Abstract
INTRODUCTION
A recent PRCT failed to demonstrate superiority of HRA over THA at low speeds. Having seen HRA walk much faster, we wondered if faster walking speed might reveal larger differences.
We therefore asked two simple questions:
Does fast or uphill walking have an effect on the observed difference in gait between limbs implanted with one HRA and one THA?
If there is a difference in gait between HRA and THA implanted legs, which is more normal?
METHODS
Participants All patients who had one HR and one THR on the contralateral side were identified from the surgical logs of two expert surgeons. Both surgeons used a posterior approach to the hip and repaired the external rotators on closure. All consenting patients were assessed using the Oxford Hip Score (OHS) to ensure they had good functioning hips.
There were 3 females and 6 males in the study group, who had a mean age of 67 (55–76) vs the control group 64 (53–82, p = 0.52). The BMIs of the two groups did not differ significantly (28 v 25, p = 0.11).
The mean average oxford score of included patients was 44 (36–48). Radiographs of all subjects were examined to ensure that implanted components were well fixed.
The mean time from THA operation to gait assessment was 4 years (1–17 yrs) and that for HRA was 6 years (0.7–10 yrs, p = 0.31). Subjects in this study had a mean TWS of 6.8 km/hr (5–9.5), and a mean TWI of 19 degrees (10–25 degrees).
RESULTS
Gait Assessment At Slow And Top Walking Speeds: Mean differences in maximum weight acceptance, maximum push off and impulse correlated strongly with increasing speeds (p < 0.005)
At top walking speed however, mean ground reaction forces were greater in the resurfacing group for four out of five of the key GRFs measured. Statistical significance was reached in two out of these variables (p = 0.03). The mean maximum weight acceptance was 71N or 8% greater in the resurfacing group.
Gait Assessment Walking On The Flat And Uphill: Once subjects reached their steepest achievable incline, there were more obvious differences between the implanted legs with maximum weight acceptance being significantly greater (p = 0.42) in the HRA implanted limb.
When the gait cycles were plotted, the HRA implanted limbs most resembled the normal asymptomatic control group (Graph 1).
DISCUSSION
The self determined top walking speeds of subjects were considerably higher than that of other studies testing arthroplasty subjects 6.8 km/hr (5.5–9.5 km/hr). There were strong correlations between the differences in weight acceptance, push- off and impulse as speed increased.
Relationship between up hill walking and gait differences: The patient self determined TWI mean average was 19 degrees (10–25 degrees). Testing people at their TWI did reveal a significant difference in favour of the HRA hip (p = 0.02)
Hip resurfacing seems to allow for greater levels of function using hill walking and speed walking on a treadmill as a surrogate.
There appears to be a functional advantage of having a HRA over THA in patients wishing to return to levels of activity more rigorous than walking at slow speeds on the flat.
