Purpose: Cyclope syndrome is described in the literature as a postoperative complication of arthroscopic anterior cruciate ligament (ACL) grafts, leading to permanent flexion. The discovery of this syndrome in ten patients before reconstruction of the ACL led us to revisit the pathophysiology.

Material and methods: Among 250 candidates for ACL grafts, ten presented a positive but dull Lachman-Trillat sign with permanent flexion greater than 10°. The rotation click was negative in two and dull in eight. KT 200 measured differential laxity greater than 4 mm in all. Nine patients were reviewed at consultation, one patient had recently undergone another operation. Clinical and radiographic findings recorded in the patient’s files and operation reports were reviewed by two observers different from the operator.

Results: Arthroscopy revealed a partial tear of the ACL in three cases, a scarred ACL nourished by the PCL in five and a full thickness tear of the ACL in two. There was a fibrous barbell nodule inserted on the tibia in all cases, a characteristic feature of cyclope syndrome. The nodule was interposed between the femur and tibia at extension and was resected in all cases. Pathology reported a ligamentoid structure undergoing fibrous organisation. At last follow-up, greater than two years for nine patients, the IKDC rating was A for six patients and B for three patients. None of the patients had a defective extension differential.

Discussion: Persistent flexion preoperatively in a patient with a torn anterior cruciate ligament suggests possible presence of a ligamento-fibrous nodule interposing between the femur and tibia at extension. This nodule can go unnoticed at arthroscopy but appears to be unmasked in the Cabott position after partial resection of the subpatellar fat. It is particularly important to look for this nodule when the stump of the torn ACL is not found and the patient has experienced a recent sprain. Since we started looking for this nodule in all cases with resection, we have no longer encountered postoperative cyclope syndrome.

Conclusion: This group of arguments strongly suggests that the conditions necessary for the constitution of cyclope syndrome are probably present before reconstruction of the anterior cruciate ligament.