Assessment of acetabular version in total hip arthroplasty: an application of Widmer's technique in a regional setting.

Background: Acetabular prosthesis positioning in total hip arthroplasty is important in reducing the risk of dislocation. Assessment of version by computed tomography scan is expensive and involves a large radiation dose. We wished to assess the value of Widmer's technique, utilizing readily available radiographs, to determine cup anteversion.

Methods: Patients who underwent primary total hip arthroplasty by the senior author (AGS) at a single regional hospital over a 5-year period were eligible for inclusion. Measurements were performed using the technique described by Widmer, utilizing standard post-operative radiographs. Statistical analysis was undertaken in SPSS v22. Significance was accepted at P < 0.05.

Results: Assessment included 109 hips in 99 patients; 63 hips with cemented cups and 46 hips with uncemented cups. Mean acetabular anteversion in the cemented group was 11.9° (0-27.7, SD: 7) and in the uncemented group was 14.1° (10.3-32.7, SD: 7.1); this difference trended towards statistical significance (P = 0.09). Test-retest measurements showed high degree of correlation (Pearson test: 0.927, P < 0.001). There were 96 of 109 hips positioned in the Lewinnek safe zone of 5-25° anteversion. The crude dislocation rate in our cohort was 6.4% (7 of 109 hips) with all dislocations occurring in hips placed in the safe zone.

Conclusion: Widmer's technique is a reliable method for calculating acetabular version in a regional hospital setting and offers the individual surgeon a ready technique of personal quality control. Cup version was not a significant factor contributing to dislocation rates in our series.