There is a wide range of reports on the prevalence of neurological injuries during scoliosis surgery, however this should depend on the subtypes and severity of the deformity. Furthermore, anterior versus posterior corrections pose different stresses to the spine, further quantifications of neurological risks are presented.

Neuromonitoring data was prospectively entered, and the database between 2006 and 2012 was interrogated. All deformity cases under the age of 21 were included. Tumour, fracture, infection and revision cases were excluded.

All “red alerts” were identified and detailed examinations of the neuromonitoring records, clinical notes and radiographs were made. Diagnosis, deformity severity and operative details were recorded.

2290 deformity operations were performed: 2068 scoliosis (1636 idiopathic, 204 neuromuscular, 216 syndromic, and 12 others), 89 kyphosis, 54 growing rod procedures, and 80 operations for hemivertebra. 696 anterior and 1363 posterior operations were performed for scoliosis (8 not recorded), and 38 anterior and 51 posterior kyphosis correction.

67 “red alerts” were identified, there were 14 transient and 6 permanent neurological injuries. 62 were during posterior stage (24 idiopathic, 21 neuromuscular, 15 syndromic (2 kyphosis), 1 growing rod procedure, 1 haemivertebra), and 5 were during anterior stage (4 idiopathic scoliosis and 1 syndromic kyphosis). Average Cobb angle was 88°. 1 permanent injuries were during correction for kyphosis, and 5 were for scoliosis (4 syndromic, 1 neuromuscular, and 1 anterior idiopathic).

Common reactions after “red alerts” were surgical pause with anaesthetic interventions (n=39) and the Stagnara wake-up test (n=22). Metalwork was partially removed in 20, revised in 12 and completely removed in 9. 13 procedures were abandoned.

The overall risk of permanent neurological injuries was 0.2%, the highest risk groups were posterior corrections for kyphosis and scoliosis associated with a syndrome. 4% of all posterior deformity corrections had “red alerts”, and 0.3% resulted in permanent injuries; compared to 0.6% “red alerts” and 0.3% permanent injuries for anterior surgery. The overall risk for idiopathic scoliosis was 0.06%.

Introduction

Somatosensory evoked potential (SSEP) monitoring allows for assessment of the spinal cord and susceptible structures during complex spinal surgery. It is well validated for the detection of potential neurological injury but little is known of surgeon's responses to an abnormal trace and its effect on neurological outcome. We aimed to investigate this in spinal deformity patients who are particularly vulnerable during their corrective surgery.

Introduction

Evidence suggests that intra-operative spinal cord monitoring is sensitive and specific for detecting potential neurological injury. However, little is known about surgeons' responses to trace changes and the resultant neurological outcome.

This pilot study assesses level of agreement between surface and fine wire electromyography (EMG), in order to establish if surface is as reliable as fine wire in the diagnosis and treatment of abnormal muscle patterning in the shoulder. 18 subjects (11 female, mean 36 years) with unstable shoulders were recruited after written consent and ethical approval. Anthropometric information and mean skinfold size for triceps, subscapular, biceps and suprailiac sites were obtained. Triple stud self adhesive surface electrodes (“Triode” – Thermo Scientific) were placed over Pectoralis Major (PM), Latissimus Dorsi (LD), Anterior Deltoid (AD) and Infraspinatus (IS) at standardised locations. A ‘Medi-Link’ dual channel surface EMG (Electro Medical Supplies) displayed a rectified smoothed signal. Patients performed five identical uniplanar standard movements (flexion, abduction, external rotation, extension and cross body adduction). After a rest period, a dual needle technique for fine wire insertion was used displaying a raw EMG signal on a ‘Sapphire II’ four channel EMG unit. An experienced examiner in each technique reported if muscle activation patterns differed from agreed normal during any movement and were blinded to the other test results. Sensitivity, specificity and kappa values for level of agreement between methods were calculated for each muscle according to the method of Altman. 15 patients were successfully tested. Sensitivity, specificity and kappa values between techniques for each muscles were PM (57%, 50%, 0.07), LD (38%, 85%, 0.22), AD (0%, 76%, −0.19) and IS (85%, 75%, 0.6). Only IS demonstrated high sensitivity and specificity and a moderate level of agreement between the two techniques. There was no correlation between skinfold size and agreement levels. Surface did not agree with wire analysis for PM, LD and AD, although IS did show moderate agreement. Subcutaneous fat did not appear to affect correlation.

We present the use of dynamic electromyographic analysis (DEMG) in the diagnosis of muscle patterning instability. DEMG’s were requested in 168 of 562 muscle patterning shoulders with suspected subclinical or clinically complex muscle patterning instability. An experienced neurophysiologist (blinded to the clinical findings and direction of instability) inserted dual-wire tungsten electrodes into pectoralis major, latissimus dorsi, infraspinatus and anterior deltoid. Muscle activity was recorded during rest, flexion, abduction, extension, and cross-body adduction. 5 investigations were abandoned. The timing and magnitude of muscle activity was noted and compared to the clinical diagnosis and direction of instability. DEMG identified a total of 204 abnormal muscle patterns in 163 shoulders. The examination was normal in 13 patients (8%). A single muscle was abnormal in 63 shoulders, 2 muscles in 55, 3 muscles in 9, and all 4 muscles in one shoulder. Over-activation of pectoralis major was identified in 58%, and latissimus dorsi in 70%, of shoulders with anterior instability. In posterior instability, latissimus dorsi was overactive in 76%, anterior deltoid in 14% and infraspinatus was under-active in 24%. Pectoralis major and Latissimus dorsi were both overactive in 38% of anterior, 29% of posterior and 38% of multidirectional instability. Abnormal muscle patterns were identified in 52 shoulders with subclinical muscle patterning. A further 98 shoulders had 134 clinically abnormal muscle patterns. These were confirmed by DEMG in 57 cases (sensitivity 43%), and DEMG’s were normal in 77 (specificity 43%). DEMG also identified 65 additional muscles as abnormal in the 98 clinically abnormal shoulders. DEMG performed by an experienced neurophysiologist provides additional information regarding abnormal muscle activation in selected complex or subtle cases of muscle patterning instability in which clinical examination has a low sensitivity and specificity.