Abstract
Objectives:
While uncommon, acute traumatic patellar dislocations can lead to recurrent symptoms of patellar instability in 15% to 45% of patients. Patellar stability is an interplay of bony and soft tissue restraints as well as anatomic factors, however, a mainstay of treatment remains reconstruction of the medial patellofemoral ligament (MPFL).
Instability events can lead to intra-articular derangements of the knee, both in the acute and chronic patellar instability setting. These findings may not always be appropriately identified on magnetic resonance imaging (MRI). The incidence of these “surprise” injuries have not been previously reported. The purpose of this study is to determine the rates of coexisting intra-articular pathology in patients with patellar instability requiring MPFL reconstruction and elucidate any discordance between preoperative MRI findings and diagnostic arthroscopy findings.
Methods:
All patients undergoing MPFL reconstruction at a single institution between 2010 and 2023 were identified and preoperative MRI reports, defined as the most recent MRI report to the date of surgery with no interval traumatic events, were queried. Records without full MRI reports as read by a radiologist or cases in which a diagnostic arthroscopy was not conducted were excluded. MRI findings were discordant from arthroscopic findings if a lesion identified on diagnostic arthroscopy was not present in the full MRI report. Procedures that were undertaken because of these missed pathologies on MRI were recorded.
Results:
A total of 640 patients were identified during the study period, and 507 complete records were ultimately included. Preoperative MRI identified patellar osteochondral lesions or cartilage fissures in 333 patients (66%), loose bodies in 119 patients (24%), lateral femoral condyle osteochondral lesions or fissures in 97 patients (19%) and meniscus tears in 47 patients (9%). Among these patients, 172 (34%) had a diagnosis at the time of arthroscopy which was not identified on the preoperative MRI.
These arthroscopic findings resulted in 75 loose body removals, 74 patellar shaving chondroplasties, 16 partial meniscectomies, 3 microfractures, 3 osteochondral lesion open reduction internal fixation, and 2 meniscal repairs which would have been missed without diagnostic arthroscopy due to discordant MRI findings.
Conclusions:
Over one-third of patients at a single institution who underwent diagnostic arthroscopy in the setting of patellar instability surgery had pathology identified which required surgical intervention that was not reported on a preoperative MRI. A comparison of MRI and diagnostic arthroscopy has been extensively reported on for other knee pathologies including ACL tear and lateral meniscal tear; however, there has been no similar investigation of the reliability of MRI for identification of concomitant pathology in the setting of patellar instability to date. The findings of this study highlight the importance of diagnostic arthroscopy in the treatment of patellar instability, the frequency with which this altered treatment, and the high preponderance of discordant MRI findings.
