Effect of capsulotomy on hip stability-a consideration during hip arthroscopy

We conducted a study to further understand the effect of capsulotomy on hip joint stability using an in vitro cadaver model. Thirteen fresh-frozen cadaveric hip specimens were subjected to an external rotation torque of 0.588 Nm. The experimental kinematics, post-process translation, and rotation data for each specimen were tested under 4 conditions: neutral flexion with capsule intact; neutral flexion with transverse capsulotomy; maximum flexion with capsule intact; and maximum flexion with transverse capsulotomy. A segmented 3-dimensional model of the femur was used to evaluate femoral head translation after application of external rotation torque. In maximum flexion, hips with intact capsules rotated less than hips with capsulotomy in the y (abduction) and z (external rotation) planes (y-plane, P = .01; z-plane, P = .02). After capsulotomy, there was a qualitative observation of increased distal, lateral, and anterior translation of the femoral head in neutral position, and a qualitative observation of increased medial, posterior, and distal translation of the femoral head in flexion. Qualitatively, after capsulotomy, hips tested in neutral position demonstrated more translation than rotation, whereas hips tested in flexion demonstrated more rotation than translation. Capsulotomy appears to permit increased rotation in maximum flexion. Hips tested in neutral trended toward more translation than rotation, whereas hips in flexion trended toward more rotation than translation. Judicious capsular management is indicated during arthroscopic hip procedures.