Bone Marrow Lesions in Osteoarthritis: Pathophysiology, Clinical Implications, and Emerging Management Strategies

Abstract

Bone marrow lesions (BMLs) have emerged as a pivotal feature in osteoarthritis (OA), correlating strongly with pain severity, disease progression, and joint dysfunction. This review synthesizes the current understanding of BMLs in OA, including their epidemiology, underlying mechanisms, clinical significance, and evolving management strategies. Recent research underscores the role of BMLs as both markers and modulators of OA pathologyF, influencing therapeutic decision-making and prognostication. Recognizing and targeting BMLs may refine OA risk stratification and drive the development of novel disease-modifying interventions.

Introduction

Osteoarthritis is the most prevalent degenerative joint disorder worldwide, characterized by progressive cartilage deterioration, subchondral bone changes, and varying degrees of synovial inflammation. Traditionally, OA management has focused on symptomatic relief and joint preservation. However, advanced imaging modalities, particularly magnetic resonance imaging (MRI), have highlighted bone marrow lesions as a major structural abnormality in OA, frequently associated with pain and radiographic progression. This article aims to provide an in-depth review of BMLs in the context of OA, integrating recent evidence and clinical guidelines to inform best practices for clinicians.

Epidemiology / Disease Burden

BMLs are observed in up to 80% of patients with symptomatic knee OA, with prevalence increasing alongside disease severity and age. The presence and size of BMLs have been linked to accelerated joint space narrowing, increased risk of total joint replacement, and poorer functional outcomes. Epidemiological studies suggest that the incidence of BMLs is higher in populations with greater mechanical joint loading, obesity, and prior joint injuries, contributing significantly to the global burden of OA-related morbidity.

Pathophysiology

BMLs are defined on MRI as ill-defined areas of increased fluid signal within the subchondral bone, reflecting a heterogeneous mix of histopathological changes. These include bone marrow edema, necrosis, fibrosis, microfractures, and increased vascularity. Mechanistically, BMLs arise from abnormal biomechanical stress on subchondral bone, leading to trabecular microdamage and increased remodeling. This pathological process is compounded by altered bone-cartilage crosstalk, inflammatory cytokine release, and neurovascular infiltration, which collectively drive pain sensitization and perpetuate local tissue damage. Recent studies have also implicated metabolic and genetic factors in modulating BML formation and persistence.

Risk Factors

Several intrinsic and extrinsic risk factors predispose individuals to BML development in the context of OA. Major contributors include advanced age, higher body mass index (BMI), knee malalignment (varus or valgus), joint instability, and previous trauma. Occupational or athletic activities involving repetitive joint loading further increase risk. Emerging evidence also links systemic factors such as metabolic syndrome, vitamin D deficiency, and subclinical inflammation to increased BML prevalence and severity.

Clinical Features

Clinically, BMLs are strongly associated with the presence and severity of joint pain, particularly in weight-bearing activities. Patients with larger or multiple BMLs often report more frequent and intense pain episodes, morning stiffness, and reduced physical function. Unlike radiographic findings, which may poorly correlate with symptoms, BMLs identified on MRI provide a more sensitive marker for symptomatic OA and can predict future cartilage loss and joint deterioration.

Diagnosis

BMLs are most reliably detected using MRI, appearing as hyperintense regions on fat-suppressed T2-weighted or proton density sequences. Conventional radiographs do not visualize BMLs, underscoring the added value of MRI in comprehensive OA assessment. Semi-quantitative scoring systems, such as the Whole-Organ Magnetic Resonance Imaging Score (WORMS) and MRI Osteoarthritis Knee Score (MOAKS), facilitate standardized evaluation of BML size, location, and progression. Differential diagnosis should consider other causes of bone marrow signal changes, including avascular necrosis, infection, and neoplasms, necessitating careful clinical correlation.

Treatment & Management

Current OA management strategies aim to reduce pain, optimize function, and slow structural progression, with BMLs increasingly recognized as therapeutic targets. Conservative interventions include weight management, physical therapy to offload affected joints, and analgesic medications such as acetaminophen or NSAIDs. Intra-articular corticosteroid or hyaluronic acid injections may provide symptomatic relief in selected cases. For refractory pain associated with large or persistent BMLs, surgical options such as subchondroplasty minimally invasive injection of bone substitute material have demonstrated promising short-term benefits in reducing pain and improving function. Importantly, optimal management requires a multimodal approach tailored to individual patient risk profiles and disease stage.

Recent Advances / Emerging Therapies

Recent translational research has focused on disease-modifying osteoarthritis drugs (DMOADs) that target subchondral bone remodeling and inflammation. Agents such as bisphosphonates, calcitonin, and selective estrogen receptor modulators have shown variable efficacy in reducing BML volume but are not yet standard of care. Biologic therapies targeting key cytokines (e.g., IL-1β, TNF-α) and small-molecule inhibitors of bone resorption are under investigation. Novel imaging biomarkers and quantitative MRI techniques are poised to enhance early detection, monitor therapeutic response, and stratify patients at high risk for rapid OA progression.

Guideline Recommendations

International guidelines from organizations such as the Osteoarthritis Research Society International (OARSI) and American College of Rheumatology (ACR) emphasize the importance of structural assessment including BMLs alongside clinical evaluation in OA management. While routine MRI screening is not universally recommended, it is considered for patients with atypical symptoms, rapid progression, or when surgical intervention is contemplated. The guidelines advocate for individualized, evidence-based interventions addressing modifiable risk factors, optimizing symptom control, and preserving joint integrity. Ongoing research is expected to refine these recommendations as more data on BML-targeted therapies become available.

Conclusion

Bone marrow lesions represent a critical and dynamic component of osteoarthritis pathogenesis, bridging the gap between structural damage and symptomatic burden. Advances in imaging, mechanistic understanding, and targeted therapies are reshaping the clinical approach to OA, with BMLs offering new opportunities for risk stratification and intervention. Continued research into the molecular drivers and therapeutic modulation of BMLs holds promise for improved patient outcomes and the development of disease-modifying strategies in osteoarthritis care.