Optimal Level of Femoral Neck for Predicting Postoperative Stem Anteversion in Total Hip Arthroplasty for Crowe Type I Dysplastic Hip

Abstract

Objective: This study aimed to investigate the optimal level of femoral neck for measuring femoral anteversion to predict postoperative stem anteversion in Crowe type I developmental dysplasia of the hip.

Methods: This retrospective study analyzed 108 Crowe type I hips that underwent THA between January 2016 and December 2017, including 70 women and 19 men with a mean age of 63.08 ± 9.13 (range, 41-83) years. The single-wedge stem was used in 37 hips, the double-wedge stem was used in 71 hips. Computed tomography scans were performed pre- and post-operation. Femoral anteversion at six levels of the proximal femur were measured via preoperative two-dimensional computed tomography. Femoral anteversion at the level of the femoral neck osteotomy plane and postoperative stem anteversion were measured via three-dimensional reconstructed models.

Results: The mean follow-up period was 18.5 months (range, 12-27). The mean preoperative Harris Hip Score was 51.5 ± 8.7 and improved to 90.4 ± 7.8 (P < 0.001) by the last follow-up. There were no intraoperative fractures, and no infections occurred during the follow-up period. Two patients developed deep venous thrombosis. There was no sign of prosthetic loosening in all hips. No significant correlations were found between the height of the femoral neck osteotomy plane and postoperative stem anteversion (r = -0.119, P = 0.220). Femoral anteversion decreased gradually from 64.00° ± 10.51° at the center of lesser trochanter to 15.21° ± 13.31° at the head-neck junction, which was changed from more to less than stem anteversion (24.37° ± 13.86°). The femoral anteversion at femoral head-neck junction (15.21° ± 13.31°) was significantly less than postoperative stem anteversion (P = 0.000), with a difference of -9.16° ± 9.27°. The femoral anteversion at the level of the osteotomy plane (28.48° ± 15.34°) was significantly more than the postoperative stem anteversion (P = 0.000), with a difference of 4.11° ± 9.56°. Among all six levels and the level of osteotomy, femoral anteversion at the 10-mm level above the proximal base of lesser trochanter (22.65 ± 12.92) displayed the smallest difference (-1.72° ± 8.90°) and a good correlation (r = 0.764) with postoperative stem anteversion for all 108 hips, with a moderate correlation of 0.465 for single-wedge stem hips and an excellent correlation of 0.821 for double-wedge stem hips.

Conclusion: For Crowe type I hips, femoral anteversion would be different if it was measured via different levels of the femoral neck. The 10-mm level above the proximal base of the lesser trochanter could be an optimum choice for measuring femoral anteversion to predict postoperative stem anteversion.

Keywords: Developmental dysplasia; Femoral anteversion; Hip; Stem anteversion; Total hip arthroplasty.

Figure 1

Measurement of femoral anteversion via two‐dimensional computed tomography. (A) Six measurement levels of femoral anteversion: level a, centre of the lesser trochanter; level b, proximal base of the lesser trochanter; level c, 5 mm above level b; level d, 10 mm above level b; level e, 15 mm above level b; level f, femoral head–neck junction; g, the level showed the most posterior points of the femoral condyles. (B) Anteversions of the anterior cortex and posterior cortex were measured respectively as the angles formed by the cortical lines (white dashed lines) and the posterior aspect of the femoral condylar line. Femoral anteversion was calculated as the average of the anterior cortex anteversion and posterior cortex anteversion (white solid line). (C) Posterior aspect of the femoral condylar line at level g.

Figure 2

Measurement of femoral anteversion and stem anteversion via three‐dimensional reconstructed computed tomography. (A) The femoral anteversion at the level of the osteotomy plane was measured as the average (thin black dashed line) of the anterior cortex anteversion and posterior cortex anteversion (black solid lines) relative to the posterior aspect of the femoral condylar line (thick black dashed line). (B) The stem anteversion was measured as the angle formed by the stem neck major axis (white dashed line) and the posterior aspect of the femoral condylar line (black dashed line).

Figure 3

Change in femoral anteversion measured at different levels. From level a to f, the femoral anteversion (FA) was reduced gradually. Level a‐f, refer to Fig. 1. White dashed line: the posterior aspect of the femoral condylar line; white solid line: the middle line of the anterior cortex and posterior cortex.

Figure 4

Correlation of femoral anteversion measured at level d with stem anteversion for all 108 hips.

Figure 5

Correlations of femoral anteversion measured at level d with stem anteversion for single‐wedge stems (A) and double‐wedge stems (B).