DOES A POSTERIOR APPROACH HIP REPLACEMENT AFFECT HIP ROTATION IN ACTIVITIES OF DAILY LIVING

AIM When a hip is replaced using a posterior surgical approach, some of the external rotator muscles are divided. The aim of this study was to assess if this surgery has a long term affect on hip rotation during activities of daily living. METHODS An electromagnetic tracking system was used to assess hip movements during the following activities:- Activity 1. Picking an object of the floor in a straight leg stance. Activity 2. Picking an object of the floor when knees are flexed. Activity 3. Sitting on a chair. Activity 4. Putting on socks, seated, with the trunk flexed forward. Activity 5. Putting on socks, seated, with the legs crossed. Activity 6. Climbing stairs. Measurements were taken from 10 subjects with bilaterally normal hips, 10 patients with a large head hip replacement, 10 patients with a resurfacing head and 10 patients with a small head hip replacement. All the hip replacement patients were at least 6 months post-op, with an asymptomatic contra-lateral native hip for comparison. Sensors were attached over the iliac crest and the mid-shaft of the lateral thigh. Data was collected as each activity was repeated 3 times. The tracker recorded hip rotation at 10 hertz, with an accuracy of 0.15 degree. RESULTS For each of the activities the Normal, Large, Resurfacing and Small Head mean external rotations were:- Activity 1. -2.9,-6.9,9.1,-0.7. Activity 2. -8.1,-6.5,-7.0,2.0. Activity 3. -15.5,-15.6,-11.7,-15.6. Activity 4. 2.2,-10.8,5.3,-3.4. Activity 5. 33.1,24.6,22.5,23.7. Activity 6. -14.6,-11.5,-13.3,-6.5. The only movement that required substantial external rotation was activity 5 (Socks - legs crossed). For this activity the Resurfacing and Small head hips had significantly less rotation than the normal group (P = 0.01 & 0.03, respectively). A t-test comparing the normal group with the large head group had a boarder line significance level of P=0.07. Significant differences were also found for the following comparisons:- Activity 1 -Normal Vs Resurfacing, Activity 4 - Normal Vs Large head and Activity 6 - Normal Vs Small head. Discussion The results for activity 5 show that patients with a Resurfacing or Small head hip have significantly less external rotation than the normal group.