Leg Length Inequality Following Total Hip Replacement. A Little Understood Complication

Total hip replacement (THR) is one of the most effective medical interventions undertaken. Leg length inequality (LLI) following total hip replacement is a recognised complication and although recognized when the operation was pioneered, has only more recently come to prominence in the literature. Understanding of LLI following THR is impeded by there being little consensus regarding definition, incidence, measurement, symptoms, treatment or even clinical significance. The thesis begins by outlining the extent of LLI using an analysis of litigation data for orthopaedic operations covered by the National Health Service Litigation Authority. The data found that LLI following THR was cited in 100 claims, 44 of which were successful and at a total cost of nearly £3.9 million. During the same time period, nearly 800,000 THRs were performed. The thesis then studies techniques to measure LLI following THR on plain radiograph. The four techniques studied were comparable in terms of inter and intra reader reliability as well as for the image acquisition protocol. The CFH-TD-LT method, has an advantage of providing information regarding the contribution of any LLI due to the components of the joint replacement. The final part of this work employs a computational model and a radiographic experiment to study the effect of femoral malposition has on the measurement of LLI using the CFH-TD-LT technique. Results indicate that errors associated with flexion and abduction are small when in isolation. However, when the malpositions are combined there is an additive effect this is not predicted by the malpositions in isolation. Extension and adduction result in a greater error of interpretation both in isolation and when combined with internal rotation, and while clinically less common, should be viewed with caution when being interpreted on plain radiograph. Perhaps just as significantly, it is only in the extremes of malposition that there is any major difference in the contribution that the cup measurement makes to the limb length. In summary, this thesis presents data regarding the validation for measurement on plain radiographs. It provides evidence to suggest that should a patient present with an LLI following THR, then a plain x-ray will give all the necessary information, even in the presence of larger angles of the clinically relevant deformities of flexion and abduction.