How to Estimate Femoral Stem Anteversion During Direct Anterior Approach Total Hip Arthroplasty

Abstract

Background: There are various traditional landmarks used to estimate the femoral component version, yet none are widely accepted by direct anterior surgeons. The purpose of this study was to compare bony landmarks easily accessible to direct anterior surgeons and to estimate which one provides the best estimate of femoral component anteversion.

Methods: A computed tomography database was used to identify 736 left entire-femur computed tomography scans. Seven visible anatomic landmarks were identified using a computer model in which a 45° virtual neck resection was made at 10 mm above the lesser trochanter. Thirteen axes, to reference the femoral stem position, were created between the 7 landmarks. Means and standard deviations (SDs) of angles between each axis and the transepicondylar axis (TEA) were compared for their precision.

Results: The traditional lesser trochanter predicted anteversion from the TEA was 34.1° (SD 9.7°). Predicted anteversion from the TEA was 3.3° (SD 8.1°) when aligned from the center of the canal to the middle of the medial calcar; 14.0° (SD 8.1°) from the center of the canal to the anterior 1/3 of the medial calcar; and 24.8° (SD 8.5°) from the center of the canal to the most anterior point on the medial calcar.

Conclusions: Compared to the lesser trochanter, 7 axes were more precise (lower SD) when predicting the version. Estimating the femoral component position, via simulated data, using 3 points along the medial calcar is a relatively precise and easily accessible tool for surgeons.

Keywords: Bony landmarks; Direct anterior approach; Femoral anteversion; Total hip arthroplasty.

Figure 1

SOMA computer model of bony landmarks and visualized vectors. Figure depicts a representative femur CT scan sliced at the level of the neck resection with (a) the landmarks constructed and (b) the axes defined. (a-d) Axes originating from the piriformis fossa are red, (e-h) those from the lateral cortex are yellow, and (k-m) those from the canal center are white. (i-j) Axes constructed by fitting a line to multiple points are dark green. The transepicondylar axis (TEA) is shown in blue.

Figure 2

Intraoperative estimation of femoral stem anteversion. (a and b) shows intraoperative photos of femoral exposure during a direct anterior total hip arthroplasty. (a) Shows the 3 lines representing the estimated stem anteversion of 3.3°, 14°, and 24.8°, from left to right, respectively. (b) Shows a femoral broach in the femoral canal during sequential broaching, with the tip of the broach approximately between the 3.3° and 14° position.