MR imaging of the knee in patients with medial unicompartmental arthroplasty : comparison among sequences at 1.5 T

Purpose: This study was done to test a series of magnetic resonance (MR) imaging sequences of the knee after medial unicompartmental arthroplasty. Materials and methods: Four patients who had undergone Oxford III medial unicompartmental arthroplasty underwent 1.5-T MR imaging of the operated knee using coronal sequences: T1-weighted spin-echo (SE), T1-weighted turbo SE (TSE), proton-density (PD)- and T2-weighted TSE, T1-weighted gradient echo (GE), short-tau inversion recovery (STIR), multi echo data image combination (MEDIC), T2*-weighted GE, volumetric interpolated breath-hold examination (VIBE), and dual-echo steady state (DESS). For each sequence, we evaluated the visibility of the anatomical structures of the central pivot, lateral compartment, and anterior compartment using a semiquantitative score (0=total masking; 1=insufficient visibility; 2=sufficient visibility; 3=optimal visibility). The sum of the scores given to each sequence was divided by the maximal sum, obtaining a percentage visibility index. Friedman and sign tests were used for statistical analysis. Results: MR examination time was 30-32 min. No patients reported pain, heat or other local discomfort. The visibility index ranged between 83% and 89% for the first four sequences without significant differences among them, 58% for STIR and 11%-36% for the last five sequences. Significant differences were found between each of the four first sequences and the remaining sequences (p<0.004) and between STIR and the last five sequences (p<0.008). Conclusions: MR imaging of the knee after medial unicompartmental arthroplasty was not associated with adverse events. An imaging protocol including SE, TSE and STIR sequences could be used to study the knee with unicompartmental arthroplasty.