- Email: [email protected]
Transforaminal Endoscopic Microdiscectomy
PERCUTANEOUS SPINE TECHNIQUES
1042-3680/96 $0.00 + .20
TRANSFORAMINAL ENDOSCOPIC MICRODISCECTOMY Hallett H. Mathews, MD
The evolution of surgical access to the spine has had an abiding goal: to develop a technique that allows maximum exposure for visualization, identification, and exploration of anatomy, pathology, and structures at risk, thus providing for dissection and documentation of surgical correction for neuropathologic anatomy. Throughout this evolutionary process, the persistent driving force has been to develop a procedure equivalent to open laminectomy but with reduced surgical morbidity. Microdiscectomy, the procedure that first met the challenge, became the benchmark for comparative analysis with minimally invasive procedures that were introduced subsequently. A generation of technical and procedural refinements allowed for the development of foraminal epidural endoscopic surgery, " microdiscectomy through a cannula." In the current era of health care delivery, cost conscious payors are beginning to question the mentality by which the most conservative procedure is done as a "first try" at surgical correction of discal pathology. Rather, the expectation points toward selection of the one most effective procedure of least morbidity as the first and only surgical option. Transforaminal endoscopic surgery has the potential to be the choice for definitive therapeutic disc surgery. Funding support for the work provided by Sofamor Danek, Inc., Memphis, Tennessee
HISTORIC PERSPECTIVES IN MINIMALLY INVASIVE SPINE SURGERY
Open spine surgery in its original form dates to Mixter and Barr16 who in 1934 described open hemilaminectomy for disc "rupture." Just prior to that time, Burman1 introduced myeloscopy for visualization of the spinal cord, this concept representing early efforts at endoscopic spine surgery. Pool18 refined Burman' s work into the theory of intrathecal endoscopy, applying ureteroscopes in the spine. Classic illustrations rendered from this work showed pathology including arachnoiditis, tumor and disc herniation, and hypertrophied ligamentum flavum resulting in spinal stenosis.19 The introduction of aspiration biopsy in the spine is credited to Ottolenghi,23 although Craig5 is recognized for refining the technique for biopsy of the vertebral body through a uniportal posterolateral approach using uniquely designed instrumentation. The marriage of visualization with percutaneous access provided the theoretical basis for spinal endoscopy. Discography of both the cervical and lumbar spine advanced the information base for needle placement. Clinicians including Cloward,3 Collis et al,4 and Holt7 developed this theory based on the original work by Key and Ford.10 These needle approaches to the disc space were used therapeu-
From the Department of Orthopaedic Surgery, Medical College of Virginia, MidAtlantic Spine Specialists, Richmond, Virginia
NEUROSURGERY CLINICS OF NORTH AMERICA VOLUME 7 •NUMBER 1•JANUARY1996
59
60
MATHEWS
tically with the introduction of needle-guided chemonucleolysis by Lyman Smith. 21 With the 1970s came exponential progress in percutaneous techniques and instrumentation. Kambin and Gellman9 concomitant with Hijikata et al6 developed cannulae systems with dedicated instrumentation for single-portal access to the disc space. The basic technique of rigid discoscopy featured needle placement for orientation followed by alternating cannula visualization with manual disc removal in a safe triangular working zone defined by the area beneath the exiting root and lateral to the traversing root in the disc space. With modification of Hijikata' s instrumentation, the Balgrist Clinic's Schreiber and Leu 20 originated "percutaneous discoscopy," biportal access to a triangular working zone with simultaneous visualization and contralateral instrumented discectomy, a procedure that became more refined with perfection of variable angle lenses. Onik et al1 7 proceeded in 1985 to introduce an automated shaver into the procedural equation, the result being automated percutaneous discectomy. 