An Unusual Cause of S1 Radicular Pain Presenting as Early Phantom Pain in a Transfemoral Amputee: A Case Report

Recent epidemiologic studies have shown back pain to be a significant cause of pain in lower-limb amputees, but only a handful of cases have reported sciatica in amputees. The symptoms are usually described as a phantom pain or neuropathic pain in the residual limb that is often refractory to conventional treatments. These symptoms typically occur with back pain and are distinct from the patient's usual symptoms. Interestingly, back pain is not a universal finding. We present a patient with presumed phantom limb pain subsequently discovered to be caused by an S1 radiculopathy. This patient's supposed phantom pain persisted despite multiple medication trials. Initial work-up revealed a sciatic neuroma at the stump. Treatments targeting this neuroma were unsuccessful. Further evaluation found that a sacroiliac joint screw placed to stabilize a pelvic fracture had intruded into the S1 neuroforamen. A diagnostic S1 nerve block temporarily relieved the patient's pain, and the screw was removed. Pain persisted and a spinal cord stimulator was placed resulting in improvement of his pain. Because conventional diagnostic tests are limited, including physical exam and electromyography, a fluoroscopically guided selective spinal nerve block proved to be a useful diagnostic tool in this patient.