ASSESSMENT OF HIP FLEXION WHEN PICKING AN OBJECT UP FROM THE FLOOR. IS THERE A DIFFERENCE BETWEEN SMALL AND LARGE BEARING HIP IMPLANTS?

Abstract

Introduction: Patients undergoing total hip arthroplasty are advised to minimise their hip flexion in the early postoperative phase, to reduce the risk of dislocation. One activity that requires hip flexion is picking an object up from the floor. The aim of this study was to investigate the amount of hip flexion required to perform this task, and to see if there is a difference between patients with small and large bearing total hip replacements.

Methods: Nineteen unilateral total hip replacement patients were recruited into the study. Nine had a small bearing (metal on plastic) implant and ten had a large bearing (metal on metal) implant. Each patient had a contra-lateral normal native hip, which provided a control for bilateral comparison.

An electromagnetic tracking system was used to measure the flexion in the operated and normal hip of each patient. Tracker sensors were placed on the iliac crest and the mid-lateral thigh. The patients were then asked to flex forward from a standing position to pick an object up off the floor. This movement was repeated 3 times. Flexion data was collected at 10Hz which was accurate to 0.15 degrees. Spinal flexion was not recorded during the task.

Patients were also asked to complete the Harris and Oxford Hip Score questionnaires to obtain qualitative data regarding their hip replacement.

Results: The mean peak flexion angles (degrees) for each group are given below:

Small bearing group:

• Operated side: Peak flexion = 79.3

• Normal side: Peak flexion = 83.4.

• Thus the bilateral difference for peak flexion was 4.1 (paired t-test, P=0.12). Large bearing group:

• Operated side: Peak Flexion = 72.7.

• Normal side: Peak Flexion = 74.0

• Thus the bilateral difference for peak flexion was 1.3 (paired t-test, P= 0.83).

Comparing the small bearing group with the large bearing group, the peak difference was 6.6. This difference was non-significant with P = 0.43.

All patients reported good – excellent functional results when completing the Harris and Oxford Hip Scores.

Discussion: The investigation showed that picking an object up from the floor requires a peak hip flexion of approximately 80 degrees. This investigation found no significant difference between the normal and operated sides. This would suggest that a Total Hip Replacement restores the “normal” range of motion in a hip joint. Furthermore, there was no significant difference between the small and large bearing hip implants.