Inter- and intra-observer reliability of patellar height measurements in patients with and without patellar instability on plain radiographs and magnetic resonance imaging

Introduction Many patella height indices exist in the literature. There is no single universally accepted radiological assessment for measuring patella height. The aims of this study were to determine which of the commonly used indices can most reliably measure patella height and compare the findings on both plain X-ray and magnetic resonance imaging (MRI) of the knee. Methods This case-controlled study compared patients with recurrent patella instability (patella group) to a control group. Two observers measured six validated patella height indices on X-ray and MRI of both groups at two separate time periods. Between-group and within-group statistical analysis was undertaken of the data. The inter- and intra-observer reliability was assessed using the intraclass correlation coefficient (ICC) and the kappa measure of agreement ( k ). Results Forty-four patients comprised the patella group and 50 patients the control group. There was a significant difference of most indices between the two groups ( p