SSEP analysis in surgery of idiopathic scoliosis: the influence of spine deformity and surgical approach

The Utility of Preoperative Neuromonitoring for Adolescent Idiopathic Scoliosis

Background

Intraoperative neuromonitoring is well established and widely used to assist in completing corrective surgery for adolescent idiopathic scoliosis (AIS) safely. The role of preoperative measurement of somatosensory evoked potentials (SSEPs) and/or transcranial magnetic stimulation (TMS) to determine if there is transpinal pathology, however, is not clear. We sought to determine if preoperative SSEP and/or TMS measurement provided clinical benefit to patients with AIS.

Methods

A review of medical charts between 2010 and 2012 was conducted for patients undergoing surgery for scoliosis. Patients with diagnoses other than AIS were excluded. Patients with incomplete preoperative or intraoperative data were also excluded. Relevant clinical information such as age, sex, number of levels fused, and major Cobb angle were recorded. Preoperative neuromonitoring measurements and intraoperative neuromonitoring results were reviewed by an attending neurologist. Any instance in which an intraoperative surgical plan or neuromonitoring result interpretation was influenced by preoperative results was recorded. Further imaging obtained based on preoperative results was noted. Any acute neurologic complication such as paralysis was noted.

Results

Eighty-one patients met inclusion criteria (64 female, 17 male). Average age was 15 years (± 1.92). Major Cobb angle at preoperative evaluation averaged 57.5 degrees (± 10.81 degrees). Ten patients had abnormal preoperative SSEP/TMS results. There were no changes in protocol during intraoperative neuromonitoring based upon preoperative neuromonitoring findings. No additional imaging was required for patients with abnormal preoperative neuromonitoring results. There was no statistically significant difference in preoperative Cobb angle between the group of patients with abnormal preoperative neuromonitoring and those with normal baseline testing.

Conclusion

Preoperative SSEP/TMS measurement prior to corrective surgery for AIS has limited utility. There were no instances in which a patient's clinical course was improved by testing. We recommend against routine use of preoperative SSEP/TMS testing for AIS patients requiring corrective surgery.

Increased spinal cord movements in cervical spondylotic myelopathy

BACKGROUND CONTEXT

Magnetic resonance imaging (MRI) is a very useful diagnostic test for cervical spondylotic myelopathy (CSM) because it can identify degenerative changes within the spinal cord (SC), disclose the extent, localization, and the kind of SC compression, and help rule out other SC disorders. However, the relationships between changes in cerebrospinal fluid (CSF) flow, cord motion, the extent and severity of spinal canal stenosis, and the development of CSM symptoms are not well understood.

PURPOSE

To evaluate if changes in the velocity of CSF and SC movements provide additional insight into the pathophysiological mechanisms underlying CSM beyond MRI observations of cord compression.

STUDY DESIGN

Prospective radiologic study of recruited patients.

PATIENT SAMPLE

Thirteen CSM subjects and 15 age and gender matched controls.

OUTCOME MEASURES

Magnetic resonance imaging measures included CSF and SC movement. Cervical cord condition was assessed by the Japanese Orthopaedic Association (JOA) score, compression ratio (CR), and somatosensory evoked potentials (SSEPs) of the tibial and ulnar nerves.

METHODS

Phase-contrast imaging at the level of stenosis for patients and at C5 for controls and T2-weighted images were compared with clinical findings.

RESULTS

Cerebrospinal fluid velocity was significantly reduced in CSM subjects as compared with controls and was related to cord CR. Changes in CSF velocity and cord compression were not correlated with clinical measures (JOA scores, SSEP) or the presence of T2 hyperintensities. Spinal cord movements, that is, cord displacement and velocity in the craniocaudal axis, were increased in CSM patients. Increased SC movements (ie, total cord displacement) both in the controls and CSM subjects were associated with altered spinal conduction as assessed by SSEP.

CONCLUSIONS

This study revealed rather unexpected increased cord movements in the craniocaudal axis in CSM patients that may contribute to myelopathic deteriorations in combination with spinal canal compression. Understanding the relevance of cord movements with respect to supporting the clinical CSM diagnosis or disease monitoring requires further long-term follow-up studies.

Impaired dynamic balance control in adolescents with idiopathic scoliosis and abnormal somatosensory evoked potentials

BACKGROUND

Both balance control dysfunction and dysfunction of the central nervous system have been proposed as being causative factors in adolescent idiopathic scoliosis (AIS), yet the relationship between these factors has not been investigated in detail. An intergroup comparative study was conducted to investigate the effect of abnormal somatosensory function on the dynamic balance parameters of girls with AIS.

METHODS

The relationship between dynamic balance control and abnormal somatosensory function seen in AIS patients was examined by studying the dynamic balance parameters in normal controls, in AIS patients with normal posterior tibial nerve somatosensory cortical evoked potentials (PTN-SCEPs), and in AIS patients with abnormal PTN-SCEPs. Gait parameters were recorded in 18 AIS girls (8 showing abnormal PTN-SCEPs and 10 showing normal PTN-SCEPs). Eight healthy age-matched volunteers served as a control group.

RESULTS

No significant left-right asymmetry of gait parameters was found for the controls or the AIS patients with normal PTN-SCEPs, whereas significantly higher gait parameters were found on the side of the curvature in the AIS patients with abnormal PTN-SCEPs.

CONCLUSIONS

Somatosensory dysfunction in AIS patients shows to have an impact on dynamic balance control. Further studies to examine the association between somatosensory dysfunction and balance control and how they may be related to the etiology of AIS are recommended.

LEVEL OF EVIDENCE

Diagnostic study, level IV (case-control study).

Preoperative radiological and electrophysiological evaluation in 100 adolescent idiopathic scoliosis patients

This is a prospective study of spinal magnetic resonance imaging (MRI), electrophysiological recordings, and neurological examinations of 100 patients admitted for surgery for adolescent idiopathic scoliosis (AIS), which was conducted to assess the prevalence of structural and functional abnormalities within the spinal cord in patients with clinically normal neurologic condition. In all patients the clinical diagnosis and intact neurological condition was ascertained by a spinal orthopedic surgeon. Full-length spinal axis MRI studies (T1/T2 sequences) and somato-sensory evoked potentials of the tibial nerves (tSSEPs) were preoperatively assessed by independent evaluators blinded to the patients' medical histories. Structural spinal cord abnormalities were found in three of 100 AIS patients on MR imaging. In one patient a Chiari malformation type 1 with an accompanying syringomyelia was diagnosed, which required a suboccipital decompression. In the other two patients small thoracic syringomyelias were diagnosed. Abnormalities of spinal cord function were detected in 68% of the 100 patients: tSSEP latencies corrected for body height were increased in 56% of the patients; pathological differences between tSSEPs on the left and right sides were present in 17% (12% in combination with a prolongation of the latency). The findings of this study indicate that MRI and electrophysiological examinations are essential to assess spinal cord abnormalities that are clinically not detectable in AIS patients. Even in patients with intact neurologic condition and clinically typical right-curved thoracic scoliosis, the possibility of intraspinal pathologies should be ruled out by MRI. It is especially important to detect structural pathologies like syringomyelia and Chiari malformation before proceeding with scoliosis surgery, as these conditions are associated with a higher neurological risk during scoliosis surgery. The electrophysiological recordings made in the present study, with the high number of pathological tSSEPs, are indicative of functional abnormalities with a subclinical involvement of the recorded neuronal pathways. The relevance of the latter findings is not yet clear, but pre-operative tSSEP examinations offer the possibility of assessing alterations in spinal cord function that are undetectable by clinical examination.