Fatty degeneration of the deltoid muscle associated with displaced proximal humerus fractures.

INTRODUCTION: The use of reverse shoulder arthroplasty (RSA) has increased dramatically over the last two decades, with many surgeons now indicating RSA for the acute management of displaced proximal humerus fractures (PHF) in the elderly. RSA relies on adequate deltoid muscle function to obtain a good outcome, yet no literature to date exists which discusses preoperative assessment of deltoid structure prior to RSA. The purpose of this study was to assess for preoperative fatty deltoid-degeneration in patients with displaced PHF.

MATERIALS AND METHODS: We reviewed the axial CT scans of 100 consecutive patients with a displaced PHF. Fatty degeneration within each of the three deltoid-heads was graded at three levels, according to Goutallier and colleagues. Fractures were classified according to Neer.

RESULTS: Seventy-nine percent of the patients were female, 75% showed 3 or 4 parts fractures. The average cross-sectional area of the posterior deltoid was greatest-representing 37%, 40% and 42% of total area at each level, respectively. Severe fatty degeneration (Stages 3 and 4) was observed in the posterior deltoid only (26%). Absence of fatty degeneration (Stage 0) was observed in < 25% of cases. The Inter-Observer-Reliability for the continuous variables proved to be high.

CONCLUSION: Preoperative deltoid fatty degeneration is common in displaced PHF in the elderly. Because CT is commonly obtained to assess fracture morphology and for preoperative planning purposes, it is an ideal tool to assess the deltoid additionally. Future studies are warranted to determine whether preoperative fatty infiltration of the deltoid correlates with mid and long term functional outcomes when RSA is used acutely to manage a PHF.

LEVEL OF EVIDENCE: Level IV-consecutive case series.