British Journal of Neurosurgery
ISSN: 0268-8697 (Print) 1360-046X (Online) Journal homepage: http://www.tandfonline.com/loi/ibjn20
Minimally invasive lumbar disc surgery G. F. G. Findlay To cite this article: G. F. G. Findlay (1992) Minimally invasive lumbar disc surgery, British Journal of Neurosurgery, 6:5, 405-408, DOI: 10.3109/02688699208995028 To link to this article: http://dx.doi.org/10.3109/02688699208995028
Published online: 06 Jul 2009.
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Date: 17 March 2016, At: 02:37
British Journal of Neurosurgery (1 992) 6,405-408
EDITORIAL
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
Minimally invasive lumbar disc surgery
The current upsurge in interest in minimally invasive or percutaneous operations for the treatment of lumbar disc prolapse belies their long and gradual development over the last 50 years. All current percutaneous techniques utilize the posterolateral approach to the lumbar spine developed for the purposes of percutaneous spinal biopsy by Robertson & Ball in 1935l and then further popularized by Ottolenghi in 19552 and Craig in 1956.3 In 1951, Hult4 reported good relief of both low back pain and sciatica following simple fenestration of the anterolateral annulus by an open retroperitoneal approach. It was, however, Hijikata who first reported his technique of 'percutaneous nucleotomy' in 1975.5 Other workers were also active at that stage. Hoppenfield had commenced a similar approach in 1974 but did not publish his results until 1989.6 Kambin & Gellman combined conventional laminectomy with percutaneous dorsolateral discal decompression as early as 1973 and they subsequently published their results of true percutaneous discectomy in 1983' having commenced that technique in 1980. A similar technique had been pioneered in Zurich from 1975 with the results of the first 40 patients being published by Schreiber & Suezawa in 1986.8 In 1985, Onik and his co-workers9 published details of their automated nucleotome which minimized the diameter of the instruments used in the percutaneous procedure. Percutaneous disc surgery is therefore not new but currently is enjoying considerable promotion and technological refinement. All minimally invasive techniques have one factor in common. The need for a precise preoperative diagnosis of the exact type of disc
herniation is paramount. These techniques are only suitable for the true contained herniation, although both chymopapain and the newer endoscopic techniques may have some success in small extrusions which have not migrated away from the disc space itself. The techniques cannot be effective in the presence of significant extrusions, sequestrations or bony entrapment of the nerve root. Currently, for such conditions interlaminar surgery remains necessary and microdiscectomy represents the only minimally invasive technique available for the treatment of such lesions. When considering percutaneous disc surgery therefore it is essential that either MRI scanning or CT discography is performed to identify the presence of a contained herniation. Unfortunately, the majority of patients who present with sciatica do not have herniations suitable for percutaneous surgery. Leu (personal communication) found that only 18% of patients were suitable for endoscopic discectomy and Mayer & Brock'O suggest that the percentage of patients with sciatica who have a contained herniation is only between 10 and 15%. Chymopapain was in fact the first truly percutaneous technique to become established in the management of lumbar disc herniation. Introduced in 1964 by Lyman Smith," enzymatic dissolution of the nucleus has had a fluctuating course. Initial fears about sideeffects such as anaphylaxis and transverse myelitis, although genuine, were distinctly overplayed as the morbidity and mortality of the procedure have always been considerably smaller than that of surgery. With the development of preoperative skin testing and the adoption of local anaesthesia, the problem of
405
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
406
Editorial
anaphylaxis has largely been resolved and the technique is restablishing itself as a useful surgical procedure. Initial studies of the efficacy of chymopapain were considerably flawed, but there now exist several excellent studies which confirm a success rate of between 70 and 85%.12-” The major drawback to chymopapain, apart from the risks referred to already, remains the incidence of severe, though temporary, back pain following the procedure. It is disappointing that the recent Paris trialI8 of low dose (2000 units) therapy has shown no statistical evidence of reduction in the incidence of back pain. Around the world, several units have developed and continue to perfect percutaneous endoscopic techniques for the treatment of lumbar discal herniation. These techniques all consist of the insertion of ‘working cannulae’ with an external diameter of some 5-6 mm down to the annulus via a posterolateral approach. This allows the insertion through these cannulae of various ingenious instruments such as ordinary forceps, flexible forceps, back-biting rongeurs and rotatory cutters to facilitate disc removal. Most techniques utilize high pressure suction to aid disc removal and some involve the use of endoscopic monitoring of the progress of the procedure. Some techniques involve a bilateral approach to allow the insertion of these tools and the use of lasers to assist in disc ablation is being explored. These techniques are still at an early stage of development and the series so far published naturally represent a highly selected group of patients who are ideal candidates for such techniques. Most are performed under local anaesthesia but usually require hospitalization for 1 or 2 days. The results reported indicate a successful outcome in between 70 and 87% of ca~es.