Michael O. Kelleher

Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: a prospective analysis of 1055 consecutive patients

OBJECT Despite the growing use of multimodal intraoperative monitoring (IOM) in cervical spinal surgery, limited data exist regarding the sensitivity, specificity, and predictive values of such a technique in detecting new neurological deficits in this setting. The authors sought to define the incidence of significant intraoperative electrophysiological changes and new postoperative neurological deficits in a cohort of patients undergoing cervical surgery. METHODS The authors conducted a prospective analysis of a consecutive series of patients who had undergone cervical surgery during a 5-year period at a university-based neurosurgical unit, in which multimodal IOM was recorded. Sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) were determined using standard Bayesian techniques. The study population included 1055 patients (614 male and 441 female) with a mean age of 55 years. RESULTS The IOM modalities performed included somatosensory evoked potential (SSEP) recording in 1055 patients, motor evoked potential (MEP) recording in 26, and electromyography (EMG) in 427. Twenty-six patients (2.5%) had significant SSEP changes. Electromyographic activity was transient in 212 patients (49.6%), and 115 patients (26.9%) had sustained burst or train activity. New postoperative neurological deficits occurred in 34 patients (3.2%): 6 had combined sensory and motor deficits, 7 had new sensory deficits, 9 had increased motor weakness, and 12 had new root deficits. Of these 34 patients, 12 had spinal tumors, of which 7 were intramedullary. Overall, of the 34 new postoperative deficits, 21 completely resolved, 9 partially resolved, and 4 had no improvement. The deficits that completely resolved did so on average 3.3 months after surgery. Patients with deficits that did not fully resolve (partial or no improvement) were followed up for an average of 1.8 years after surgery. Somatosensory evoked potentials had a sensitivity of 52%, a specificity of 100%, a PPV of 100%, and an NPV of 97%. Motor evoked potential sensitivity was 100%, specificity 96%, PPV 96%, and NPV 100%. Electromyography had a sensitivity of 46%, specificity of 73%, PPV of 3%, and an NPV of 97%. CONCLUSIONS Combined neurophysiological IOM with EMG and SSEP recording and the selective use of MEPs is helpful for predicting and possibly preventing neurological injury during cervical spine surgery.

Intraoperative multimodality monitoring in adult spinal deformity: analysis of a prospective series of one hundred two cases with independent evaluation.

Study Design. A retrospective analysis of prospectively collected data of 102 consecutive adult patients who underwent intraoperative neurophysiological monitoring (IOM) during spinal deformity corrective surgery. Objective. To report the sensitivity and specificity of combined IOM in this study population using the postoperative neurologic examination as the “gold standard.” Summary of Background Data. IOM is recommended during corrective spinal surgery and has been widely used in the pediatric deformity population. However, there are limited data describing the application of IOM in adults undergoing spinal deformity corrective surgery. Methods. The study group consisted of 102 patients undergoing spinal deformity corrective surgery between 2001 and 2004. Patients were monitored using at least 2 or more electrophysiological methods including somatosensory-evoked potentials (SSEP), motor-evoked potentials (MEP), and electromyography (EMG). Results. The mean age of patients was 41.5 years (±17). The majority of the operative procedures involved instrumented fusion from thoracic to lumbar/sacral spine (n = 55), thoracic-pelvis fusion (n = 26), and a combined total of 32 osteotomies (including 25 pedicle subtraction osteotomies and 7 Smith-Peterson osteotomies). SSEPs were recorded successfully in 101 (99%), EMGs in 89 of 102 (87%), and MEPs in 12 of 16 (75%). Five cases were true positives (4.95%), and these were all detected by combined monitoring (2-SSEP, 2-EMG, 1-MEP). There were no false positives with SSEPs, but EMG resulted in 30 of 89 (34%) false positives. There were 4 false negatives with SSEPs, which reduced its sensitivity to 33%. There was 1 false negative with EMG, and 0 with MEPs. When these results were collated, the overall sensitivity of combined multimodality IOM in this adult deformity series was 100%, specificity 84.3%, PPV 13.9%, and NPV 97%. The combined sensitivity in the osteotomy group (n = 32) was 67%, specificity 98%, PPV 80%, and NPV 96%. In comparison, there were no IOM abnormalities in those patients who had in situ/minor corrective procedures (n = 18; largely adult degenerative scoliosis). Conclusion. Multimodality IOM of spinal cord sensory and motor function during surgical correction of adult spinal deformity is feasible and provides useful neurophysiological data with an overall sensitivity of 100% and a specificity of 84.3% (67% and 98%, respectively in patients undergoing major deformity correction).

Success and failure of minimally invasive decompression for focal lumbar spinal stenosis in patients with and without deformity.

