Pretibial cyst formation after anterior cruciate ligament reconstruction with a hamstring tendon autograft.

We report a case of pretibial cyst formation, which is a rare complication, after anterior cruciate ligament (ACL) reconstruction. The patient had undergone ACL reconstruction at age 18 and complained of pain and swelling localized on the anteromedial aspect of the ipsilateral proximal tibia 2 years postoperatively. Magnetic resonance imaging showed a multilocular fluid-filled cyst arising from the outlet of the tibial bone tunnel. Open resection of the cyst was performed and communication between the tibial tunnel and the joint space was confirmed arthroscopically. The cavity of the tibial tunnel was packed with cancellous bone to seal off a water channel. The laboratory examination revealed slightly concentrated chondroitin sulfate in the cyst fluid compared with the articular fluid, despite histologic observation of no glycosaminoglycan synthesis in the cells of the cyst wall. These findings indicated that leakage of the articular fluid via the tibial tunnel might have caused the pretibial cyst after ACL reconstruction.