~~~O It J ~seems - * ~ clear that there is relatively little to choose between each technique and that the results depend primarily on two factors: first, the correct selection of patients; and secondly, on the accuracy of the intradiscal placement of the instrumentation which can often be difficult especially at
L5/S1. Shepperd et al.23 reported a success rate of only 41% when the instruments were placed within the centre of the nucleus but this rose to 81% when a more posterior nuclear placement was combined with back-biting forceps to remove as much as possible of the protruding disc material. These endoscopic techniques require great skill and patience with the shortest operating time being in the order of 50 min (Mayer, personal communication). However, the automated nucleotome reported by Onik et aL9 represents a much simpler technique, primarily due to the small size of the instrument. In a multicentre report, Onik et reported a 75% success rate which has been supported by several other studies of this technique which has been widely deployed, especially in the USA. However, as in all other percutaneous techniques with the exception of chymopapain, no statistically relevant controlled studies are available as yet to validate these reported success rates. Currently, a longterm randomized prospective study comparing automated nucleotomy with microdiscectomy is being conducted in Liverpool. One problem in the interpretation of the results of the preliminary reports of the various techniques of percutaneous disc surgery is the relative lack of information about the patients actually treated. Critics of these techniques often suggest that at least part of the success stems from the treatment of patients at an early stage of their history of radicular pain when many could be expected still to recover spontaneously. Most studies state that the patients included have failed conservative therapy prior to the procedure but relatively few give further details and there certainly have been no trials comparing any of these techniques against continued conservative therapy. However, the average length of conservative therapy prior to endoscopic discectomy reported by Kambin & Schaffer2’ was 803 days. Whether this represented continual radicular pain for that time or a recurring history was not clear. A further problem in interpreting the place of these techniques is the virtual absence of data concerning recurrence rates. As the ma-
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
Editorial jority of the published work is relatively recent, this is perhaps understandable. However, the fact that most of these procedures (especially automated nucleotomy) remove relatively small volumes of disc material makes late recurrence a real concern. Only the most recent techniques involving endoscopy, complex instrumentation and lasers remove amounts of disc comparable to that removed by most microdiscectomists. Although there remain questions to be answered, the current evidence suggests that with the most careful patient selection and surgical technique, satisfactory success rates can be achieved. There are many obvious advantages to these procedures. The ability to cure patients by a percutaneous operation which does not traverse the spinal canal, which can be performed under local anaesthesia and requires either day-case or minimal hospitalization is an attractive goal. In successful cases, relief of radicular pain is rapid in most (87%of the successful cases reported by Kambin & Schaffer2' were free of pain by 1 week). Figures for speed of return to work are also impressive. Shepperd et al.23reported that 47% of those who returned to work were able to do so within 2 weeks and, by 3 weeks, this figure had risen to 77% in the series of Davis & Onik.25 Nevertheless, despite these striking and enticing achievements, there has to remain a question mark over these procedures. Is it appropriate to invest at this stage in the time, instrumentation and surgical skills which these techniques undoubtedly require when perhaps only less than 15%of patients with sciatica are suitable for percutaneous disc surgery? Percutaneous and minimally invasive disc surgery requires a high level of skill and interest and it is perhaps inevitable that the standards of success reported in these early papers may not be replicated when used in less enthusiastic hands.
