Marrow adipose tissue accumulation following anterior cruciate ligament reconstruction: A narrative review

Marrow adipose tissue (MAT) is no longer considered a passive filler but a dynamic component of the bone marrow niche that actively regulates bone metabolism. This narrative review focuses on the dynamics of MAT accumulation following anterior cruciate ligament (ACL) reconstruction. Experimental studies, including rat models, demonstrate that ACL reconstruction induces MAT accumulation, which is further promoted by postoperative joint immobilization or non-weight-bearing. While MAT accumulation induced by immobilization or non-weight-bearing in intact joints is reversible upon remobilization or reloading, MAT accumulation induced by postoperative immobilization or non-weight-bearing following ACL reconstruction fails to recover even after subsequent remobilization or reloading. These findings suggest that the recovery mechanism observed in intact joints is disrupted in the post-ACL reconstruction environment, leading to potentially irreversible negative effects. In addition, this review highlights that the pathophysiology of surgery-induced MAT accumulation is distinct from pharmacological influences. For example, corticosteroid-induced MAT accumulation early after ACL reconstruction is reversible following treatment discontinuation, indicating that the reversibility of MAT accumulation is fundamentally dependent on the initiating stimulus. Furthermore, sex-related dimorphism is evident, with estrogen likely exerting a protective effect that delays MAT accumulation following ACL reconstruction in females. Given the potential contribution of aberrant MAT accumulation to osteoarthritis pathogenesis, future research should prioritize elucidating the biological crosstalk between MAT and non-osseous tissues, particularly articular cartilage. Clarifying the regulatory mechanisms underlying post-surgical MAT accumulation will be essential for developing effective preventive and therapeutic strategies aimed at preserving joint integrity and improving long-term patient outcomes.