Investigating the Influence of Oxford Unicompartmental Knee Arthroplasty Keel on Sagittal Plane Stresses: A Finite Element Analysis

Purpose The specific impact of keel placement and tibial implant position on stress reduction and fracture risk in the sagittal plane of the Oxford unicompartmental knee arthroplasty (UKA) system remains unclear. Therefore, this study aimed to investigate the stresses produced by the Oxford UKA keel in the sagittal plane to better understand their effects on fracture risk and optimize surgical outcomes. Methods This retrospective study included 89 patients who underwent Oxford UKA. The effects of the position and size of the tibial component on the anterior and posterior cortical distances were assessed using postoperative sagittal radiographs. Finite element analysis was performed using three-dimensional surface models of the trabecular and cortical bones of the tibia created from preoperative computed tomography-Digital Imaging and Communications in Medicine data. Results Clinical analysis data showed a correlation between the posterior placement of the tibial component and the distance between the posterior cortex and keel. The smaller size of the tibial component predominantly reduced the distance between the posterior cortex and the keel. Finite element analysis showed that moving the medial loading point of the tibia posteriorly increased the keel's exposure to posterior cortical stresses. Posterior displacement of the tibial component and additional posterior transection of the keel further increased the stresses in the tibial diaphyseal cortex. Conclusion Posterior placement and small size of the tibial component, as well as posterior osteotomy of the keel, were associated with increased stresses in the sagittal plane resulting from the Oxford UKA keel.