An Alternative Intraoperative Radiographic Method for Optimizing Cup Inclination during Total Hip Arthroplasty

During total hip arthroplasty (THA), the location of the acetabular prosthesis is very important for guaranteeing successful surgery. However, this remains a challenge for many surgeons. This study aimed to investigate the feasibility of using the intraoperative fluoroscopic iliopubic tangential angle (IPTA) to determine the valgus angles of acetabular prostheses.

In the first stage, the IPTA and valgus angles of native acetabula were defined and measured in 102 THAs obtained from the picture archiving and communication systems of our hospital. Obturator foramen morphology was also measured and divided into groups according to the axial length ratio. Correlations between obturator foramen morphology and IPTA and valgus angles of native acetabula were then determined. In the second stage, angular differences (angle θ) between the IPTA and valgus angles of native acetabula were measured during unilateral THA in 136 patients to determine whether this is a stable value that could be used as a reference for placement of acetabular prostheses. Postoperative data such as Harris Hip Score (HHS) scores and complications were collected and evaluated.

The average IPTA at the apex of the true acetabulum was 58.8° ± 4.1°. The average valgus angle of native acetabula was 43.1° ± 3.9° and angle θ was 15.7° ± 1.3°. Obturator foramen morphology was divided into five groups according to the axial length ratio. IPTA was closely related to obturator foramen morphology (Pearson r = 0.489, P ≈ 0.000). Angle θ was stable and independent of obturator foramen morphology. When the IPTA and angle θ were used as references for placing acetabular prostheses in 136 THAs, the average postoperative valgus angles of acetabular prostheses was 45.13° ± 4.07° and the good-to-excellent rate was 97.05%. There were no short-term complications such as fracture, dislocation or infection. The average HHS score 6 months after surgery was 37.2 higher than the preoperative score, this difference being significant (P < 0.01). Neither infection nor dislocation was found 6 months after surgery.

The IPTA (at the apex of the true acetabulum) and angle θ (obtained by intraoperative fluoroscopy) are consistent in determining the postoperative valgus angle of acetabular prosthesis during THA. Thus, IPTA and angle θ are of value in guiding placement of acetabular prostheses; in particular, this method can facilitate the learning of young surgeons.