Estimation of cup orientation on intraoperative fluoroscopy in total hip arthroplasty: how safe is the safe zone—an experimental study

Background

Accurate acetabular cup orientation in total hip arthroplasty (THA) is crucial for successful outcomes. Intraoperative fluoroscopy may be used to evaluate acetabular cup placement. This study aimed to evaluate the accuracy of purely visual estimation of cup inclination and anteversion using intraoperative fluoroscopy, considering different surgeon experience levels and cup designs.

Methods

Thirty-five surgeons with varying levels of experience participated in the study. Standardized fluoroscopic images depicting two different cementless acetabular cup designs placed in a bone model were used. Inclination values ranged from 20 to 60°, while anteversion values ranged from 0 to 40°, both in 5° increments, resulting in 162 combinations of cup orientation. Each participant received a randomly compiled sequence of all images and was provided with instructions for estimating inclination and anteversion angles, and was asked additionally to categorize cup orientations into predefined safe zones, utilizing two definitions: (a) an institutional safe zone (inclination 35 to 45°, anteversion 10 to 20°), and (b) the safe zone according to Lewinnek et al. (inclination 30 to 50°, anteversion 5 to 25°). Participants had no time limit and were not allowed to use measuring tools during the estimation process.

Results

No significant difference in the precise estimation of inclination and anteversion was found among surgeons of varying experience levels. However, the ability to correctly identify whether cup orientation fell within predefined safe zones improved with surgical experience and seniority. Cup design influenced estimation of inclination, with one design showing superior accuracy. Estimation of anteversion remained consistent across designs. The influence of anteversion on inclination estimation and vice versa was minimal. Safe zone definitions did not significantly affect classification accuracy between cup designs.

Conclusion

While surgical experience did not improve angle estimation accuracy in degrees, it was associated with more accurate identifications of positions within clinically relevant safe zones. Cup design influenced inclination estimation. Our findings emphasize the importance of precise cup positioning in THA and highlight areas for potential improvement in surgical practice and training.