JOINT-SPACE WIDTH IN THE AXIAL VIEW OF THE PATELLOFEMORAL JOINT - DEFINITIONS AND COMPARISON WITH MR-IMAGING

Purpose: To validate a bony landmark on the dorsal aspect of the patel la for measurement of the interbone distance in the axial radiogram of the patellofemoral joint (PFJ); to assess the reproducibility of this radiogram and the minimal joint-space (MJS) width measurements in the medial and lateral compartments of the PFJ in this view; and to relat e the MJS of the PFJ to MR-detected cartilage defects in the same join t. Material and Methods: Fifty-seven individuals with chronic knee pai n (aged 41-58 years, mean 50 years) were examined with an axial view o f the PFJ in the standing position. The MJS was measured with a mm-gra ded ruler. On the same day, an MR examination was performed with proto n density-and T2-weighted turbo spin-echo sequences on a 1.0 T imager. We noted the cartilage defects in the PFJ in axial and sagittal MR im ages, and the shape of the subchondral cortex of the medial and latera l articular surfaces of the patella in sagittal MR images. Results and Conclusion. The bony landmark was found on all articular surfaces. Th e axial view of the PFJ and the MJS measurements were reproducible. An MJS of <5 mm showed high specificity for MR-detected cartilage defect s. Thus an MJS of 5 mm proved to be a limit in the diagnosis of joint- space narrowing in the PFJ in middle-aged individuals with chronic kne e pain.