Nonrandom evolution of end-stage osteoarthritis of the lower limbs.

OBJECTIVE Patients with unilateral hip or knee replacements for end-stage osteoarthritis (OA) are at high risk for future progression of OA in other joints of the lower extremities, often requiring additional joint replacements. Although the risks of future surgery in the contralateral cognate joints (i.e., contralateral hip replacement after an initial hip replacement) have been evaluated, the evolution of end-stage hip OA to OA involving the knee joints, and vice versa (i.e., noncognate progression) has not been investigated. Because characterization of OA progression in noncognate joints may shed light on the pathogenesis of multijoint OA, we investigated the pattern of evolution of end-stage lower extremity OA in a large, clinical cohort. METHODS Total joint replacement (TJR) was selected as a marker of end-stage OA, and a database comprising all lower extremity TJRs performed at a large referral center between 1981 and 2001 was accessed. Of the 5,894 patients identified, 486 patients with idiopathic OA who underwent hip replacement and 414 who underwent initial knee replacement were analyzed to determine the relative likelihood of subsequent TJRs. Patients with the systemic inflammatory arthropathy, rheumatoid arthritis (RA), were evaluated as a control population because RA progression is not considered to be a primarily mechanically mediated process. RESULTS The contralateral cognate joint was the most common second joint to undergo replacement in both the OA and the RA groups. However, in OA patients for whom the second TJR was in a noncognate joint, that joint was >2-fold more likely to be on the contralateral limb than on the ipsilateral limb (hip to knee P < 0.001; knee to hip P = 0.013). In contrast, among the RA cohort, the evolution was random and no laterality for noncognate TJR was observed at either the hip or the knee (P = 0.782). CONCLUSION This characterization of end-stage lower extremity OA demonstrates that the disease evolves nonrandomly; after 1 joint is replaced, the contralateral limb is significantly more likely to show progression of OA than is the ipsilateral limb. Thus, OA in 1 weight-bearing joint appears to influence the evolution of OA in other joints. The absence of such laterality in RA suggests that OA progression may be mediated by extrinsic factors such as altered joint loading.