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Cams and Pincer Impingement Are Distinct, Not Mixed: The Acetabular Pathomorphology of Femoroacetabular Impingement

Clinical Orthopaedics and Related Research® volume 468, pages 2143–2151 (2010)Cite this article

Abstract

Background

Many impinging hips are said to have a mix of features of femoral cam and an overcovered acetabulum causing pincer impingement. Correction of such a mixed picture by reduction of the cam lesion and the acetabular rim is the suggested treatment.

Questions/purposes

We therefore asked two questions: (1) Is the acetabulum in cam impingement easily distinguishable from the pincer acetabulum, or is there a group with features of both types of impingement? (2) Is version or depth of socket better able to distinguish cam from pincer impingement?

Methods

We analyzed the morphologic features of the acetabulum and rim profile of 20 normal, healthy hips, 20 with cams and 20 with pincers on CT. Pelvises were digitized, orientated to the best-fit acetabular plane, and a rim profile was plotted.

Results

Cam hips were shallower than normal hips, which in turn were shallower than pincer hips (84° ± 5° versus 87° ± 4° versus 96° ± 5°, respectively). The rim planes of cam, normal, and pincer hips had similar version (23°, 24°, 25°), but females were 4° more anteverted than males.

Conclusions

We concluded cam and pincer hips are distinct pathoanatomic entities. Cam hips are slightly shallower than normal, whereas pincers are deeper.

Clinical Relevance

Before performing surgery for cam-type femoroacetabular impingement, surgeons should consider measuring the acetabular depth. The cam acetabulum is shallower than normal and may be rendered pathologically shallow by acetabular rim resection leading to early joint failure.

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Acknowledgments

We thank Robin Richards for developing the software and Louise Brown for statistical advice.

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Authors and Affiliations

  1. Department of Orthopaedics, Imperial College, Charing Cross Hospital, London, W6 8RF, UK

    Justin Cobb MCh, Kartik Logishetty BSc, Kinner Davda MRCS & Farhad Iranpour MD

Authors
  1. Justin Cobb MCh
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  2. Kartik Logishetty BSc
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  3. Kinner Davda MRCS
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  4. Farhad Iranpour MD
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Correspondence to Justin Cobb MCh.

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Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.

Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.

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Cobb, J., Logishetty, K., Davda, K. et al. Cams and Pincer Impingement Are Distinct, Not Mixed: The Acetabular Pathomorphology of Femoroacetabular Impingement. Clin Orthop Relat Res 468, 2143–2151 (2010). https://doi.org/10.1007/s11999-010-1347-z

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  • DOI: https://doi.org/10.1007/s11999-010-1347-z

Keywords

  • Alpha Angle
  • Ischial Eminence
  • Femoroacetabular Impingement
  • Subtend Angle
  • Anterior Pelvic Plane