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. 2013 Jan;86(1021):20120182.
doi: 10.1259/bjr.20120182.

Discrete mineralisation of the acetabular labrum: a novel marker of femoroacetabular impingement?

W R Cooke  1 , H S Gill, D W Murray, S J Ostlere
Affiliations

Discrete mineralisation of the acetabular labrum: a novel marker of femoroacetabular impingement?

W R Cooke et al. Br J Radiol. 2013 Jan.

Abstract

Femoroacetabular impingement (FAI) is increasingly thought to play a role in the development of hip osteoarthritis, but is difficult to define clinically and on imaging. This study investigates mineralisations of the acetabular labrum (MALs), which are small, discrete foci of dense radio-opacity within the region of the acetabular labrum. The study aims to characterise MALs and test the hypothesis that MALs are associated with FAI. CT images and radiographs of 106 hips in 66 individuals without known FAI were reviewed for the presence of MALs. The anatomical locations of the MALs in the acetabular labrum were measured. Three current radiographic markers of FAI were recorded in hips with MALs and in age- and gender-matched hips without MALs: centre-edge angle and acetabular version angle as measures of pincer impingement, and alpha angle as a measure of cam impingement. MALs were identified in 18% of hips (n=19). Hips with MAL had a larger mean alpha angle (p=0.013) than those without. MALs were found to be located anterosuperiorly and posterosuperiorly within the labrum, consistent with coup and contrecoup impingement lesion locations reported for FAI. No significant association was found between MAL and centre-edge angle or version angle. Our data demonstrate that MALs are associated with increased alpha angle and thus may be linked to cam-type FAI. MALs have not previously been associated with FAI. This correlation may give further insight into the disease process underlying hip osteoarthritis and might represent a future radiographic marker of cam-type FAI.

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Figures

Figure 1
Figure 1
Images showing the same mineralisation of the acetabular labrum. From left to right: coronal CT image, axial CT image, plain radiograph.
Figure 2
Figure 2
Measurement of version angle. The axial CT image where the acetabular cup is deepest was used to measure version angle (i.e. the image where the medial wall of the acetabulum was most medial). Version angle was measured about the posterior edge of the acetabulum, between a line (A) to the anterior edge of the acetabulum and a line (B) perpendicular to the line joining the posterior edges of the acetabulum.
Figure 3
Figure 3
Measurement of centre–edge angle. Centre–edge angle was measured on radiographs or CT localiser images, about the centre of the femoral head, between a line (A) running perpendicular to the line joining the two ischial tuberosities (i.e. the superior axis) and a line (B) to the lateral edge of the acetabulum.
Figure 4
Figure 4
Measurement of alpha (α) angle. The axial oblique CT image running along the axis of the neck of the femur was used to measure the alpha angle (top). The alpha angle was measured about the centre of the femoral head, between a line joining the centre of the femoral neck and a line to the point at which the femoral head first exceeds a perfect circle anteriorly (bottom).
Figure 5
Figure 5
Measurement of the mineralisation of the acetabular labrum (MAL) position.
Figure 6
Figure 6
Markers of femoroacetabular impingement in MAL-positive and MAL-negative hips. MAL, mineralisation of the acetabular labrum.
See this image and copyright information in PMC

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