Delayed knee locking after complicated anterior cruciate ligament reconstruction despite good stability using a bio-transfix

We describe a case of delayed cyst formation that presented as intermittent knee locking after complicated anterior cruciate ligament (ACL) reconstruction using a Bio-TransFix implant in a 21-year-old male patient. During femoral fixation, we could not pull out the guide wire that was temporarily used for the femoral fixation. However, stability was good, and the guide wire was not removed. This was shown to be a wrong type of fixation in a later study. During follow-up, the patient was satisfied and stability was relatively good until 18 months post-operatively. From the 2nd post-operative year, he experienced intermittent knee swelling and locking and pain around the lateral femoral condyle. Follow-up magnetic resonance imaging showed a large cyst around the broken wire tip, but the reconstructed ACL was fine.