Had failed t12/l1 fixation 8 yrs ago. i'm experiencing numb fingertips, toes and bum. other times excruciating pain in thumbs and big toe. any link?

Yes and no: Big toe and "bum" discomfort in a failed t-12 l-1 fusion likely has spinal neural impingement(s) in the lower vertebral spine. Pain in thumb and numbness in fingertips is likely caused by thoracic outlet syndrome secondary to a tilted shoulder hemi-girdle as a result of a functional scoliosis secondary to the failed spinal fusion procedure and interference with normal biomechanics of the back.