Cup positioning relative to the acetabular rim planned with three-dimensional computed tomography improves precision in total hip arthroplasty: a randomized controlled trial.

BACKGROUND

Accurate acetabular cup positioning is essential for successful total hip arthroplasty (THA) outcomes. The conventional mechanical alignment guide (MAG) method provides moderate accuracy. We developed a novel technique for cup positioning that utilizes preoperative three-dimensional computed tomography (3D-CT) planning based on the native acetabular rim's relative position and compared cup orientation between this method and the MAG technique.

METHODS

A randomized controlled trial with 120 patients undergoing primary THA via the posterolateral approach targeted cup positions of 40° radiographic inclination (RI) and 20° radiographic anteversion (RA). The control group (n = 40) used a MAG for cup placement, while the study group (n = 80) utilized preoperative 3D-CT to measure native RI, calculate RA, and determine the cup overhang distance (COD). The cup inclination was positioned relative to the superior rim point and the transverse acetabular notch. The cup anteversion was adjusted to achieve overhang at the posterior or anterior rim point according to the planned COD. Postoperative RI and RA were assessed using tilt-adjusted plain radiographs and CT scans. The percentages of cups positioned within 5° of the target position (RI/RA of 40°/20° ± 5°), and within the Grammatopoulos aiming zone (RI/RA of 40°/20° ± 10°) were compared between the two groups.

RESULTS

The mean RI was 41.7° ± 5.4° (range, 33°-59°) in the control group and 39.9° ± 3.2° (range, 33.8°-45.5°) in the study group (p = 0.019). The mean RA was 19.5° ± 7.6° (range, 3°-33°) in the control group and 20.2° ± 3.3° (range, 12.9°-28.3°) in the study group (p = 0.356). Cup alignment within 5° of the target was achieved in 86.2% (69 hips) of the study group and 32.5% (13 hips) of the control group (p < 0.001). The study group had a significantly higher percentage of cups within Grammatopoulos aiming zone (100% vs. 77.5%, p < 0.001).

CONCLUSIONS

3D-CT-guided cup positioning relative to the acetabular rim can enhance the precision of cup placement in THA to achieve alignment within 5° of the target position.

TRIAL REGISTRATION

Thai Clinical Trials Registry (TCTR 20201220001). Registered on 20 December 2020. Prospectively registered.