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A Quantitative Method to Assess Focal Acetabular Overcoverage Resulting From Pincer Deformity Using CT Data

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Clinical Orthopaedics and Related Research®



Current assessment techniques for focal acetabular overcoverage are neither consistent nor quantitatively accurate.


We propose: (1) a method to precisely quantify the amount of focal acetabular overcoverage in a patient’s pincer deformity based on CT data; (2) to evaluate the consistency of this method; and (3) to compare the method with conventional radiographic assessments.


We developed a method to assess focal acetabular overcoverage using points selected from CT scans along the acetabular rim after realigning the pelvis into a neutral position. Using four resampled and segmented pelvic CT scans of cadaveric specimens with virtually induced impingement, two observers independently tested the algorithm’s consistency. Our algorithm assessed the amount of focal acetabular overcoverage using CT data and projected data from reconstructed radiographs.


(1) We successfully showed the feasibility of the software to produce consistent, quantitative measurements. (2) Testing showed the average difference between observers in aligning the pelvis was 0.42°, indicative of a consistent approach. (3) Differences between measurements on three-dimensional (3-D) CT and simulated radiographs were significant.


The proposed method represents a new avenue in consistently quantifying focal acetabular overcoverage using CT models while correcting for pelvic tilt and rotation. Our analysis confirms AP hip radiograph simulations overestimate the amount of overhanging acetabular rim in a pincer deformity.

Clinical Relevance

This technique has potential to improve preoperative diagnostic accuracy and enhance surgical planning for correction of a pincer deformity resulting from focal acetabular overcoverage.

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We thank Dr Ofri Sadowsky for generously providing the software necessary to construct DRRs.

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Correspondence to Ryan J. Murphy MS.

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One or more of the authors (RJM, MA, TKS) have received funding from grant number 3 R01 EB006839 of the National Institute of Biomedical Imaging and Bioengineering (NIH/NIBIB) and grant number 1T32EB006351 from the NIH. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.

This work was performed at Johns Hopkins University and the Johns Hopkins University Applied Physics Laboratory, Baltimore, MD, USA.

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Murphy, R.J., Subhawong, T.K., Chhabra, A. et al. A Quantitative Method to Assess Focal Acetabular Overcoverage Resulting From Pincer Deformity Using CT Data. Clin Orthop Relat Res 469, 2846–2854 (2011).

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