We can only speculate about the reasons why there is normal shoulder function despite the complete removal of the deltoid muscle. In the normal shoulder, a combination of muscles generates a complex movement: anterior deltoid, supraspinatus, coracobrachialis, long head of biceps brachii, and clavicular portion of pectoralis major act together to provide power and movement in forward flexion. Abduction in the scapular plane is generated by the middle portion of the deltoid, supraspinatus, and a coupled force between subscapularis and infraspinatus [
12,
13]. A selective bloc of the suprascapular or axillary nerve showed that the deltoid muscle provides 50% of the power for forward elevation and abduction in the plane of the scapula. Supraspinatus and infraspinatus generate almost 50% of the torque; infraspinatus acts mostly above 90 degrees of abduction. Electromyographic studies [
14] showed a silent signal before 90 degrees of abduction. In the absence of deltoid and rotator cuff muscles, other muscles cannot generate enough torque to overcome gravity but act as a movement generator [
12,
13]. Of interest, our patient showed excellent strength in abduction in the plane of the scapula without deltoid muscle. In addition, an MRI of his shoulder at 11-years follow-up showed normal shoulder muscles, without intraarticular degenerative changes. Although up to 20% of the patients with a complete deltoid dysfunction may achieve full (passive) range of shoulder motion [
6,
15], our patient also had very good strength. Altogether, this implies that the other shoulder muscles can compensate for the loss of deltoid function after its complete removal in early childhood. Isolated deltoid resection is a rare procedure, even more in the pediatric population, and consequently it is difficult to make recommendations regarding the need for reconstruction or not based on this specific case. On the other hand, the excellent long-term follow-up of this patient with an annual physical examination and medical photography have showed that excellent function and strength remain over years without reconstruction.