Orthopaedic and spine surgery
Method
Spinal fusion
In orthopaedics and spine surgery, intraoperative neuromonitoring (IONM) is mainly used during resection of spinal tumours and during pedicle screw placement for spinal corrections such as scoliosis correction or spinal fusion. During the various surgeries, depending on the intervention, the spinal cord and/or the spinal nerves is/are at risk of being injured as a result of distraction, manipulation and resection. In addition, there is a risk of ischaemia due to arterial occlusion (see also vascular surgery).
Neuromonitoring method during spinal fusion
During spinal fusion, one or more vertebral bodies of the cervical, thoracic or lumbar spine are fused together to treat spinal instability. Indications include unstable fractures, severe or progressive scoliosis or spondylolisthesis that cannot (or can no longer) be treated with conservative methods.
Depending on the intervention, three methods (EMG, SEP, MEP) are usually used for intraoperative neuromonitoring during spinal fusion.
Electromyographic monitoring is used to assess possible pedicle perforation during pedicle screw placement. EMG is suitable for both percutaneous and open pedicle screw placement.[1]
EMG monitoring during percutaneous pedicle screw placement
Please note that the following recommendations on neuromonitoring during spinal fusion are of a general nature. The patient’s individual vital parameters, the existing surgical situation and the technology used should always be considered.
During spinal fusion, a bipolar stimulation probe is placed in the pedicle or the vertebral body via a previously inserted Kirschner wire (<1,6 mm OD) and brought into the screw position to be tested. Electrical stimulation is used to detect a breach of the pedicle wall. During spinal fusion, the EMG signals are recorded in the respective target muscles of the arms and legs, matching the vertebral heights.[1]
The required stimulation current for an EMG response signal is compared with a defined current threshold depending on the type of cervical, thoracic and lumbar/sacral interventions.
>> If the stimulation current is under this current threshold, the position of the Kirschner wire should be changed.
>> If the required stimulation current is above the current threshold or equal to it, a pedicle screw can be placed in this position.
EMG monitoring during open pedicle screw placement
The stimulation probes are used during spinal fusion in the open pedicle drill hole for palpation of the pedicle wall and for monopolar or bipolar stimulation of the spinal nerves through the pedicle wall.[1]
Evoked potentials during spine surgery such as spinal fusion or scoliosis correction
SEPs[1] and MEPs[2] allow immediate status assessment of the nerve structures between the stimulation and recording site during spinal fusion or scoliosis.
>> SEPs are triggered by stimulation of peripheral nerves, e.g. the median nerve at the level of the wrists or the tibial nerve at the level of the ankles. The stimulation impulse travels along the nerve and through the dorsal sensory tracts of the spinal cord up to the primary sensory cortex where it is recorded as SEP.
>> The aim of MEP recording is to activate the motor cortex through electrical stimulation in order to contract functionally related muscle groups. MEP recording during spinal fusion is used to assess and document the structural and functional integrity of the motor tracts of the spinal cords and the motor part of the spinal nerves.[2]
References
1. Isley, M. R. The Neurodiagnostic Journal: Current Trends in Pedicle Screw Stimulation Techniques: Lumbosacral, Thoracic, and Cervical Levels (2012)
2. Ulkatan S. et al. Monitoring of Scoliosis Surgery with Epidurally Recorded Motor Evoked Potentials (D Wave) Revealed False Results, Clinical Neurophysiology 117, No. 9 (2006)