The hip joint: forces needed for distraction and appearance of the vacuum phenomenon.

Joint traction and other mobilization techniques are commonly used in physical therapy for patients with osteoarthrosis. The aim of this study has been to: (a) measure the separation of the joint surfaces in the normal hip joint during application of different forces; (b) investigate whether or not the degree of separation was influenced by the position of the joint; (c) compare hip joint laxity in men and women; (d) find the traction force needed to cause the appearance of vacuum phenomena. To achieve a separation in the hip joint, a traction force of at least 400 N must be applied. The distraction was greater in the loose packed position than in the close packed position at equal force and in both males and females. Vacuum phenomena appeared at between 400 and 600 N of traction, varying with joint position.