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Morphologic and angular planning for cam resection in femoro-acetabular impingement: value of the omega angle

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Abstract

Purpose

The alpha angle is used to quantify in a single plane the head–neck junction deformity of cam femoro-acetabular impingement (FAI). When the deformity overlaps the superior retinaculum, femoral head osteoplasty in this area can jeopardise intra-articular vascular structures. This study proposes a new angular measure of the linear radial extension of cam deformity as a planning tool for bone resection and compares the accuracy of femoral head osteoplasty using open and arthroscopic surgery.

Methods

Twenty-five symptomatic patients operated on for FAI were included in this study. Radial magnetic resonance imaging (MRI) was done before and after surgery. Bi-dimensional coordinates of the vascular foramina and radial extension of the deformity (omega angle) were measured. This extension was correlated with the vascular foramina location and alpha-angle value. Accuracy of resection and hip function were evaluated before and after surgery.

Results

The cam lesion frequently extended posteriorly. No relation between values of alpha and omega angles was found. Cam resection was complete in 88 % of cases; there was a significant improvement in outcome score after surgery.

Conclusions

This study showed that alpha angle, measured in one plane, was not a predictor of the radial extension of cam deformity. To achieve a full resection, it was frequently necessary to extend the femoral head osteoplasty over the retinacular area. Pre-operative determination of the omega angle and location of the vascular foramina helped improve cam resection safety and accuracy.

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Acknowledgments

We thank the Hospital da Luz Radiology department for providing MRI equipment and all the processing software necessary for geometrical analysis

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, Hospital da Luz, Avenida Lusíada, 100, 1500-650, Lisbon, Lisbon, Portugal

    Paulo Renato Amaral Rego

  2. Department of Radiology, Hospital da Luz, Lisbon, Portugal

    Vasco Mascarenhas & Augusto Gaspar

  3. Department of Orthopaedic Surgery, University Hospitals Coventry and Warwickshire, West Midlands, UK

    Filipe S. Oliveira

  4. Department of Orthopaedic Surgery, Hospital Beatriz Angelo, Lisbon, Portugal

    Pedro C. Pinto & Joana Ovídio

  5. Department of Orthopaedic Surgery, Hospital Universitari Vall d’Hebron, Universitat Autònoma de Barcelona, Barcelona, Spain

    Diego G. Collado

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  1. Paulo Renato Amaral Rego
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  2. Vasco Mascarenhas
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  3. Filipe S. Oliveira
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Correspondence to Paulo Renato Amaral Rego.

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The authors declare that they have no conflict of interest and there was no founding involved in the preparation of this manuscript

Ethical approval

This article does not include results of experimental investigations on humans, and as a retrospective study, formal consent was not required. Informed consent from all patients was obtained on a routine basis for surgical procedures. We obtained formal consent from our institutional review board to perform geometric analysis on imaging files.

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Rego, P.R.A., Mascarenhas, V., Oliveira, F.S. et al. Morphologic and angular planning for cam resection in femoro-acetabular impingement: value of the omega angle. International Orthopaedics (SICOT) 40, 2011–2017 (2016). https://doi.org/10.1007/s00264-015-3053-7

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  • DOI: https://doi.org/10.1007/s00264-015-3053-7

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