Association of leg-length inequality with knee osteoarthritis: a cohort study.

BACKGROUND Leg-length inequality is common in the general population and may accelerate development of knee osteoarthritis. OBJECTIVE To determine whether leg-length inequality is associated with prevalent, incident, and progressive knee osteoarthritis. DESIGN Prospective observational cohort study. SETTING Population samples from Birmingham, Alabama, and Iowa City, Iowa. PATIENTS 3026 participants aged 50 to 79 years with or at high risk for knee osteoarthritis. MEASUREMENTS The exposure was leg-length inequality, measured by full-limb radiography. The outcomes were prevalent, incident, and progressive knee osteoarthritis. Radiographic osteoarthritis was defined as Kellgren and Lawrence grade 2 or greater, and symptomatic osteoarthritis was defined as radiographic disease in a consistently painful knee. RESULTS Compared with leg-length inequality less than 1 cm, leg-length inequality of 1 cm or more was associated with prevalent radiographic (53% vs. 36%; odds ratio [OR], 1.9 [95% CI, 1.5 to 2.4]) and symptomatic (30% vs. 17%; OR, 2.0 [CI, 1.6 to 2.6]) osteoarthritis in the shorter leg, incident symptomatic osteoarthritis in the shorter leg (15% vs. 9%; OR, 1.7 [CI, 1.2 to 2.4]) and the longer leg (13% vs. 9%; OR, 1.5 [CI, 1.0 to 2.1]), and increased odds of progressive osteoarthritis in the shorter leg (29% vs. 24%; OR, 1.3 [CI, 1.0 to 1.7]). LIMITATIONS Duration of follow-up may not be long enough to adequately identify cases of incidence and progression. Measurements of leg length, including radiography, are subject to measurement error, which could result in misclassification. CONCLUSION Radiographic leg-length inequality was associated with prevalent, incident symptomatic, and progressive knee osteoarthritis. Leg-length inequality is a potentially modifiable risk factor for knee osteoarthritis. PRIMARY FUNDING SOURCE National Institute on Aging.