Controlling Leg Length Change During Total Hip Arthroplasty Using 3D Modeling and a Single Intraoperative Distance Measurement.

BACKGROUND: Leg length inequality following total hip arthroplasty (THA) is a major cause of patient dissatisfaction. This study evaluated the accuracy and feasibility of a workflow combining computed tomography (CT)-based preoperative planning with a single intraoperative linear distance measurement for leg length restoration in primary THA. METHODS: A consecutive series of 40 patients undergoing primary, mixed reality-assisted THA using a minimally invasive superior capsulotomy approach was analyzed. Preoperative three-dimensional (3D) planning calculated the distance between the prosthesis shoulder and the greater trochanter. This measurement was replicated intraoperatively to predict leg length change. Actual leg length change was assessed using pre- and postoperative standing electronic optical scan (EOS) images and compared with the intraoperative prediction. RESULTS: Preoperative leg length inequality averaged -2.4 ± 5.9 mm (range, -13 to 9). Predicted leg length change was 3.6 ± 3.1 mm (range, -2 to 15), whereas actual postoperative change measured 3.7 ± 3.1 mm (range, -2 to 12). This resulted in a mean absolute error of 0.1 ± 1.8 mm (range, -3.0 to 3.2). Leg length was restored within ± three mm in 95% of patients (38/40) and within ± five mm in 100% of patients (40 of 40). CONCLUSION: Patient-specific 3D planning combined with a single intraoperative measurement achieved highly accurate leg length restoration in primary THA. This streamlined workflow may improve leg length control compared with intraoperative image assessment, conventional navigation, or robotics.