The clinical relevance of limb length discrepancy (LLD) after total hip arthroplasty gains attention as the number of total hip arthroplasties increases. Although several techniques are commonly used to assess LLD using a pelvic radiograph, their accuracy is not well established. This study measures LLD using different techniques viewing the pelvis and compares the measurements with the true LLD.
Pelvic landmarks used included the femoral head, lesser trochanter, acetabular teardrop, ischial tuberosity, and tibial plafond. The true LLD was determined by finding the difference in distance between the lowest point of the ischial tuberosity and the tibial plafond as well as the top of the femoral head to the center of the tibial plafond for each lower limb.
Using pelvic landmarks to assess LLD is significantly different (P < .001) from the true LLD. The difference in distance from the center of the tibial plafond to the ischial tuberosity was not significantly different from the measurement from the top of the femoral head to the center of the tibial plafond (P = .08). Also, using the acetabular teardrop as a landmark has less reliability when compared to the ischial tuberosity.
Owing to the extensive variety of pathologies that are associated with LLD, preoperative planning should include an assessment of any preexisting LLD. Although it may be reasonable to compare pelvic measurements preoperatively and postoperatively to assess for changes, the data from this study do not support the estimation of the true LLD using a pelvic radiograph.