Lesions of the acetabular labrum in residual dysplasia of the hip joint. Biomechanical considerations regarding pathogenesis and treatment

The capsular-labrum-complex consists of the triangular fibrocartilaginous l abrum, which is fixed at the bony acetabular ring and supported by the liga mentum transversum actetabuli in the caudal part. In a normally developed a nd correctly orientated acetabulum, the femoral head is symmetrically cover ed by the contact area of the lunate surface. The vertical component of the resultant hip joint force concentrically meets the horizontal weight beari ng surface: Evenly distributed compressive forces are transmitted; the caps ular-labrum-complex does not have to compensate excessive shear or tension. In contrast, in a "dysplastic" acetabulum the femoral head is poorly cover ed by the pathologically orientated lunate surface: The lunate surface is s loping in an anterolateral direction, leading to tension and shear on the s uperolateral capsular-labrum-complex, which becomes a secondary stabilizer ("guide rail") against the decentering femoral head. The vertical component of the resultant hip force eccentrically meets the oblique weight bearing surface, causing extra stress in the labrum: The capsular-labrum-complex is trying to compensate this biomechanical stress with hypertrophy (Type IB). Progressive mechanical decompensation of the capsular-labral-complex might lead to tears (Type IIB) or complete avulsions (Type IIIB) of the labrum. In conclusion labral lesions result from pathobiomechanics caused by residu al hip dysplasia (RHD). Logically, the basic therapeutic principle can only be corrective osteotomy.