17 By 1987, Mayer and Brock13 reported on a 40-patient randomized study that showed percutaneous endoscopic discectomy to be an equal and often superior option to microdiscectomy. The benchmark, microdiscectomy, had its first real competition and would never again return to its isolated acceptance. By the late 1980s, clinical applications for flexible fiberoptic technology attracted interest. Epiduroscopy was introduced by Stoll22 as an adjunct to open procedures for inspection of pathology and verification of surgical outcome. This technique was parlayed into a multicenter Food and Drug Administration Investigational Device Exemption (IDE) study of percutaneous epidural visualization. By 1991, the procedure's success in the absence of complications resulted in clinical approval that ignited the fires of interest and development in working channel endoscopy. At the same time, laser-assisted, nonvisualized percutaneous lumbar discectomy was in clinical trials by Choy et al 2working with various wavelengths, the most prevalent being the KTP 532-nm band. Mathews and Stoll pressed forward with the successful development of a flexible and steerable working channel spinal endoscope made possible by ongoing refinement of optics. Maxwell12 validated endoscopic theory and applications with a 1993 report of decreased
complications in endoscopy-assisted open microdiscectomy versus traditional microdiscectomy. As a progression of thought, Matthews investigated working channel endoscopy and transforaminal approaches to the disc space. This work resulted in the introduction of foraminal epidural working channel endoscopic surgery for access to far lateral herniations and lumbar disc sequestra. 11 MICRODISCECTOMY: THE BENCHMARK
When introduced, the advantages of microdiscectomy gained wide acceptance and set a standard to which minimally invasive spine surgery could be compared. By description, microsurgery is epidural exploration that allows for inspection of neuroanatomy and visualization of pathology by movement of nerves or other structures. The advantages of microdiscectomy include greater precision in the surgical field owing to less removal of bony and ligamentous structures with greater visualization through magnification and illumination, and a decrease in morbidity compared with classic laminectomy techniques. The early percutaneous procedures that addressed central and posterocentral pathology could not achieve the goals of microdiscectomy. Chemonucleolysis was nonselective, with morbidity that included anaphylaxis and disc space collapse. Percutaneous manual discectomy was also nonselective and featured visualization after the fact, not concurrent with surgical identification and dissection. Automated percutaneous discectomy was a nonspecific disc deflation procedure without reference to pathology in the absence of visualization. Laser discectomy also fell into the ranks of a nonspecific depressurization procedure where visualization was denied and laser effects in proximity to neurovascular structures caused concern. Thus, a review of the early minimally invasive procedures, both nucleotomy techniques and disc pressure reduction procedures, shows nonspecific intradiscal therapy with concurrent visualization of neuroanatomy being marginal or absent. THE CHALLENGE TO MICRODISCECTOMY
With spinal endoscopy, new terminology was introduced that implies visualization of
TRANSFORAMINAL ENDOSCOPIC MICRODISCECTOMY
anatomy and application of advanced mm1mally invasive techniques and instrumentation. The crucial elements for advanced techniques in spinal endoscopy are a thorough understanding of neuroanatomy and spatial orientation in the working space, because differential endoscopic lenses necessitate manipulation to obtain a clear, specific anatomic image. In addition, mastery of the procedure mandates dedication to an intensive learning curve. Epidural endoscopy made possible the inspection and exploration of the epidural space and access within the disc to address intradiscal pathology. With the patient awake, the posterolateral approach at 8 to 12 cm off the midline allowed for lateral docking. Emphasis was on avoidance of neuroanatomy, hence the requirement for an awake patient. Refinement of epidural endoscopy resulted in the technique of foraminal epidural endoscopic surgery (FEES), which allows access for visualization of anatomy and identification of neuropathology followed by documented surgical correction.
