Background: We report and compare two constructs that incorporate C1-C2 transarticular screw fixation with cervical lateral-mass screw fixation: the Axis lateral mass plate system and the Vertex screw/rod system (both from Medtronic Sofamor Danek, Memphis, TN). Methods and Results: Patient 1 had post-laminectomy kyphosis with abnormal movement at C1-C2 after decompression for a Chiari malformation. We used the Axis system to place C1-C2 transarticular screws with C3-7 lateral mass screws and T1 pedicle screws. This patient had excellent bone-fusion mass with no motion on flexion/extension films. Patient 2 had severe cervical spondylosis and prior posterior cervical laminectomies from C3 to C6. He had developed C1/2 instability and an anterolisthesis of C2 on C3. We used the Vertex system to place C1-C2 transarticular screws with C3 and C4 lateral-mass screws. This patient had a solid bony fusion from C1 to C4. Conclusions: In our experience, the Vertex system more easily accommodates severe degenerative cervical curvatures and combines C1-2 transarticular screws with lateral mass screws than the Axis system.

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Morphological and electrophysiological analysis was conducted to elucidate the pathophysiology which causes the discrepancy between radiological and clinical findings in post-operative syringomyelic patients with Chiari type I malformation. MRI analysis were performed on 28 cases of syringomyelia treated in our institute from 1988 to 1995 diagnosed with Chiari type I malformation with hemi-lateral symptoms in which the syrinx postoperatively collapsed or shrank. The expansion of syrinx in the direction of posterior gray horn was measured at the C6 level from the pre-operative MRI findings and compared with the outcome. A significant difference in the expansion of syrinx in the direction of posterior gray horn was found between improved and non-improved group. Median nerve somatosensory evoked potential (SEP) was carried out bilaterally on 13 patients and lower cervical N13 (lcN13), which is presumed to display the post-synaptic potential of posterior gray horn, was monitored. The diminishing rate of the lcN13 amplitude of the symptomatic side was measured in relation to the contralateral side. In all of the 13 patients, the amplitude of lcN13 was minimized in the symptomatic side. A significant difference in the diminishing rate of lcN13 was found between the improved and non-improved groups. The expansion of the pre-operative syrinx is related to the diminishing rate of lcN13. There seems to be a common marginal limit between the expansion of syrinx and the reduction of the potential of posterior gray horn in the transition of the outcome. The results from this study suggest that irreversible damage of posterior gray horn is the cause of discrepancy between radiological and clinical findings.

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In the treatment of lytic spondylolisthesis wide decompression and fusion are usually performed. However, lumbar fusion is invasive and has a high risk, especially in the advanced. In this report the patients with lumbar spinal stenosis and pars defect have been reviewed clinically and radiologically to determine whether the fusion is needed or not. A total 24 patients more than fifty-year-old with an average of 64.7-year-old were reviewed. The mean follow-up time was 34.4 months. The spondylolysis was seen at L4 in 6 cases, L5 in 13, L3+L4 in 1, L4+5 in 3, and L3+L4+L5 in 1. Out of these 24 patients spondylolisthesis was shown in 19 patients. In L4 spondylolysis spinal stenosis was seen at L3/4 in 2, L4/5 in 3, and L3/4+L4/5 in 1. In L5 spondylolysis stenosis was shown at L3/4 in 1, at L4/5 in 8, L3/4+L4/5 in 3, and L5/S1 in 1. In six patients treated with laminectomy, pedicle screw fixation, and posterolateral fusion, two showed good, and four fair. Radicular pain continued in two patients and low back pain persisted in two. Two patients developed new stenosis at the proximal segments and required second operation. In 12 patients with fenestration procedures alone, three patients exhibited excellent, and nine good. The surgical outcomes were neither related to the degree of olisthesis nor to the age of patients. Follow up radiographs showed no progression of slippage. These results seem to suggest that lumbar fusion is not necessary in the treatment of lumbar spinal stenosis with pars defect, especially in patients more than fifty-year-old.

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