Iannotti, Jp, Codsi, Mj, Kwon, Yw, Derwin, K, Ciccone, J, Brems, Jj Porcine small intestine submucosa augmentation of surgical repair of chronic two-tendon rotator cuff tears. A randomized, controlled trial. Journal of bone and joint surgery. American volume 2006; 6: 1238-1244