Background/Purpose: Bone marrow lesions (BMLs) are of high interest in osteoarthritis for their association with pain and structural progression. They are characterized on magnetic resonance (MR) images as ill-defined areas of hyper intensity on fat-suppressed, T2 weighted, and short tau inversion recovery (STIR) sequences and of intermediate or low intensity on T1 weighted sequences in comparison with normal subchondral bone. Our understanding of the underlying mechanism of action of BMLs will be increased by histopathological studies of the subchondral bone. Therefore, we performed a systematic literature review.

Methods: We searched relevant databases up to May 2016 without language restrictions for articles describing the histology of BMLs in patients with primary osteoarthritis. We identified 503 unique records that were screened independently by two authors. Based on title and abstract we excluded 463 records (agreement 96.0%, k=0.65), and for the remaining 40 records we retrieved full-text papers to assess eligibility. Finally, we included 11 articles in this review by mutual agreement. Due to heterogeneity between studies meta-analysis was not possible.

Results: All studies used specimens from total joint replacement surgery (knee n=7; hip n=4). Study size ranged from 6 to 60 patients (median 15). Studies differed in histological and radiological methods (e.g. in vivo (n=8) versus ex vivo (n=3) imaging and imaging sequences). Most reported histological findings in BMLs were fibrosis (knee n=7; hip n=3), necrosis (knee n=4; hip n=3) and trabecular abnormalities (knee n=5; hip n=2). Bone marrow edema (n=5) was predominantly reported in hip studies (n=3), and less in knee studies (n=2). Other reported findings were: hyper vascularity or blood vessel hyperplasia (n=5), bone remodelling (n=3) and increased bone volume fraction (n=4). Two knee studies correlating topography of MR imaging with histology, compared subchondral bone with and without BMLs. Both studies demonstrated fibrosis, necrosis and trabecular abnormalities were increased in BMLs compared to control subchondral bone. In three knee studies micro-computed tomography was used showing that trabeculae of BMLs were thicker and more plate-like shaped than trabeculae in control specimens.

Conclusion: Published data summarized in this systematic review indicated that several histological features are reported in BMLs; consistently reported are fibrosis, necrosis and trabecular abnormalities. How and whether these histological features are related is not clear. However, to think of BMLs as merely reflecting increased water content within the bone marrow, is an outdated notion. Since some histological findings indicate an active process, BMLs might not only characterize disease stage, but could also help to identify those patients at high risk of structural progression. A better understanding of pathological processes underlying BMLs could potentially lead to new targets in osteoarthritis treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/histology-of-bone-marrow-lesions-in-osteoarthritis-a-systematic-literature-review/