Assessment of the mechanical axis in adolescent tibia vara.

To assess precision of measurement, the mechanical axis was determined by two independent observers on 52 radiographs of 15 obese patients with adolescent tibia vara. Special, but simple, modifications in radiographic technique are described that allow simultaneous exposure of the hip, knee, and ankle joints. Even in this challenging population, assessment of the alignment of the lower extremity is possible with excellent precision using the mechanical axis. In 42 of the 52 radiographs, the two independent observers differed by less than or equal to 1 degree. The mechanical axis is superior to measurement of the tibial-femoral shaft angle for evaluation of lower extremity alignment.