 3 on p. 39). Obtain detailed information about each treatment, including its name, the dose and frequency, length of time it was taken, its effects, and any possible side effects. Inquire about the use of skeletal muscle relaxants, opioids, nonsteroidal antiinflammatory drugs, and systemic and topical corticosteroids. Question the patient who has taken antiinflammatory drugs about GI distress or signs of bleeding.

In addition to drugs taken for treatment of a musculoskeletal problem, ask the patient about drugs that can have detrimental effects on this system. Some of these drugs and their potential side effects include antiseizure drugs (osteomalacia), phenothiazines (gait disturbances), corticosteroids (avascular necrosis, decreased bone and muscle mass), and potassium-depleting diuretics (muscle cramps and weakness). Question women about their menstrual history. Episodes of premenopausal amenorrhea can contribute to the development of osteoporosis.⁷ Ask postmenopausal women about their use of hormone therapy. Inquire about calcium and vitamin D supplements for both women and men.

Surgery or Other Treatments.

Obtain information about past hospitalizations related to a musculoskeletal problem. Document the reason for hospitalization; the date and the duration; and the treatment, including ongoing rehabilitation. Also record details of emergency treatment for musculoskeletal injuries. Obtain specific information regarding any surgical procedure, postoperative course, and complications. If the patient experienced a period of prolonged immobilization, consider the possible development of osteoporosis and muscle atrophy.

Functional Health Patterns.

The use of functional health patterns assists in organizing the assessment data. Table 62-2 summarizes specific questions to ask in relation to functional health patterns.

TABLE 62-2

HEALTH HISTORY
Musculoskeletal System

Health Perception–Health Management Pattern

• Describe your usual daily activities.

• Do you experience any difficulties performing these activities?* Describe what you do if you experience difficulty in dressing, preparing meals and feeding yourself, performing basic hygiene, writing or using the phone, or maintaining your home.

• Do you have to lift heavy objects? Do your work or exercise habits require repetitive motion or joint stress? Describe any specialized equipment you use or wear when you work or exercise that helps protect you from injury.

• Do you take any drugs or herbal products to manage your musculoskeletal problem? If so, what are their names and what are the expected effects?

Nutritional-Metabolic Pattern

• What is your usual daily intake of food and snacks?

• Do you have difficulties preparing your food?

• What dietary supplements do you take? (Ask specifically about calcium, vitamin D supplements, and herbal products.)

• What is your weight? Describe any recent weight loss or gain.

Elimination Pattern

• Does your musculoskeletal problem make it difficult for you to reach the toilet in time?*

• Do you need any assistive devices or equipment to achieve satisfactory toileting?*

• Do you experience constipation related to decreased mobility or to drugs taken for your musculoskeletal problem?*

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