Hi,
Noted the history about your 70 year old Mother having had a fall 8 months ago but still has pain in the right back and weakness in right shoulder.
The possible causes in presence of normal X-rays indicate one of the following:
Frozen shoulder.
Tear of capsule of shoulder joint.
Myalgia or
Fibromyalgia at the back area which can be post-traumatic as it did not heal completely after the fall.
Please get the following things done for proper diagnosis:
MRI if the affected shoulder joint can tell a lot, X-rays only show
fracture or dislocation and nothing else.
Clinical evaluation by an Orthopedic Surgeon.
This will lead to a proper diagnosis.
Till then put the right arm and forearm in a sling to give complete rest.
Anti-inflammatory medications as would be advise.
Also take an opinion of a Physiotherapist, helps a lot in management.
Follow the advise and if there is any tear of capsule she may need a corrective surgery.
Hope I have answered your query. Let me know if I can assist you further.
Regards,
Dr. T. Chandrakant, General Surgeon