Hi Mazztm00
On Universal Credit (UC), "substantial risk" is a criterion within the Work Capability Assessment (WCA) that means there's a strong possibility of serious harm to a claimant's physical or mental health if they were found not to have Limited Capability for Work (LCW) or Limited Capability for Work-Related Activity (LCWRA). This applies even if the claimant doesn't score enough points for LCW, as it acts as a safety net for those whose health would be significantly impacted by undertaking work-related activities or being deemed fit for work. If you have had surgery that hasn't worked for you back and you are facing further surgery, you could be at substantial risk of further damage to your back before it is operated on. Being on high levels of pain medication will have an impact on your ability to get to work, and actually do the work if you got there. I would get proof from your doctor and any letters from the hospital regarding current diagnosis, symptoms and medication.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems