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Journal of the American Academy of Orthopaedic Surgeons 80 Open hemilaminectomy to treat symptomatic intervertebral disk her- niation, described by Mixter and Barr in 1934, 1 set the standard for subsequent surgical techniques. The trend since has been to develop less invasive surgical procedures for the treatment of radiculopathy second- ary to herniated disk. The concept of minimally invasive spine surgery is to provide surgical options that optimally address the disk pathol- ogy without producing the types of morbidity commonly associated with open surgical procedures. Min- imally invasive techniques are not, however, a panacea for all lumbar disk pathology. These techniques are designed to treat nerve root com- pression alone as the source of ra- diculopathy in patients with acute primary disk herniations. Radiculopathy has been attrib- uted to the production of chemical mediators that result from the com- pression and/or leakage of degen- erative nuclear material through annular tears. These chemical me- diators may result in inflammation and may affect the large and small sensory afferent nerve fibers. 2,3 Phospholipase A 2 and nitric oxide synthase from extruded or migrated disk fragments have been specifi- cally cited as possible agents related to the pathophysiology of radicu- lopathy. 4 Minimally Invasive Techniques: An Overview First-generation minimally invasive methods were blind percutaneous techniques, including chemonucleo- lysis, percutaneous nucleotomy, automated percutaneous nucleot- omy, and laser disk decompression. The development of fiberoptic visu- alization with rigid discoscopes and flexible endoscopes allowed more advanced methods to be undertak- en, including biportal arthroscopic intradiscal diskectomy and percuta- neous intradiscal and epidural uni- portal techniques through postero- lateral, posterior interlaminar, or foraminal approaches. The stan- dard for evaluation of percutaneous techniques became open microdisk- ectomy, considered the benchmark for comparison. A recently devel- oped percutaneous variation of the standard laminotomy technique is endoscopic diskectomy. Laparo- scopic transperitoneal and retroperi- toneal approaches to herniated nuclear pathology also have been introduced. Dr. Mathews is Associate Clinical Professor, Department of Orthopaedic Surgery, Virginia Commonwealth University, Medical College of Virginia, Richmond, VA. Ms. Long is Clinical Researcher, MidAtlantic Spine Specialists, Richmond. One or more of the authors or the departments with which they are affiliated has received something of value from a commercial or other party related directly or indirectly to the sub- ject of this article. Reprint requests: Dr. Mathews, Suite 200, 7650 Parham Road, Richmond, VA 23294. Copyright 2002 by the American Academy of Orthopaedic Surgeons. Abstract Hemilaminectomy with diskectomy, the original surgical option to address intervertebral disk herniation, was superseded by open microdiskectomy, a less invasive technique recognized as the surgical benchmark with which minimally invasive spine surgery techniques have been compared as they have been devel- oped. These minimally invasive surgical techniques for patients with herniated nucleus pulposus and radiculopathy include laser disk decompression, arthro- scopic microdiskectomy, laparoscopic techniques, foraminal endoscopy, and microendoscopic diskectomy. Each has its own complications and requires a long learning curve to develop familiarity with the technique. Patient selection, and especially disk morphology, are the most important factors in choice of tech- nique. The optimal candidate has a previously untreated single-level herniation with limited migration or sequestration of free fragments. J Am Acad Orthop Surg 2002;10:80-85 Minimally Invasive Techniques for the Treatment of Intervertebral Disk Herniation Hallett H. Mathews, MD, and Brenda H. Long, MS, RN Perspectives on Modern Orthopaedics Hallett H. Mathews, MD, and Brenda H. Long, MS, RN Vol 10, No 2, March/April 2002 81 Advances in minimally invasive surgery relate to a number of factors: understanding of a technique’s abili- ty to effect nerve root decompres- sion, development of approaches that are based on the location of the disk pathology, and the refinement of diagnostic modalities to aid in lo- cating specific disk pathology. Ad- vances in fiberoptic visualization have been a factor, as has refined surgical instrumentation. Better patient selection has resulted from experience with individual tech- niques as well as an appreciation of technique-related complications and outcomes. In addition, improved fluoroscopic imaging and navigation systems have enhanced the safety and predictability of minimally inva- sive techniques when performed by experienced endoscopic surgeons. Perhaps the most notable advan- tage of minimally invasive tech- niques is the ability they provide to surgically address and resolve her- niated nuclear pathology without the morbidity associated with inci- sion of the paraspinal muscle in tra- ditional open techniques. Enhanced visualization of the surgical field allows the pathology to be seen and permits both identification and avoidance of injury to the neurovas- cular structures. The surgical field can be surveyed before conclusion of the