Thank you for your query
Sudden onset of pain associated with numbness points to nerve injury
With a history of fall and a surgery, the risk of developing disc /bone disease
with spinal nerve
compression is more.
Given that his usual medications are not helping, I suspect a new pathology.
I recommend you see his spine surgeon
who could do some tests and imaging studies (CT scan) to look for these problems.
The severity and extent of the problem will determine the treatment and prognosis.
In the meantime, try to avoid any action/movement/posture that triggers these symptoms. Notice if it gets worse when he lays down on a particular side or sits for long periods or uses his arms and hands a lot (like at a computer or driving)
Mention your observations to his doctor.
If he has sudden muscle weakness
, numbness that lasts longer, severe pain, please go the ER right away.
Hope I've helped. Feel free to get back to us if you need further clarification.
With you both good health