Hi
Without your physios exact diagnosis it is very hard to prescribe exercises, or suggestions. Definitely however based on what you have described, i would star the athletes on stretching the vastus lateralis and the ITB (the outer quad muscle and Iliotibial band), and start strengthening the vastus medialis (VM). A good exercises that doesn't place stress the knee joint and still can help strengthen the VM is Straight leg lifts. They should be done in sets of 10 times on each side. Start with 5 sets of 10 and work your way up to 10 sets of 10.
To perform straight leg lifts:
1. Lie down on your back with one leg bent and one leg straight.
2. Next, perform a posterior pelvic tilt to protect your back from injury. To do this, draw your umbilicus (belly button)
toward the floor. If you are doing this correctly, your back should be flat against the floor/mat. You can also check your
technique by putting your hand under the small of your back, on the floor, and flatten your back so that your back is
"crushing" your hand.
3. With your toes pointed to the ceiling, keep your knee straight and lift your leg up to about 45 degrees.
a. It shouldn’t be raised higher than the bent knee.
4. Slowly lower your leg back to the floor.
(es.oncolink.org/coping/pdf/OncoLink_
Exercises.pdf)
(beats me having to explain)
Also if you have access to leg extension machine you can have your son do leg raises with a light weight (with Full ROM, as research is mixed on best ROM to activate the VM) and the feet turned in. This burns, and will help strengthen the VM.
I would be careful with diagnosing OSD without the the presence of the standard symptoms, like redness around the tibial tuberosity, pain with palpation of the tibial tuberosity, sweeling around that area, pain experienced with walking up stairs, and if you can get it for free a MRI (from side)) but given that he has had a growth spurt it could be as this is a prime time for kids to get it.
I have coached a gymnast with OSD and it can be quite restrictive at times. Best thing is rest at first (and given that you have the holiday that is great), with lots of hamstring and calf strengthing. Minimal knee bending exercises and stretches of the quad.... for more information on OSD check out an article i wrote on the topic
"
A look at the pathophysiology and rehabilitation of Osgood-Schlatter Syndrome"
It will give a good idea of what to do if he has OSD.