FORAMINAL EPIDURAL ENDOSCOPIC SURGERY
The foraminal approach is effective in the treatment of paramedian, foraminal, and extraforaminal herniations. It begins at 9 to 13 cm off the midline. Then, under visualization, there is flat entry under the pars and superior articulating facet and through the foramen with annular docking medially next to the traversing root. This access allows both epidural and intradiscal intervention in a safe neural triangular working zone. This zone is defined by the exiting root (nerve root that exits through the foramen at the level of the approach), the traversing root medially (root exiting the foramen at the level below the approach), and the disc. With foraminoscopy, there is direct, enhanced visualization and illumination of neurovascular structures as with microdiscectomy. Neuroanatomy is in clear view throughout the procedure, allowing greater insp ection than with microdiscectomy. Unlike microdiscectomy, w here nerve structures often must be moved for surgical access, foraminal epidural endoscopy allows for exploration and dissection under the neuroanatomy with little nerve root manipulation. Full visual ex-
61
ploration of both the foraminal and epidural space allows pathology to be addressed as it is encountered, making this approach one that is neither pathology dependent nor directed, as with most early percutaneous procedures. The design of the endoscope, with its optics and illumination, fosters access to free and sequestered disc fragments. The instrumentation for FEES features a 4.5 mm outer diameter 2.5 mm working channel endoscope with 30,000 pixel optical resolution for refined real-time visualization with a depth of field equaling 2 to 30 mm and a 70degree field of view. Work by Mirkovic et al1 5 has validated the size-dependent anatomy relative to the epidural safe zone, concluding that nothing greater than 4.5 mm can reach most areas for foraminoscopic inspection, dissection, and documentation. A host of manual epidural instruments facilitates surgical intervention in the patient w ho is placed prone on a radiolucent frame. Local and propofol (Diprivan) anesthesia allows an awake patient for surgeon-patient dialog during the procedure. A needle is placed on the skin surface at the surgical disc level for fluoroscopic verification prior to surgical entry. Accurate needle placement verified by AP and lateral fluoroscopic images precedes endoscopic intervention. For verification of pathology, discography may precede the foraminoscopic procedure. FEES is an approach and technique that is different from other percutaneou s disc procedures in that it is more aggressive, is anatomy directed and pathology targeted, and allows entry into the volar epidural space. It clearly challenges microdiscectomy in providing enhanced visu alization through optics and illumination, allowing for greater flexibility in the ability to explore anatomy and to target pathology and allowing for diminished morbidity, because there is absence of destabilizing incisional trauma. FEES provides a potential field of vision and surgical working zone that exceeds microdiscectomy, and the decreased surgical trauma coupled with intraoperative irrigation keeps bleeding to a minimum. Risk of infection, often related to the extent of surgical intervention and time at surgery, is reduced significantly in this brief, irrigated, incisionfree procedure. PATIENT SELECTION
John McCulloch, a staunch proponent of microdiscectomy has observed that, " the results
62
MATHEWS
of surgery are determined far more by patient selection than by surgical technique . . . the microscope will not perform the surgery and it will not secure a good result." 14 This also is true in FEES. Patient selection is critical to ensuring a surgical outcome that is acceptable to both patient and physician. Patients present with leg pain greater than back pain, most having undergone an average of 6 months of conservative care. MR imaging is the most specific cost-effective study to confirm disc pathology. The inclusion criterion for FEES is a virgin paramedian, foraminal or extraforaminal herniation that is contained or is noncontained at less than 50% of the canal diameter within the confines of the axilla and the pedicle in the absence of bulges or stenosis. The surgical contraindications include previous surgery, multilevel or pure central pathology, and sequestered pathology at the pedicular level as well as stenosis and morbid obesity. A chronic pain history or extended lost time under workers' compensation may influence a clinically satisfactory outcome negatively. Although not a contraindication, disc pathology at the LS/Sl level may prove inaccessible at surgery owing to the relative difficulty of the approach as well as steep iliac wing anatomy in some patients. With proper selection, patients do well based on preoperative education, outpatient surgery, and regular follow-up. Clinical experience demonstrates a predominance of patients back to work within 1 week of surgery.
SUMMARY
Hudgins, one of the pioneers in microdiscectomy, commenting in 1983 about that procedure, cited its safety because surgeons could see better. He also acknowledged the advantages of less incisional and anatomic structural morbidity, all factors that foster timely recovery and reduced expense. 8 McCulloch observed that the more limited the exposure of the dura and nerve roots, the less likely is the development of scar tissue, which he heralds as the "essence of microsurgery." 14 FEES, because of minimally invasive access with optimum visualization and illumination, rises to the challenges posed by microdiscectomy. It seems worthy of the identity, "microdiscectomy through a cannula." With FEES, dissection can venture into the canal and epi-
dural space (upstairs) or proceed intradiscally (downstairs) as pathology dictates. It is epidural surgery that introduces the concept of planned epidural dissection for intracanal pathology correction, which may or may not relate to the annulus and the posterior longitudinal ligament (PLL). FEES, as it has evolved, achieves the desired goals of minimally invasive spine surgery. There is less scarring and less instability both early and late. Clear visualization virtually eliminates the risk of surgical intervention at the wrong level and the likelihood of recurrence is reduced because of the intraoperative ability to verify correction of pathology. In addition, the surgical versatility of FEES for selected complex discal pathology has reduced the indications for open surgery. Spine surgery is now into its fourth generation, having entered a phase w here " less is more" -where advances in technology and surgical technique offer ever-expanding options by minimal access. It is through commitment to pure scientific investigational attitude that minimally invasive techniques, such as transforaminal endoscopic microdiscectomy, will be validated for efficacious, cost-effective surgical treatment of discal pathology.
