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Osteoarthritis Cartilage. 2014 Feb;22(2):218-25. doi: 10.1016/j.joca.2013.11.007. Epub 2013 Nov 21.

Cam impingement: defining the presence of a cam deformity by the alpha angle: data from the CHECK cohort and Chingford cohort.

Author information

1
Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: r.agricola@erasmusmc.nl.
2
Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: e.waarsing@erasmusmc.nl.
3
Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: geraint.thomas@ndorms.ox.ac.uk.
4
Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: andrew.carr@ndorms.ox.ac.uk.
5
Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: m.reijman@erasmusmc.nl.
6
Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands; Department of General Practice, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: s.bierma-zeinstra@erasmusmc.nl.
7
Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: sion.glyn-jones@ndorms.ox.ac.uk.
8
Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands; Department of Biomechanical Engineering, Delft University of Technology, Delft, The Netherlands; Department of Orthopaedics and Rheumatology, University Medical Centre Utrecht, Utrecht, The Netherlands. Electronic address: h.h.weinans@umcutrecht.nl.
9
Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: nigel.arden@ndorms.ox.ac.uk.

Abstract

INTRODUCTION:

Cam impingement is characterized by abnormal contact between the proximal femur and acetabulum caused by a non-spherical femoral head, known as a cam deformity. A cam deformity is usually quantified by the alpha angle; greater alpha angles substantially increase the risk for osteoarthritis (OA). However, there is no consensus on which alpha angle threshold to use to define the presence of a cam deformity.

AIM:

To determine alpha angle thresholds that define the presence of a cam deformity and a pathological cam deformity based on development of OA.

METHODS:

Data from both the prospective CHECK cohort of 1002 individuals (45-65 years) and the prospective population-based Chingford cohort of 1003 women (45-64 years) with respective follow-up times of 5 and 19 years were combined. The alpha angle was measured at baseline on anteroposterior radiographs, from which a threshold for the presence of a cam deformity was determined based on its distribution. Further, a pathological alpha angle threshold was determined based on the highest discriminative ability for development of end-stage OA at follow-up.

RESULTS:

A definite bimodal distribution of the alpha angle was found in both cohorts with a normal distribution up to 60°, indicating a clear distinction between normal and abnormal alpha angles. A pathological threshold of 78° resulted in the maximum area under the ROC curve.

CONCLUSION:

Epidemiological data of two large cohorts shows a bimodal distribution of the alpha angle. Alpha angle thresholds of 60° to define the presence of a cam deformity and 78° for a pathological cam deformity are proposed.

KEYWORDS:

Alpha angle; Cam deformity; Cam impingement; Definition; Femoroacetabular impingement; Hip OA

PMID:
24269636
DOI:
10.1016/j.joca.2013.11.007
[Indexed for MEDLINE]
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