Adipose-to-muscle area ratio at the knee is superior to BMI in predicting post-operative outcome following arthroscopic meniscectomy

Purpose To determine if measurement of leg adipose tissue area by MRI is a better predictor of post-operative clinical outcome compared to body mass index (BMI) following arthroscopic meniscectomy. Methods Patients that underwent an arthroscopic partial meniscectomy between 2011 and 2016 were identified and a retrospective chart review was performed. Patients with additional knee pathology other than a meniscal tear with or without associated articular cartilage injury were excluded. Leg adipose tissue and muscle area measurements at the level of the knee joint were performed for patients on their preoperative axial magnetic resonance imaging (MRI) study and adipose-to-muscle area ratio (AMR) was calculated. Correlations among AMR, BMI, and post-operative clinical outcomes were compared. Results A total of 74 patients (32 females and 42 males) were included (mean age 50.0 years, std. dev. 12.3 years). 35 patients underwent a partial medial meniscectomy, 15 underwent a partial lateral meniscectomy, and 24 underwent both. Linear regression analysis showed that the AMR, compared to BMI, had a significantly stronger correlation to both mean post-operative Knee Injury and Osteoarthritis Outcome Score (KOOS) across all 5 subscales (KOOS 5 ) and Tegner Current score. Patients that had cartilage damage and concurrent chondroplasty tended to be older and have lower post-operative KOOS 5 compared to those with no cartilage damage. AMR was also significantly correlated to age and BMI. Conclusions The current study demonstrates that compared to BMI, leg adiposity as determined by the ratio of adipose tissue to muscle area on axial MRI (AMR), is a stronger predictor of functional outcome following meniscectomy. This suggests a role of obesity in the progression of OA beyond the increased joint forces associated with increased BMI. Level of evidence IV, retrospective case series.