Two patients diagnosed with congenital kyphoscoliosis without preoperative neurological dysfunction were included. Written informed consent was obtained from both patients for publication of this case report and any accompanying details and images. During the correction surgery, spinal cord function was monitored using transcranial MEPs and SEPs. Abnormal SEPs were defined as > 50% decrease in amplitudes and/or > 10% increase in latencies than the baseline; abnormal MEPs were classified as > 50% decrease in amplitude than the baseline [10, 11]. One patient experienced postoperative neurological deficits and abnormal neurological monitoring was detected during the revision surgery. The other patient suffered abnormal IOM. Transvertebral transposition of the spinal cord was performed in both patients to restore SEPs and MEPs signals successfully, and the operative steps are illustrated in Fig. 1.
Case 1
A 16-year-old boy presented with a 13-year history of congenital kyphoscoliosis. Brace treatment for 11 years was ineffective, and the curve progressed in recent years. Preoperative radiography revealed a Cobb angle of 105° and a flexibility index of 23% in the thoracic spine (Fig. 2a). The preoperative appearance showed the rib hump, thoracic trunk shift, and shoulder imbalance (Fig. 2b). Correction surgery, including multilevel Ponte osteotomies [12] and posterior spinal fusion of T3-L2, was arranged.
No abnormal IOM signal was detected throughout the surgery (Fig. 2e, f). However, 6 hours postoperatively, the muscle strength was markedly decreased (right lower limb: grade 0; left lower limb: grade 3). The emergency CT scan did not reveal any misplacement of the pedicle screw, and postoperative intraspinal hematoma was suspected. One hour later, the muscle strength was continually decreasing (right: grade 0; left: grade 0). Then, revision surgery was conducted immediately with the rods and two screws at the apex removed and laminectomy performed, but no intraspinal hematoma was found. The wake-up test still demonstrated no voluntary movement in both lower limbs. Meanwhile, the SEPs decreased > 70%, and the MEPs was totally lost. Simultaneously, the surgical team, including surgeons, neurophysiologists, and anesthesiologists, was taking steps to identify the possible causes according to a standard checklist for IOM alert [13]. Finally, all the interference factors such as mechanical injury, pulling out of electrodes, low body temperature, muscle relaxant usage, low mean arterial pressure, and abnormal hemoglobin levels were excluded.
At last, we found that the spinal cord was stretched and closely attached to the wall of the spinal canal at the concave side with high tension, which could cause spinal cord compression. Therefore, we decided to remove the internal wall of the concave spinal canal at the apex of the curve. Subsequently, the MEPs of the left and right lower limbs was recovered partially and slightly, respectively (Fig. 2g, h). The entire wall of the concave spinal canal at the apex of the curve was then removed. After the transvertebral transposition of the spinal cord was completed, the bilateral SEPs and MEPs were progressively recovered (Fig. 2i, j), and the correction surgery continued. Immediately after the patient woke up, his muscle strength recovered dramatically (right: grade 3; left: grade 4).
Additionally, the sensation of the lower limbs was almost normal, and the muscle strength was nearly normal before discharge. Postoperative radiography of the entire spine and appearance revealed satisfactory correction (Fig. 2c, d). At the 3-month follow-up, he could return to normal life. No obvious loss of correction and neurological dysfunction was observed at the final follow-up (2 years).
Case 2
A 19-year-old girl presented with a lifelong history of congenital kyphoscoliosis. Preoperative radiographic images of the entire spine exhibited a Cobb angle of 84° in the thoracic region with kyphosis of 55° (Fig. 3a). The preoperative appearance showed the shoulder imbalance and trunk shift (Fig. 3b). Correction surgery, including one-level pedicle subtraction osteotomy [14] and posterior spinal fusion, was scheduled.
Transpedicular screws were placed according to the preoperative plan. Asymmetrical pedicle subtraction osteotomy of T9 and posterior spinal fusion of T4-L1 were performed. After the correction of the main thoracic curve, the amplitude of SEPs decreased significantly, and then the MEPs was lost (Fig. 3e, f). The follow-up wake-up test confirmed acute paraplegia. The surgical team then tried to identify the possible causes according to the checklist for IOM alert, and all the interference factors were excluded. Meanwhile, removal of the rods and laminectomy was performed. Five minutes later, both the SEPs and MEPs were lost. Finally, high tension of the spinal cord was detected at the apex of the curve, and the spinal cord was closely attached to the wall of the concave spinal canal, which caused compression. The two pedicle screws at the apex on the concave side were then removed. Additionally, the wall of the concave spinal canal was removed and enlarged. Subsequently, the bilateral SEPs still showed no change, but the right MEPs was partially recovered (Fig. 3g, h). About 15 minutes later, the right MEPs was normalized, and the bilateral SEPs and left MEPs were partially recovered (Fig. 3i, j). Afterward, the correction surgery was started again. At the end of the surgery, the bilateral SEPs showed total recovery, and the left MEPs was almost recovered (Fig. 3k).
The muscle strength and sensation of the right lower limb were almost normal, and the left lower limb had slight hypoesthesia and weakness (muscle strength: grade 4) before discharge. Postoperative radiography of the entire spine and appearance revealed satisfactory correction (Fig. 3c, d). The muscle strength and sensation of both lower limbs had returned to normal at the 3-month follow-up. No obvious loss of correction and neurological dysfunction were observed at the final follow-up (18 months).