Metal-artifact reduced MR imaging for reverse shoulder arthroplasty: findings 1 year after surgery

To describe typical MRI findings 1 year after reverse total shoulder arthroplasty (rTSA) implantation.

Metal artifact reduction (MARS) MRI including CSSEMAC techniques was prospectively acquired in N = 25 consecutive patients (18/25 female; 61-80 years) 1 year after rTSA. MRI findings of bone and soft tissue and artifact reduction were assessed semi-quantitatively. Clinical Constant-Murley scores (CMS) were obtained, including its subscores pain, activities-of-daily-living (ADL), range-of-motion (ROM), and strength. Preoperative MRI was available in 13/25 subjects. Statistical analyses included descriptive statistics, Spearman correlations, nonparametric tests, and multivariable regression models.

MARS MRI of rTSA showed overall good image quality. Subacromial edema (88%), mild effusion (52%), and synovitis (44%) were frequent postoperative findings. Synovitis was associated with more pain (B = -2.044, 95% CI [-3.617, -0.470], p = 0.039) and lower strength (B = -4.497, 95% CI [-7.101, -1.893], p = 0.008). Minor bone marrow edema (BME) at the shaft was found in all subjects (100%). BME in Gruen zone 4 (88%) and 6 (80%) was most frequent. A higher number of Gruen zones with BME correlated significantly with lower ADL (R = -0.532, p = 0.024). There was a significant increase in fatty infiltration between pre- and postoperative images for the midacromial deltoid muscle (1 (IQR, 1-1) versus 2 (IQR, 1-2), p = 0.008; postoperatively present 100%). It was associated with an increase in deltoid length (chi-square 4.35, p = 0.037), but not with inferior clinical scores. However, fatty infiltration of the more anterior deltoid muscle was associated with lower ADL (B = -3.064, p = 0.008).

Subacromial edema, minor shaft BME, and fatty infiltration of the midacromial deltoid muscle were typical, asymptomatic MRI findings 1 year after rTSA.