Objective: The reliability of radiographic measurements has been studied in pediatric hips, but less has been published on the adult hip, and none have examined the reliability of measurements for the location of the center of rotation (COR) of the hip joint. We have investigated the reliability of various radiographic variables with a focus on the COR.
Materials and methods: The study was carried out on a standardized format for anterior-posterior radiographs of the pelvis. The measured variables were; (A) the distance from a sagittal reference line to the COR, (B) the distance from the sagittal reference line to the proximal end of the lateral cortical line of the femur, (C) the distance from the sagittal reference line to the medial rim of the acetabulum, (D) the distance from the horizontal reference line to the roof of the acetabulum, and (E) the distance from the horizontal reference line to the COR. One observer (JAB) conducted the measurements twice separated by a time interval of 45-60 days to assess intra-observer reliability, and the first measurements of JAB were compared to those performed by another observer (OR) to assess inter-observer reliability.
Results: Intraclass correlation coefficients were above 0.98 for all measurements, and the minimum and maximum values that statistically include 95% of the observer differences were all within -3 to +3 mm.
Conclusions: These measurements proved to have high reliability and agreement of both within the same observer and between two observers. They should therefore be reproducible in a clinical setting.