Abstract
Proper positioning of the acetabular cup deters dislocation after total hip arthroplasty (THA) and is therefore a key focus for orthopedic surgeons. The concept of a safe zone for acetabular component placement was first characterized by Lewinnek et al. and furthered by Callanan et al. The safe zone concept remains widely utilized and accepted in contemporary THA practice; however, components positioned in this safe zone still dislocate. This study sought to characterize current mass trends in cup position identified across a large study sample of THA procedures completed by multiple surgeons. This retrospective, observational study reviewed acetabular cup position in 1,236 patients who underwent THA using computer-assisted navigation (CAS) between July 2015 and November 2017. Outcomes included acetabular cup position (inclination and anteversion) measurements derived from the surgical navigation device and surgical approach. The overall mean cup position of all recorded cases was 21.8° (±7.7°, 95% CI = 6.7°, 36.9°) of anteversion and 40.9° (±6.5°, 95% CI = 28.1°, 53.7°) of inclination (Table 1). For both anteversion and inclination, 65.5% (809/1236) of acetabular cup components were within the Lewinnek safe zone and 58.4% (722/1236) were within the Callanan safe zone. Acetabular cups were placed a mean of 6.8° of anteversion (posterior/lateral approach: 7.0°, anterior approach: 5.6°) higher than the Lewinnek and Callanan safe zones whereas inclination was positioned 0.9° higher than the reported Lewinnek safe zone and 3.4° higher than the Callanan safe zone (Figure 1,2). Our data shows that while the majority of acetabular cups were placed within the traditional safe zones, the mean anteversion orientation is considerably higher than those suggested by the Lewinnek and Callanan safe zones. The implications of this observation warrant further investigation.
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