Magnetic resonance imaging of the knee after medial unicompartmental arthroplasty

Objective: We evaluated safety and potential diagnostic value of magnetic resonance (MR) imaging of the knee treated with medial unicompartmental arthroplasty (MUA). Methods: The treated knee of 8 patients who underwent MUA was studied with four different 1.5-T MR sequences. Two radiologists independently evaluated eleven anatomical items using a score from 0 (not assessable) to 3 (completely assessable). The sum of the scores for each sequence was divided by the potential maximal sum, obtaining a percentage visibility index (PVI) for each item. Results: No adverse effect was reported during or within 30 min after the exam. Posterior cruciate ligament was unseen in all patients by both observers. The following PVIs were reported for the remaining ten items: femoral-patellar relationship 83-100%; femoral-patellar cartilage 92-100%; Hoffa's fat pad 75-92%; patellar ligament 79-100%; lateral meniscus 100%; femoral-tibial lateral joint 100%; lateral collateral ligament 96-100%; anterior cruciate ligament 54-83%; femoral-tibial lateral cartilages 92-100%; posterolateral corner 100%. Agreement between readers was found in 331/352 (94%) evaluations (k = 0.74-0.78). Conclusions: MR imaging after MUA offers a safe and reproducible evaluation of residual knee anatomy except for cruciate ligament, and can be used to follow-up these patients.