procedure, and the diskectomy itself can be inspected and docu- mented on videotape. In addition, these procedures generally are done on an outpatient basis. Patients usu- ally require minimal analgesic med- ication and have a timely return to activities of daily living, including work. Little, if any, postoperative rehabilitative therapy is necessary. Consequently, the overall economic impact of minimally invasive tech- niques in most instances is less than that of open techniques. Disadvantages to minimally invasive surgery for the herniated disk are few. Primarily, the learn- ing curve for the surgeon and his or her staff is steep. Mastery of the neurovascular anatomy is required, and familiarity with the spatial ori- entation of the endoscopic field is critically important. The goal of minimally invasive techniques is either disk debulking or selective fragment removal to alter disk morphology and subse- quently abate nerve root compres- sion. Selective fragmentectomy may remove an obstructive disk herniation mechanically. However, intradiscal depressurization and lavage also may improve symptoms without significant change in neural anatomy. Good results have been achieved without significant change in neural anatomy following the procedure. The governing factor in considering a minimally invasive procedure is patient selection. 5 Indications for Minimally Invasive Spine Surgery Except in emergent circumstances, such as rapidly progressive neuro- logic deficits or the threat of cauda equina syndrome, 6 to 8 weeks of nonsurgical treatment with appro- priate medication and conservative care is routine before proceeding with surgical intervention. The ideal candidate should have unilateral radicular pain radiating into the foot, with leg pain greater than back pain. Positive straight leg raising is often present. The radicular pain may be described as lancinating and/or aching. Other complaints can include numbness, tingling, and weakness, along with decreased sen- sation to light touch and pin prick. Because herniation can result in canal stenosis relative to the size of the herniation, some patients com- plain of pseudoclaudication. Location of the herniation dic- tates the appropriate minimally invasive approach. Magnetic reso- nance imaging is the most effective radiologic test for visualizing disk pathology and achieving a defini- tive correlation with patient presen- tation. Diskography, although con- troversial, may be especially helpful in the diagnosis when symptoms are equivocal and the pain genera- tor can be isolated through symp- tom provocation. 6 Optimal candidates for minimal- ly invasive access are those with a single-level herniation that has not previously undergone surgery and occupies <50% of the spinal canal, with limited migration or sequestra- tion of free fragments. Scarring or other deviations in normal anatomy that may have resulted from previ- ous surgical intervention at a de- fined level are a relative contrain- dication to minimally invasive revi- sion surgery for disk herniation recurrence. Developmental spinal stenosis and minimal disk hernia- tion presenting as only a small bulge also are relative contraindications. Techniques, Complications, and Results Early Techniques Open microdiskectomy, the benchmark procedure with which percutaneous and minimally inva- sive techniques are compared, uti- lizes a small incision and a micro- scope or loupe magnification rather than an endoscope. The technique is similar to minimally invasive tech- niques in regard to patient selection and indications. Compared with percutaneous techniques, especially foraminal epidural endoscopy, diskectomy is limited in its ability to address sequestered free fragments with significant migration. Open diskectomy allows the surgeon to visualize the pathology and neu- rovascular anatomy, but in this tech- nique, the anatomic structures often must be gently manipulated (rather than avoided) for optimal access to the disk–nerve root compression interface. The overall rate of suc- Treatment of Intervertebral Disk Herniation Journal of the American Academy of Orthopaedic Surgeons 82 cessful outcomes for diskectomy has been reported to range from 76% to 100%. 7 Other studies demonstrate that the rate and type of complica- tions are similar to those of mini- mally invasive spine surgery. 8 The most common complications are neurovascular trauma, diskitis, and cerebrospinal fluid leak. 8,9 Diskec- tomy, like minimally invasive tech- niques used to treat lumbar disk herniations, has a learning curve that, once achieved, must be main- tained through regular application. Percutaneous techniques currently have few applications, given the more advanced procedures now ac- cepted. These early blind techniques addressed central and posterocentral pathology and were nonselective: their basic mechanism of action was a debulking of the nucleus pulposus without directly addressing the her- niation. The result was depressur- ization and relief of tension on annu- lar fibers as well as involution of the nucleus, essentially withdrawing the compressive nerve pathology back into the annular confines. 10 Chemonucleolysis caused dena- turization of the intervertebral nucleus and a relative disk debulk- ing. Allergic reactions and even anaphylaxis occurred in approxi- mately 1% of patients treated with chymopapain. 