Peroneal tendinopathy at the cuboid?

[Dugal]

I'm not particularly sure what you are trying to say.

Back is clear.

Also found relative immobility of the left midtarsal joint, limiting midfoot movement.

[neurospast]

What I am trying to say is that the orthosis might be the cause of the problems and as soon as you get rid of 1 problem the next 1 may lurk around the corner. If you think of how a different movement of the foot (e.g. midtarsal joint limiting midfoot movement) the orthosis might make this problem worse and to my opinion should be looked at prior to do anything else. A bad foot movement might cause peroneus syndrom, knee problems, hipproblems etc. I would like to think that a piriformis problem is closely related to SI problems and if the muscle tone of the pirifomis goes up,some form of neurological problems might occur since the Ischiadicus nerve is close by.
Ps after my personal experience a lot of atletes have not really a good core stability.