There are two general conditions in which muscle atrophy occurs after a fracture.
In the first case, muscle atrophy around the fracture site may occur after a fracture because the patient has developed disuse muscle atrophy due to reduced movement of the limb during treatment of the fracture, due to pain and long-term immobilisation of the affected limb. This type of muscle atrophy can gradually recover with rehabilitation exercises and muscle activity.
In the second case, the nerves around the fracture are damaged, resulting in muscle atrophy and dysfunction in the area innervated by the nerve; this type of severe nerve damage often does not recover on its own and requires surgery. It is best to consult a specialist for the exact condition.