References l. Burman MS: Myeloscopy or the direct visualization
of spinal cord. J Bone Joint Surg 13:395, 1931 2. Choy DS, Case RB, Fielding W, et al: Percutaneous laser nucleolysis of lumbar discs. N Engl J Med 317:771, 1987 3. Cloward RB: Anterior herniation of a ruptured lumbar intervertebral disc: Comments on the diagnostic value of the diskogram. Arch Surg 64:457, 1952 4. Collis JS, Gardner WJ: Lumbar discography: An analysis of 1000 cases. J Neurosurg 19:452, 1962 5. Craig FS: Vertebral body biopsy. J Bone Joint Surg Am 38:93, 1956 6. Hijikata S, YamagishiN,Nakayama T, et al: Percutaneous discectomy: A new treatment method for lumbar disc herniation. Journal of Toden Hospital 5:5, 1975 7. Holt EP Jr: The question of lumbar discography. J Bone Joint Surg 50:720, 1968 8. Hudgins WR: The role of rnicrodiscectomy. Orthop Clin North Am 14:589, 1983 9. Kambin P, Gellman H: Percutaneous lateral discectomy of the lumbar spine: A preliminary report. Clin Orthop 174:127, 1983 10. Key JA, Ford LT: Experimental intervertebral disc lesions. J Bone Joint Surg 30:621, 1948 11. Mathews HH: Foraminoscopic approach to lumbar disc sequestrum: A surgical technique for closed free fragment removal [abstract 17]. In Program and Ab-
TRANSFORAMINAL ENDOSCOPIC MICRODISCECTOMY
12. 13.
14. 15.
16.
stracts of the Seventh Annual International Intradiscal Therapy Society, Aberdeen, 1994 Maxwell KM: Spinal endoscopy: Clinical indications and outcomes. Presented at Current Concepts in Spinal Endoscopy, Williamsburg, August 27- 28, 1993 Mayer HM, Brock M: Percutaneous endoscopic discectomy: Surgical technique and preliminary results compared to microsurgical discectomy. J Neurosurg 78:216, 1993 McCulloch JA: Microdiscectomy. In Rothman RH, Simeone FA (eds): The Spine, ed 3. Philadelphia, WB Saunders, 1992, p 770 Mirkovic S, Schwartz DG, Glazer KG: Anatomic considerations in lumbar posterolateral percutaneous procedures [abstract 6]. In Programs and Abstracts of the 9th Annual Meeting, North American Spine Society, Minneapolis, MN, 1994 Mixter WJ, Barr JS: Rupture of intervertebral disc with involvement of spinal canal. N Engl J Med 211:201, 1934
63
17. Onik G, Maroon JC, Davis GW: Automated percutaneous discectomy: A prospective multi-institutional study. Neurosurgery 2:228, 1990 18. Pool JL: Myeloscopy: Diagnostic inspection of cauda equina by means of a myeloscope. Archives of Neurology and Psychiatry 39:1308, 1938 19. Pool JL: Myeloscopy: Intraspinal endoscopy. Surgery 11:169, 1942 20. Schreiber A, Leu HJ: Percutaneous nucleotomy: Technique with discoscopy. Orthopedics 14:439, 1991 21. Smith L: Enzyme dissolution of the nucleus pulposus in humans. JAMA 187:137, 1964 22. Stoll JE: Endoscopic spacial orientation and surgical approaches in the epidural space. Presented at Current Concepts in Spinal Endoscopy, Williamsburg, July 2324, 1993 23. Valls J, Ottolenghi CE, Schajowicz F: Aspiration biopsy in the diagnosis of lesions of vertebral bodies. JAMA 136:376, 1948 Address reprint requests to
Hallett H. Mathews, MD 7650 Parham Road, Suite 200 Richmond, VA 23294
1042-3680/96 $0.00 + .20
TRANSFORAMINAL ENDOSCOPIC MICRODISCECTOMY Hallett H. Mathews, MD
The evolution of surgical access to the spine has had an abiding goal: to develop a technique that allows maximum exposure for visualization, identification, and exploration of anatomy, pathology, and structures at risk, thus providing for dissection and documentation of surgical correction for neuropathologic anatomy. Throughout this evolutionary process, the persistent driving force has been to develop a procedure equivalent to open laminectomy but with reduced surgical morbidity. Microdiscectomy, the procedure that first met the challenge, became the benchmark for comparative analysis with minimally invasive procedures that were introduced subsequently. A generation of technical and