Anterior cruciate ligament avulsion fracture following medial unicompartmental knee arthroplasty: A case report

Abstract

Introduction Anterior cruciate ligament (ACL) avulsion fracture after unicompartmental knee arthroplasty (UKA) has not been reported until recently. We describe a case of ACL avulsion fracture that developed after medial UKA. Case presentation A 57-year-old woman underwent UKA for right medial compartment osteoarthritis. She developed knee pain and swelling at 2 weeks after UKA, and radiographs showed an ACL avulsion fracture at 3 weeks after UKA. After conservative treatment failed, the fracture was fixed using screws. After 5 months from internal fixation, bone union was confirmed, and the screws were removed. At 16 months after removing screws, there was no further complication. Discussion The patient did not exhibit a fracture on the radiograph taken immediately after UKA. We carefully re-examined the radiographs and observed a 5-mm horizontal cement shadow on the lateral side of the tibial component. It is thought that excessive lateral resection of the proximal tibia during UKA may have resulted in a micro fracture and this outcome. In the present case, the posterior slope angle of the tibial component measured postoperatively was 11.5 degrees. The angle of more than 7 degrees along with excessive horizontal resection of the proximal tibia probably increased load on the ACL. Conclusion If patients exhibit a horizontal cement shadow near the tibial component and a higher posterior slope angle of the tibial component on the radiograph after UKA, surgeons should be aware of possible ACL avulsion fracture and perform additional radiological examinations in patients with continuous knee pain and swelling.