Effect of acetabular labrum tears on hip stability and labral strain in a joint compression model.

BACKGROUND: Acetabular labrum tears are now commonly diagnosed in young and active patients. Because the role of the acetabular labrum is incompletely understood, it is critical to determine how these tears affect native hip biomechanics.

HYPOTHESIS: Radial and circumferential labral tears significantly decrease hip stability and significantly alter strain patterns in the anterior and anterior-superior acetabular labrum.

STUDY DESIGN: Controlled laboratory study.

METHODS: Twenty-two human cadaveric hips without evidence of degeneration or dysplasia were assigned to a circumferential tear (n = 11) and a radial tear (n = 11) group. The hips were tested in a neutral position with an average compressive force of 25 N. In the circumferential tear group, the labral states were intact; 1-, 2-, and 3-cm circumferential tears; a 3-cm partial labrectomy; and a full labrectomy. In the radial tear group, the labral states were intact; a radial tear; a 1-, 2-, and 3-cm partial labrectomy; and a full labrectomy. The effect of labral injury on the stability ratio (peak dislocation force/compressive loads) and labral strain in the anterior and anterior-superior labrum was analyzed using repeated-measures analysis of variance.

RESULTS: There was no significant difference in stability ratio after circumferential tears 3 cm or less in size compared with the intact labral state. Strain in the anterior and anterior-superior labrum was either unchanged or increased after circumferential labral tear. There was no significant difference in stability ratio after a radial tear or a 1-cm partial labrectomy compared with the intact labral state. A 2-cm partial labrectomy significantly decreased the stability ratio. Anterior and anterior-superior labral strain significantly decreased after a radial tear.

CONCLUSION: Under the influence of joint compression in a neutral hip position, the acetabular labrum continues to resist femoral head dislocation despite detachment from the acetabular rim. A radial tear in the acetabular labrum decreases adjacent labral strain, but removal of 2 cm or more of the acetabular labrum is needed before hip stability decreases.

CLINICAL RELEVANCE: The findings suggest that the acetabular labrum continues to function to resist femoral head translation despite chondral-labral separation and that labral preservation, particularly with larger tears, may be important for maintaining hip stability. Further studies are needed to determine the effect of partial labral excision on the stability ratio with the hip in provocative positions such as extension, external rotation, and abduction.