Uncommon complication after revision hip surgery.
Cauda equina syndrome is an uncommon complication of ankylosing spondylitis characterized by the slow and insidious development of severe neurologic impairment related to dural ectasia. This report describes a unique case of cauda equina syndrome in a patient with ankylosing spondylitis after hip revision surgery. A 70-year-old man with long-standing ankylosing spondylitis underwent standard hip revision surgery; combined spinal and general anesthesia was administered. Pain was controlled with intravenous opioids postoperatively (patient-controlled analgesia). As per routine protocol, on the first postoperative day, the patient remained supine on a hip abduction pillow; mobilization was initiated on the second postoperative day. On postoperative day 1, the patient had severe low back pain that was controlled with patient-controlled analgesia. On postoperative day 2, the Foley catheter was removed and the patient sat and dangled. Back pain persisted while supine; in addition, the patient noticed involuntary loss of urine. On postoperative day 3, the patient had below-the-knee numbness that progressed to saddle anesthesia and foot flexor and extensor weakness. An epidural hematoma was suspected and urgent magnetic resonance imaging was performed, which showed severe degenerative stenosis at the L4-L5 level (mainly by dense ligamentum flavum). An L4-L5 decompression and instrumented fusion was performed; intraoperatively, L4-L5 was found to be the sole mobile segment. The extension of the spine in the supine position that completely obliterated the spinal canal was considered the mechanism of cauda equina syndrome. The intensity of back pain is a good indicator of a severe spinal lesion; however, pain can be dampened by intravenous opioids. High suspicion is required in patients with preexisting spinal pathology, such as ankylosing spondylitis.