I'm currently seeing a prolotherapy MD in Nashville for a calf injury. According to another doc at a well-regarded sports medicine clinic, it's a Grade 2 Medial Head Gastroc tear. Prognosis from the sports medicine doctor was 1) return to running in 5-8 weeks 2) return to high-level competition in 6 months, 3) 90% recovery to full strength in 12 months, and 4) eventual full 100% recovery.
The prolotherapy doctor did not give a time frame per se, but we are working to allow me to attempt a WR in my age group in the indoor 4x800m in 8 1/2 weeks.
Twenty four hours after my first series of injections (6), I'm much better but still not able to walk normally, much less run. He also does PRP injections. He said that I might get slightly faster results with PRP injections, but the cost would be significantly higher.
I have no idea if prolotherapy would work on arthritic knees, but I'd check it out before stem cell therapy.
Here's a link comparing PRP to stem cell treatments by my doctor.
http://prolotherapynashville.com/prp-platelet-rich-plasma/