Correlation Between Synovial Fluid Biomarkers and Leg-Fat Area Ratios in Patients Undergoing ACL Reconstruction With or Without an Associated Meniscectomy.

Purpose: This study attempts to establish whether local adiposity of the knee at the level of the joint line is associated with alterations in synovial fluid biomarker concentrations in patients undergoing ACL reconstruction with or without an associated meniscectomy.

Methods: Patients undergoing ACL reconstruction were prospectively enrolled at the time of surgery from July 2011 to January 2015. Synovial fluid samples were collected just prior to incision and the concentrations of 10 biomarkers of interest were determined using a multiplex magnetic bead immunoassay. Knee adiposity was assessed via measures of leg fat area using magnetic resonance axial T2 images at the level of the joint line. Measurement was determined by subtracting the sum of the joint area, consisting of bony and muscle areas, from the total leg area with six different ratios assessed. Groups were evaluated by injury type (isolated ACL, ACL + meniscal injury, and total cohort). The correlation between synovial fluid biomarker levels and leg fat area ratios was evaluated using Spearman's correlation.

Results: There were 22 females and 26 males, with a mean age of 33.8 years (± 10.5) and a mean BMI of 25.3 (± 4.0). In the setting of isolated ACL injury, there was a statistically significant correlation between leg fat ratios and interleukin- 6, vascular endothelial growth factor, and interleukin-1 receptor antagonist. In patients with concomitant meniscal tears, there was an inverse correlation between leg fat ratios and monocyte chemoattractant protein-1.

Conclusion: The leg fat to total leg volume ratio and leg fat to joint space volume ratio were the most consistent measures for alterations in post-injury synovial fluid biomarker concentrations. Analysis of synovial fluid at the time of ACL reconstruction demonstrated significant correlations between specific leg-fat area ratios and synovial fluid biomarker concentrations. Local adiposity around the knee joint appears to modulate the biochemical environment of the joint and can clinically help guide prognostic discussions with the patient.