11 Postoperatively, radiographs of treated patients often demonstrated disk space col- lapse. 12 In some centers, chemo- nucleolysis currently is used in con- junction with epiduroscopy in the treatment of migrated or seques- tered free fragments. The technique is more popular in Europe than in the United States. 11 Gogan and Fraser 13 reported an 80% success rate at 10-year follow-up with chemonucleolysis, and similar suc- cess has recently been reported in a European study. 14 However, nota- ble neurovascular complications and transverse myelitis, probably resulting from the inadvertent intro- duction of chymopapain intrathe- cally, has substantially decreased the use of chemonucleolysis. Percutaneous nucleotomy and automated percutaneous nucleotomy are both blind, intradiscal, nonselec- tive techniques for disk debulking or deflation with disk involution from the site of neural compression. Complications have included trau- ma or injury to neural or vascular structures, diskitis, and cerebro- spinal fluid leaks, as well as the po- tential for bowel perforation. In one multicenter study, 15 success rates for automated percutaneous diskec- tomy in carefully selected patients ranged from 55% to 85%. Because these results are less satisfactory than those achieved with other tech- niques, this procedure has largely fallen out of favor. Laser disk decompression is a blind, nonspecific disk depressur- ization procedure resulting in grad- ual withdrawal of disk compression on the nerve root. Because it is a blind procedure, complications have paralleled those of the blind nu- cleotomy techniques. An additional concern related to complications early in the use of laser disk decom- pression was the heat associated with direct-firing wavelengths delivered by probes in proximity to neurovascular structures. 16 In cen- ters where this technique is still in use, successful outcomes have ranged from 50% to 89%, 10,17 imply- ing various outcomes in nonprospec- tive, nonrandomized studies with resulting inconsistent data. Recent application of the holmium:YAG cool, side-firing laser in conjunction with endoscopic visualization appears to be a promising option in selected patients. 16 Recent Techniques The combination of fiberoptic technology with arthroscopic can- nulae led to the development of rigid discoscopes and rod-lens endoscopes, and thus to visualized selective microdiskectomy. Arthro- scopic microdiskectomy can be either uniportal or biportal (Fig. 1), depending on the targeted herniated pathology. Small central herniations can be approached uniportally; bi- portal access is dictated for large central herniations and subligamen- tous and sequestered herniations. Dedicated instrumentation sized to arthroscopic application allows for manual or automated selective disk decompression at the pathologic Figure 1 Arthroscopic microdiskectomy technique: the biportal approach to a paracentral disk herniation. The instrument enters through the right foramen to allow access to the disk herniation. Triangulation occurs within the disk nucleus. (Adapted with permission. 12 ) R Nucleus L Hallett H. Mathews, MD, and Brenda H. Long, MS, RN Vol 10, No 2, March/April 2002 83 site. Complications with this tech- nique are minimal, but infection (two cases), transient peroneal neu- ropraxia (two cases), and transient skin hypersensitivity (five cases) have been reported, for a complica- tion rate of 3% in one large series of patients spanning 10 years. 18 Theo- retic complications related to trau- ma to neurovascular structures and perineural/intraneural fibrosis have not been reported. The success rate for this technique ranges from 75% to 98%. 18-21 The laparoscopic anterior ap- proach to the lumbar spine for pri- mary disk herniations began to be used in the mid-1980s and early 1990s. This technique allows access to contained disk herniations, as well as to some extruded and mi- grated fragments, through either a transperitoneal or retroperitoneal approach (Fig. 2). Complications including diskitis and segmental instability have been reported. 22 Trauma to major vascular structures is a potential complication that can result in marked morbidity. This laparoscopic procedure requires an approach surgeon as well as unique, expensive instrumentation. Sur- geons also must anticipate a steep learning curve. These factors con- tributed to long surgical times with- out any decrease in hospital lengths of stay. This has led to surgical costs that far exceed those of other minimally invasive techniques. 23 With an early success rate of only 69% for treatment of disk hernia- tion, the transperitoneal approach has now been adapted for use in anterior lumbar interbody fusion at L5/S1. 22 Foraminal epidural endoscopy is a diskectomy technique that ad- dresses paramedian, foraminal, and extraforaminal disk herniations. It can also access migrated and se- questered free fragments in the epidural space when they are limit- ed to confines of the axilla and the pedicle. Such access is facilitated by appropriately sized endoscopes with varied lens angles; foraminal and extraforaminal disk herniations are technically demanding for stan- dard microscopic techniques. The foraminal endoscopic technique allows visualization of the patholo- gy and avoidance of neurovascular structures at risk, as well as visual- ization of the selective diskectomy and documentation of the surgical effect at the time of the procedure (Fig. 3). As with arthroscopic micro- diskectomy, manual and automated instrumentation sized to the work- ing channel of the endoscope allows Figure 2 Laparoscopic diskectomy technique. R = retroperitoneal space. The instruments are inserted on the left side, with the smooth pituitary instrument traversing the retroperi- toneum through the psoas muscle. The trochar needle is placed through the posterolateral approach. (Adapted with permission. 