KINEMATIC ASSESSMENT OF HIP MOVEMENT WHEN PICKING AN OBJECT UP

Abstract

Introduction: Hip replacement patients are prone to dislocations during extreme hip movement in the early post operative period. An activity of daily living that puts them at risk of dislocation is picking an object off the floor. The aim of this study was to assess the movement of the hip using different techniques to pick an object of the floor.

Methods: An electromagnetic tracking system was used to assess hip movements for four different techniques in picking an object from the floor. These were -

1. Flexing forward to pick an object up between the feet.

2. Standing to the side of the object and bending to pick it up.

3. Squatting to pick an object up between the feet. 4. Kneeling on one knee to pick up.

Measurements were taken from 40 hips in 20 normal subjects aged 21 to 61. Sensors were attached over the iliac crest and the mid-shaft of the lateral thigh. Data was then collected from the magnetic tracker as each technique was repeated 3 times. The system recorded hip flexion and rotation data at 10 hertz, with an accuracy better than 1 degree. Data was then analysed and the mean readings for each technique were compared.

Results: For each of the four techniques listed above the respective mean (SD) results were:

• Flexion: 81.4 (27.5), 83.3 (27.6), 93.3 (28.7) and 33.5 (17.6) degrees.

• Extension: −0.2 (2.0), −0.3 (1.8), −0.1 (2.5) and 0.4 (3.2) degrees.

• Internal rotation: 3.4 (5.9), 1.6 (3.8), 10.1 (10.4) and 9.5 (7.1) degrees.

• External rotation: 13.0 (8.6), 22.7 (13.8), 13.2 (6.9) and 7.5 (7.0) degrees.

The most significant movements for each technique were flexion and external rotation.

The movements with the least and most flexion were kneeling (33.5 deg) and squatting (93.3 deg). They were significantly different with a paired t-test p< < 0.001.

The movement with the least and most external rotation were kneeling (7.5 deg) and side pick up (22.7 deg). They were significantly different with a paired t-test, p< < 0.001.

Conclusion: This study has found that the most effective technique to pick up an object from the floor is kneeling as this has the least amount of flexion and external rotation. We conclude that this is the safest technique in carrying out this activity in the early post operative stage for patients who have undergone a total hip replacement.