MRI templating for Oxford partial knee replacement femoral component - a novel sizing method.

Background: Correct sizing of Oxford Medial Unicompartmental Knee Replacement (OUKR) femoral component can be challenging. Incorrect sizing can increase risk of bearing dislocation or revision. This study aimed to assess the accuracy of a simple but novel templating method in sizing the femoral component in OUKR.

Methods: A single surgeon retrospective study was performed reviewing all patients who underwent OUKR between April 2017 and May 2024 comparing those sized with the templating method with those sized by standard means. The method consisted of a circular fit over the posterior medial condyle of the femur on sagittal T2-weighted MRI sequence from which the component size was templated. Comparison between the groups was made by analyzing post operative radiographs for correct component sizing. Correctly sized components had a posterior condylar overhang of 0-4 mm. An interobserver reliability assessment of the templating method was conducted.

Results: 121 OUKR met the selection criteria with 61 in the MRI templated group and 60 in the standard group. The MRI group was significantly more likely to have correctly sized femoral components than the standard group (72 % vs 54 %, p = 0.04). Average deviation from the correct size was also significantly lower in the MRI group (1.7 mm vs 2.3 mm, p = 0.01). Interobserver reliability was 75.9 % with Cohen's Kappa 0.59 (p = 0.09).

Conclusion: Our novel preoperative MRI templating technique is a simple and useful tool that can improve sizing accuracy in UKR when compared with traditional intraoperative sizing methods.