Walton
407
References
1 Robertson RC, Ball RP. Destructive spine lesions. Diagnosis by needle biopsy. J Bone Jt Surg 1935; 17~749-58. 2 Ottolenghi CE. Diagnosis of orthopedic lesions by aspiration biopsy: results of 1061 punctures. J Bone Jt Sure 1955: 37A.443-64. 3 Crayg FS. Vertebral body biopsy. J Bone Jt Surg 1956; 38A:93-102. 4 Hult L. Retroperitoneal disc fenestration in low back pain and sciatica. Acta Orthop Scand 1956; 20:342. 5 Hijikata S, Yamagishi M, Nakayama T, Oomori K. Percutaneous nucleotomy: a new treatment method for lumbar disc herniation. J Toden Hosp 1975; 539. 6 Hoppenfield S. Percutaneous removal of herniated lumbar discs. Clin Orthop Re1 Res 1989; 238:92-7. 7 Kambin P, Gellman H. Percutaneous lateral discectomy of the lumbar spine-a preliminary report. Clin Orthop Re1 Res 1983; 174:127-32. 8 Schreiber A, Suezawa Y. Transdiscoscopic percutaneous nucleotomy in disk herniation. Orth Rev 1986; 15:75-8. 9 Onik G, Helms CA, Ginsberg L, Hoaglund FT, Morris J. Percutaneous lumbar diskectomy using a new aspiration probe. AJNR 1985; 6290-3. 0 Mayer HM, Brock M. Percutaneous disc surgery. In: Findlay G, Owen R, eds. A textbook of spinal surgery. Oxford: Blackwells, 1992709-18. 1 Smith L. Enzyme dissolution of the nucleus pulposus in humans. JAMA 1964; 187:137-40. 2 McCulloch JA. Chemonucleolysis. J Bone Jt Surg 1977; 598~45-52. 3 Benoist M, Bouillet R, Mulholland R. Chemonucleolysis: results of a European survey. Acta Orthop Belg 1983; 49:32-47. 4 Javid MJ, Nordby EJ, Ford L T et al. Safety and efficacy of Chymopapain(Chymodiactin) in herniated nucleus pulposus with sciatica: results of a randomized double-blind study. JAMA 1983; 2499489-94. 5 Fraser RD. Chymopapain for the treatment of intervertebral disc herniation: the final report of a doubleblind study. Spine 1984; 9:815-18. 6 McDermott DJ, Agre K, Brim M et al. Chymodiactin in patients with herniated lumbar intervertebral disc(s): an open-label, multicenter study. Spine 1985; 10242-9. 7 Grindulis KA, Finlay DB, Nichol FE. Chemonucleolysis of lumbar intervertebral disc prolapse with chymopapain: outcome after 1 year. Clin Rheumatol 1987; 6:42-9. 18 Benoist M, Bonneville J-F. A randomized double-blind study to compare low dose (ZOO0 units) to standard dose (4000 units) Chymopapain in the management of herniated lumbar intervertebral discs. Presented at the 2nd Annual Meeting of the European Spine Society, Rome, 1991. G. F. G. FINDLAY19 Kambin P, Sampson S. Posterolateral percutaneous suction-excision of herniated lumbar intervertebral Centre for Neurology and discs: report of interim results. Clin Orthop 1986; 207:37. Neurosurgely, Walton Hospital, 20 Hijikata S. Percutaneous nucleotomy: a new concept technique and 12 years' experience. Clin Orthop Re1 Rice Lane, Res 1989; 238:9-23. Livevool L9 IAE, UK. 21 Kambin P, Schaffer JL. Percutaneous lumbar discec-
408
Editorial
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
tomy: review of 100 patients and current practice. Clin Orthop Re1 Res 1989; 238:24-34. 22 Schreiber A, Suezawa Y, Leu H. Does percutaneous nucleotomy with discoscopy replace conventional discectomy? Eight years of experience and results in treatment of herniated lumbar disc. Clin Orthop 1989; 238:35-42. 23 Shepperd JA, James SE, Leach AB. Percutaneous disc surgery. Clin Orthop 1989; 238:43-9.
24 Onik G, Mooney V, Maroon JC et al. Automated percutaneous discectomy: a prospective multiinstitutional study. Neurosurgery 1990; 26:228-33. 25 Davis GW, Onik G. Clinical experience with automated percutaneous lumbar discectomy. Clin Orthop 1989; 238:98-103.
