Determining OA vs Other Types of Arthritis

59yo F with PMHx of arthritis; psoriasis; gout and HTN presents with chronic back pain, frequently 7/10. Has been taking Celebrex 200mg as well as 5mg hydrocodone up to 3 times a day – previously treated with topical diclofenac; oral diclofenac; tramadol; cyclobenzaprine; topical lidocaine; prednisone; meloxicam. She notes that most medications help initially but overtime quit working. Unfortunately she does not have insurance and is unable to be referred to rheumatology. I suspect that she likely has underlying psoriatic arthritis. Her last x-rays of her knee were performed in 2020 that showed mild degeneration. Lumbar spine showed grade 1 anterolisthesis at L5-S1 and facet arthrosis. She had marked degenerative change in the right femoral acetabular joint and moderate degenerative change on the left. She had bilateral SI joint arthritis. She has history of compression deformity of T11 through L1 vertebral bodies. She is taking alendronate.

She is having severe pain on R groin and knee which is limiting her ability to ambulate; sleep. She describes pain as a deep tooth ache/red hot poker in the knee whether she is using it or not. Diclofenac 50mg TID helps but by end of day not getting relief from it.  I suspect she likely needs hip replacement on the R.

My question: how would I determine OA vs psoriatic vs other arthritis and would she be a candidate for MTX?

I have written 10 mg prednisone taper pack (6 day) today as well as decadron 8mg IM. If she has significant response to this; I advised we can do intermittent steroids but would limit to 3-4 treatments a year to try to avoid overuse/side effects.

Do you have any guidance on long term steroid use in a patient such as this?