The LHM hip replacement tended to restore leg length and hip resurfacing restored femoral offset the most accurately (Table 1). The newer hip resurfacing showed the smallest change in femoral offset with an average difference of -0.08 mm (a non-significant difference). This is contrary to previous studies, where femoral offset has consistently been found to be significantly reduced in hip resurfacing, with variable effects on leg length. This may relate to a tendency to place the femoral head component into a valgus alignment (thereby reducing femoral offset and increasing leg length), to avoid varus alignment, which itself, is associated with increased risk of femoral neck fracture. In our study, the aim was to accurately align the femoral component, matching the patient's own anatomy.
The other two hip replacements, large head metal-on-metal and small head THRs showed a significant difference between the operated and unoperated femoral offsets (Table 2). This indicates that the concept of hip resurfacing is superior in restoring hip biomechanics. Additionally, hip resurfacing provides better stability due to the large-diameter femoral head. It also demands less bone resection from the femoral head, with preservation of the femoral neck when compared to the other two techniques described in this paper, it therefore is less likely to alter the femoral offset .
Altogether 19/20 patients with hip resurfacing and 4/20 patients with large head metal-on-metal and small head THR replacement met the set standard for leg length restoration. This shows hip resurfacing was superior at reproducing leg length. The one patient who did not meet the set standard after hip resurfacing had a large difference in leg length of -19.19 mm. This is an anomaly which affected the overall average result for this group. If this measurement was excluded from the study then hip resurfacing would show the smallest reduction in leg length rather than the large head metal hip replacement.
Girard et al  performed the only prospective randomised trial on this subject. They compared hip resurfacing and small head THR in two homogenous groups of 120 patients. Similarly to our study they also showed hip resurfacing produced less discrepancy in leg length and femoral offset than small head THR. They concluded that hip resurfacing was superior because the anatomy of the hip is less distorted during the surgery and the large metal head provides hip stability. Overall, the study by Girard et al  favours hip resurfacing to reduce leg length and femoral offset discrepancy.
Research by Silva et al  looked at the leg length and femoral offset discrepancies in pre and postoperative radiographs of 90 patients who underwent small head THR and hip resurfacing. They found that the leg length and femoral offset discrepancy was higher in hip resurfacing. Silva et al  concluded that small head THR was more suitable than hip resurfacing for patients who have a either a preoperative leg length discrepancy of more than 10 mm or a low femoral offset.
Loughead et al  also reviewed postoperative radiographs of 54 patients who underwent small head THR and hip resurfacing. They reported an increase in leg length with hip resurfacing, concluding that resurfacing did not produce more accurate restoration of hip biomechanics, and that the advantage of hip resurfacing was likely related to the larger femoral head. This theory has not been supported by our findings.
The limitations of this study include the stringent inclusion/exclusion criteria which eliminated many patients. This accounted for the small sample size and limited the internal validity. There is some selection bias as the participants were chosen from one surgeon and one institution. This limits the external validity of the study. Furthermore, the study's methodology provided level IV evidence and therefore the results should be interpreted carefully.
When deciding which surgical hip replacement technique is superior it is also necessary to evaluate clinical improvement, survivorship, longevity and peri-operative factors including surgical time, hospital stay, complications, total blood loss and costs (£5515 for hip resurfacing, £4195 for hip replacements ). Hip resurfacing carries an increased risk of femoral neck fractures, aseptic loosening and metal wear . However, hip resurfacing reduces the risk of postoperative hip dislocation due to its larger femoral head and allows easier revision surgery to a small head THR due its increased bone stock . A randomised controlled trial by Loughead et al  showed an 82% clinical improvement and 7% perioperative complications in 35 patients undergoing hip resurfacing compared to 79% and 13% respectively in 33 patients with a small head THR.