Possibly you are experiencing a complication of the fracture: Radial nerve injury , which occurs in up to 18% of humeral shaft fractures. Most of these nerve injuries are neurapraxic (reversible nerve damage) or axonotmetic (reversible axonal damage)types, 90% of which resolve to at least grade IV strength in 3-4 months. Four months has been noted to be an adequate period for humeral shaft fractures to heal. I can recommend you a reevaluation by your orthopedic surgeon and do rehab to increase the range of motion, use therabands of progressive strenghts and start flexibility and stretching exercise to progressively built muscle strenght and mobility (i.e. towel behind back, finger walking up the wall, etc.).
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