Hypothesis: The deltoid muscle is in continuity with the distal arm fascia and musculature.
Materials and methods: Ten fresh-frozen upper extremity cadaveric specimens were dissected to determine the insertional anatomy of the deltoid muscle. Measurements were made with micro-calipers and acetate grid sheets. The deltoid tendon and fibrous aponeurosis was in continuity with the lateral intermuscular septum posteriorly and the lateral aspect of the brachialis and deep brachial fascia anteriorly in all ten specimens. This interconnection remained in continuity following complete release of the deltoid insertion.
Results: The width of the insertion of the anterior head of the deltoid was a mean of 7.3 mm, the middle averaged 4.7 mm, and the posterior averaged 7.8 mm. The mean length of the anterior insertion was 70 mm, the middle was 48.4 mm, and the posterior was 63.4 mm. The mean width of the deltoid tendon and the investing fascia at the superior margin of the insertion was 21.9 mm and at the inferior margin 13.1 mm.
Discussion: Deltoid muscle integrity is critical to shoulder function. The deltoid insertion, however, is often partially released during surgical approaches for internal fixation of proximal humerus fractures and shoulder arthroplasty. Partial detachment without repair as performed during surgical approaches should not result in complete loss of continuity of the deltoid insertion.
Conclusion: Knowledge of the distal insertion and interconnections of the deltoid allows for more anatomic repair following extended releases during complex fracture fixation or revision surgery.