Complication risks of the foraminal approach to the lumbar spine: it's corellation with foraminal anatomy, variations, and anomalous structures in the "hidden zone"

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Anthony T. Yeung M.D.
Arizona Institute For Minimally Invasive Spine Care

Address:
Phoenix
AZ

Citation: A. Yeung : Complication risks of the foraminal approach to the lumbar spine: it's corellation with foraminal anatomy, variations, and anomalous structures in the "hidden zone". The Internet Journal of Minimally Invasive Spinal Technology. 2009 Supplement II - to IJMIST Vol III No 4

Abstract

Purpose: The trans-foraminal approach to the lumbar spine is an excellent minimally invasive portal to the spine that has gained interest in recent years as an approach for interbody fusion and far lateral disc herniations. This approach, however, traverses the "hidden zone" of Mac Nab, and is still unfamiliar territory for many traditional spine surgeons. With the recent development of endoscopic surgery, pitfalls of the foraminal approach are important to surgeons in order to avoid adverse clinical outcomes. This is best learned from the experience of endoscopic spinal surgeons and a through knowledge of the normal, variant, and patho-anatomy of the foramen. Method: Complications and adverse side effects 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. Painful patho-anatomy was confirmed by spinal probing, and recorded in vivo on analog video and DVD. Discogenic pain reproduction was correlated intra-operatively by evocative chromodiscography. Pain reproduction was correlated with abnormal discogram patterns that were 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 has 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 dysaesthesia of varied severity. Dysaesthesia 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: Dysaesthesia 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 neuro monitoring 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 foraminal normal and patho anatomy. The use of foraminal epidural injections intra-operatively, post-operatively, and in the management of post-operative dysaesthesia 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

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