22 ) Figure 3 Foraminal endoscopic diskectomy technique compared with the extraforaminal approach. The foraminal approach allows direct dissection and removal of herniated material. (Adapted with permission. 12 ) R R Exiting root Herniated disc Dura mater Traversing root Foraminal approach Extraforaminal approach Transpsoas retroperitoneal approach Posterolateral needle Treatment of Intervertebral Disk Herniation Journal of the American Academy of Orthopaedic Surgeons 84 for diskectomy or fragment removal tailored to the morphology respon- sible for the radiculopathy. The complication rate for endoscopic foraminal diskectomy in one large study was 5%. 24 There is potential for trauma to neurovascular struc- tures, diskitis, and cerebrospinal fluid leak, although the risk is mini- mized by the excellent visualization. The success rate has recently been reported at 78%. 25 Key to the suc- cess of foraminal epidural endo- scopic surgery are patient selection and, at surgery, familiarity with the spatial orientation and with the anatomy at risk. The learning curve is steep, and success with this tech- nique requires regular use. 26 For- aminal epidural endoscopic surgery has been equated to open micro- diskectomy as “microdiscectomy through a cannula.” 26 Microendoscopic diskectomy through the interlaminar approach allows endoscopic intervention for a broad range of disk pathology. This technique is indicated for all forms of disk herniation (Fig. 4) as well as for associated pathology, such as lat- eral recess or central canal stenosis. Microendoscopic diskectomy is per- formed through a slightly larger tubular distractor and thus closely approximates open microdiskec- tomy. It requires an approach to the pathology through the paraspinous musculature. Dilators are placed in succession until the optimum win- dow for surgical exposure is achieved. A tubular retractor is then placed that allows use of a working channel endoscope, through which both disk and bony pathology can be addressed. The surgical system and technique allow for attention either intradiscally or extradiscally in an area that can span from the pedicle to the midline. Complica- tions are similar to those of arthro- scopic microdiskectomy and forami- nal epidural endoscopy; in addition, there is the potential for cauda equina syndrome, epidural scarring, and segmental instability. This tech- nique is appropriate not only for disk pathology previously not treated surgically but also for recurrence. In their preliminary series, the devel- opers of this technique reported a complication rate of one patient in 41 (3%), with all patients reporting good to excellent results in follow-up based on modified MacNab crite- ria. 27 This series included patients who underwent surgery for lateral herniations, herniations within the spinal canal, and free-fragment pathology. 27 Summary Early blind, nonspecific intradiscal techniques have been superseded by a variety of low-morbidity, min- imally invasive surgical options that offer treatment for patients with radiculopathy secondary to disk pathology tailored to their re- spective pathologies. These proce- dures provide results comparable to those of microdiskectomy done with magnification and may poten- tially have advantages for some specific indications. Dural sac Exiting nerve root Intervertebral disk L5 Herniation Central Paramedian Foraminal Extraforaminal Figure 4 Disk herniations approachable by interlaminar techniques and selectively by other minimally invasive techniques. Central: open microdiskectomy, microendoscopic diskectomy, biportal approach. Paramedian: open microdiskectomy; microendoscopic diskectomy; uniportal, biportal, or foraminal approach. Foraminal: open foraminal approach, microendoscopic diskectomy, endoscopic foraminal approach. Extraforaminal: open far lateral approach, microendoscopic diskectomy, extraforaminal endoscopy. L4 Hallett H. Mathews, MD, and Brenda H. Long, MS, RN Vol 10, No 2, March/April 2002 85 References 1. Mixter WJ, Barr JS: Rupture of inter- vertebral disc with involvement of spinal canal. N Engl J Med 1934;211: 210-215. 2. 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Foley KT, Smith MM: Microendo- scopic discectomy. Tech Neurosurg 1997;3:301-307. . be surveyed before conclusion of the procedure, and the diskectomy itself can be inspected and docu- mented on videotape. In addition, these procedures generally are done on an outpatient basis result in canal stenosis relative to the size of the herniation, some patients com- plain of pseudoclaudication. Location of the herniation dic- tates the appropriate minimally invasive approach of neurovascular structures at risk, as well as visual- ization of the selective diskectomy and documentation of the surgical effect at the time of the procedure (Fig. 3). As with arthroscopic