Objective <p>To describe MRI application in the follow-up of subacromial balloon implantation and to show MRI findings of early displacement, balloon morphologies, and their potential association with synovitis and chondrolysis within the first-year post-implantation.</p> Materials and methods <p>Data were retrospectively collected from 18 consecutive shoulder MRI studies performed in symptomatic cases after balloon implantation. MRI studies were done randomly once during the first year after balloon implantation in a single tertiary-care institution. MRI studies performed after 1&#xa0;year of implantation were excluded (<i>n</i> = 3). Normal subacromial versus displaced balloon location, morphology of the subacromial or displaced balloon, type of synovitis, and evolution of synovitis and chondropathy compared to presurgical MRI studies were recorded. Arthroscopic surgery for balloon replacement was not performed as reference standard. Descriptive statistics were utilized to display the findings: chi-square and Fisher’s exact tests to assess associations between implant morphology and evolution of synovitis or chondropathy; Kruskal–Wallis and post hoc tests to assess associations between implant morphology and time since surgery.</p> Results <p>The balloon was posteriorly displaced in the glenohumeral joint or in the subdeltoid bursa in most cases (72.22%). The displaced balloon showed folded, band-like or pseudomass morphologies, and the morphology type was statistically associated with point time from surgery (<i>p</i> = 0.021). Papillary synovitis largely prevailed (77.7%). No statistical association was found between implant morphology and evolution of synovitis or chondropathy (<i>p</i> &gt; 0.05).</p> Conclusion <p>In symptomatic patients following subacromial ballon implantation, MRI is useful in diagnosing complications including displacement, collapse and reactive synovitis.</p>