procedural refinements allowed for the development of foraminal epidural endoscopic surgery, " microdiscectomy through a cannula." In the current era of health care delivery, cost conscious payors are beginning to question the mentality by which the most conservative procedure is done as a "first try" at surgical correction of discal pathology. Rather, the expectation points toward selection of the one most effective procedure of least morbidity as the first and only surgical option. Transforaminal endoscopic surgery has the potential to be the choice for definitive therapeutic disc surgery. Funding support for the work provided by Sofamor Danek, Inc., Memphis, Tennessee
HISTORIC PERSPECTIVES IN MINIMALLY INVASIVE SPINE SURGERY
Open spine surgery in its original form dates to Mixter and Barr16 who in 1934 described open hemilaminectomy for disc "rupture." Just prior to that time, Burman1 introduced myeloscopy for visualization of the spinal cord, this concept representing early efforts at endoscopic spine surgery. Pool18 refined Burman' s work into the theory of intrathecal endoscopy, applying ureteroscopes in the spine. Classic illustrations rendered from this work showed pathology including arachnoiditis, tumor and disc herniation, and hypertrophied ligamentum flavum resulting in spinal stenosis.19 The introduction of aspiration biopsy in the spine is credited to Ottolenghi,23 although Craig5 is recognized for refining the technique for biopsy of the vertebral body through a uniportal posterolateral approach using uniquely designed instrumentation. The marriage of visualization with percutaneous access provided the theoretical basis for spinal endoscopy. Discography of both the cervical and lumbar spine advanced the information base for needle placement. Clinicians including Cloward,3 Collis et al,4 and Holt7 developed this theory based on the original work by Key and Ford.10 These needle approaches to the disc space were used therapeu-
From the Department of Orthopaedic Surgery, Medical College of Virginia, MidAtlantic Spine Specialists, Richmond, Virginia
NEUROSURGERY CLINICS OF NORTH AMERICA VOLUME 7 •NUMBER 1•JANUARY1996
59
60
MATHEWS
tically with the introduction of needle-guided chemonucleolysis by Lyman Smith. 21 With the 1970s came exponential progress in percutaneous techniques and instrumentation. Kambin and Gellman9 concomitant with Hijikata et al6 developed cannulae systems with dedicated instrumentation for single-portal access to the disc space. The basic technique of rigid discoscopy featured needle placement for orientation followed by alternating cannula visualization with manual disc removal in a safe triangular working zone defined by the area beneath the exiting root and lateral to the traversing root in the disc space. With modification of Hijikata' s instrumentation, the Balgrist Clinic's Schreiber and Leu 20 originated "percutaneous discoscopy," biportal access to a triangular working zone with simultaneous visualization and contralateral instrumented discectomy, a procedure that became more refined with perfection of variable angle lenses. Onik et al1 7 proceeded in 1985 to introduce an automated shaver into the procedural equation, the result being automated percutaneous discectomy. 17 By 1987, Mayer and Brock13 reported on a 40-patient randomized study that showed percutaneous endoscopic discectomy to be an equal and often superior option to microdiscectomy. The benchmark, microdiscectomy, had its first real competition and would never again return to its isolated acceptance. By the late 1980s, clinical applications for flexible fiberoptic technology attracted interest. Epiduroscopy was introduced by Stoll22 as an adjunct to open procedures for inspection of pathology and verification of surgical outcome. This technique was parlayed into a multicenter Food and Drug Administration