Ritalin and bony healing

I have a 9 year old boy 5 months post ACL reconstruction who has developed Sever's Calcaneal Apophysitis. He has had the heel pain for 14 weeks now, (just started with me) has been recieving physio (calf stretches, night splints, heel raise, new shoes) and it is just getting worse. I am attempting to find any information/studies or professional opinions on Ritalin slowing bone healing. I know it can cause growth retardation, he is very small for 9, however, is it affecting his bony healing of the Sever's and ACL recon or not? What is the mechanism that Ritalin slows the growth. MIMS online doesnt help and our pharmacy department was not helpful.
Appreciate any assistance
Thanks