Abstract
The use of hip resurfacing arthroplasty (HRA) has largely regressed due to the fear of metal-on-metal bearings. However committed HRA users continue to assert the functional advantages that a geometry retaining implant would have on a patient”s hip. Currently worldwide, HRA is only recommended to men who demand an active lifestyle. Despite this precarious indication, it is not clear to what extent HRA has on higher activity function. The aim of this study was to determine the functional extent to which could be achieved with HRA. The primary objective is to assess the loading pattern change for patients implanted with HRA at high walking speeds and inclinations. The second objective is to compare their loading features to a healthy group to determine if a normal gait pattern could be achieved.
Between 2012 and 2016, a total of 28 prospective unilateral HRA patients were analysed on an instrumented treadmill from a single centre. All 28 patient patients had a uniform implant type and had no other lower limb operations or disease. Perioperative plain orthogonal radiographs were used to measure hip length and global hip offset change. A healthy control group (n=35) were analysed to compare. All HRA patients gait characteristics were assessed at incrementally higher speeds and inclinations to determine the extent of improvement HRA has on a challenging activity. A Student t-test along with a multivariate analysis was done with significance set at α=0.05. Weight and height variance was accounted with Hof normalisation.
The HRA and control group were reasonably matched for age (57 vs 55yrs), BMI (27 vs 25) and height (175 vs 170cm) respectively. Hip measurements revealed less than 5mm change for all cases. The mean time from initial preoperative gait assessment to postoperative assessment was 30 months (24–48months). The mean top walking speed for controls was 1.97m/s and postoperatively 2.1 m/sec for the HRA group. The significant (p<0.001) loading change during flat walking can be seen with restoration of symmetry. Walking at an inclination demonstrated a marked change during weight acceptance (p<0.001) and a loading pattern returning to near normal.
This prospective study found HRA patients walking faster than age matched controls. They demonstrated a significant change in their loading pattern, by significantly shifting load from the unaffected side to the implanted side. Uphill walking, an activity which requires more hip flexion, demonstrated a change in stance phase which was near normal. This small comparative study confirms near physiological function can be achieved with HRA at higher activity levels.
