The impact of surgeons' visual angle misperception on acetabular cup positioning accuracy: a retrospective multicentre cohort study.

Background: Precise acetabular cup placement in total hip arthroplasty (THA) heavily relies on surgeons' visual judgment of angles. However, whether inherent visual angle misperception among surgeons affects surgical outcomes remains unclear. This study is the first to reveal that surgeons universally exhibit visual angle misperception, a key factor causing the cup implant positioning deviations in THA.

Methods: We validated this phenomenon through three steps. Experimental Validation: Five surgeons were asked completed 2D angle assessments to verify the visual angle misperception. Surgical Simulation: A self-developed "Dynamic Angle-Measuring System (DAMS)" simulated cup implantation for assessing the impact of angle misperception on cup orientation. Clinical Data: Retrospective analysis of 853 THA cases (683 patients) between 2015 and 2019 were collected for comparing mismatches between actual cup angles and surgeons' target angles, and between experienced and junior surgeons.

Results: All surgeons exhibited visual angle misperception in 2D and 3D angle assessments, with greater impact on anteversion than abduction angles. In in vitro simulations, discrepancies between actual and targeted anteversion angles were statistically significant (e.g., 16.8° vs. 20.0°, 22.6° vs. 25.0°; P < 0.05). These findings were corroborated in the in vivo data (e.g., 15.3° vs. 20.0°, 22.4° vs. 25.0°; P < 0.05), with an individualized fixed deviation among surgeons. Clinically, increased surgical experience only reduced the dispersion (SD value) without eliminating visual angle misperception bias.

Conclusions: Our study is the first to provide that visual angle misperception is a hidden cause of cup positioning bias in THA, and experience alone cannot eliminate this bias causing by visual angle misperception, although experience reduced variability in placement. Recognizing and addressing this cognitive bias, and further targeted training to improve spatial perception, compensate inherent angle misperception bias, may lead to better patient outcomes.