American Hip Institute

2015- Domb et al. Validating a Modified Circle Theorem Method for the Measurement of Acetabular Cup Anteversion on Plain Radiography with Intra-Operative Data from Robotic Assisted Total Hip Arthroplasty

Farid Amirouche, PhD a, Giovanni F. Solitro, PhD a, Siva Chandrasekaran, MD b, Benjamin G. Domb, MD c, MarkH. Gonzalez, MDa

Abstract
This study aims to validate a modified circle theorem method for the calculation of true version of the acetabular component on anteroposterior x-rays with intra-operative version data derived from robotic assisted total hip arthroplasty (THA). Planar anteversion measurements recorded intraoperatively in 80 THAs were correlated to measurements on anteroposterior radiographs. The mean anteversion of the cohort measured by the robotic system and on plain radiography was 21.2° ± 2.0° and 19.9° ± 3.4° respectively and 97.5% of cases were in a 30% relative error. The correlation between the true and planar measurements of anteversion on plain radiographs was strong (Pearson correlation coefficient of 0.9422). We conclude that the circle theorem method can be validated with data from robotic guided THA.

Acetabular cup position affects stability, range of motion and impingement in total hip arthroplasty (THA) [1]. Inclination and anteversion are the two most commonly analyzed parameters of cup positioning [2]. Lewinnek et al proposed a safe zone for acetabular inclination of 15°±10° to minimize dislocation rates [3].More recently, Dorr et al defined a safe zone for combined anteversion of the acetabulum and femur of 25° to 50° [4]. Following on fromthis, Nakashima et al demonstrated that THAswith a combined anteversion (Fig. 1) outsideof the range of 40° to 60°were 5.8 timesmore likely to dislocate than those within this range [5].

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