Abstract

Introduction: The trans-foraminal approach to the lumbar spine is an excellent minimally invasive portal to the spine that has gained interest in recent years. This approach is used mostly for T-LIF and far lateral disc herniations. With the recent development of endoscopic surgery, knowledge of the pitfalls of foraminal anatomy are important in order to avoid adverse clinical outcomes. This is best learned from the experience of endoscopic spinal surgeons and a thorough knowledge of the normal, variant, and patho-anatomy of the foramen. Purpose: Complications and adverse side effects, with techniques of intra- and post-operative management encountered in over 3,000 patients and 8,000 lumbar discs undergoing endoscopic decompression for painful degenerative conditions of the lumbar spine are retrospectively reviewed. Method: In vivo-endoscopic documentation of patho-anatomy by video tape and DVD recording of the surgical procedure has produced images that allows study of the patho-anatomy encountered. Painful patho-anatomy was confirmed by spinal probing. Discogenic pain reproduction was correlated intra-operatively by evocative chromodiscography™. Pain reproduction was correlated with abnormal discogram patterns that was compared with Mri findings. Indigocarmine dye was mixed 1:10 with Isovue 300 to stain the degenerated nucleus and adjacent structures in the path of the injectate. Extraforaminal, foraminal, and intradiscal normal and patho-anatomy, included routine visualization of the annulus, the traversing and exiting nerves at each operative level , and the epidural space. Findings: The most common endoscopic finding was degenerative nucleus and inflammatory tissue in the disc and annulus, a common finding in painful disc herniations. Inflammation, granulation tissue, and an inflammatory membrane denote chronicity. An inflammatory membrane in the annulus was associated with severe back pain produced by low pressure low volume discography. The pain is not always concordant, but usually severe, just from distending the disc annulus. Foraminal osteophytes could be seen tethering and irritating the exiting nerve, producing perineural scar tissue that is difficult to see with open approaches. “Anomalous” nerves in the “hidden zone” of MacNab identified pain generators in-vivo that have not been emphasized in the literature. Foraminal branches of either the traversing or exiting nerve (furcal nerves) are contributed to the symptom complex. Furcal nerves are difficult to differentiate from a conjoined nerve. Autonomic nerves are also present, confirmed by endoscopic biopsy. Results: Working near the Dorsal Root Ganglion is a risk by itself, a known risk factor in any foraminal surgery. Ablation or removal of nerves in the inflammatory membrane results in decreased axial back pain and sciatica, but may also produce a side effect of dysesthesia of varied severity. Dysesthesia occurs between 5-15% of the time, depending on the patho genesis of the painful condition. It is usually very mild and completely self limited and temporary. Discussion: Dysesthesia responds to Lyrica or Neurontin, foraminal nerve blocks, and lumbar sympathetic blocks. It can be associated with motor weakness that usually resolves, unless there is significant co-morbidity such as peripheral neuropathy, and seizure disorders. Pre-operative Consent should include usually transient neuropathic pain. Post Operative Neuropathic pain staying the same or worsening may not be able to be completely eliminated, and is a risk of the endoscopic procedure, even with neuromonitoring utilizing continuous EMG. Conclusion: A through discussion of the risks associated with foraminal endoscopic surgery must be explained to any patient undergoing foraminal endoscopic surgery. It is similar to the risk of trans-canal surgery. It has unique risks due to variations in foraminalnormal and patho-anatomy. The use of foraminal epidural injections intra-operatively, post-operatively, and in the management of post-operative dysesthesia will decrease this adverse side effect of foraminal surgery to approximately 1% of patients with mild permanent sensory or motor residuals. The overall risks and surgical morbidity are still less than posterior trans-canal surgery