In this in vitro study of thehip joint we examined which soft tissues act as primary and secondarypassive rotational restraints when the hip joint is functionallyloaded. A total of nine cadaveric left hips were mounted in a testingrig that allowed the application of forces, torques and rotationsin all six degrees of freedom. The hip was rotated throughout acomplete range of movement (ROM) and the contributions of the iliofemoral(medial and lateral arms), pubofemoral and ischiofemoral ligamentsand the ligamentum teres to rotational restraint was determinedby resecting a ligament and measuring the reduced torque requiredto achieve the same angular position as before resection. The contributionfrom the acetabular labrum was also measured. Each of the capsularligaments acted as the primary hip rotation restraint somewherewithin the complete ROM, and the ligamentum teres acted as a secondaryrestraint in high flexion, adduction and external rotation. Theiliofemoral lateral arm and the ischiofemoral ligaments were primaryrestraints in two-thirds of the positions tested. Appreciation ofthe importance of these structures in preventing excessive hip rotationand subsequent impingement/instability may be relevant for surgeonsundertaking both hip joint preserving surgery and hip arthroplasty.Cite this article: Bone Joint J 2015; 97-B:484–91.
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