Study Design. Observational cohort study. Retrospective review of prospectively collected outcomes data. Objective. The purpose of this study was to evaluate the clinical efficacy of minimally invasive (MIS) decompression for focal lumbar spinal stenosis (FLSS) in patients with and without deformity. Summary of Background Data. MIS, facet-preserving decompression has the potential of offering a significantly less morbid alternative to decompression and fusion in patients with leg dominant symptoms from degenerative spondylolisthesis and/or scoliosis. Methods. Single surgeon, consecutive series (n = 75), evaluated over 5 years. All patients had MIS lumbar laminoplasty (bilateral decompression from a unilateral approach) for FLSS (1–2 level). Patients had leg dominant, claudicant/radicular pain. Patients were divided into 4 groups: (A) stenosis with no deformity, n = 22; (B) stenosis with spondylolisthesis only, n = 25; (C) stenosis with scoliosis, n = 16; and (D) stenosis combined with spondylolisthesis and scoliosis, n = 12. The primary clinical outcome measures were the Oswestry Disability Index (ODI) and surgical revision rate. Preoperative and postoperative standing radiographs were assessed. Results. The average age was 68 years (40–89) with a mean time from surgery of 36.5 months (18–68). Average clinical improvement in ODI was 49.5% to 23.9% [mean postoperative follow-up of 31.8 months (24–72): group A = mean of 34.6; B = 28.9; C = 32.7; D = 30 months]. Incidence of preoperative grade I spondylolisthesis was 46%. Spondylolisthesis progression (mean = 8.4%) occurred in 9 patients and 2 patients developed spondylolisthesis. Overall revision rate was 10% [repeat decompression alone (n = 2) and decompression and fusion (n = 6)]. Subgroup analysis of preoperative and postoperative ODI and revision rate revealed (A) 48% to 18.7%, 0%; (B) 48% to 24.6%, 4%; (C) 50.7% to 31.5%; 25%; and (D) 53% to 22%, 25%, respectively. The revision rate for patient with scoliosis (C + D) was significant (P = 0.0035) compared with those without. Six of the 8 revised patients had a preoperative lateral (rotatory) listhesis (3 in C and 3 in D). Conclusion. MIS decompression alone for leg dominant symptoms is a clinically effective procedure in the majority of patients including those with degenerative spondylolisthesis or scoliosis. However, patients with scoliosis, particularly those with lateral listhesis, have a significantly higher revision rate that needs to be considered in operative decision-making.

Electrical conductivity measurement: a new technique to detect iatrogenic initial pedicle perforation

Pedicle screw fixation has achieved significant popularity amongst spinal surgeons for both single and multi-level spinal fusion. Misplacement and pedicle cortical violation occurs in over 20% of screw placement and can result in potential complications such as dysthesia, paraparesis or paraplegia. There have been many advances in techniques available for navigating through the pedicle; however, these techniques are not without drawbacks. A new electrical conductivity-measuring device, previously evaluated on the porcine model to detect the pedicle violation, was evaluated amongst nine European Hospitals to be used in conjunction with the methods currently used in that centre. This new device is based on two original principles; the device is integrated in the drilling or screwing tool. The technology allows real-time detection of perforation through two independent parameters, impedance variation and evoked muscle contractions. Data was collected twofold. Initially, the surgeon was given the device and a comparison was made between the devices ability to detect a breech and the surgeon’s ability to detect one using his traditional methods of pedicle preparation. In the second module of the study, the surgeon was limited to using the electrical conductivity detection device as their sole guide to detect pedicle breaches. A comparison was made between the detection ability of the device and the other detection possibilities. Post-operative fine cut CT scanning was used to detect the pedicle breaches. Overall, the 11 trial surgeons performed a total of 521 pedicle drillings on 97 patients. Initially there were 147 drillings with 23 breaches detected. The detection rate of these breaches were 22/23 for the device compared to 10/23 by the surgeon. Over both parts of the study 64 breaches (12.3%) were confirmed on post-operative CT imaging. The electrical conductivity detection device detected 63 of the 64 breaches (98.4%). There was one false negative and four false positives. This gives the device an overall sensitivity of 98% and specificity of 99% for detecting a pedicle breach. The negative predictive value was 99.8%, with a positive predictive value of 94%. No adverse event was noted with the use of the electrical conductivity device. Electrical conductivity monitoring may provide a simple, safe and sensitive method of detecting pedicle breech during routine perforation of the pedicle, in the course of pedicle screw placement.

The use of ciliary neurotrophic factor to promote recovery after peripheral nerve injury by delivering it at the site of the cell body

SummaryDespite a body of evidence showing that various neurotrophic factors support the survival of nerve cells and stimulate axonal outgrowth, doubt remains about their optimal site of application as well as the more compelling question of what clinical benefit, if any, they would confer. Ciliary neurotrophic factor (CNTF) supports the survival of motorneurons in vitro and in vivo. Direct delivery of CNTF to the cell bodies may help reduce the side effects and overcome the problem of rapid systemic clearance. The aim of this study was to establish whether nerve regeneration may be improved upon by the controlled addition of a specific humoral neurotrophic substance (CNTF) at the level of the cell body. Three groups of five adult sheep were used. The first group acted as normal controls. In the second and third groups, the median nerve was divided and repaired using an epineurial suture technique. In the second group, CNTF was supplied into the CSF at the level of C6 by an implanted osmotic pump. In the third group physiological saline was placed in the osmotic pump. The animals underwent comprehensive electrophysiological and isometric tension experiments at six months. All of the animals had reduced electrophysiological, morphometric and isometric tension indices after surgery compared to normal. The CNTF group had better results than the saline group in the following; (1) area and amplitude of the muscle action potential (2) the percentage of tetanus and muscle mass preserved after repair. These differences were only statistically significant for amplitude of the muscle action potential. No statistical difference was found in the morphological indices (fibre diameter, axon diameter, myelin thickness and internodal length) between the CNTF and saline groups. CNTF does not confer a functional benefit when applied at the level of the cell body.

