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

Abstract

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.

Keywords: femoroacetabular impingement; hip dysplasia; hip pain.

Fig. 1.

FV is the relative rotation between the femoral neck and femoral shaft. FV is represented as the angle between (a) line AB that extends through the femoral head center and bisects the proximal femoral neck and (b) line EF that aligns with the distal femoral condyles. A vertical reference line CD perpendicular to the coronal axis of the pelvis is used to assist with angle calculation.

Fig. 2.

AV describes the extent the acetabulum surrounds the femoral head in the transverse plane. The AV angle defined by points ABD is formed by line AB connecting the anterior and posterior acetabular rims and vertical line CD perpendicular to the coronal axis of the pelvis.

Fig. 3.

LCEA represents the superolateral femoral head coverage provided by the acetabulum. The LCEA is defined by points ABC and is formed by line CD perpendicular to the transverse axis of the pelvis drawn from femoral head center and line BA line from the femoral head center to the superolateral point of acetabulum.

Fig. 4.

FNA is formed by (a) line AB that extends through the femoral head center and bisects the proximal femoral neck and (b) line EF bisecting the femoral shaft. A vertical reference line CD perpendicular to the transverse axis of the pelvis is used to assist with angle calculation.

Fig. 5.

AA represents the femoral head–neck junction concavity. The 3 a.m. position is shown. The AA is defined by points ABC and is formed by line BC from the femoral head center to the point on the anterolateral head–neck junction where the radius of the femoral neck first becomes greater than the radius of the femoral head and line BA line drawn from the femoral head center through the center of the femoral neck.