This registry-based cohort study analyzed 2,061 consecutive THA and hip resurfacing cases at Massachusetts General Hospital (2004–2008). It asked what percentage of acetabular cups are optimally positioned and which patient or surgical factors independently predict malpositioning. Abduction (30°–45°) and version (5°–25°) angles were measured from postoperative radiographs using digital software.
Half of acetabular cups are malpositioned even at elite centers — and the Lewinnek safe zone (anteversion 5°–25°, abduction 30°–50°) remains the most widely cited positioning target precisely because straying outside it raises dislocation risk.
When you are scrubbed on a THA, the surgical approach is the single most powerful modifiable risk factor you can influence. MIS carries a sixfold malpositioning penalty vs. Posterolateral. In any MIS case, or when the surgeon averages fewer than 20–30 THAs per year, intraoperative navigation is not a luxury. The data here directly support its routine use.
In obese patients, expect landmark identification to be harder and position your retractors and your mental expectations accordingly. The compounding effect of obesity plus a low-volume surgeon plus MIS pushes malpositioning probability above 90%.
This paper is why many high-volume programs now feed monthly cup positioning data back to individual surgeons. Real-time registry feedback is the quality-improvement tool the authors implemented directly as a result of these findings.
This registry-based cohort study analyzed 2,061 consecutive THA and hip resurfacing cases at Massachusetts General Hospital (2004–2008). It asked what percentage of acetabular cups are optimally positioned and which patient or surgical factors independently predict malpositioning. Abduction (30°–45°) and version (5°–25°) angles were measured from postoperative radiographs using digital software.
Half of acetabular cups are malpositioned even at elite centers — and the Lewinnek safe zone (anteversion 5°–25°, abduction 30°–50°) remains the most widely cited positioning target precisely because straying outside it raises dislocation risk.
When you are scrubbed on a THA, the surgical approach is the single most powerful modifiable risk factor you can influence. MIS carries a sixfold malpositioning penalty vs. Posterolateral. In any MIS case, or when the surgeon averages fewer than 20–30 THAs per year, intraoperative navigation is not a luxury. The data here directly support its routine use.
In obese patients, expect landmark identification to be harder and position your retractors and your mental expectations accordingly. The compounding effect of obesity plus a low-volume surgeon plus MIS pushes malpositioning probability above 90%.
This paper is why many high-volume programs now feed monthly cup positioning data back to individual surgeons. Real-time registry feedback is the quality-improvement tool the authors implemented directly as a result of these findings.