Investigational Device Exemption (IDE) study of percutaneous epidural visualization. By 1991, the procedure's success in the absence of complications resulted in clinical approval that ignited the fires of interest and development in working channel endoscopy. At the same time, laser-assisted, nonvisualized percutaneous lumbar discectomy was in clinical trials by Choy et al 2working with various wavelengths, the most prevalent being the KTP 532-nm band. Mathews and Stoll pressed forward with the successful development of a flexible and steerable working channel spinal endoscope made possible by ongoing refinement of optics. Maxwell12 validated endoscopic theory and applications with a 1993 report of decreased
complications in endoscopy-assisted open microdiscectomy versus traditional microdiscectomy. As a progression of thought, Matthews investigated working channel endoscopy and transforaminal approaches to the disc space. This work resulted in the introduction of foraminal epidural working channel endoscopic surgery for access to far lateral herniations and lumbar disc sequestra. 11 MICRODISCECTOMY: THE BENCHMARK
When introduced, the advantages of microdiscectomy gained wide acceptance and set a standard to which minimally invasive spine surgery could be compared. By description, microsurgery is epidural exploration that allows for inspection of neuroanatomy and visualization of pathology by movement of nerves or other structures. The advantages of microdiscectomy include greater precision in the surgical field owing to less removal of bony and ligamentous structures with greater visualization through magnification and illumination, and a decrease in morbidity compared with classic laminectomy techniques. The early percutaneous procedures that addressed central and posterocentral pathology could not achieve the goals of microdiscectomy. Chemonucleolysis was nonselective, with morbidity that included anaphylaxis and disc space collapse. Percutaneous manual discectomy was also nonselective and featured visualization after the fact, not concurrent with surgical identification and dissection. Automated percutaneous discectomy was a nonspecific disc deflation procedure without reference to pathology in the absence of visualization. Laser discectomy also fell into the ranks of a nonspecific depressurization procedure where visualization was denied and laser effects in proximity to neurovascular structures caused concern. Thus, a review of the early minimally invasive procedures, both nucleotomy techniques and disc pressure reduction procedures, shows nonspecific intradiscal therapy with concurrent visualization of neuroanatomy being marginal or absent. THE CHALLENGE TO MICRODISCECTOMY
With spinal endoscopy, new terminology was introduced that implies visualization of
TRANSFORAMINAL ENDOSCOPIC MICRODISCECTOMY
anatomy and application of advanced mm1mally invasive techniques and instrumentation. The crucial elements for advanced techniques in spinal endoscopy are a thorough understanding of neuroanatomy and spatial orientation in the working space, because differential endoscopic lenses necessitate manipulation to obtain a clear, specific anatomic image. In addition, mastery of the procedure mandates dedication to an intensive learning curve. Epidural endoscopy made possible the inspection and exploration of the epidural space and access within the disc to address intradiscal pathology. With the patient awake, the posterolateral approach at 8 to 12 cm off the midline allowed for lateral docking. Emphasis was on avoidance of neuroanatomy, hence the requirement for an awake patient. Refinement of epidural endoscopy resulted in the technique of foraminal epidural endoscopic surgery (FEES), which allows access for visualization of anatomy and identification of neuropathology followed by documented surgical correction.
