Poster 300: A Novel Magnetic Resonance Imaging (MRI) Scoring System to Evaluate Patellofemoral Osteoarthritis

OBJECTIVES: Knee osteoarthritis (OA) is a common degenerative or post-traumatic condition, and may affect one or more compartments, including the medial and lateral tibiofemoral or patellofemoral articulations. Isolated patellofemoral osteoarthritis (PFOA) has been reported in 24% of women and 11% of men aged > 55 years presenting for evaluation of knee pain. PFOA is a result of abnormal mechanical loading across the patellofemoral joint, often related to prior instability, trauma, malalignment or post- surgical changes. Treatment of PFOA typically includes a trial of conservative management, including physical therapy, injections and activity modification. Operative treatment involves joint preservation (i.e., cartilage restoration procedures, tibial tubercle osteotomy, or lateral lengthening) and joint replacement (patellofemoral arthroplasty) procedures. In contrast to the tibiofemoral compartments, the current literature lacks a reliable magnetic resonance imaging (MRI) scoring system to quantitatively evaluate patellofemoral cartilage degeneration. The present study aims to describe, apply and assess the inter-observer reliability of a novel MRI scoring system for assessment of the patellofemoral cartilage. METHODS: We conducted a query of an institutional database to identify all patients who underwent patellofemoral arthroplasty by the senior surgeon (S.M.S.) between January 2012 and December 2021. Patients with poor quality or lacking preoperative knee MRI were excluded. MRI scans were performed on 1.5 or 3.0-Tesla magnets utilizing dedicated extremity coils and standardized clinical imaging protocols consistent with International Cartilage Regeneration and Joint Preservation Society (ICRS) guidelines for the assessment of articular cartilage. Preoperative MRI scans were reviewed and patellofemoral cartilage was scored by a fellowship-trained musculoskeletal radiologist and a fellowship- trained orthopedic knee surgeon using our novel MRI scoring system. The novel semi-quantitative MRI patellofemoral scoring system includes assessment of patellar and trochlear cartilage, bony architecture, patellofemoral alignment, and synovitis (Table 1). For statistical analysis, inter-observer agreement was assessed using Cohen-Kappa coefficient for categorical variables, and intraclass correlation coefficient (ICC) for the total score. The measurement agreement for reach variable and total score was interpreted according to the Landis and Koch criteria: 0 - 0.2, slight; 0.21 - 0.4, fair; 0.41 - 0.6, moderate; 0.61 - 0.80, substantial; 0.81 - 1.0, almost perfect. RESULTS: A total of 72 patients were included in the final analysis. The mean (± standard deviation) age and body mass index (BMI) of all patients was 53.30±7.72 years and 27.3±5.37 kg/m, respectively. Patellar bone edema and patellar cysts demonstrated moderate inter-observer agreement. All cartilage features, trochlear bone edema and cysts, osteophytes, subchondral remodeling, patellar height, and synovitis demonstrated substantial inter-observer agreement. Patellofemoral alignment and total score demonstrated almost perfect inter-observer agreement (Table 2 and Figure 1). CONCLUSIONS: The novel MRI scoring system for PFOA proposed by the authors is an attempt to develop a comprehensive method to assess patellofemoral joint cartilage degeneration, including evaluation of patellar and trochlear cartilage changes, bony architecture, patellofemoral alignment, and synovitis. Importantly, all features of the scoring system demonstrated at least moderate inter-observer agreement, with the majority of variables and total score demonstrating substantial to near perfect agreement. Future studies should aim to validate this scoring system in patients with and without patellofemoral arthritis and attempt to correlate scores with clinical outcomes.