Abstract
Bone marrow lesions (BMLs), identified by MRI, are defined as a region of cancellous bone with high T2 and low T1 signal intensity. They are associated with various knee pathologies including spontaneous osteonecrosis of the knee (SPONK), AVN, trauma (fracture and bone contusion), following arthroscopy and secondary to overuse (i.e., after completing a marathon). They also are commonly recognised in patients with knee OA (referred to as OA-BMLs) and their substantial importance in knee OA pathogenesis has been recently identified. Depending upon the etiology (i.e., bone contusion, overuse, etc.) of the BML, these lesions can be “acute” in nature and spontaneously resolve over time. However, OA-BMLs generally are considered to be a “chronic” condition and overtime they have been shown to often persist and increase in size. Retrieval studies following THA and TKA, in patients with a preoperatively identified BML, have greatly expanded our understanding of OA – BMLs and these investigations consistently identify the critical role subchondral bone plays in OA disease progression. Histologic, histochemical and mechanical studies of OA-BMLs demonstrate significant alternations from healthy subchondral bone. The effected bone contains regions where fibrous tissue has replaced cancellous bone, microfractures are present and vascularity is increased. There is an increased concentration of inflammatory mediators and the bone structural integrity is compromised.
Standard radiographs of the knee correlate only modestly with patient symptoms, but conversely, the presence of an OA-BML is an extremely strong predictor of pain and knee joint dysfunction. Felson et al. reported this relationship. In a large group of patients with painful knee OA, 77.5% of these patients had a BML. Both the presence and size of the BML, following multiregression analysis, were significant predictors of knee pain severity.
Additionally, likely secondary to inadequate subchondral bone plate support, the presence of an OA-BML is associated with subchondral bone attrition (SBA). SBA leads to collapse of the subchondral bone plate and progressive joint deformity.
Based on the association of an OA-BML with pain, joint dysfunction and deformity, it is not surprising that these lesions are prognostic for patients seeking knee arthroplasty. Several studies have demonstrated that the odds of knee arthroplasty performance are substantially higher in patents with an OA-BML.
This enhanced understanding of knee OA pathogenesis and the critical role of subchondral bone in this process creates an opportunity for development of novel prevention and treatment strategies. Prevention of OA-BML formation has been considered and pharmacologic interventions proposed. Recent studies have reported positive results for treatment with bisphosphonates in patients with knee OA. One study reported significant pain and OA-BML size reduction in patients receiving a bisphosphonate for 4 months.
A strategy aimed at repairing and/or enhancing subchondral bone compromised by an OA-BML has also been proposed. Early results reported with this intervention are encouraging, but preliminary.
