Inferior outcomes for medial unicompartmental knee arthroplasty (UKA) patients with preoperative medial tibial bone marrow lesions (BMLs) were recently reported. The purpose of this study was to compare the location and severity of BML on postoperative outcomes after medial UKA and TKA using a larger sample size and more rigorous magnetic resonance imaging (MRI) evaluation.
BML were graded on preoperative MRIs from 174 UKAs performed between 2009 and 2013 using the MRI Osteoarthritis Knee Score criteria. Grading was performed by a single evaluator blinded to the patient's outcome. MRIs from a matched group of 174 TKAs were then evaluated. Preoperative and postoperative Knee Society Knee Scores, Pain Scores, and Function Scores (FSs) were then compared between UKA and TKA patients based on the location and severity of BMLs.
Overall medial-side BML severity (sum of tibia, femur, and patellar grades) did not affect Pain Score or FS; however, UKA and TKA patients with more severe BMLs had greater preoperative-to-postoperative gains in Knee Society Knee Scores (P = .05). When evaluating individual regions, UKA patients with more severe medial tibial BML had significantly greater gains in FS than those without BML, whereas the opposite was true for TKA patients (P = .02). Similarly, UKA and TKA patients with patellar lesions had greater gains in FS than those without BML (P = .05). Medial femoral BML did not appear to affect outcomes for either UKA or TKA patients.
Medial tibial BMLs were not associated with inferior outcomes. Clinically, these results suggest that BMLs should not be considered a contraindication for medial UKA.