Bony abnormalities of the hip joint: a new comprehensive, reliable and radiation-free measurement method using magnetic resonance imaging

OBJECTIVES To develop comprehensive and reliable radiation-free methods to quantify femoral and acetabular morphology using MRI. METHODS 32 hips (16 subjects, 6 with intra-articular hip disorder (IAHD); 10 controls) were included. A 1.5T magnetic resonance system was used to obtain 3D fat suppressed gradient echo images at the pelvis and distal femora. After acquisition, pelvic images were post-processed to correct for coronal, axial and sagittal rotation. Measurements performed included acetabular version (AV), femoral version (FV), lateral center edge angle (LCEA), femoral neck angle (FNA) and alpha angle (AA) at 3, 2, 1 and 12 o'clock. Two experienced raters, a musculoskeletal radiologist and an orthopaedic physical therapist, and a novice rater, a research assistant, completed reliability testing. Raters measured all hips twice with minimum 2 weeks between sessions. Intraclass Correlation Coefficients were used to determine rater reliability; standard error of measurements was reported to estimate the reasonable limits of the expected error in the different raters' scores. RESULTS Interrater reliability was good to excellent for all raters for AV, FV, FNA, and LCEA (ICCs: 0.82-0.98); good to excellent between experienced raters (ICCs: 0.78-0.86) and poor to good between novice and experienced raters (ICCs: 0.23-0.78) for AA. Intrarater reliability was good to excellent for all raters for AV, FV and FNA (ICCs: 0.93-0.99); for one experienced and novice rater for LCEA (ICCs: 0.84-0.89); moderate to excellent for the experienced raters for AA (ICCs: 0.72-0.89). Intrarater reliability was poor for the second experienced rater for LCEA (ICC: 0.56), due to a single measurement error and for the novice rater for AA (ICCs: 0.17-0.38). CONCLUSION We described MRI methods to comprehensively assess femoral and acetabular morphology. Measurements such as AV, FV and FNA and the LCEA can be made reliably by both experienced and novice raters, however the AA measurement was reliable only among experienced raters.