ISSN: 0268-8697 (Print) 1360-046X (Online) Journal homepage: http://www.tandfonline.com/loi/ibjn20
Minimally invasive lumbar disc surgery G. F. G. Findlay To cite this article: G. F. G. Findlay (1992) Minimally invasive lumbar disc surgery, British Journal of Neurosurgery, 6:5, 405-408, DOI: 10.3109/02688699208995028 To link to this article: http://dx.doi.org/10.3109/02688699208995028
Published online: 06 Jul 2009.
Submit your article to this journal
Article views: 5
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ibjn20 Download by: [Ams/Girona*barri Lib]
Date: 17 March 2016, At: 02:37
British Journal of Neurosurgery (1 992) 6,405-408
EDITORIAL
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
Minimally invasive lumbar disc surgery
The current upsurge in interest in minimally invasive or percutaneous operations for the treatment of lumbar disc prolapse belies their long and gradual development over the last 50 years. All current percutaneous techniques utilize the posterolateral approach to the lumbar spine developed for the purposes of percutaneous spinal biopsy by Robertson & Ball in 1935l and then further popularized by Ottolenghi in 19552 and Craig in 1956.3 In 1951, Hult4 reported good relief of both low back pain and sciatica following simple fenestration of the anterolateral annulus by an open retroperitoneal approach. It was, however, Hijikata who first reported his technique of 'percutaneous nucleotomy' in 1975.5 Other workers were also active at that stage. Hoppenfield had commenced a similar approach in 1974 but did not publish his results until 1989.6 Kambin & Gellman combined conventional laminectomy with percutaneous dorsolateral discal decompression as early as 1973 and they subsequently published their results of true percutaneous discectomy in 1983' having commenced that technique in 1980. A similar technique had been pioneered in Zurich from 1975 with the results of the first 40 patients being published by Schreiber & Suezawa in 1986.8 In 1985, Onik and his co-workers9 published details of their automated nucleotome which minimized the diameter of the instruments used in the percutaneous procedure. Percutaneous disc surgery is therefore not new but currently is enjoying considerable promotion and technological refinement. All minimally invasive techniques have one factor in common. The need for a precise preoperative diagnosis of the exact type of disc
herniation is paramount. These techniques are only suitable for the true contained herniation, although both chymopapain and the newer endoscopic techniques may have some success in small extrusions which have not migrated away from the disc space itself. The techniques cannot be effective in the presence of significant extrusions, sequestrations or bony entrapment of the nerve root. Currently, for such conditions interlaminar surgery remains necessary and microdiscectomy represents the only minimally invasive technique available for the treatment of such lesions. When considering percutaneous disc surgery therefore it is essential that either MRI scanning or CT discography is performed to identify the presence of a contained herniation. Unfortunately, the majority of patients who present with sciatica do not have herniations suitable for percutaneous surgery. Leu (personal communication) found that only 18% of patients were suitable for endoscopic discectomy and Mayer & Brock'O suggest that the percentage of patients with sciatica who have a contained herniation is only between 10 and 15%. Chymopapain was in fact the first truly percutaneous technique to become established in the management of lumbar disc herniation. Introduced in 1964 by Lyman Smith," enzymatic dissolution of the nucleus has had a fluctuating course. Initial fears about sideeffects such as anaphylaxis and transverse myelitis, although genuine, were distinctly overplayed as the morbidity and mortality of the procedure have always been considerably smaller than that of surgery. With the development of preoperative skin testing and the adoption of local anaesthesia, the problem of
405
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
406
Editorial
anaphylaxis has largely been resolved and the technique is restablishing itself as a useful surgical procedure. Initial studies of the efficacy of chymopapain were considerably flawed, but there now exist several excellent studies which confirm a success rate of between 70 and 85%.12-” The major drawback to chymopapain, apart from the risks referred to already, remains the incidence of severe, though temporary, back pain following the procedure. It is disappointing that the recent Paris trialI8 of low dose (2000 units) therapy has shown no statistical evidence of reduction in the incidence of back pain. Around the world, several units have developed and continue to perfect percutaneous endoscopic techniques for the treatment of lumbar discal herniation. These techniques all consist of the insertion of ‘working cannulae’ with an external diameter of some 5-6 mm down to the annulus via a posterolateral approach. This allows the insertion through these cannulae of various ingenious instruments such as ordinary forceps, flexible forceps, back-biting rongeurs and rotatory cutters to facilitate disc removal. Most techniques utilize high pressure suction to aid disc removal and some involve the use of endoscopic monitoring of the progress of the procedure. Some techniques involve a bilateral approach to allow the insertion of these tools and the use of lasers to assist in disc ablation is being explored. These techniques are still at an early stage of development and the series so far published naturally represent a highly selected group of patients who are ideal candidates for such techniques. Most are performed under local anaesthesia but usually require hospitalization for 1 or 2 days. The results reported indicate a successful outcome in between 70 and 87% of ca~es.