Both groups will have CSF and blood sampled at pre-defined intervals in order to evaluate CSF cytokine expression after acute spinal cord injury. For comparison against the injured condition, CSF and blood from a normal group of uninjured individuals will be obtained. These individuals will be patients undergoing hip or knee surgery under a spinal anesthetic, where a small sample of CSF can be taken when their intrathecal space is accessed for the anesthesia.