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Objective:
The anatomic and orthopaedic literature has recently emphasized the role of patellar stabilizers adjacent to the medial patellofemoral ligament (MPFL): the medial quadriceps tendon femoral ligament (MQTFL), medial patellomeniscal ligament (MPML), and medial patellotibial ligament (MPTL). Now, in addition to the MPFL, surgical reconstruction is performed for the MQTFL and MPTL. To provide a baseline for subsequent investigation into MRI diagnosis of injury, the objective of this study is to report the MRI visibility of the primary and secondary ligamentous stabilizers of the patella.

Materials and Methods:
A pilot study of consecutive noncontrast knee MRI (3T) examinations was performed retrospectively at our institution. Subjects were excluded if they had more than one knee MRI, a clinical history of patellar maltracking or a history of prior dislocation, surgery, tumor, or infection involving the knee region. Two blinded independent readers (a musculoskeletal imaging fellow and senior radiology resident) scored four structures independently: the MPFL, MQTFL, MPML, and MPTL. Structures were scored using a 5-point Likert-scale for visibility (0 - not visualized, 1 - probably not visualized, 2 - partial visualization < 50%, 3 - partial visualization > 50%, and 4 - fully visualized) and injury (0 - normal signal intensity, 1 - edema signal at the expected course of the ligament, 2 - partial tear, 3 - complete tear, 4 - complete tear with fiber laxity). For statistical analysis, reader scores were averaged. In addition, a second review by one reader was performed more than 2 weeks after the initial review. Inter- and intrareader reliability were calculated using Cohen’s weighted kappa coefficient.

Results:
Knee MRI scans were analyzed for 52 patients (60% women; mean age, 57 years; age range, 20-89 years) with a clinical concern for internal derangement not related to patellar instability. The MPFL was visualized or mostly visualized (Likert score > 3) by both readers in 92% (48/52) of cases. There were no cases of MPFL injury. Visibility of the secondary stabilizers with mean visibility scores and standard errors were: MQTFL 3.4 +- 0.19, MPTL 2.6 +- 0.14, and MPML 1.2 +- 0.14. MRI findings consistent with injury to a secondary patellar stabilizer was observed in one case (2%) that was scored as a partial tear in the MPTL. No partial or complete tears were seen in the MQTFL or MPML. Intra- and interrater reliability were calculated with a weighted kappa coefficient of 0.65 and 0.64, respectively.

Conclusion:
The MPFL is typically visualized on routine knee MRI, but the secondary patellar stabilizers are less conspicuous and often challenging to visualize. With knowledge of secondary patellar stabilizer anatomy, these ligaments may be visualized with good inter- and intrareader reliability in many patients without a history of patellar instability.