Forearm extension + supination problem

Hi, I'm 35 years old male, I have a "problem" with my left arm whole life;

At birth, there was some problem with my nervers in left armpit, so for the whole first year I had immobilised left hand in upper position (above the head).

Afterwards my parents did some workouts for my hand and it generaly turned out just fine, opposed to not being able to use it at all.

So the problem is I cannot extend forearm in elbow to the fullest (cca 15 degrees to full extension) + I cannot fully supinate the forearm (it goes cca halfway).

For the extension, I don't think there's an elbow lockout or something, it feels like tendon & biceps need to be streched, using proper technique.

As for forearm supination I cannot tell realy, its all connected, so when I try to face out my left palm, whole left arm starts "working" on it :)


Could you please tell me what would be appropriate exercises for my hand and how should I approach fixing it (if it is fixable since I'm 35)?

Thank you very much!

Nikola