The term “massive and irreparable” is difficult to define: are we referring to a mechanical problem where it is impossible for the surgeon to mobilize the tendon of the rotator cuff to its insertion at the tuberosity of the humeral head or to a muscle that has no potential to function even if it were repaired or both.
The above judgment also varies from surgeon to surgeon: some experienced surgeons would be able to mobilize the tendons arthroscopically to a satisfactory degree and report good results after repair.  Others would regard it as futile effort to try and mobilize such tendons and resort to tendon transfers (pectoralis major for subscapularis tears and latissimus dorsi for posterosuperior tears). Some surgeons even regard the previously mentioned situations to require initial insertion of reverse prostheses.
When examining the literature on the viability of the muscles of the torn tendons great variation in opinion is again evident. The one school would regard the appearance of the muscles on CT and MRI and the implied fatty infiltration as all-important and for the advance stages not advise repair. Others have also indicated the possibility of impairment of suprascapular nerve function in massive tears as relevant and attempt to separate the group where this is apparent and do a concomitant nerve release. A few experienced surgeons have claimed to observe recovering muscle function after arthroscopic repair of tendons where the muscles seemed to have no potential as judged by conventional imaging.
Interposition techniques using various synthetic materials to bridge the tendinous gap have been attempted for many years but have largely failed. A recently reported technique using a biological interposition of acellular human dermal matrix may have promising potential but longer follow-up period is required. 
Consensus does exist in shoulders with absent cuff function, usually accompanied by anterosuperior subluxation of the humeral head and “pseudo-paralysis” of the shoulder. For this problem, especially in the elderly the reverse prosthesis has shown good results in the medium term. A less fortunate indication for this prosthesis is failed cuff repair where the coracoacromial arch has been compromised by surgery and often results in significant pain and poor function. A detailed history of the evolution of the reverse geometry prosthesis is published in the current issue 
At the Cape Shoulder Institute, treatment of massive tears is based on the following protocol: In younger individuals, special effort is made to repair the rotator cuff arthroscopically, often irrespective of the imaging results. We do not regard open repair for massive tears as more successful and the latter may even have the complications of impairment of the coracoacromial arch and disastrous results. In the older patient with a painful shoulder and large tear, satisfactory results may also be achieved with arthroscopic repair. Tendon transfers are used very sparingly, the most commonly done being pectoralis major transfer for irreparable tears of the subscapularis muscle tendon. In younger patients with irreparable tears, cuff replacement with the Graft Jacket has shown surprisingly good results. Suprascapular nerve release is regarded as a possibility in the surgical management of these tears, but its role is not entirely clear. In the elderly with massive tears and poor function, the advent of the reverse prosthesis has been most helpful in his otherwise very difficult problem.