Total hip arthroplasty (THA) is a successful operation with predictable results in patients with end-stage hip arthritis. Poor component placement, orientation or sizing on either the acetabular or femoral side increases the risk of a poor outcome. In particular on the femoral side, not restoring offset or introducing a leg length discrepancy are issues that can be avoided with good surgical technique and planning. A Calliper has been used since 1992 in Musgrave Park Hospital, Belfast as a method of intraoperative simple hip navigation to help determine the position of femoral head centre and aid femoral side reconstruction. The Calliper system has certain limitations and so a new system, the Femoral Head Navigation System (FHNS) is being developed. The aim of this thesis was to compare the FHNS to the current Calliper system in terms of the ability to determine the position of femoral head centre during THA. The further subject of this thesis was to research alternative methods and to validate the underlying assumptions made by the proposed method of the FHNS. These included, that femoral head diameter can be measured accurately, that the Head Centre Location Device (HCLD) part of the FHNS is accurate, that the femoral head is grossly spherical, that the posterior femoral head surface is less affected than the superior or anterior surface by osteoarthritis and fmally that the Trochanteric Fossa is a reliable entry point for the proximal femoral axis. The results showed that the mean accuracy in determining the position of femoral head centre for the FHNS (1. 1 mrn, range 0.0 to 3.3 mm) was statistically more accurate than the original Calliper system (4.0mm, range 0.5 to 11.0mm) (p=O.003). These findings along with the results of the validation experiments suggest that the FHNS has a potential role in THA in improving the surgical technique for determining the position of femoral head centre and inserting the femoral component.