Can herniated discs, stenosis t-spine with loosening hardware from fusion cause pain in buttocks, groin and lower legs with weakness?

Possibly: It seems like your fusion goes from the lower Tspine into the Lspine so yes there is a possibility that if the fusion has failed and/or if disc herniation are present this could cause many of your pain symptoms in buttock, groin area. The weakness seems to suggest a neurological process that could come from T or Lspine. Incontinence, spasticity, balance problems are other things to look out for.