Atlas of pathophysiology, 2 Edition

Part II - Disorders

Musculoskeletal disorders

Osteoarthritis

Osteoarthritis, the most common form of arthritis, is a chronic condition caused by deterioration of joint cartilage. It usually affects weight-bearing joints (knees, feet, hips, lumbar vertebrae). Osteoarthritis is widespread (affecting more than 60 million persons in the United States) and is more common in women. Typically, its earliest symptoms manifest in middle age and progress. Osteoarthritis may be secondary to the wear and tear of aging (idiopathic) or to some abnormal initiating event.

Osteoarthritis is the most common cause of disability in the United States. Disability depends on the site and severity of involvement and can range from minor limitation of finger movement to severe disability in persons with hip or knee involvement. The rate of progression varies, and joints may remain stable for years in an early stage of deterioration.

Causes

Idiopathic (contributing factors)

·   Metabolic—endocrine disorders such as hyperparathyroidism

·   Genetic—decreased collagen synthesis

·   Chemical—drugs that stimulate collagen-digesting enzymes in synovial membranes, such as corticosteroids

·   Mechanical factors—repeated stress

Secondary (identifiable predisposing event)

·   Trauma (most common)

·   Congenital deformity

·   Obesity, poor posture

·   Occupational stress

Pathophysiology

Osteoarthritis occurs in synovial joints. The joint cartilage deteriorates, and reactive new bone forms at the margins and subchondral areas of the joints. The degeneration results from damage to the chondrocytes. Cartilage softens with age, narrowing the joint space. Mechanical injury erodes articular cartilage, leaving the underlying bone unprotected. This causes sclerosis, or thickening and hardening of the bone underneath the cartilage.

Cartilage particles irritate the synovial lining, which becomes fibrotic and limits joint movement. Synovial fluid may be forced into defects in the bone, causing cysts. New bone, called osteophyte (bone spur), forms at joint margins as the articular cartilage erodes, causing gross alteration of the bony contours and enlargement of the joint.

Signs and symptoms

·   Deep, aching joint pain

·   Stiffness in the morning and after exercise (relieved by rest)

·   Crepitus, or grating of the joint during motion

·   Heberden's nodes (bony enlargements of distal interphalangeal joints)

·   Altered gait from contractures

·   Decreased range of motion

·   Joint enlargement

·   Localized headaches (may be direct result of cervical spine arthritis)

·   Bouchard's nodes (bony enlargement of proximal interphalangeal joint)

Diagnostic test results

·   Erythrocyte sedimentation rate is elevated.

·   X-rays show:

§  narrowing of joint space or margin

§  cystlike bony deposits in joint space and margins, sclerosis of the subchondral space

§  joint deformity

§  bony growths

§  joint fusion.

·   Arthroscopy reveals bone spurs and narrowing of the joint space.

Treatment

·   Weight loss to reduce stress on the joint

·   Balanced rest and exercise

·   Medications, including aspirin and other nonsteroidal anti-inflammatory drugs; propoxyphene, acetaminophen, glucosamine, celecoxib

·   Support or stabilization of joint with crutches, braces, cane, walker, cervical collar, or traction

·   Intra-articular injections of corticosteroids (every 4 to 6 months) to try to delay node formation in fingers.

Surgical treatment (for severe disability or uncontrollable pain)

·   Arthroplasty—partial or total replacement of joint with prosthetic appliance

·   Arthrodesis or laminectomy—fusion of bones, primarily in spine

·   Osteoplasty—scraping and lavage of deteriorated bone

·   Osteotomy—changing alignment of bone to relieve stress on joint

P.227

OSTEOARTHRITIS OF THE HAND, KNEE, AND HIP

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