Reliability study of measuring leg length discrepancy in patients with total hip arthroplasty using the tip of the greater trochanter

Background Although the tip of the greater trochanter is widely used in THA to adjust leg length discrepancy (LLD), its accuracy and reliability are still unknown. The aim of this study was to investigate the reliability of measuring LLD in patients with total hip arthroplasty using the distance from the tip of the greater trochanter to the inter-teardrop line Methods 128 patients who underwent THA in our department with preoperative and postoperative bilateral hips anteroposterior(AP) radiographs were reviewed. The distance between the bilateral anterior superior iliac spine and the medial malleolus (ASIS-MM) was measured before and after the operation. The distances from the vertex of the lesser trochanter to the bi-ischial line(LT-BI), the distance from the vertex of the lesser trochanter to the inter-teardrop line(LT-IT) and the distance from the tip of greater trochanter to the inter-teardrop line(GT-IT) were measured on the bilateral hips AP radiograph preoperatively and postoperatively. Taking X-ray magnification into account when measuring data. Use one-way ANOVA and paired t test to compare the differences between the four methods. The agreements between the four methods was evaluated using Bland-Altman analysis. Results There was no statistical difference between the four methods. Comparing GT-IT with MM-ASIS, ,LT-IT and LT-BI, the preoperative P values were 0.369, 0.581, and 0.402, and the postoperative P values were 0.755, 0.502 and 0.233. Comparing LT-BI with MM-ASIS and LT-IT, the P values were 0.151 and 0.372 preoperatively, and 0.179 and 0.917 postoperatively. Comparing LT-IT with MM-ASIS, the P value was 0.924 before surgery and 0.291 after surgery. Bland-Altman indicated that there were good agreements between GT-IT and LT-IT. Conclusion It is highly reliable to evaluate the LLD of patients with THA by using the difference in the distance between the tip of the greater trochanter and the inter-teardrop line.