Kinematic assessment of hip movement when retrieving an object from the floor.

Background: Activities that require extreme hip movement can dislocate hip implants in the early post operative phase. One such activity is retrieving an object from the floor. The aim of this study was to assess hip movement using four different techniques to accomplish this task. This assessment would identify the techniques least likely to cause a hip dislocation.

Methods: An electromagnetic tracker was used to measure the movement of 50 hips in 25 normal subjects. Sensors were attached over the iliac crest and the mid-shaft of the lateral thigh. Data was then collected for 3 repetitions of each of the following retrieval techniques:--1. Flexing forward to pick up an object between the feet. 2. Flexing to pick up an object lateral to the foot. 3. Squatting to pick up an object between the feet. 4. Kneeling on one knee to pick up beside the knee.

Results: Kneeling required a mean movement of 30.4 degree(s) flexion and 7.2 degree(s) external rotation. This was significantly less than all the other techniques (paired t-test, P << 0.001). Squatting required 87.4 degree(s) flexion and 10.1 degree(s) internal rotation.

Conclusion: The study showed that squatting had the most flexion and internal rotation, whereas kneeling has the least flexion. Thus, to minimise the dislocation risk when retrieving an object from the floor, kneeling should be adopted and squatting should be avoided.