 Arthrophobrosis is a common complication following ACL reconstruction surgery. This disorder is characterized by the overgrowth of collagen and scar tissue that limits patients' range of motion and causes pain and joint stiffness. Arthrophobrosis has been linked to factors such as sex, time from ACL injury to surgery, and previous knee surgery, but the biological factors that give rise to the disorder are unclear. A study of 11 patients who developed arthrophobrosis after ACL reconstruction suggests two proteins could be at play, basic fibroblast growth factor, or BFGF, and RANTES. Researchers matched patients with arthrophobrosis to one or two other patients who did not develop arthrophobrosis. Patients were matched based on age, sex, BMI, smoking status, time from ACL injury to surgery, and other existing injuries. Potential biomarkers were extracted from synovial fluid and their levels on the day of surgery were compared. Results showed that concentrations of RANTES were significantly higher among patients who developed arthrophobrosis requiring further surgery. Single biomarker models revealed that RANTES, as well as BFGF, were associated with an increased risk of developing postoperative knee stiffness requiring treatment. Some caution is warranted in interpreting these findings given the small sample of patients examined in this study and the variability in the volume of synovial fluid extracted from each patient on the day of surgery. Still, the results do offer some guidance. Synovial levels of RANTES and BFGF might serve as screening tools to identify and understand the types of patients who are at risk of developing arthrophobrosis following ACL reconstruction surgery. With further research, investigators may discover medications or treatments that disrupt the inflammatory pathways that lead to arthrophobrosis, reducing the distress experienced by patients and the cost associated with the management of this complication.