Are merchant views useful for patellofemoral osteoarthritis?

Abstract

Purpose: To evaluate the effectiveness of merchant view radiographs (MVR) to identify and grade patellofemoral osteoarthritis (PFOA) relative to MRI. Methods: A cohort of patients who underwent partial meniscectomy at a single large institution aged at least 45 years with a knee MRI within the preceding 6 months and with MVR within the preceding year was selected. PFOA was evaluated on MVR using KL grading (0-4) and minimum joint space width (mJSW) by a musculoskeletal (MSK) radiologist or a trained medical student. Size and depth of cartilage loss in the patellofemoral compartment was graded on MRI by an MSK radiologist using clinically used grading systems. MRI findings were classified into none, mild, moderate, or severe categories apriori. Positive and negative predictive values (PPV and NPV) and ROC curves for KL grading were calculated for detecting PFOA on MRI as none or mild (negative) versus moderate or severe (positive). Prediction models were built for comparing ROC curves for KL and mJSW variables. Results: 442 patients were identified with MVR and MRI. MVR KL grades of 0 or 1 had relatively good NPV for OA on MRI (81.3%, 95% CI: [75.1%, 78.5%]). MVR KL grades of 4 had similarly good PPV (86.7%, 95% CI: [69.5%,99%] ). MVR KL grades of 2 had relatively poor NPV (68.0%) and KL grades of 3 had similarly poor PPV (69.0%). MVR KL grades of 2 and 3 accounted for 62.6% of the radiographs. ROC areas were poor to fair for KL grading (ROC area 0.696) and for a mJSW model (ROC area 0.686). A model with both KL and JSW (ROC area 0.709) was not significantly better than just KL grading (p=0.623). Conclusions: MVR may be diagnostically useful for PFOA when they are essentially normal (KL 0 or 1) or very abnormal (KL 4). MRI should be more strongly considered if there is mild to moderate radiographic PFOA (KL 2 or 3), as radiographs are less accurate at these grades.Tabled 1MRI vs X-ray PFOAKL grade PF = 0KL grade PF = 1KL grade PF = 2KL grade PF = 3KL grade PF = 4MEDIAN JSW_PFMRI=non213059717.6MRI=mild2942901117.1MRI=moderate713461326.4MRI=severe262427115.4 Open table in a new tab