Background The success of THA largely depends on correct placement of the individual components. Traditionally, these have been placed freehand using anatomic landmarks, but studies have shown poor accuracy with this method. Questions/purposes Specifically, we asked (1) does using fluoroscopy lead to more accurate and greater likelihood of cup placement with the Lewinnek safe zone than does freehand cup placement; (2) is there a learning curve associated with the use of fluoroscopy for cup placement; (3) does the use of fluoroscopy increase operative time; and (4) is there a difference in leg length discrepancy between freehand and fluoroscopic techniques? Methods This series consisted of 109 consecutive patients undergoing primary THA, conversion of a previous hip surgery to THA, and revision THA during a 24-month period. No patients were excluded from analysis during this time. The first 52 patients had cups placed freehand, and then the next 57 patients had acetabular components placed using fluoroscopy; the analysis began with the first patient treated using fluoroscopy, to include our initial experience with the technique. The abduction, version, and limb length discrepancy were measured on 6-week postoperative pelvic radiographs obtained with the patient in the supine position. Operative time, sex, age, BMI, diagnosis, operative side, and femoral head size were recorded as possible confounders. Results Cups inserted freehand were placed in the ideal range of abduction (30°-45°) and anteversion (5°-25°) 44% of the time. With fluoroscopy, placement in the Lewinnek safe zone for both measures significantly increased to 65%. The odds of placing the cup in the Lewinnek safe zone for abduction and version were 2.3 times greater with the use of fluoroscopy (95% CI, 1.2-5.0; p = 0.03). Patients undergoing primary THAs (32 freehand, 35 C-arm) had cup placement in the safe zone for abduction and version 44% of the time freehand and 57% of the time with fluoroscopy, which failed to reach statistical significance. There was no difference in operative time, patient age, sex, operative side, diagnosis, limb length discrepancy, or femoral head size between the two groups. Conclusions The use of fluoroscopy to directly observe pelvic position and acetabular component placement increased the success of placement in the Lewinnek safe zone in this cohort of patients having complex and primary THAs. This is a simple, low-cost, and quick method for increasing successful acetabular component alignment. The study population included a large proportion of patients

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Purpose This study evaluates acetabular cup position in the setting of revision total hip arthroplasty (THA) with severe acetabular bone defects. Methods With a definition of safe zone of abduction (30-50°) and anteversion (5-25°), acetabular cup position was measured by a digital image analysis program for 34 patients with Paprosky type III acetabular bone defects. Results There were 24 cups (71 %) for abduction and 26 cups (76 %) for anteversion located in the safe zone. Nineteen cups (56 %) were within the safe zone for both abduction and anteversion. There was no dislocation, however one cup out of the safe zone resulted in early cup failure due to aseptic loosening. Conclusions The acetabular cup positioning in patients with Paprosky type III defects was 'optimal' in half of the cases. The prevalence of optimal acetabular cup position was similar to those reported in primary THA, suggesting that the presence of a large acetabular bone defect may not be a significant risk factor for suboptimal acetabular cup positioning in the setting of revision THA.

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