Background/Purpose: Osteoarthritis (OA) of the knee is one of the most common causes of disability in the U.S. Often overlooked, OA specific to the patellofemoral joint of the knee (PFJ OA) is highly prevalent, and often occurs in isolation from tibiofemoral (TFJ) OA. While MRI-detected structural damage in the PFJ are related to the development of TFJ lesions, little is known about the clinical significance of these lesions, or the impact of cumulative tissue damage across the four subregions of the PFJ (medial/lateral patella and trochlea). The purpose of this study is to determine the cross-sectional relationship of the number of PFJ subregions with structural MRI-defined tissue damage with knee pain, performance-based function, and physical activity in people with or at high risk of knee OA.   

Methods: We performed a cross-sectional analysis using 60-month data from the NIH-funded Multicenter Osteoarthritis Study. OA features in the four PFJ subregions were scored semi-quantitatively using the WORMS method by two musculoskeletal radiologists. We created a 3 level exposure variable for the number of PFJ subregions with structural damage: (0, 1 or 2,  3 or 4). Three different MRI features were assessed separately: full-thickness cartilage damage (WORMS 2.5, 5-6), bone marrow lesions (BMLs) (≥1), and definite osteophytes (≥2) in the PFJ.  Relation of number of PFJ subregions to knee pain severity (VAS pain) and repeated chair stand time was assessed using ANCOVA. Relation of the odds of at least mild pain with stairs (WOMAC pain scale) and walking < 6,000 steps/day (a level of physical activity associated with risk of incident functional limitation) was assessed using logistic regression. Separate models were created for each PFJ MRI feature. Each analysis was adjusted for age, sex, BMI, previous knee injury/surgery, and coincident TFJ MRI feature.

Results: 1099 knees had complete MRI WORMS readings and performance based function assessed at the 60-month visit. The mean (SD), age and BMI of this sample was 66.8 (7.5) and 29.6 (4.8), respectively; 65% were female. In general, a higher number of PFJ subregions with any MRI-defined structural damage were associated with higher pain levels and longer time to complete 5 chair stands than those with fewer subregions affected (Table 1). Participants with full-thickness cartilage damage or BMLs in 3 or 4 compartments had three times the odds of pain on climbing stairs (Table 2). Participants with full-thickness cartilage damage in at least three compartments or osteophytes in at least one compartment have 2.3 and 2.1 times the odds of walking < 6,000 steps/day (Table 2).

Conclusion: Having damage in multiple subregions of the PFJ is associated with increased pain, decreased function, and greater odds of walking < 6,000 steps/day. The specific outcomes affected depended on the type of tissue damage, with full-thickness cartilage damage appearing to have the most impact across all outcomes. In addition to cartilage damage, osteophytes are associated with walking less steps/day, and BMLs with pain on stair climbing.

Maxwell et al PF OA MRI table

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/relation-of-mri-detected-structural-damage-in-the-patellofemoral-joint-to-pain-and-performance-based-function-the-most-study/