Background/Purpose: Knee osteoarthritis (OA) occurs in both the patellofemoral joint (PFJ) and tibiofemoral joint (TFJ). Little is known about the natural history of OA and it has been hypothesized, based on findings from radiographic studies, that OA occurs first in the PFJ and subsequently progresses to involve the TFJ. This has not been evaluated using MRI, which is more sensitive than radiographs to identify structural damage, particularly in the PFJ. The purpose of this study was to describe patterns of change in cartilage loss and bone marrow lesions (BMLs) among knee joint compartments over 7 years. Specifically, we describe whether disease remains isolated to one compartment or develops in the other, and which compartment tended to be initially involved. 

Methods: The Multicenter Osteoarthritis (MOST) Study is a NIH-funded longitudinal cohort study of 3,026 individuals with or at risk for knee OA. Participants had MRI of their knee at baseline and 84-month of follow up. Two musculoskeletal radiologists used the Whole Organ Magnetic Resonance Score (WORMS) to assess cartilage morphology and BMLs in the PFJ and TFJ at baseline and 7 years. At baseline and 84-months, knees were categorized as having full-thickness cartilage loss (any region within a compartment with WORMS 2.5, 5 or 6) isolated to the PFJ, isolated to the TFJ, mixed (both PFJ and TFJ) or no full-thickness loss in either compartment. In sensitivity analyses any cartilage loss (WORMS ≥2) and any BML (WORMS ≥1) were used to categorize disease in knee compartments.

Results: 994 knees had complete MRI readings at baseline and 84-months. The mean age and BMI at baseline were 61.7 (±7.5) years and 29.7 (± 4.7) kg/m², respectively, and 61% were female. Among 570 knees without full-thickness cartilage loss at baseline, the incidence of isolated PFJ, isolated TFJ and mixed full-thickness cartilage loss was 12, 13 and 5%, respectively. The remaining 70% did not develop full-thickness cartilage loss at follow up. Among 334 knees that had full-thickness cartilage loss isolated to the PFJ or TFJ at baseline, only 62 (19%) developed full-thickness cartilage loss in the other compartment while 272 (81%) continued to only have the initial compartment affected with full-thickness cartilage loss. Among 62 knees that started with isolated full-thickness loss in the PFJ or TFJ and developed full-thickness cartilage loss in the other compartment, it more often progressed from the PFJ 44 (71%) than from the TFJ 18 (29%). Similar patterns were seen in sensitivity analyses when disease was defined using any cartilage loss and any BML.

Conclusion: Over 7 years of follow-up it is uncommon for cartilage loss and BMLs to “spread” to the other compartment in the knee. Furthermore, of knees that develop cartilage loss and BMLs in the other compartment, most knees start with damage isolated to the PFJ, suggesting that mixed disease may start in the PFJ.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/changes-in-knee-compartment-distriubtion-of-cartilage-loss-and-bone-marrow-lesions-over-7-years-the-most-study/