Wang, Allan W., et al. "Autologous tenocyte implantation, a novel treatment for partial-thickness rotator cuff tear and tendinopathy in an elite athlete." BMJ case reports 2013 (2013): bcr2012007899. says:
The tendon injury was considered not amenable to surgery. As symptoms were recalcitrant to physiotherapy and conventional injection, the decision was made for treatment with ATI.
In what cases is a tendon injury considered not amenable to surgery?