Gary Onik and Wendell A. Gibby
It is approaching 20 years since we published the initial article introducing automated percutaneous lumbar discectomy (APLD).1 At that time, there was tremendous resistance to the concept of a minimally invasive treatment for herniated lumbar discs. Chemonucleolysis had rushed onto the scene with great fanfare, only to be destroyed by the occurrence of devastating complications, such as transverse myelitis. At that time there was essentially no field of minimally invasive lumbar spine surgery.
The concept of minimally invasive lumbar spine surgery, exemplified by APLD, has stood the test of time. Based on the massive amount of data accumulated on APLD, percutaneous discectomy gained its own CPT code, emerging from the twilight zone of experimental procedures. Those most opposed to the concept of minimally invasive spine surgery, the neurosurgical community, have acknowledged its impact on the treatment of patients with herniated discs.2
Although perhaps not reaching its full potential in the volume of cases performed, APLD has had a significant impact on the evolution of disc therapy; it has been extremely successful in achieving its major goal, that of safety. The original intent of APLD was to have a highly safe, minimally invasive treatment for lumbar disc herniations, with a reasonable success rate. At least 170,000 APLD procedures (probably more, since outside the United States the disposable instrument has been routinely resterilized) have been performed with a mortality rate of zero: there has never been a report of death associated with the procedure. In over 50 published series, there has been no instance of permanent nerve injury or great vessel damage, the only reported complication being discitis at a rate of 0.2%, equivalent to that of discog-raphy.3,4 It can now be said unequivocally that APLD is the safest treatment available for herniated lumbar discs. Contrast this with open discectomy, or even microdiscectomy, as reported by Ramirez and
Thisted,5 who examined the complication rate associated with 28,000 open discectomies. In this study, there was a major complication in 1 of 64 patients, with a major neurological complication associated in 1 of 334 patients; amazingly, 1 of 1700 patients died from the procedure. Another prospective study reported by Stolke et al.6 examined the intraoperative complication rate associated with lumbar discectomies carried out by experienced neurosurgeons. In 481 procedures, a complication rate of 14% was reported, including one death, three nerve injuries, and a discitis rate of approximately 1%.
The use of the operating microscope and the decreased size of the resultant incision, constituting the so-called microdiscectomy, has not appreciably decreased the complication rate associated with lumbar spine surgery as indicated by the article published by Pappas et al.7 In 654 microdiscectomies, they reported two major vascular injuries, one of which resulted in death. A major bowel injury was also reported. It was basically in response to this situation of high-morbidity lumbar disc surgery that APLD was successfully developed.
Theoretically, APLD works by centrally decompressing the nucleus pulposus, with that decreased pressure transmitted through the rent in the annulus to the herniation. This results in decreased pressure on the affected nerve. The success rate of any percutaneous procedure based on the concept of central disc decompression is, therefore, highly dependent on selecting patients with pathology that is amenable to such an approach. The success rate of APLD has been reported anywhere from 43 to 85% depending on patient selection criteria. The major limitation, however, is that when only the strictest selection criteria are used, approximately 10% of the herniated disc population would be candidates for the procedure, which would still constitute approximately 40,000 cases a year.
It is the balancing of the very low morbidity associated with APLD that makes it competitive, in certain patient populations, with open discectomy, which reports higher success rates of over 90%. It is of interest, however, that when microdiscectomy is examined in a prospective fashion with the criterion of patient satisfaction included, the success rate falls to approximately 75%, very similar to the percutaneous methods.8
Other percutaneous disc removal methods are available, including laser disc decompression, biportal percutaneous disc decompression in which a scope is used to examine the disc during removal, and the so-called arthroscopic microdiscectomy by Kambin. Common to all methods is the problem of patient selection already alluded to, since none has been shown to consistently remove free fragments. Most important, however, these methods have all been associated with significantly greater morbidity than APLD. For example, laser discectomy has been reported to cause osteonecrosis of the vertebral body endplates due to adjacent heating.9 For radiologists considering entering this field, we suggest getting experience with APLD before considering the other variations of percutaneous disc decompression that are associated with a higher inherent morbidity.
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