The T-line as an intraoperative landmark for reproducing the native femoral anteversion during hip arthroplasty

Abstract

Three-dimensional computed tomographic (CT)-based preoperative planning for total hip arthroplasty (THA) enabled us to evaluate the cut surface of the femoral neck osteotomy. When we planned the stem placement in 20° of anteversion, we noticed that the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was coincident with the component torsion in many cases. We attempted to evaluate the accuracy of the T line for reproducing the native femoral anteversion during THA comparing it with the midcortical line, the reference guide previously reported by Suh. The institutional review board allowed a retrospective review of CT images of 100 normal hip joints. We performed virtual THA using the non-anatomic straight stem at three different cutting heights of 5, 10, or 15 mm above the lesser trochanter. The anteversion of the stem implanted parallel to the T line or midcortical line was measured. The mean difference of the stem anteversion using the T line and the native femoral anteversion was -0.77º (95 % CI: -1.92º to 0.38º), 0.69º (95 % CI: -0.42º to 1.79º) and 3.38º (95 % CI: 2.29º-4.46º) at cutting heights of 5, 10 and 15 mm, respectively. Using the midcortical line, stems tended to retroversion. Aligning the stem parallel to the T line on the cut surface provides a good reproduction of the femoral anteversion. The T line can be an useful intraoperative reference guide for the anteversion of the femoral component in THA for patients without severe hip deformity.