Living and working with arthritis

Hello folks , I'm new to the forum so apologies in advance if a similar question has been asked.

I have worked my entire life as an engineering machinist, a job that dictates that I stand for long periods of time and also involves heavy lifting and manual handling. Only recently my leg locked , I fell whilst turning round with a heavy machine vice . I have done this job since leaving school and I am now 57, so 41 years in a stood up job which is now taking its toll on my health. I flat feet, have suffered from plantar fascitis and after a single x-ray have been told I have arthritis in my knee, I've had a single steroid injection in my knee which offered initial relief, though I feel pain and discomfort in most of my joints . My tolerance to pain is starting to wear a little thin. A recent discussion with my line manager and HR where I raised my health concerns hasn't yielded a positive outcome , as they say they can't make any reasonable adjustments to assist me in the workplace.

Has anyone been in a similar situation to me , do you have any advice on where I stand legally in terms of work etc. How do I approach my doctor for a more in-depth diagnosis in the other areas where I feel pain . Are there any other treatments which might benefit me?

Any advice greatly appreciated

Peter