Frameless stereotactic image-guided C1-C2 transarticular screw fixation for atlantoaxial instability: review of 20 patients.

OBJECTIVE: We retrospectively studied 20 adults who underwent C1-C2 transarticular screw (TAS) fixation utilizing frameless stereotaxy. METHODS: The study group comprised 13 men and 7 women, with a mean age of 63 years (range 12-87 years). All patients demonstrated clinical and radiographic evidence of C1-C2 instability. The cause of the instability was trauma in 11 patients, rheumatoid arthritis in 6 patients, failed prior surgery in 2 patients, and congenital malformation in 1 patient. All patients underwent stabilization with C1-C2 TASs using image-guided frameless stereotaxy. RESULTS: There were no new or worsening neurologic symptoms reported at 18-month follow-up. Motor weakness improved in seven of nine patients, myelopathy in seven of seven, and gait in three of six patients in whom these deficits were present preoperatively. Postoperative complications included one surgical site abscess, one cutaneous pressure ulcer, and one iliac crest donor site infection. Of 36 screws placed, 33 (92%) were well positioned. Normal C1-C2 alignment was achieved in 17 of 20 (85%) patients. In 4 of 20 cases, screw implant, which was thought to be anatomically difficult, if not impossible, on the basis of routine magnetic resonance or computed tomography imaging, was actually accomplished successfully using surgical navigation. CONCLUSIONS: C1-C2 TAS placement is a safe and accurate surgical technique that may improve neurologic function. Use of intraoperative navigation can facilitate achieving difficult surgical trajectories that match the patient's anatomy, thus allowing TAS implant in patients who otherwise would not be candidates for this type of internal fixation.

Neurophysiological monitoring for safe surgical tethered cord syndrome release in adults.

BACKGROUND: Release of tethered spinal cord by sectioning of the filum terminale carries a significant risk of injury to the neighboring motor and sensory nerve roots. Intraoperative neurophysiological monitoring techniques can help to minimize these adverse neurologic outcomes. METHODS: We performed a retrospective review of 67 consecutive patients undergoing tethered cord release. We excluded 52 pediatric patients which limited our study to 15 adult patients treated during a four year period, including patients with a thick filum, low lying conus, myelomeningocele, filum tumor, spinal cord malformation, and/or lipoma. Clinical outcomes were determined from postoperative follow-up visits. Two patients were lost to follow up and were excluded from the clinical outcome analysis. Electrical stimulation of the filum terminale and lumbo-sacral nerve roots in conjunction with electromyogram (EMG) recording was performed intraoperatively. RESULTS: The mean electrical threshold for EMG response during stimulation of the filum terminale was 37.1 volts (V), range 15 to 100 V. In comparison, the lowest threshold obtained by direct stimulation of the ventral nerve roots was a mean of 1.46 V, with a range of 0.1 to 7 V. More than 70% of the patients studied demonstrated a filum to motor root threshold ratio of 100:1 or greater. No patient developed new neurologic symptoms or signs postoperatively. Bowel and bladder function improved in 46% of patients, back pain in 39% and motor function in 31%. Eight percent reported decline in bladder control and worsening back pain postoperatively. CONCLUSIONS: The often dramatic difference in the threshold of the filum terminale and adjacent motor nerve roots (100:1) helps to identify, isolate, and safely section the filum terminale. Tethered cord release using intraoperative neurophysiological monitoring is safe and in the majority of cases leads to improvement or at least, stabilization of neurologic function. Monitoring prevented intraoperative nerve root injury that might have resulted in immediate onset of new neurologic deficits caused by the surgical procedure.

Split spinal cord malformation in an elderly patient: case report.

Split spinal cord malformations (SCM) typically present in childhood and rarely in adulthood. Very little is known about the SCMs in the elderly, and the diagnosis can be easily missed. A 73-year-old woman with a childhood history of scoliosis and late ambulation milestones presented with a 2-year history of worsening low back pain and progressive difficulty walking. She had a mild gait disturbance with 4/5 weakness in left ankle dorsiflexion. Magnetic resonance imaging revealed a bifid spinal cord contained in a single thecal sac and a tethered cord with low-lying conus at L3. The patient was taken to the operating room and a soft-tissue median septum, as well as all other adhesions, was removed. The filum terminale was identified, coagulated, and divided. Six weeks later, the patient reported decreased back pain, improvement in ambulation, and markedly decreased used of narcotics for her back and leg pain. Her left ankle dorsiflexion strength improved to 4+/5. This patient had two hemicords encased in a single dural tube separated by a nonrigid, fibrous median septum and an associated tethered cord. Adult presentation of SCM is extremely rare. This case highlights the need to consider split cord malformation and tethered cord in the differential diagnosis not only for adults but also the elderly presenting with back pain, scoliosis, and difficulty walking.