Do you have imaging?? It is useful to know if you are dealing with tendinosis, tendonitis, significant tear??? how old is he?? Are hormones OK? Estrogen is needed for tendon healing so if low E than will have trouble healing. Always look up the chain as well-shoulder and neck issues will often cause the elbow to remain problematic. IN ONE STUDY MORE THAN HALF OF RECALCITRANT EPICONDYLITIS HAD ISSUES WITH ROtator CUFF AND LACKED FULL SHOULDER ROM. If al that checks out then, can add TB4 to the mix. I often use botox in this gorup as well . ANd a topically applied NTG to improve vascular flow.
https://academic.oup.com/painmedicine/article/21/9/1971/5658647?login=true
Dr Yurth