Importance of Intraoperative Neuromonitoring in Simultaneous Release of Tethered Cord and Corrective Surgery for Severe Kyphoscoliosis Deformity: A Case Report

Background Data: Kyphoscoliosis in conjunction with tethered cord is a rare and challenging spinal deformity to treat. The availability of intraoperative monitoring in recent times has helped reduce the incidence of operative neurological complications in spine deformity corrective surgery. The present case report underlines the value and utility of intraoperative neuromonitoring in corrective surgery for kyphoscoliosis. Study Design: Case report. Purpose: To report the importance of intraoperative neuromonitoring in the release of tethered cord along with deformity correction. Case Report: A 14-year-old male patient presented with a one-month history of progressive weakness in both lower extremities. Radiographs showed that he had thoracic kyphoscoliosis with a 30-degree scoliotic curve together with a 70-degree kyphotic curve with an apical vertebra of T12. The preoperative MRI and CT showed that the spinal cord was entrapped by the apical vertebra and a butterfly vertebra was noted at T12. This resulted in the right half being smaller in size, with the resultant convexity to the left side. The conus was low-lying and tethered at the L3 level. The patient underwent detethering of the cord with corrective surgery for kyphoscoliosis in the same setting under intraoperative neuromonitoring. Results: Scoliosis was corrected to 20 degrees and kyphosis was corrected to 40 degrees. The motor evoked potentials (MEPs) that previously showed very feeble tracings now showed persistent positive potentials. The SSEPs remained constant and the same as baseline throughout. The patient’s spinal cord function improved from Frankel C to Frankel D. A good trunk balance was evident at the two-month follow-up. Conclusion: Intraoperative neuromonitoring allowed safe and effective detethering and maintained correction of the kyphoscoliosis. (2021ESJ234)


INTRODUCTION
Kyphoscoliosis in conjunction with tethered cord is a rare and challenging spinal deformity to treat. 5 Tethered cord is a progressive condition caused by anchoring of the spinal cord due to various developmental anomalies or pathologies, which results in a spectrum of neurological deficits and spinal deformities. 2 Classically, it is a constellation of signs and symptoms that occurs due to longitudinal traction on the caudal end of the spinal cord (the conus medullaris). 8 Kyphoscoliosis is defined as the deviation of the normal curvature of the spine in the sagittal and coronal planes and can include rotation of the spinal axis. The range of Cobb's angle for moderate kyphoscoliosis is from 25 to 100 degrees, whereas that of severe kyphoscoliosis is greater than 100 degrees. 4 Tethered cord as a direct cause of scoliosis was first demonstrated by Mclone et al. in 1990. There was partial regression of scoliosis in patients following surgery for myelomeningocele repair and the release of the tethered cord. 9 The availability of intraoperative monitoring in recent times has helped reduce the incidence of operative neurological complications in spine deformity corrective surgery. 7 Reliable intraoperative monitoring enables surgeons to perform these complex and challenging surgical procedures, which involve significant manipulation of the spinal cord with a greater degree of safety. 1 The present case report underlines the value and utility of intraoperative neuromonitoring in the corrective surgery for kyphoscoliosis. Case Report: A 14-year-old male patient presented to our institute with a one-month history of progressive weakness in both lower extremities. He had normal gestation and development only except for a small hump on his back at birth, which was not associated with any abnormal skin signs such as dermal sinus tracts, hairy patches, or skin appendages. At the age of 4 years, the patient was formally diagnosed with scoliosis, which was treated with brace therapy at a local hospital. This treatment proved unsuccessful in the prevention of the curve progression. At the first visit to our clinic, the patient presented with progressive weakness in both lower limbs with jerky movements suggestive of severe spasticity with a spastic gait. The patient had marked kyphoscoliosis in the thoracic spine with a global lower extremity weakness. The left side was weaker than the right side. He was able to walk with support at the first visit, but the spastic paraparesis progressed to make the patient wheelchair-bound in the next three weeks. The patient did not give any history of backache or bowel and bladder disturbances. On physical examination, there was a prominent hump in the thoracic spine with no abnormal cutaneous manifestations. The right lower limb motor power was 3/5 and the left lower limb motor power was 2/5. There was no visible atrophy. The deep tendon reflexes were exaggerated, and the Babinski sign was present bilaterally. There was no significant sensory loss detected. Radiographs showed that he had thoracic kyphoscoliosis with a 30-degree scoliotic curve and a 70-degree kyphotic curve with an apical vertebra of T12 ( Figure 1). The preoperative MRI and CT showed that the spinal cord was entrapped by the apical vertebra, and a butterfly vertebra was noted at T12 ( Figure  2). This resulted in the right half being smaller in size, with the resultant convexity to the left side. The conus was low-lying and tethered at L3 level and there was also an associated syrinx was seen from D7 to L2 level. The patient was planned for detethering of cord with corrective surgery for the kyphoscoliosis in the same setting. The report was approved by our Institutional Review Board, and the family gave written informed consent before the surgery. The report was conducted according to the WMA Declaration of Helsinki: Ethical Principles for Medical Research Involving Human Subjects.

