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

## TL;DR

This study examines typical MRI findings one year after reverse shoulder surgery, showing common soft tissue and bone changes that do not affect clinical outcomes.

## Contribution

The study introduces metal-artifact reduced MRI techniques to identify typical postoperative findings in reverse shoulder arthroplasty patients.

## Key findings

- Subacromial edema, mild effusion, and synovitis were frequent postoperative MRI findings.
- Synovitis was linked to increased pain and reduced strength in patients.
- Fatty infiltration in the midacromial deltoid muscle was common but not associated with worse clinical scores.

## Abstract

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.

The online version contains supplementary material available at 10.1007/s00256-025-05121-y.