A new method of measuring leg length discrepancy on radiograph in patients undergoing total hip arthroplasty

Objective: To investigate the reliability of the distance between the tip of the greater trochanter and inter-teardrop line (GT-IT) in evaluating the leg length discrepancy (LLD) in patients underwent total hip arthroplasty (THA). Methods: Patients who underwent THA in Xi'an Honghui Hospital from August 2015 to February 2016 were enrolled in this study. The patients were measured for bilateral hips anterior-posterior (AP) radiograph preoperatively and postoperatively. Four distances measured, included: GT-IT, the tip of lesser trochanter and bi-ischial line (LT-BI); LT-IT and the anterior superior iliac spine and the medial malleolus (ASIS-MM). Magnification factor was considered when calculating absolute values. Intraclass correlation coefficient (ICC) was used to detect the reliability of the measurement data. Single factor analysis and paired t test were performed to compare data among the methods. Results: The ICC values of the four groups were greater than 0.80, which showed excellent agreement in the measurements. Single factor analysis of variance showed there were no statistically significant differences in the LLDs of the four groups preoperatively and postoperatively (F=0.914, 0.886, both P>0.05). There was no significant differences in preoperative and postoperative LLD between group GT-IT and group ASIS-MM, LT-BI or LT-IT(t=-1.544-1.114, all P>0.05). The LLDs were comparable between group LT-BI, ASIS-MM and LT-IT both preoperatively and postoperatively (t=1.577, 0.976, 1.344, -0.087, all P>0.05). And the LLD in group LT-IT and ASIS-MM were equivalent preoperatively and postoperatively (t=0.130, 1.063, both P>0.05). Bland-Altman plot illustrated high level of agreements between the four methods. Conclusion: Great reliability can be obtained with the GT-IT in evaluating the LLD in patients undergoing THA.