In deltoid flap reconstruction, part of the powerful superficial muscle that moves the shoulder - the deltoid - is transferred as a pedunculated muscle flap to the deeper tissues, where it is used to cover the RC defect. After 6 weeks, when the flap reconstruction has healed, the newly integrated muscle flap takes over part of the lost RC function and is at least able to recentre the head of humerus in the socket to a point where effective, pain-free movement of the shoulder is possible in most cases. However, the raw, general strength of the reconstructed shoulder is less than that of a normal shoulder. Deltoid flap reconstruction is illustrated in the drawings and photos below. I can also lend you a video of this complex operation if you are interested.