Abstract

Introduction: Access to anatomic structures in percutaneous dorso-lateral, endoscopic assisted monoportal disc surgery may vary in individual patients, and special techniques may be needed to gain access and to avoid injury to spinal structures. A major limitation of endoscopic disc surgery, especially in removing lateral fragments, is the fact that that it is usually performed under local anesthesia because the patients full cooperation is required to give continual information on radicular symptoms. To reduce stress on both the patient and the surgeon we can perform the surgery under general anesthesia with free-run electromyography recordings from characteristics muscles for the nerve root exiting through the foramen. Abnormal EMG changes in the form of spikes or bursts were recorded in case of direct contact, through traction or newly in evoked electrical stimulation of the exiting nerve root. On the other hand radiological considerations are important in determining the so called excursion zone. Therefore and in addition we present a navigational study showing the limitations of the system in means of disc level, orientation of the facet joints, and in terms of the cannula entry point. Technical notes: We used the VectorVision2 of the BrainLab navigation system. A CT-scan of the pathological segment was matched with conventional intraoperative X-rays in two planes (CT-Fluoro Matching). After this procedure we could calibrate the endoscope, allowing a visualisation of the scope from the entry point to the disc and to the spinal canal and spinal foramen in multiplanar orientation. Results: Targeting foraminal and xtraforaminal disc herniation in every disc level, even in L5/S1,is feasible. Removing of the fragments under visual control is possible and allows the complete decompression of the exiting nerve root. Medio-lateral disc herniations with clearly visualisation of the traversing nerve root can be targeted in upper lumbal segments (L3/4-L1/2) using a 45° entry angle of the scope. In relation to the anatomical orientation of the facet joints these herniations can be accessible with a far lateral approach in L4/5. Visualisation of the spinal canal via this approach is impossible in L5/S1. Using a more cephalad entry point of the instruments a visualisation of the lateral recess is feasible at which in L4/5 and L5/S1 bone resection using a drill or laser application is neccesary.