A New Method to Predict Postoperative Stem Anteversion in Total Hip Arthroplasty for Developmental Dysplasia of the Hip

Abstract

Background: Preoperative evaluation of femoral anteversion to predict postoperative stem anteversion aids the selection of an appropriate prosthesis and optimizes the combined anteversion in total hip arthroplasty (THA) for developmental dysplasia of the hip (DDH). The conventional prediction methods are based on the femoral anteversion measurement at the location of the femoral head and/or neck. However, varied differences between femoral anteversion and postoperative stem anteversion were demonstrated. This study investigated the predictive role of a new method based on the principle of sagittal three-point fixation.

Methods: From January 2017 to December 2018, a total of 133 DDH hips that underwent THA were retrospectively analyzed. There were 76 Crowe type I, 27 type II, and 30 type III hips. The single-wedge stem was used in 49 hips, and the double-wedge stem was used in 84 hips. Preoperative native femoral anteversion at the femoral head-neck junction, anterior cortex anteversion at 2 levels of the lesser trochanter, posterior cortex anteversion at 5 levels of the femoral neck, and postoperative stem anteversion were measured using two-dimensional computed tomography. Predictive anteversion by the new method was calculated as the average anteversion formed by the anterior cortex at the lesser trochanter and the posterior cortex at the femoral neck.

Results: For hips with different neck heights, different Crowe types, different stem types, or different femoral anteversions, native femoral anteversion showed widely varied differences and correlations with stem anteversion, with differences ranging from -1.27 ± 8.33° to -13.67 ± 9.47° and correlations ranging from 0.122 (p = 0.705, no correlation) to 0.813. Predictive anteversion formed by the anterior cortex at the lesser trochanter proximal base and posterior cortex 10 mm above the lesser trochanter proximal base showed no significant difference with stem anteversion, with less varied differences (0.92 ± 7.52°) and good to excellent correlations (r = 0.826).

Conclusion: Adopting our new method, predictive anteversion, measured as the average anteversion of the anterior cortex at the lesser trochanter proximal base and posterior cortex 10 mm above the lesser trochanter proximal base, predicted postoperative stem anteversion more reliably than native femoral anteversion.

Keywords: Developmental Dysplasia of the Hip; Femoral Anteversion; Stem Anteversion; Total Hip Arthroplasty.

Figure 1

The fixation of the femoral stem in the sagittal plane: (A) The anterior to posterior image after total hip arthroplasty (THA); (B) Computed tomography (CT) reconstruction image in the sagittal plane after THA; (C) Posterior cortex (PC) at the femoral neck; (D) Anterior cortex (AC) at the lesser trochanter (LT); (E) The stem is circular or elliptical at the distal stem.

Figure 2

Flowchart depicting data selection and categorization of the study.

Figure 3

The anteversion measurement of the anterior cortex and posterior cortex. (A) Six measurement levels of the proximal femur: Level a, center 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, the femoral head–neck junction. (B) The anteversion of the posterior cortex (PC) at Levels b, c, d, e, and f is measured as the angle formed by the cortical line (white solid line) and the posterior condylar axis (black dashed line). (C) The anteversion of the anterior cortex (AC) at Levels a and b is measured as the angle formed by the cortical line (white solid line) and the posterior condylar axis (black dashed line).

Figure 4

A representative case of anteversion measurement based on our novel method. (A) The preoperative X‐ray of a 66‐year‐old female with a DDH history. (B) The postoperative X‐ray of that patient. (C) The anteversion of the anterior cortex at level b was measured, and the anteversion angle was 12.3°. (D) The anteversion of the posterior cortex at level d was measured, and the anteversion angle was 32.5°. (E) The anteversion of the postoperative prosthesis axis was measured, and the anteversion angle was 22.2°. Based on our method, the predicting postoperative stem anteversion was 22.4°, which was pretty close to the actual stem anteversion (AC, anterior cortex; PC, posterior cortex; PA, prosthesis axis).