Abstract
Labral hypertrophy is a distinct feature in hip dysplasia. Occasionally, very small, hypotrophic labra are observed. However, there is no literature concerning this pathology. We investigated if the size of the labrum correlated with any radiologic parameters reflecting the amount of acetabular coverage. It was hypothezised that there is a negative correlation between labrum size and acetabular coverage. Labra were categorized into three groups depending on the relation between length of the articular sided surface and height of bony attachment. Labra with a height:length ratio of 2 were classified as hypotrophic, with a height:length ratio of 1 as normal and with a ratio of 0.5 as hypertrophic. Labral cross-sectional areas (CSA) were measured on radial magnetic resonance imaging-arthrography slices using the measuring tool of the PACS system of 20 hips with hypotrophic labra (group 1), 20 hips with normal labral appearance (group 2) and 10 hips with hypertrophic labra (group 3). These values were then analyzed against following parameters: neck-shaft-angle (NSA), lateral center-edge angle (LCE), acetabular index (AI), femoral extrusion index (FEI) and acetabular retroversion index (ARI). Analyses of variance were used to determine differences in mean values between the three groups. Mean labral CSA differed significantly between all groups (group 1: 12.1 ± 2.9 mm2; group 2: 25.2 ± 6.2 mm2; group 3: 41.1 ± 12.3 mm2; P < 0.001). NSA, LCE, AI and FEI all showed a significant difference between group 3 and 1 or 2. The ARI showed no difference between groups. Stepwise linear regression analyses showed a significant correlation between LCE angle and labral CSA with a corrected R2-value of 0.301. Labral CSA correlates with the LCE. No statistically significant difference between groups 1 and 2 concerning the LCE, AI or FEI could be identified. Nevertheless, group 1 had the highest mean coverage of all groups, hips with hypertrophic labra the lowest.
Highlights
The normal acetabular labrum acts as an extension of the articular surface of up to 27%, increasing acetabular volume by up to 30%, providing a seal-effect that resists distraction of the femoral head and enhances joint stability [1,2,3,4]
Labral cross-sectional areas (CSA) were measured on radial magnetic resonance imaging-arthrography slices using the measuring tool of the PACS system of 20 hips with hypotrophic labra, 20 hips with normal labral appearance and 10 hips with hypertrophic labra. These values were analyzed against following parameters: neck-shaft-angle (NSA), lateral center-edge angle (LCE), acetabular index (AI), femoral extrusion index (FEI) and acetabular retroversion index (ARI)
Our study aimed to investigate if hips with hypotrophic labra have deeper hips with more bony acetabular coverage, so that the small size could be explained as a consequence of increased coverage and decreased forces acting at the labro-acetabular-interface, possibly thereby disincentivizing the labrum to further hypertrophy during its development
Summary
The normal acetabular labrum acts as an extension of the articular surface of up to 27%, increasing acetabular volume by up to 30%, providing a seal-effect that resists distraction of the femoral head and enhances joint stability [1,2,3,4]. The labral blood supply derives from radial branches of a periacetabular vascular ring, which is mainly fed by the superior and inferior gluteal arteries, with minor contributions from the medial and lateral circumflex femoral arteries and intrapelvic vessels [11]. This blood supply enables healing of the labrum after tearing or repair, as described by Audenaert et al [12].
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