Determination of leg length discrepancy. A comparison of weight-bearing and supine imaging.

Leg length discrepancy (LLD) may be determined by comparison of leg (lower extremity) lengths measured during physical examination or by radiographic means. Leg lengths may be measured with the patient in standing, weight-bearing position or in supine position. We used a low dose digital radiographic unit to test the hypothesis that there is a difference in LLD determined from radiographs obtained with the patient standing and those obtained with the patient supine. Conventional physical examination measurements also were compared with the radiographic measurements. The amount of LLD that is clinically meaningful has not been established, although 10 to 12 mm has been used as a threshold difference of clinical meaningfulness in the past. Analysis of our data, using 10 mm as the threshold of difference, reveals high level correlation by linear regression analysis and no significant difference by t-test between measurements obtained from standing and supine radiographs. A weak correlation and statistical difference existed between each set of radiographic measurements and physical examination measurements.