Osteoarthritis (OA) is one of the most common diseases affecting the general population and is characterized by progressive, noninflammatory degenerative changes primarily involving the hips, knees, spine, hands, and feet. Among veterans the incidence and prevalence of OA is considerably higher than the incidence found in the general population. A study examining active-duty service members between 1999 and 2008 reported a 19-fold higher incidence in service members aged > 40 years compared with those aged < 20 years.1 In addition, women and African American service members seem to have a higher incidence of OA compared with other populations. Overall, the economic burden of OA is estimated to approach or exceed $60 billion annually and will continue to increase due to longer life expectancies in veterans. 2,3 Much of this burden relates to a lack of disease-modifying treatment and inadequacy of analgesic therapy.
Patterns of Osteoarthritis
The strongest risk factor associated with OA is age. Osteoarthritis is the most common cause of pain and disability in the elderly population. 4 A heritable component seems to be associated with primary OA as shown by family risk studies. 5 Estrogenic effects seem to protect younger women, whereas postmenopausal women are at greater risk after age 50 years. Previous joint trauma and activities have a large impact on the risk of developing OA later, particularly those activities and occupations requiring high-impact joint loading, such as those often seen in veterans. Other modifiable risk factors include smoking and obesity. The risk for knee OA has been found to increase 30-fold in patients with a body mass index > 30. 6
Several OA disease patterns exist. The disorder can be characterized as primary or secondary. Primary OA classically presents in the aging male or postmenopausal female involving the apophyseal joints of the lumbar and cervical spine; base of the thumb (first carpometacarpal,[CMC] joint); proximal or distal interphalangeal joints (PIPs and DIPs) of the hand, knee, or hip; or the first metatarsophalangeal joint. The disease may be localized to 1 joint (localized OA) or involve multiple joints (generalized OA). The disease is more common in men aged < 45 years and more common in women aged > 45 years. In either sex, progression with age is a prominent feature.
Rarely, patients may present with inflammatory arthritis in a distribution typical of OA that is not associated with psoriasis or another disease. This form is known as inflammatory or erosive OA. A minority of cases present with rapidly progressive hip or knee degeneration, the cause of which is unknown. Osteoarthritis involving the metacarpophalangeal joints (MCPs), wrists, elbows, shoulders, or ankles is much less common. Patients with radiographic evidence of OA at these sites should be evaluated for a cause of secondary OA.
Patients often develop secondary OA in the setting of inflammatory arthritis, crystal-induced arthritis, and other systemic diseases. Causes of secondary OA should be considered when OA manifests in an atypical joint. Common causes of secondary OA are outlined in Table 1. A careful history may undercover a prior diagnosis of gout, calcium pyrophosphate deposition disease, or infectious arthritis in the affected joint. An important metabolic cause of secondary OA is hemochromatosis, which can lead to osteophytic change primarily in the second and third MCPs. Patients with diabetes mellitus-associated neuropathy may develop destructive changes in the foot (Charcot joint).