Radiographs play a central role in the evaluation of the extent of arthritic change and the quantification of morphological parameters characteristic of femoroacetabular impingement (FAI) and/or dysplasia. Reporting of these parameters is widespread in the literature, occasionally as an instrument for data pooling in collaborative research endeavors. Yet, the metrological properties of commonly used radiographic descriptors of acetabular and femoral architecture relevant to the field of hip preservation have not been reviewed systematically. The purpose of the present review was twofold: (1) to identify the current body of data available on the reliability of commonly used radiographic descriptors of the pre-arthritic hip and (2) to collate best practices and methodological pearls and pitfalls from the existing investigations that have explored the reliability of these radiographic measures.
Article screening methodology involved an extensive search of 2 databases (PubMed Central, Embase). Metrological reliability data and best practices and frequencies with which these practices have been reported in existing investigations were extracted from the methods of the included studies. The radiographic parameters that were chosen as a focus for the present review were based on a discussion among a number of experienced hip-preservation surgeons.
Forty-three articles met all inclusion criteria and were included in this review. Eleven recurring components of study design were isolated from the included investigations as being critical for minimizing bias in the assessment of the reliability of these radiographic morphological parameters. Sixteen (37.2%) of the included studies reported the use of at least 1 quality-control measure for ensuring radiographic integrity. The radiographic parameters with the most reliability data included the lateral center-edge angle (22 studies), the Tönnis angle (14 studies), and the alpha angle (18 studies). Categorical markers of acetabular retroversion and the extent of osteoarthritis have been less-frequently studied with respect to their reliability, with the exception of the crossover sign, which was evaluated in 11 of the included studies.
The radiographic parameter with the most metrological evidence in support of its reliability was the lateral center-edge angle (with 22 [100%] of 22 studies reporting acceptable reliability), whereas the Tönnis grade of osteoarthritis consistently demonstrated subpar interrater and intrarater reliability. Side-arm investigations for testing reliability may be needed by individual studies to prove the validity of data-pooling practices as collaborative endeavors continue to become more widespread.