~~~O It J ~seems - * ~ clear that there is relatively little to choose between each technique and that the results depend primarily on two factors: first, the correct selection of patients; and secondly, on the accuracy of the intradiscal placement of the instrumentation which can often be difficult especially at
L5/S1. Shepperd et al.23 reported a success rate of only 41% when the instruments were placed within the centre of the nucleus but this rose to 81% when a more posterior nuclear placement was combined with back-biting forceps to remove as much as possible of the protruding disc material. These endoscopic techniques require great skill and patience with the shortest operating time being in the order of 50 min (Mayer, personal communication). However, the automated nucleotome reported by Onik et aL9 represents a much simpler technique, primarily due to the small size of the instrument. In a multicentre report, Onik et reported a 75% success rate which has been supported by several other studies of this technique which has been widely deployed, especially in the USA. However, as in all other percutaneous techniques with the exception of chymopapain, no statistically relevant controlled studies are available as yet to validate these reported success rates. Currently, a longterm randomized prospective study comparing automated nucleotomy with microdiscectomy is being conducted in Liverpool. One problem in the interpretation of the results of the preliminary reports of the various techniques of percutaneous disc surgery is the relative lack of information about the patients actually treated. Critics of these techniques often suggest that at least part of the success stems from the treatment of patients at an early stage of their history of radicular pain when many could be expected still to recover spontaneously. Most studies state that the patients included have failed conservative therapy prior to the procedure but relatively few give further details and there certainly have been no trials comparing any of these techniques against continued conservative therapy. However, the average length of conservative therapy prior to endoscopic discectomy reported by Kambin & Schaffer2’ was 803 days. Whether this represented continual radicular pain for that time or a recurring history was not clear. A further problem in interpreting the place of these techniques is the virtual absence of data concerning recurrence rates. As the ma-
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
Editorial jority of the published work is relatively recent, this is perhaps understandable. However, the fact that most of these procedures (especially automated nucleotomy) remove relatively small volumes of disc material makes late recurrence a real concern. Only the most recent techniques involving endoscopy, complex instrumentation and lasers remove amounts of disc comparable to that removed by most microdiscectomists. Although there remain questions to be answered, the current evidence suggests that with the most careful patient selection and surgical technique, satisfactory success rates can be achieved. There are many obvious advantages to these procedures. The ability to cure patients by a percutaneous operation which does not traverse the spinal canal, which can be performed under local anaesthesia and requires either day-case or minimal hospitalization is an attractive goal. In successful cases, relief of radicular pain is rapid in most (87%of the successful cases reported by Kambin & Schaffer2' were free of pain by 1 week). Figures for speed of return to work are also impressive. Shepperd et al.23reported that 47% of those who returned to work were able to do so within 2 weeks and, by 3 weeks, this figure had risen to 77% in the series of Davis & Onik.25 Nevertheless, despite these striking and enticing achievements, there has to remain a question mark over these procedures. Is it appropriate to invest at this stage in the time, instrumentation and surgical skills which these techniques undoubtedly require when perhaps only less than 15%of patients with sciatica are suitable for percutaneous disc surgery? Percutaneous and minimally invasive disc surgery requires a high level of skill and interest and it is perhaps inevitable that the standards of success reported in these early papers may not be replicated when used in less enthusiastic hands.
