Aims

This study aimed to use intraoperative free electromyography to examine how the placement of a retractor at different positions along the anterior acetabular wall may affect the femoral nerve during total hip arthroplasty (THA) when undertaken using the direct anterior approach (THA-DAA).

Aims. Spinal deformity surgery carries the risk of neurological injury. Neurophysiological monitoring allows early identification of intraoperative cord injury which enables early intervention resulting in a better prognosis. Although multimodal monitoring is the ideal, resource constraints make surgeon-directed intraoperative transcranial motor evoked potential (TcMEP) monitoring a useful compromise. Our experience using surgeon-directed TcMEP is presented in terms of viability, safety, and efficacy. Methods. We carried out a retrospective review of a single surgeon’s prospectively maintained database of cases in which TcMEP monitoring had been used between 2010 and 2017. The upper limbs were used as the control. A true alert was recorded when there was a 50% or more loss of amplitude from the lower limbs with maintained upper limb signals. Patients with true alerts were identified and their case history analyzed. Results. Of the 299 cases reviewed, 279 (93.3%) had acceptable traces throughout and awoke with normal clinical neurological function. No patient with normal traces had a postoperative clinical neurological deficit. True alerts occurred in 20 cases (6.7%). The diagnoses of the alert group included nine cases of adolescent idiopathic scoliosis (AIS) (45%) and six of congenital scoliosis (30%). The incidence of deterioration based on diagnosis was 9/153 (6%) for AIS, 6/30 (20%) for congenital scoliosis, and 2/16 (12.5%) for spinal tuberculosis. Deterioration was much more common in congenital scoliosis than in AIS (p = 0.020). Overall, 65% of alerts occurred during rod instrumentation: 15% occurred during decompression of the internal apex in vertebral column resection surgery. Four alert cases (20%) awoke with clinically detectable neurological compromise. Conclusion. Surgeon-directed TcMEP monitoring has a 100% negative predictive value and allows early identification of physiological cord distress, thereby enabling immediate intervention. In resource constrained environments, surgeon-directed TcMEP is a viable and effective method of intraoperative spinal cord monitoring. Level of evidence: III. Cite this article: Bone Joint J 2021;103-B(3):547–552

Purpose of the study: Neurophysiological monitoring during pedicular screw insertion has been used to verity bone integrity of instrumented pedicles. The purpose of this study was to determine, experimentally, whether the EMG thresholds after stimulation of dorsal pedicular screws depend on the distance between the nerve structures and the screw, or on the interposition of different tissues. Material and methods: EMG thresholds were recorded after stimulation of 18 VPD in fivde pigs, by varying the distance between the screws and the spinal cord (2, 6, 10 mm). The thresholds were recorded after rupture of the median pedicular cortical and after interposition of different tissues (blood, muscle, fat and bone) between the screws and the spinal cord. In four patients with a hemivertebra, four pedicular screws sere stimulated at insertion, just after resection of the hemivertebra. Results: The average intensity of the EMG thresholds was 5.60±1.90mA when the screws were in contact with the dural sac. When the distance was 2 mm, the average threshold reached ±3.42 mA, at 6 mm 13.59±6.27 mA and at 10mm, 15.86±5.83 mA (p< 0.05). Rupture of the median pedicular cortical and interposition of different biological tissues in experimental animals did not modify the stimulation thresholds of the dorsal pedicle screws. In the four operated patients with resection of a hemivertebra, the EMG stimulation thresholds exhibited a wide spread but did not provide any evidence for a significant change related to interposition of different tissues. The impedance of the bone material was higher than muscle or adipose tissue. In these patients, the distance from the screw to the spinal cord was not correlated with a modification in the stimulation threshold. Discussion: Further clinical study is needed to better understand the stimulation role of the EMG in the implantation of pedicular screws, considering that this technique does not determine pedicle rupture. Conclusion: In experimental animals, the electrical impedance appears to depend on the distance between the screw and the nerve structures but not on the integrity of the median pedicular cortical. Response to intensity does not appear to be related to the type of interpositioned tissue

Purpose of the study: Fixing the pedicles can be difficult to achieve during surgical treatment of scoliosis involving the thoracic spine because of the vertebral rotation raising the risk of neurological and vascular disorders. Use of extrapedicular thoracic screws has been proposed for more adapted and safe fixation. No clinical data has been published concerning the safety of these screws. Material and methods: This multicentric retrospective clinical and radiological study included 467 thoracic screws in 34 patients operated for scoliosis. Neurophysiological monitoring was used for all procedures. Screws were positioned free hand without radioscopic control. Pedicular screws were inserted in T10, T11, T12. Extra-pedicular screws were inserted for thoracic vertebrae above T10 to T4. Correction was achieved with rods bent in situ. The purpose of this study was to evaluate the position of the thoracic screws within the vertebral body and in relation to the great vessels and the cord. The position of the screws in the thoracic spine was studied by two independent observers reading multiple thin-slice CT images. The observers noted malposition as: 1) penetration into the canal more than 2 mm, 2) less than 1 cm hold in the vertebral body, 3) screw protrusion more than 2 mm beyond the vertebral cortical. Results: Screw malposition was observed for 9 of 161 pedicular screws (5.4%) and for 21 of 306 (6.8%) thoracic screws. None of the screw malpositions had a clinical expression. There was one episode of thoracic effusion associated with thoracoplasty. Two patients required revision (one for poor indication and one for disincarceration). There were no postoperative deep infections. Three cases of intercostals neuralgia subsided within three months. Conclusion: Insertion of thoracic screws for fixation and correction is a useful technique with few complications. It enables better 3D correction and better control of the deformation. Screw malposition in this series was similar to that observed with classical pedicular techniques. There was no major complication associated with thoracic screws

Ulnar nerve function, during and after open reduction and internal fixation of fractures of the distal humerus with subperiosteal elevation of the nerve, was assessed by intra-operative neurophysiological monitoring. Intermittent recording of the compound muscle action potentials was taken from the hypothenar muscles in 18 neurologically asymptomatic patients.

The mean amplitude of the compound muscle action potential after surgery was 98.1% (sd 17.6; −37% to +25%). The amplitude improved in six patients following surgery. Despite unremarkable recordings one patient had progressive paresis. Motor impairment is unlikely if the compound muscle action potential is continuously preserved and not reduced by more than 40% at the end of surgery. Temporary decreases in amplitude by up to 70% were tolerated without clinical consequences. However, repeated clinical examination is obligatory to recognise and treat early post-operative palsy.