Journal
Surgical Technique: A posterior midline incision was made from T6 to L4 level. An L3 to S1 laminectomy was performed, and the tethered filum terminale was released after the dissection and confirmation under electrophysiological monitoring ( Figure 3). Pedicle screws were placed in T8, T9, T10, L1, L2, and L3 on the right side and T9, T10, L1, L2, and L3 on the left side using the freehand technique. Corpectomy of the malformed D11 and D12 vertebral bodies was performed. A titanium cage was used at the corpectomy site at D11-D12, applying a compressive force on the temporary rod on the convex side and a distractive force on the concave side. The permanent rod was anchored thoroughly to the pedicle screws   (Figure 4). The surgery was performed with continuous electrophysiological monitoring. The MEPs were not recordable at the time of incision ( Figure 5). The SSEP recordings were normal. The detethering was uneventful without any changes noted on SSEPs and MEPs (Figure 6). Fixation and reduction were made with constant monitoring of SSEP and MEP tracings. We noted intermittent positive potentials in the MEP recording. The temporary rod was then replaced with a contoured permanent rod. Total surgical time was 358 minutes and approximate blood loss was 900 ml. Immediately postoperatively, we were pleasantly surprised to note very encouraging MEP tracings. The patient's postoperative course was uneventful. The patient could walk independently at the end of the 5th week postoperatively. The postoperative scans showed that the scoliosis was corrected to 20 degrees and kyphosis was corrected to 40 degrees. The MEPs, previously showing very feeble tracings, now showed persistent positive potentials. The SSEPs remained constant and the same as baseline throughout (Figures 7 and 8). The patient's spinal cord function improved from Frankel C to Frankel D. A good trunk balance was evident at the 2-month follow-up.

DISCUSSION
Neuromuscular scoliosis is a deformity that is difficult to treat. It is seen to progress even after skeletal maturity. This is associated with limited mobility of the spinal column and flexion increases the traction on the spinal cord. 6 Decision-making in congenital kyphoscoliosis depends on the natural history of progression; clinical and radiological assessment is absolutely essential. Detection of the intraspinal and other associated anomalies becomes relevant in deciding appropriate surgical management. 3 The goals of surgery are to correct the deformity, produce a balanced spine and a leveled pelvis, and obtain a solid spinal fusion. 6 In the rare situation of treating kyphoscoliosis with a concomitant tethered cord, there are two schools of thought. One school of surgeons considers that it is unnecessary to perform detethering of the cord until the patient develops any symptoms.
The other school of thought advocates a 2-stage strategy of deformity correction between 3 and 6 months after detethering of cord. This is done to avoid undue stretching and traction on the already deformed spinal cord. 8 Detethering the cord followed by corrective surgery for the kyphoscoliosis at the same sitting has not been reported in the literature review. Therefore, this case has been reported as a novel approach to deal with this unusual presentation. The SSEPs assess the functional integrity of the sensory pathways from the peripheral nerve through the dorsal column and to the sensory cortex. Monitoring the dorsal column integrity with SSEP is the most commonly used technique in spinal surgery. Since the mid-1990s, combined MEP and SEP monitoring has been routinely used for spinal surgeries. The motor potentials are evoked with transcranial electrodes placed on the scalp over the motor cortex area of the skull. 7 Intraoperative neurophysiologic monitoring

RECOMMENDATIONS
Intraoperative neuromonitoring is an essential modality in patients undergoing cord detethering and deformity correction. It is a tool that cannot simply be substituted for its reflective results over spinal cord functions in a live feed mode intraoperatively.