Can Anatomic Measurements of Stem Anteversion Angle Be Considered as the Functional Anteversion Angle?

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Radiology

Background:

• Stem anteversion is crucial for preventing implant impingement in total hip arthroplasty (THA).
• Anatomical stem anteversion measurements may not reflect functional femoral anteversion due to axial rotation.
• Evaluating femoral rotational angle (FRA) in different positions is necessary to understand functional anteversion.

Purpose of the Study:

• To measure the femoral rotational angle (FRA) in supine and standing positions before and after total hip arthroplasty (THA).
• To evaluate the difference between anatomic and functional femoral anteversion measurements.
• To assess the variability of FRA and its implications for THA outcomes.

Main Methods:

• Retrospective analysis of 191 hips (174 patients) undergoing THA for osteoarthritis.
• Measurement of FRA using computed tomography (CT) segmentation and 2D-3D registration in supine and standing positions, pre- and post-operatively.
• Calculation of the proportion of cases with absolute FRA <15° in both positions.

Main Results:

• Preoperative FRA averaged 0.3° ± 8.3° (supine) and -4.5° ± 8.8° (standing).
• Postoperative FRA averaged -3.8° ± 9.0° (supine) and -14.3° ± 8.3° (standing).
• The percentage of hips with absolute FRA <15° decreased from 70% preoperatively to 45% postoperatively.

Conclusions:

• Significant variability exists in femoral rotational angle (FRA), particularly after THA.
• Postoperative FRA measurements show substantial changes, especially in the standing position.
• Anatomical stem anteversion may not accurately represent functional femoral anteversion after THA.