Effect of locally administered ciliary neurotrophic factor on the survival of transected and repaired adult sheep facial nerve

OBJECTIVE to determine whether the administration of Ciliary Neurotrophic Factor (CNTF) at the site of repaired facial nerve enhances regeneration in the adult sheep model. METHODS Ten adult sheep were divided into 2 groups: control and study group (CNTF group). In the CNTF group, the buccal branch of the facial nerve was transected and then repaired by epineural sutures. CNTF was injected over the left depressor labii maxillaris muscle in the vicinity of the transected and repaired nerve for 28 days under local anesthesia. In the CNTF group, the sheep were again anesthetized after nine months and the site of facial nerve repair was exposed. Detailed electrophysiological, tension experiments and morphometric studies were carried out and then analyzed statistically. RESULTS The skin CV min, refractory period, Jitter and tension parameters were marginally raised in the CNTF group than the control but the difference was statistically insignificant between the two groups. Morphometric indices also did not show any significant changes in the CNTF group. CONCLUSION CNTF has no profound effect on neuronal regeneration of adult sheep animal model. KEYWORDS CNTF; Neurtrophic factors; Sheep; Facial nerve; Regeneration.

Lateral mass screw fixation of complex spine cases: a prospective clinical study

The purpose of this paper was to report our experience with lateral mass screw fixation when used in a variety of complex cervical pathologies. A prospective observational study was undertaken of all patients who underwent lateral mass screw fixation for complex spinal pathology. There were 59 patients. Pathology included cervical spondylosis with deformity 58%, rheumatoid arthritis 19%, tumours 15%, multiple level trauma 8%. The median follow-up time was 23 months. The patients myelopathy scores improved in 64% of patients. 79% reported an improvement in their neck disability scores. 73% had improvement in their visual analogue pain score. Sixty-one per cent had preoperative high signal change on T2WI MRI. Sixty per cent had loss of normal cervical lordosis on presentation or were kyphotic. Sixty-four per cent of patients had grade 3 compression on MRI (Singh). Postoperative alignment was maintained in all cases. No late kyphotic deformity occurred. Lateral mass screw fixation can be used effectively and safely for different cervical spine pathologies with good functional and radiological outcome.

The Burden of Motorcycle-Related Neuro-Trauma in Ireland and Associated Helmet Usage

Motorcycles represent less than 2% of the licensed vehicles but motorcyclists account for 12% of road deaths in Ireland. The British Road Safety Authority has introduced the Sharp programme, which hopes to save 50 lives in the U.K. each year alone by helping riders to choose the best-fitting and safest helmets. We evaluated the pattern of head injuries sustained by motorcyclists referred to the two neurosurgical centres Beaumont Hospital and Cork University Hospital in Ireland and ascertained if the new SHARP guidelines could be of benefit in reducing the burden of motorcycle related neurotrauma and disability in Ireland. Despite Ireland having mandatory helmet laws almost a quarter of our motorcyclists with traumatic brain injury were unhelmeted. A significant reduction in mortality and morbidity is predicted if all motorcyclists in Ireland were to wear helmets that satisfied the SHARP criteria

Intermittent atlantoaxial subluxation caused by a prolapsing neurofibroma. Case report.

In this report, the authors describe a unique case of intermittent high cervical cord compression caused by a prolapsing neurofibroma at the C1-2 level. This 21-year-old man with known neurofibromatosis Type 1 presented with a mass between the anterior arch of the atlas and the odontoid peg, causing atlantoaxial dissociation and cord compression. The cervicomedullary compression appeared to be caused in part by the neurofibroma but also by the abnormal alignment and thickening of the ligaments between the clivus and C-2. Preoperative imaging repeated on the morning of surgery revealed that the atlantoaxial dissociation had reduced with relief of cord compression and the lesion prolapsed inferiorly. The authors discuss this unusual lesion and describe the associated operative findings and surgical management.

Association of intracranial hypertension without ventriculomegaly and Chiari malformation: a dangerous combination

With the increased use of MRI, tonsillar ectopia, the hallmark of the adult Chiari malformation (ACM) is being more frequently recognized. However, in some cases, the patients symptoms do not fit with the classical presentation for ACM, but are similar to intracranial hypertension (IH). The latter may be difficult to diagnose in absence of ventricular enlargement. We report a case of ACM and IHWV due to carcinomatous meningitis.