E-Stim Question

Hello.  I am a new user to the site.  I wondered if anyone had any experience with starting e-stim nearly two years after an accident (c5) that caused spinal cord injury.  My son was able to recover almost fully, but as he got into weightlifting (recently), he realized atrophy and an inability to gain muscle mass in his right chest muscle.  He also has weakness in his right tricep.  He has recently started using an e-stim machine at home, but I wonder if it can be effective this long after the injury?  Thank you for any insights you may have.