Summary

MRI templating improves Oxford UKR femoral sizing

Abstract

Background

Intraoperative sizing of Oxford Medial Unicompartment Knee Replacement (UKR) femoral component can lead to posterior overhang or underhang resulting in impingement or instability, respectively. This study aimed to assess the reliability of femoral component templating for Oxford Medial Uni-compartment Knee Replacements using a novel simple measurement on preoperative MRI compared with the traditional intraoperative sizing technique.

Methods

A single surgeon retrospective study was performed reviewing all patients who underwent Oxford Medial UKR between April 2017 to May 2024 were reviewed. From January 2022 onwards patients were sized preoperatively using sagittal MRI scans with a circle of best fit over the medial posterior femoral condyle corresponding to Oxford femoral component dimensions. Postoperative radiographs were assessed for size and position by measuring posterior femoral overhang or under-hang and implant flexion angle via an independent orthopaedic clinician. MRI templating was performed by two Orthopaedic clinicians to assess reproducibility.

Results

112 Oxford medial UKR were performed in 99 patients. 62 UKRs were sized via manual intraoperative method and 49 were sized via the preoperative MRI method. Mean femoral overhang or under-hang in the manually sized group was 3.29mm compared with 2.97mm in the MRI templated group. The manual group had more outliers with 37.1% having greater than 4mm overhang or underhang compared with 20% in the MRI group (p-value 0.024). A correlation coefficient of 0.79 was found between the two orthopaedic clinicians for MRI templating method.

Conclusion

Preoperative MRI based femoral component sizing results in reduced number of outliers with greater than 4mm overhang or underhang for Oxford UKRs.