Hip arthroplasty is a successful intervention for symptomatic end stage arthritis of the hip. However it remains an imperfect procedure due in many respects to the difficulty in reproducing biomechanics for each individual patient. Reproduction of femoral offset and leg length ensures appropriate muscle balancing which allows for hip biomechanics to be restored. In addition adequate soft tissue balancing reduces the risk of complications such as dislocations and nerve injuries. Post- operative functional performance may also be affected by the implant technology being used as well as surgical accuracy. However little is known as to what functional performance is to be expected following hip arthroplasty, especially when function is measured at fast speeds and walking inclines. This thesis will explore the gait of patients prospectively through pre to post-operative stages, in an attempt to ascertain what gait changes can be expected following hip arthroplasty. Furthermore the gait assessments will focus on higher end function, when walking at fast speeds. Following this, this thesis aims to assess whether gait differences are evident when different implants are used, and judge whether they may be a functional advantage to using different implants in hip reconstruction. Surgical accuracy is paramount, when avoiding complications alluded to earlier. This thesis explores whether rapid prototyping technology can be utilised to aid accurate insertion a femoral stem as part of a pre-clinical test. Finally this thesis will also test the association of implant size and failures that has been alluded to from national joint registries.