Walton
407
References
1 Robertson RC, Ball RP. Destructive spine lesions. Diagnosis by needle biopsy. J Bone Jt Surg 1935; 17~749-58. 2 Ottolenghi CE. Diagnosis of orthopedic lesions by aspiration biopsy: results of 1061 punctures. J Bone Jt Sure 1955: 37A.443-64. 3 Crayg FS. Vertebral body biopsy. J Bone Jt Surg 1956; 38A:93-102. 4 Hult L. Retroperitoneal disc fenestration in low back pain and sciatica. Acta Orthop Scand 1956; 20:342. 5 Hijikata S, Yamagishi M, Nakayama T, Oomori K. Percutaneous nucleotomy: a new treatment method for lumbar disc herniation. J Toden Hosp 1975; 539. 6 Hoppenfield S. Percutaneous removal of herniated lumbar discs. Clin Orthop Re1 Res 1989; 238:92-7. 7 Kambin P, Gellman H. Percutaneous lateral discectomy of the lumbar spine-a preliminary report. Clin Orthop Re1 Res 1983; 174:127-32. 8 Schreiber A, Suezawa Y. Transdiscoscopic percutaneous nucleotomy in disk herniation. Orth Rev 1986; 15:75-8. 9 Onik G, Helms CA, Ginsberg L, Hoaglund FT, Morris J. Percutaneous lumbar diskectomy using a new aspiration probe. AJNR 1985; 6290-3. 0 Mayer HM, Brock M. Percutaneous disc surgery. In: Findlay G, Owen R, eds. A textbook of spinal surgery. Oxford: Blackwells, 1992709-18. 1 Smith L. Enzyme dissolution of the nucleus pulposus in humans. JAMA 1964; 187:137-40. 2 McCulloch JA. Chemonucleolysis. J Bone Jt Surg 1977; 598~45-52. 3 Benoist M, Bouillet R, Mulholland R. Chemonucleolysis: results of a European survey. Acta Orthop Belg 1983; 49:32-47. 4 Javid MJ, Nordby EJ, Ford L T et al. Safety and efficacy of Chymopapain(Chymodiactin) in herniated nucleus pulposus with sciatica: results of a randomized double-blind study. JAMA 1983; 2499489-94. 5 Fraser RD. Chymopapain for the treatment of intervertebral disc herniation: the final report of a doubleblind study. Spine 1984; 9:815-18. 6 McDermott DJ, Agre K, Brim M et al. Chymodiactin in patients with herniated lumbar intervertebral disc(s): an open-label, multicenter study. Spine 1985; 10242-9. 7 Grindulis KA, Finlay DB, Nichol FE. Chemonucleolysis of lumbar intervertebral disc prolapse with chymopapain: outcome after 1 year. Clin Rheumatol 1987; 6:42-9. 18 Benoist M, Bonneville J-F. A randomized double-blind study to compare low dose (ZOO0 units) to standard dose (4000 units) Chymopapain in the management of herniated lumbar intervertebral discs. Presented at the 2nd Annual Meeting of the European Spine Society, Rome, 1991. G. F. G. FINDLAY19 Kambin P, Sampson S. Posterolateral percutaneous suction-excision of herniated lumbar intervertebral Centre for Neurology and discs: report of interim results. Clin Orthop 1986; 207:37. Neurosurgely, Walton Hospital, 20 Hijikata S. Percutaneous nucleotomy: a new concept technique and 12 years' experience. Clin Orthop Re1 Rice Lane, Res 1989; 238:9-23. Livevool L9 IAE, UK. 21 Kambin P, Schaffer JL. Percutaneous lumbar discec-
408
Editorial
Downloaded by [Ams/Girona*barri Lib] at 02:37 17 March 2016
tomy: review of 100 patients and current practice. Clin Orthop Re1 Res 1989; 238:24-34. 22 Schreiber A, Suezawa Y, Leu H. Does percutaneous nucleotomy with discoscopy replace conventional discectomy? Eight years of experience and results in treatment of herniated lumbar disc. Clin Orthop 1989; 238:35-42. 23 Shepperd JA, James SE, Leach AB. Percutaneous disc surgery. Clin Orthop 1989; 238:43-9.
24 Onik G, Mooney V, Maroon JC et al. Automated percutaneous discectomy: a prospective multiinstitutional study. Neurosurgery 1990; 26:228-33. 25 Davis GW, Onik G. Clinical experience with automated percutaneous lumbar discectomy. Clin Orthop 1989; 238:98-103.
