Atlantoaxial and craniocervical arthrodesis in children: a tomographic study comparing suitability of C2 pedicles and C2 laminae for screw fixation.

STUDY DESIGN: Analysis of C1-C2 tomographic anatomy in a cohort of healthy children. OBJECTIVE: Compare suitability of C2 laminae and C2 pedicles for screw placement. SUMMARY OF BACKGROUND DATA: Surgeons have applied several techniques for craniocervical and atlantoaxial spondylodesis to address congenital or developmental abnormalities in children. Constructs with pedicle or transarticular screws are effective to stabilize the craniocervical junction; however, these fixation points are not suitable in all patients. Translaminar screw placement in C2 has been safely performed in children; yet, suitability of C2 laminae and C2 pedicles has not been systematically compared. METHODS: Applying chi2 test, we compared suitability for screw placement in 46 C2 pedicles and 46 C2 laminae on digital images of axial reconstructions of cervical CT scans of 23 children who had been admitted to the same hospital due to head or neck injury. On the same scans, we estimated suitability for screw placement in 46 lateral masses of C1. RESULTS: Twenty-four percent of C2 pedicles and 65% of C2 laminae were deemed suitable for 3.5-mm screw placement, and the difference was statistically significant (P < or = 0.0001, chi2 15.88). Forty-one percent of C2 pedicles and 80% of C2 laminae were deemed suitable for 3.0-mm screw placement, and the difference was statistically significant (P < or = 0.0001, chi2 14.78). Ninety-five percent of C1 lateral masses were deemed suitable for 3.5-mm screw placement. CONCLUSION: C2 laminae represent a viable fixation point for C1-C2 and craniocervical arthrodesis in children. This information can be useful for preoperative planning.

Transcranial motor-evoked potentials combined with response recording through compound muscle action potential as the sole modality of spinal cord monitoring in spinal deformity surgery.

STUDY DESIGN: This study is a prospective review of all spinal cord monitoring procedures in our unit from 1999 to 2004 in patients undergoing spinal deformity correction surgery. OBJECTIVE: To report the sensitivity and specificity of transcranial motor-evoked potentials (MEP) and compound muscle action potential (CMAP) monitoring as the sole modality in spinal deformity correction surgery. SUMMARY OF BACKGROUND DATA: Combined spinal cord monitoring with somatosensory-evoked potentials and MEP has been widely used. The use of CMAP as the only modality has not been widely used and its efficacy has not been fully elucidated. METHODS: The intraoperative monitoring outcomes were compared with patient's postoperative clinical outcomes. The sensitivity and specificity were calculated and determined for our monitoring protocol. RESULTS: Transcranial MEPs were measured in 144 patients in 172 procedures. In 2 patients (3 procedures), we were unable to record any CMAPs. There were 15 intraoperative monitoring changes. There were no new postoperative neurological deficits. CONCLUSION: The monitoring criteria are sufficiently strict to achieve a sensitivity of 1.0 and a specificity of 0.97. Monitoring of CMAPs alone has been adequate to avoid clinical neurological deficits.

Transient loss of motor-evoked responses associated with caudal injection of morphine in a patient with spondylolisthesis undergoing spinal fusion.

A 7-year-old girl having posterior spinal fusion for Grade 3 anterior spondylolisthesis at the L5/S1 level was administered 2.5 mg of morphine in 10 ml saline via the caudal epidural route before surgery. Motor-evoked responses were markedly diminished in her lower limbs for 1 h following this but returned spontaneously. She suffered no neurological injury. The cause for this is postulated to be transient cauda equina compression from the volume of injectate. This complication of caudal injection has not been reported before. The possible mechanisms for this are discussed. We believe that significant L5/S1 spondylolisthesis should be considered a contraindication to the use of caudal epidural injections.