FORAMINAL EPIDURAL ENDOSCOPIC SURGERY
The foraminal approach is effective in the treatment of paramedian, foraminal, and extraforaminal herniations. It begins at 9 to 13 cm off the midline. Then, under visualization, there is flat entry under the pars and superior articulating facet and through the foramen with annular docking medially next to the traversing root. This access allows both epidural and intradiscal intervention in a safe neural triangular working zone. This zone is defined by the exiting root (nerve root that exits through the foramen at the level of the approach), the traversing root medially (root exiting the foramen at the level below the approach), and the disc. With foraminoscopy, there is direct, enhanced visualization and illumination of neurovascular structures as with microdiscectomy. Neuroanatomy is in clear view throughout the procedure, allowing greater insp ection than with microdiscectomy. Unlike microdiscectomy, w here nerve structures often must be moved for surgical access, foraminal epidural endoscopy allows for exploration and dissection under the neuroanatomy with little nerve root manipulation. Full visual ex-
61
ploration of both the foraminal and epidural space allows pathology to be addressed as it is encountered, making this approach one that is neither pathology dependent nor directed, as with most early percutaneous procedures. The design of the endoscope, with its optics and illumination, fosters access to free and sequestered disc fragments. The instrumentation for FEES features a 4.5 mm outer diameter 2.5 mm working channel endoscope with 30,000 pixel optical resolution for refined real-time visualization with a depth of field equaling 2 to 30 mm and a 70degree field of view. Work by Mirkovic et al1 5 has validated the size-dependent anatomy relative to the epidural safe zone, concluding that nothing greater than 4.5 mm can reach most areas for foraminoscopic inspection, dissection, and documentation. A host of manual epidural instruments facilitates surgical intervention in the patient w ho is placed prone on a radiolucent frame. Local and propofol (Diprivan) anesthesia allows an awake patient for surgeon-patient dialog during the procedure. A needle is placed on the skin surface at the surgical disc level for fluoroscopic verification prior to surgical entry. Accurate needle placement verified by AP and lateral fluoroscopic images precedes endoscopic intervention. For verification of pathology, discography may precede the foraminoscopic procedure. FEES is an approach and technique that is different from other percutaneou s disc procedures in that it is more aggressive, is anatomy directed and pathology targeted, and allows entry into the volar epidural space. It clearly challenges microdiscectomy in providing enhanced visu alization through optics and illumination, allowing for greater flexibility in the ability to explore anatomy and to target pathology and allowing for diminished morbidity, because there is absence of destabilizing incisional trauma. FEES provides a potential field of vision and surgical working zone that exceeds microdiscectomy, and the decreased surgical trauma coupled with intraoperative irrigation keeps bleeding to a minimum. Risk of infection, often related to the extent of surgical intervention and time at surgery, is reduced significantly in this brief, irrigated, incisionfree procedure. PATIENT SELECTION
John McCulloch, a staunch proponent of microdiscectomy has observed that, " the results
62
MATHEWS
of surgery are determined far more by patient selection than by surgical technique . . . the microscope will not perform the surgery and it will not secure a good result." 14 This also is true in FEES. Patient selection is critical to ensuring a surgical outcome that is acceptable to both patient and physician. Patients present with leg pain greater than back pain, most having undergone an average of 6 months of conservative care. MR imaging is the most specific cost-effective study to confirm disc pathology. The inclusion criterion for FEES is a virgin paramedian, foraminal or extraforaminal herniation that is contained or is noncontained at less than 50% of the canal diameter within the confines of the axilla and the pedicle in the absence of bulges or stenosis. The surgical contraindications include previous surgery, multilevel or pure central pathology, and sequestered pathology at the pedicular level as well as stenosis and morbid obesity. A chronic pain history or extended lost time under workers' compensation may influence a clinically satisfactory outcome negatively. Although not a contraindication, disc pathology at the LS/Sl level may prove inaccessible at surgery owing to the relative difficulty of the approach as well as steep iliac wing anatomy in some patients. With proper selection, patients do well based on preoperative education, outpatient surgery, and regular follow-up. Clinical experience demonstrates a predominance of patients back to work within 1 week of surgery.
SUMMARY
Hudgins, one of the pioneers in microdiscectomy, commenting in 1983 about that procedure, cited its safety because surgeons could see better. He also acknowledged the advantages of less incisional and anatomic structural morbidity, all factors that foster timely recovery and reduced expense. 8 McCulloch observed that the more limited the exposure of the dura and nerve roots, the less likely is the development of scar tissue, which he heralds as the "essence of microsurgery." 14 FEES, because of minimally invasive access with optimum visualization and illumination, rises to the challenges posed by microdiscectomy. It seems worthy of the identity, "microdiscectomy through a cannula." With FEES, dissection can venture into the canal and epi-
dural space (upstairs) or proceed intradiscally (downstairs) as pathology dictates. It is epidural surgery that introduces the concept of planned epidural dissection for intracanal pathology correction, which may or may not relate to the annulus and the posterior longitudinal ligament (PLL). FEES, as it has evolved, achieves the desired goals of minimally invasive spine surgery. There is less scarring and less instability both early and late. Clear visualization virtually eliminates the risk of surgical intervention at the wrong level and the likelihood of recurrence is reduced because of the intraoperative ability to verify correction of pathology. In addition, the surgical versatility of FEES for selected complex discal pathology has reduced the indications for open surgery. Spine surgery is now into its fourth generation, having entered a phase w here " less is more" -where advances in technology and surgical technique offer ever-expanding options by minimal access. It is through commitment to pure scientific investigational attitude that minimally invasive techniques, such as transforaminal endoscopic microdiscectomy, will be validated for efficacious, cost-effective surgical treatment of discal pathology.
