A method, that may be computer implemented, is provided for selecting prefabricated components of a hip prosthesis comprising a femoral stem 1, a femoral head 2 and an acetabular cup component 3 for use in hip replacement surgery. The method includes determining a planned leg length correction pre-operatively from measurements and image data (e.g. x-rays) and identifying a suitable prosthetic implant assembly for achieving the planned leg length correction. A measured vertical height of a resected femoral head of a patients femur is determined in the vertical direction and the diameter of a suitable acetabular cup component is determined following the preparation of a receiving acetabular site. The measured vertical height b is deducted from a predetermined prosthetic implant assembly height a to provide a calculated leg length correction, and the planned leg length correction is compared with the calculated leg length correction. The calculated leg length correction may be recalculated with alternative components if the difference between the two components exceeds a threshold value (e.g. 2 to 6mm).
