Musculoskeletal Aging: Osteoarthritis

The major components of the integrated musculoskeletal system are the muscles, bones, and joints. Aging is defined as the progressive degradation of biological function over time that results from an accumulation of biological damage that eventually exceeds the repairing capacities of the body. Age-associated changes in joint tissues include roughening of the articular cartilage surface and osteophyte formation. Chondrocytes are the main cells in charge of cartilage repair. With aging, chondrocytes experience a reduced proliferative capacity and a reduced synthetic capacity to produce matrix components. The cartilage undergoes thinning due to less hydration while the collagen network becomes stiffer. The cartilage then becomes less deformable or able to respond to compression and more prone to injury. Age-related joint changes are usually not severe enough to cause significant cartilage erosion.

Osteoarthritis (OA) is a type of arthritis characterized by chronic low-grade inflammation based on systemic inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Osteoarthritis, thought to be a misnomer for a noninflammatory condition, usually presents with evidence of local inflammation early on. It is considered to be a joint failure because multiple tissues are involved, including the synovium (joint lining), the underlying bone, the periarticular tissue, and the cartilage. OA prevalence increases with age, and it is calculated that by 65 years of age two thirds of the population will have radiographic evidence of OA in at least one joint. Before 50 years of age, men have more OA than do women, but this inverts after 50 years of age except for hip OA (always more prevalent in men). OA affects the hands, spine, hips, and knees, and it usually spares the ankles, wrists, and shoulders. African American men are 35% more likely than White men to have hip OA. Evidence also suggests an inverse relationship between OA and osteoporosis, both of which are frequent conditions in the elderly. Radiography remains the standard for diagnosing this condition. Magnetic resonance imaging (MRI) is more specific, but its cost precludes its pervasive use. Eburnation (indicative of full-thickness cartilage loss), osteophytes (bone buildup around the edge of the joint), and joint space narrowing (JSN) are the main radiographic and anatomical findings.

OA includes structural changes different from aging such as progressive cartilage loss, remarkable osteophyte formation, thickening of the joint capsule, and sclerosis of subchondral bone. OA morphological changes have been noted to begin during the fourth decade of life and become increasingly prevalent up to the eighth decade, a suggested upper limit after which the incidence of the disease appears to level off or possibly decline. In centenarians, the prevalence of symptomatic OA of the hip, knee, shoulder, or spine is only 54%. OA is not necessarily a consequence of aging, and factors associated with longevity may also protect individuals from developing OA.

Meniscal tears (damage to the special pads inside the knee joint) are highly prevalent in both asymptomatic [Page 398]and clinically osteoarthritic knees of older individuals. However, osteoarthritic knees with meniscal tears are not more painful than those without tears, and meniscal tears do not affect functional status. For a meniscectomy to be successful, the meniscal tear must be the source of the pain. Meniscal tears are also very common in asymptomatic older adults, being found in as many as 65% of asymptomatic individuals evaluated by MRI.

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