References l. Burman MS: Myeloscopy or the direct visualization
of spinal cord. J Bone Joint Surg 13:395, 1931 2. Choy DS, Case RB, Fielding W, et al: Percutaneous laser nucleolysis of lumbar discs. N Engl J Med 317:771, 1987 3. Cloward RB: Anterior herniation of a ruptured lumbar intervertebral disc: Comments on the diagnostic value of the diskogram. Arch Surg 64:457, 1952 4. Collis JS, Gardner WJ: Lumbar discography: An analysis of 1000 cases. J Neurosurg 19:452, 1962 5. Craig FS: Vertebral body biopsy. J Bone Joint Surg Am 38:93, 1956 6. Hijikata S, YamagishiN,Nakayama T, et al: Percutaneous discectomy: A new treatment method for lumbar disc herniation. Journal of Toden Hospital 5:5, 1975 7. Holt EP Jr: The question of lumbar discography. J Bone Joint Surg 50:720, 1968 8. Hudgins WR: The role of rnicrodiscectomy. Orthop Clin North Am 14:589, 1983 9. Kambin P, Gellman H: Percutaneous lateral discectomy of the lumbar spine: A preliminary report. Clin Orthop 174:127, 1983 10. Key JA, Ford LT: Experimental intervertebral disc lesions. J Bone Joint Surg 30:621, 1948 11. Mathews HH: Foraminoscopic approach to lumbar disc sequestrum: A surgical technique for closed free fragment removal [abstract 17]. In Program and Ab-
TRANSFORAMINAL ENDOSCOPIC MICRODISCECTOMY
12. 13.
14. 15.
16.
stracts of the Seventh Annual International Intradiscal Therapy Society, Aberdeen, 1994 Maxwell KM: Spinal endoscopy: Clinical indications and outcomes. Presented at Current Concepts in Spinal Endoscopy, Williamsburg, August 27- 28, 1993 Mayer HM, Brock M: Percutaneous endoscopic discectomy: Surgical technique and preliminary results compared to microsurgical discectomy. J Neurosurg 78:216, 1993 McCulloch JA: Microdiscectomy. In Rothman RH, Simeone FA (eds): The Spine, ed 3. Philadelphia, WB Saunders, 1992, p 770 Mirkovic S, Schwartz DG, Glazer KG: Anatomic considerations in lumbar posterolateral percutaneous procedures [abstract 6]. In Programs and Abstracts of the 9th Annual Meeting, North American Spine Society, Minneapolis, MN, 1994 Mixter WJ, Barr JS: Rupture of intervertebral disc with involvement of spinal canal. N Engl J Med 211:201, 1934
63
17. Onik G, Maroon JC, Davis GW: Automated percutaneous discectomy: A prospective multi-institutional study. Neurosurgery 2:228, 1990 18. Pool JL: Myeloscopy: Diagnostic inspection of cauda equina by means of a myeloscope. Archives of Neurology and Psychiatry 39:1308, 1938 19. Pool JL: Myeloscopy: Intraspinal endoscopy. Surgery 11:169, 1942 20. Schreiber A, Leu HJ: Percutaneous nucleotomy: Technique with discoscopy. Orthopedics 14:439, 1991 21. Smith L: Enzyme dissolution of the nucleus pulposus in humans. JAMA 187:137, 1964 22. Stoll JE: Endoscopic spacial orientation and surgical approaches in the epidural space. Presented at Current Concepts in Spinal Endoscopy, Williamsburg, July 2324, 1993 23. Valls J, Ottolenghi CE, Schajowicz F: Aspiration biopsy in the diagnosis of lesions of vertebral bodies. JAMA 136:376, 1948 Address reprint requests to
Hallett H. Mathews, MD 7650 Parham Road, Suite 200 Richmond, VA 23294