Natural History of Quantitative Fatty Infiltration and 3D Muscle Volume After Nonoperative Treatment of Symptomatic Rotator Cuff Tears

Abstract

Background: The severity of fatty infiltration (FI) predicts the treatment outcome of rotator cuff tears. The purpose of this investigation was to quantitatively analyze supraspinatus (SSP) muscle FI and volume at the initial presentation and after a 3-month minimum of conservative management. We hypothesized that progression of FI could be predicted with initial tear size, FI, and muscle volume. Methods: Seventy-nine shoulders with rotator cuff tears were prospectively enrolled, and 2 magnetic resonance imaging (MRI) scans with 6-point Dixon sequences were acquired. The fat fraction within the SSP muscle was measured on 3 sagittal slices, and the arithmetic mean was calculated (FISSP). Advanced FISSP was defined as ≥8%, pathological FISSP was defined as ≥13.5%, and relevant progression was defined as a ≥4.5% increase in FISSP. Furthermore, muscle volume, tear location, size, and Goutallier grade were evaluated. Results: Fifty-seven shoulders (72.2%) had normal FISSP, 13 (16.5%) had advanced FISSP, and 9 (11.4%) had pathological FISSP at the initial MRI scan. Eleven shoulders (13.9%) showed a ≥4.5% increase in FISSP at 19.5 ± 14.7 months, and 17 shoulders (21.5%) showed a ≥5-mm3 loss of volume at 17.8 ± 15.3 months. Five tears (7.1%) with initially normal or advanced FISSP turned pathological. These tears, compared with tears that were not pathological, had significantly higher initial mediolateral tear size (24.8 compared with 14.3 mm; p = 0.05), less volume (23.5 compared with 34.2 mm3; p = 0.024), more FISSP (9.6% compared with 5.6%; p = 0.026), and increased progression of FISSP (8.6% compared with 0.5%; p < 0.001). An initial mediolateral tear size of ≥20 mm yielded a relevant FISSP progression rate of 81.8% (odds ratio [OR], 19.0; p < 0.001). Progression rates of 72.7% were found for both initial FISSP of ≥9.9% (OR, 17.5; p < 0.001) and an initial anteroposterior tear size of ≥17 mm (OR, 8.0; p = 0.003). Combining these parameters in a logistic regression analysis led to an area under the receiver operating characteristic curve (AUC) of 0.913. The correlation between FISSP progression and the time between MRI scans was weak positive (ρ = 0.31). Conclusions: Three risk factors for relevant FI progression, quantifiable on the initial MRI, were identified: ≥20-mm mediolateral tear size, ≥9.9% FISSP, and ≥17-mm anteroposterior tear size. These thresholds were associated with a higher risk of tear progression: 19 times higher for ≥20-mm mediolateral tear size, 17.5 times higher for ≥9.9% FISSP, and 8 times higher for ≥17-mm anteroposterior tear size. The presence of all 3 yielded a 91% chance of ≥4.5% progression of FISSP within a mean of 19.5 months. Level of Evidence: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.