Delayed Fracture After Medial Unicompartmental Knee Replacement: Two Cases of Peri-Implant Fracture

Unicompartmental knee arthroplasty (UKA) is widely performed for medial compartment knee osteoarthritis due to its benefits of faster recovery, preservation of knee kinematics, and long-term survival. However, complications such as peri-implant fractures can occur. Most fractures are reported within three months postoperatively, but this study highlights two cases of delayed fractures occurring four and seven years after UKA, emphasizing the importance of long-term follow-up. In Case 1, a 79-year-old woman experienced a tibial peri-implant fracture seven years after UKA. Bone density loss and stress shielding were suspected contributors. Treatment involved conversion to stemmed total knee arthroplasty (TKA), which resulted in fracture union and restored function. In Case 2, a 73-year-old woman developed a fracture four years post-UKA. Following plate fixation and subsequent re-fracture, she underwent stemmed TKA, achieving fracture union and improved knee function. The exact cause of delayed fractures remains uncertain, but likely factors include age-related bone density reduction and stress shielding due to the implant. Unlike acute fractures, delayed fractures present unique challenges, and internal fixation may not ensure long-term stability. Stemmed TKA provides reliable stability, reduces micromotion, and promotes fracture healing. These cases underscore the importance of monitoring bone quality in UKA patients and considering stemmed TKA as a preferred treatment for delayed peri-implant fractures.