Radiographs are often used to determine the varus/ valgus alignment of the prosthesis in relation to the long axis of femur. This is usually considered to be one of the important parameters in predicting early mechanical failure of the total hip replacement.

The measurements made by the University of Dundee X-Ray Analysis Software and skilled manual operators of the varus and valgus angulations of hip prosthesis in relation to the femoral shaft were compared for inter and intra-observer reliability.

The manual measurements were carried out on the same randomly selected digitised images of 78 postoperative X-rays by two independent observers and by the same analysis software twice.

The results of the study showed a very high agreement between the readings of the two methods (the largest difference was 0.6 degrees) and two observers (the largest difference being 0.08 degrees) indicating excellent intra and inter observer reliability. The lowest correlation was 0.82 and this was between software reading 1 of observer 1 and software reading 1 of observer 2. The highest correlation of 0.99 was between software reading 1 and software reading 2 for the same observer. The software analysed the x-rays with precision and accuracy and was much faster than manual measurement. A further benefit of the computerised method is an unskilled operator can be trained in 15 minutes to use the software