Harvard Women's Health Watch

In the journals: Unequal leg length may be a risk for osteoarthritis of the knee

Osteoarthritis of the knee is a common condition in which the cartilage covering the ends of the bones of the knee joint breaks down, permitting the bones to grind against each other. This painful condition affects 6% of the adult population in the United States, causing considerable disability and reduced quality of life. The exact cause of the disorder is unclear, but some research has suggested that people with unequal leg lengths are more likely to have the condition. Now, a study has confirmed an association between discrepant leg length and an increased risk of progressive or new-onset knee osteoarthritis. The results were published in the Annals of Internal Medicine (March 2, 2010).

Measuring leg length

illustration of ways to measure leg length

In the Annals study, leg length was measured with x-rays and defined as the distance from the center of the ball of the hip joint (femoral head) to the front of the ankle above the joint (tibial mid-plafond point). A tape measure is less precise but much simpler to use: with the patient lying on her back, the clinician measures from the bony point on the front of the pelvic bone (anterior superior iliac spine) to the bony part of the inner ankle joint (medial malleolus).

As part of the nationwide Multicenter Osteoarthritis Study, researchers collected data on 3,026 adults ages 50 to 79 who had knee pain or were at risk for knee osteoarthritis. X-rays were taken to measure leg length and evaluate knee osteoarthritis at the start of the study and after 30 months. People whose legs differed in length by at least 1 centimeter (almost a half-inch) were more likely than people with equal-length legs to have osteoarthritis at the start of the study and more likely to develop the symptoms during the study. Any symptoms they had at the start were also more likely to get worse. The shorter leg was most often affected.

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