Prevalence of MRI-detected mediopatellar plica in subjects with knee pain and the association with MRI-detected patellofemoral cartilage damage and bone marrow lesions: data from the Joints On Glucosamine study.

Background: The mediopatellar plica is a synovial fold representing an embryonic remnant from the developmental process of the synovial cavity formation in the knee. We aimed to examine the frequency of MRI-detected mediopatellar plica and its cross-sectional association with MRI-detected cartilage damage and bone marrow lesions (BMLs) in the patellofemoral joint (PFJ) in a cohort of subjects with knee pain.
Methods: 342 knees with chronic frequent knee pain were evaluated for MRI-detected mediopatellar plica (type A, B or C according to the modified Sakakibara classification). Cartilage damage (scored 0 to 6) and BMLs (scored 0 to 3) were semiquantitatively assessed in four subregions of the PFJ on MRI. Hoffa-synovitis and effusion-synovitis were graded 0 to 3. Patellar length ratio (PLR), lateral patellar tilt angle (LPTA), bisect offset (BO), and sulcus angle (SA) were measured on MRI. The presence of mediopatellar plica and its association with cartilage damage and BMLs in the PFJ was assessed using logistic regression after adjusting for age, gender, body mass index, PLR, LPTA, BO, SA, and Hoffa- and effusion-synovitis.
Results: 163 (47.7%) knees exhibited mediopatellar plica (76 (22.2%) type A, 69 (20.2%) type B, and 18 (5.3%) type C) on MRI. Significant cross-sectional associations of MRI-detected mediopatellar plica and cartilage damage were observed for the medial patella (adjusted odds ratio (aOR) 2.12, 95% CI 1.23-3.64 for all types combined, and aOR 4.20, 95% CI 1.92-9.19 for type B lesion), but not for the anterior medial femur or the lateral PFJ. No associations were found between the presence of MRI-detected mediopatellar plica and BMLs in any patellofemoral subregion.
Conclusion: On MRI, types A and B mediopatellar plicae were commonly observed in this cohort of subjects with knee pain. MRI-detected mediopatellar plica was cross-sectionally associated with higher likelihood of the presence of MRI-detected medial patellar cartilage damage after adjustment for confounders.