Summary

MRI optimises pre-operative assessment of medial compartment in patients undergoing unicompartmental knee arthroplasty compared to radiographs alone. 

Abstract

Aims
For unicompartmental knee arthroplasty (UKA), patient selection using correct indications can optimise post-surgical outcomes. The current gold standard for assessing eligibility is with radiographs, however magnetic resonance imaging (MRI) may allow for more accurate assessments of cartilage damage. We aimed to evaluate the utility of MRI for pre-operative assessment of medial UKA patients by: 1) comparing OA severity of the medial, lateral and patellofemoral (PF) compartments when assessed using MRI compared with standard radiographs, and 2) investigating associations of these two assessments with post-operative clinical outcomes.

Patients and Methods
This study had ethical approval. Retrospective review was performed for 85 primary medial UKA between 1 January 2017 and 31 December 2021. The main outcomes measures were pre-operative cartilage loss and patient-reported clinical outcomes. Pre-operative cartilage loss was recorded using the International Cartilage Repair Society (ICRS) classification using MRI, and Kellgren-Lawrence (K-L) scores from radiographs. Patient-reported clinical outcomes were measured using pre-op, early (6-week) and late (1- or 2-year) Oxford Knee Score (OKS) change scores.

Results

Use of MRI had improved accuracy over radiographs. In the medial compartment, 37 (44%) patients had less severe radiographic K-L scores (1 to 3), however, all patients had the most severe MRI ICRS scores (4). For patients with mild K-L scores (0 and 1), 20 (43%) and 7 (78%) patients had more severe ICRS scores (3 and 4) within their lateral and PF compartments, respectively. No associations were found between ICRS or K-L scores and OKS for any of the compartments.

Conclusion

MRI optimises pre-operative assessment of medial compartment UKA patients compared to radiographs alone. This study suggests that cartilage loss in the PF compartment assessed using MRI is not considered a contraindication for UKA.