If your mother did not have a follow-up appointment with anyone to re-evaluate her after the closed reduction of her shoulder dislocation, now would be a good time for that. In fact, given your description of her inability to move that arm, some type of follow-up would be advised.
It’s possible that fear of re-dislocation has immobilized her and that she actually has intact motion. But a prolonged period of time (three months) without moving it could also result in a frozen shoulder. There is also the fact that up to 40 per cent of all patients who dislocate the shoulder anteriorly (forward dislocation) also have additional injury to some other area of the shoulder.
The most common associated injuries reported include axillary nerve palsy, brachial plexus injury, detachment of the rotator cuff, and fracture of the greater tuberosity (bony bump on the head of the humerus). Any combination of these injuries is also possible.
Older patients (60 years old and older) are at greatest risk of multiple-nerve injuries. According to a recent study, women who dislocate the shoulder during low-energy falls make up the bulk of the group with associated (additional) shoulder injuries. This group is especially at risk for dislocation with associated injuries involving nerve damage. The same study showed that anyone with a rotator cuff tear or greater tuberosity fracture is also at increased risk for nerve deficits.
Your mother may need nothing more than a quick physical examination to confirm that nothing is wrong. She may just need encouragement to move the arm and use it normally once again. But if there is nerve damage, bone fracture, or some other injury then additional imaging (X-rays, CT scans, MRIs) may be needed. The sooner the problem is identified, the better her chances are for full recovery with proper treatment.