Thymol turbidity test is associated with the risk of cyclops syndrome following anterior cruciate ligament reconstruction

Background: Cyclops nodule formation is a serious complication after anterior cruciate ligament (ACL) reconstruction. The purpose of our study was to investigate whether an increase in thymol turbidity test (TTT) values is involved in the development of cyclops nodule formation or cyclopoid scar formation following ACL reconstruction. Methods: Between 2011 and 2014, 120 cases underwent outside-in ACL reconstruction. Forty-seven patients who had high TTT values were individually matched for age, sex, body mass index, and meniscus injury to a low TTT value group of 47 patients. The primary outcome was the occurrence of cyclops nodule formation or cyclopoid scar formation. All 94 patients were divided into 3 groups using surgical records and intra-operative video to enable a sub-analysis. The groups were a no-cyclops group, a cyclopoid group, and a cyclops group. Blood examinations, including TTT, and knee range of motion evaluations were performed before surgery, 3 months after surgery, and 1 year after surgery. Results: There were no differences in preoperative demographic data between the two groups. TTT values did not significantly influence cyclopoid scar formation (OR, 1.67; 95% CI, 0.62 to 4.66; p = 0.362). However, patients with cyclops nodule formation showed significantly higher TTT values than the control patients. (OR, 9.34; 95% CI, 1.94 to 90.3; p = 0.002). Knee extension loss was observed in the cyclopoid and cyclops groups 3 months after reconstruction. In the cyclops group, arthroscopic resection of the cyclops nodule was performed 3 months after reconstruction. Eventually, almost full range of motion was restored in all patients. Conclusions: High TTT values before ACL reconstruction were an indicator of cyclops nodule formation. Furthermore, cyclopoid scar formations may not be the result of an individual's immune reaction but that of extension loss in the early post-reconstruction phase.