Abstract
Intro
Across much of medicine, activity levels predict life expectancy, with low levels of activity being associated with increased mortality, and higher levels of activity being associated with longer healthier lives. Resurfacing is a technically demanding procedure that has suffered significant fallout from the failure of a couple of poorly performing designs. However strong evidence associates resurfacing with improved life expectancy in both the short and longer term following surgery.
We wondered if there was any relationship between the function of hips following surgery and the extent of that surgery. Could a longer stem inside the femur be the reason for a slightly reduced step length? We proposed the nul hypothesis that there was no clinically relevant difference between stem length and gait.
Method
After informed consent each subject was allowed a 5 minute acclimatisation period at 4km/hr on the instrumented treadmill (Kistler Gaitway, Amherst, NY). Their gait performance on an increasing incline at 5, 10 and 15%. At all 0.5km incremental intervals of speed, the vertical component of the ground reaction forces, center of pressure and temporal measurements were collected for both limbs with a sampling frequency of 100Hz over 10sec.
They were also asked to log onto our JointPRO website and report their function using Oxford, EQ5D, and Imperial scores.
Owing to current restrictions in indications, the patient groups selected were not comparable. However, from our database of over 800 patients who have been through the gait lab. 82 subjects were tested from 2 diagnostic groups (29 conventional THR, 27 hip resurfacing) and compared with a slightly younger group of 26 healthy controls. Patients were excluded if less than 12 months postop, or with any other documented joint disease or medical comorbidities which might affect gait performance.
Body weight scaling was also applied to the outputted mechanical data to correct for mass differences. All variables for each subject group were compared to each other using an analysis of variance (ANOVA) with Tukey post hoc test with significance set at α=0.05.
Results
The experimental groups were reasonably matched for sex, height and BMI, although the controls were rather younger, and the hip replacements rather older (young hip resurfacings were excluded for lack of good controls). Any differences did not reach significance. Oxford hip scores and EQ5D were almost identical for the two experimental groups.
The THR group walked 10% slower than control (1.8 (±0.2)m/sec vs 2.0 (±0.1)m/sec). while the HRA group walked 5% faster (2.1(±0.2)m/sec). The difference between THR and control was significant (p<0.05). (See Figure 1)
Discussion
This data records a 15% difference in top walking speed between THR and HRA, far exceeding the 5% threshold of clinical relevance. We therefore consider this improved functional outcome to be clinically relevant, and report with increasing confidence that hip resurfacings is an effective intervention in the treatment of hip disease with clinically relevant superiority over THR, even in a group with an average age of 60.
