Inflammation, meniscal damage and bone marrow lesions are the most influential factors in the pathogenesis of knee OA, a large MRI study shows.

Using data from the ongoing Osteoarthritis Initiative (OAI) study of 4796 individuals with or at high risk of knee OA the researchers found that only indicators of inflammation and meniscal tear associated significantly with subsequent radiographic knee OA.

The strongest one-year predictors were bone marrow lesions and inflammation, found the study authors that included David Hunter from the Royal North Shore Hospital in Sydney.

However they also found that cartilage damage did not increase the risk of OA, a discovery that they said emphasised the role of non-cartilaginous features in early disease as well as disease progression.

[the findings] also supported “the strategy of targeting the subchondral bone in early disease as an important treatment approach,” they wrote.

Writing in an accompanying editorial Timothy McAlindon from Tufts Medical Center in Boston said the findings showed knee OA could no longer be viewed as a monotonic disorder of hyaline cartilage.

“Other processes appear to be more influential, including the presence of inflammation and structural damage to the meniscus and subchondral bone,” he wrote.

While it is possible to hypothesise a number of potential pathological trajectories to multi structural joint failure, it is clear that we need to change the construct of OA as we teach it to students, trainees and colleagues, he said.

“That old paradigm has arguably stifled research and progress in this field for decades,” he said.

The researchers used a nested case control design to select cases from all OAI time points. They then evaluated MRIs from each OAI visit for each of the selected 710 knees for a range of structural pathologies that included damage to hyaline, meniscal cartilage damage, subchondral bone marrow lesions and synovitis).