Mechanical strains passing through the acetabular labrum modify its shape during hip motion: an anatomical study

• Ollivier Matthieu
• Le Corroller Thomas
• Parratte Sebastien
• Chabrand Patrick
• Argenson Jean-Noël
• Gagey Olivier

The function of the hip labrum during hip motion remains poorly known. Our hypothesis was that acetabular labrum will deform and change its shape during adduction to abduction movement consecutively to variation of strains passing from the acetabulum to the femoral head. An ex vivo anatomical study was conducted to analyse the morphological parameters variation of the mid-portion of the labrum (length, thickness, shape, deformation) as well as femoro-labral strains during hip adduction to abduction movement. Ten fresh-frozen, unpaired human cadaver hemi-pelvises were obtained. To best approximate the clinical reality, fresh-frozen cadaver tissues were utilized. The hemi-pelvises were split sagittally in two equal parts through a plane crossing the femoral neck and femoral head centres. The hemi-pelvises were rigidly mounted on a test platform using a custom-made fixture, and a seven hundred Newton load was applied through the iliac wing, with a unidirectional movement (adduction/abduction) of the acetabulum above the fixed femur. Variations of strain passing from the labrum to the femoral head or neck were analysed using captors fixed on the acetabular edge. From 20A degrees to 40A degrees of abduction labral length decreased from a median of 5.8 (5.5-6.4 mm) to 4.6 (4-5.4 mm), labral edge angle increased from a median of 33.1 (31.1A degrees-40A degrees) to 52.3 (41.4A degrees-58.8A degrees), labral sectional area decreased from a median of 22.1 (17-27.1 mm(2)) to 14.2 (12-16.8 mm(2)) all p = 0.001. Femoro-labral strains were maximal at 40A degrees of abduction [median 0.1 N mm(-2) (0.1-3.1 N mm(-2))] and minimal at 30A degrees adduction (median 0 N mm(-2) (0-0.1 N mm(-2)) and p = 0.001). The morphological variations of the mid-portion of the labrum during hip motion reflect strains passing from the labrum to the femoral head. Those elements may provide clues to understand the mechanical role of the labrum during abduction. The acetabular labrum bears a direct mechanical role during hip motion, thus resecting the hip's labrum during surgery might be detrimental for hip joint's biomechanics as it might modify strains distribution between the acetabulum and femur.