Assessing reproducibility for radiographic measurement of leg length inequality after total hip replacement

Leg length inequality (LLI) as a result of total hip replacement can cause considerable morbidity. Although LLI was described when the technique was popularised in the 1960s, it remains a significant challenge to arthroplasty surgeons. This study reviews the established practice for the measurement of LLI on plain antero-posterior radiograph, and compares these techniques to two methods used locally. The radiographs of 35 patients were measured using four techniques. All four methods yielded an interclass correlation co-efficient of ≥0.90 for inter reader reliability. This study shows that the four methods are comparable for reliability, while a composite method, measuring from the centre of femoral rotation to the inferior teardrop and then to the lesser trochanter, has the added advantage of providing extra information on component position as well as an overall measure of LLI.