o 148·396X/ 85/ 1602·014 1$02.00/ 0
`NEUROSCRGERY
`Copyright ~ 1985 by the Co ngress of Neurological Surgeons
`
`Vol. 16. No.2. 1985
`Printed in U.S.A.
`
`Percutaneous Discectomy: An Anatomical Study
`
`Steven L. Kanter, M.D., and William A. Friedman, M .D.
`
`Depal'lmenl a/Nellrological SlIrgery. Unill('/'sily a/Florida. Gainewille. Flaricia
`
`Percutaneous discectomy is a viable alternative in the treatment of herniated intervertebral discs of the lumbar spine.
`Anatomical analysis of the retroperitoneal surgical path utilizing computed tomograph y suggests that the risk of vascular
`injury is negl igible at the L-4. L-5 level, but substantial at the L-5 , S-I level. In addition , one-third of patients otherwise
`suitable for percutaneous discectomy have segments of bowel obstructing the surgical path. Obtaining an abdominal
`computed tomographic scan with the patient in the surgical position seems to be a valuable screening technique in the
`evaluation of candidates for this procedure. (Neurosurgery 16: 141 - 147, 1985)
`
`Key words: Back pain, Computed tomography, Intervertebral disc displacement, Lumbar disc surgery, Percutaneous
`discectom y, Retroperitoneal anatom y
`
`(\J ,
`
`I . Drawing of a cross sectio n of the abdo men at the level of
`FIG.
`the L·4. L·S interspace with a 40 French chest tu be inserted just
`above the iliac crest and positioned at the lateral aspect of the di sc
`space. Note the specially lengthened rongeur positioned to remove
`disc material in piecemea l fashion. The sympto matic side is down
`a nd th e surgical approach is th ro ugh th e asy mptomat ic side. This is
`necessitated by the a ngle of the surgical instruments. (Fro m Friedma n
`WA : Percuta neo us discectom y: An alternati ve to chemo nucleolysis?
`Ne urosurge ry 13:542- 547, 1983.)
`
`INTRODU CTION
`
`Recentl y, less invasive altern ati ves for the treatment of
`herni ated intervenebra l di scs of the lumbar spine have been
`widely publicized. The m ost well-known of these approaches
`is the intradiscal injection of a chemonucleolytic agent. At
`the U ni ve rsity of Florida. another procedure has been used
`on selected patients for the treatm ent of lumbar herniated
`
`discs. This procedure, called percutaneous di scectomy (PO),
`involves an approach to the L-4, L-5 herni ated nucleus pul(cid:173)
`posus via a 40 French chest tube inserted through the patient's
`side just above the iliac crest (Fig. I). The tube is passed
`through the retroperitoneal soft tissues and the psoas muscle
`and is carefull y positioned with flu oroscopi c guidance at the
`lateral border of the intervertebral di sc. Specially lengthened
`in struments are then inserted through the chest tube to re-
`
`141
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`NUVASIVE 1037
`NuVasive, Inc. v. Warsaw Orthopedic, Inc.
`IPR2013-00206
`IPR2013-00208
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`142
`
`KANTER AND FRIEDMAN
`
`A'eliroslirger.l', Vol. 16. NO.2
`
`FIG. 2. Abdominal CT scan, immediately above the level of Ihe iliac crest passing near the L-4, L-S interspace, obtained with the patient in
`the supine positio n. The aorta and inferior vena cava (arr()lrheads) a re ventral to the vertebral body. They present no obstruction to a lateral
`approach 10 the di sc space through the psoas muscle (11'ide arrows). The aorta. as in this case, is frequently calcified .
`
`move the disc in pi ecemeal fashion . The total surgical time is
`approximately I S minutes. At the writing of this paper. 15
`patients have undergo ne this procedure at the University of
`Florida. The details of the operative technique as well as
`selection of patients and postoperative results have been dis(cid:173)
`cussed by Friedman (J). The potential disadvantages of PD
`involve th e possibility of damage to structures located in the
`retroperitoneal surgical path. Catastrophic complications
`could result from damage to the major vessels (aorta, inferior
`vena cava. iliac vessels) or the bowel. This study was under(cid:173)
`taken to assess the potential incidence of these problems.
`
`MATERIALS AND METHODS
`
`Thirty-five abdominal computed tomographic (CT) scans
`at the leve l of the lumbar spine were analyzed. Twenty-five
`CT scans of supine patients with abdominal complaints were
`obtained using a Phillips Tomoscan 310 body scanner (Phil(cid:173)
`lips Medical Systems. Inc., Shelton. Connecticut). All were
`officially interpreted as normal by a stafT radiologist. Care was
`taken to exclude abdominal CT scans of patients who were
`under 18 years old or that revealed evidence of previous
`abdominal operation. The slice selected for analysis was at or
`immediatel y adjacent to the iliac crest. thus passing near the
`L-4. L-S interspace (Fig. 2).
`Five scans were obtained as above, but the slice selected for
`a nalysis was approx imatel y at the level of the L-S. S- J inter(cid:173)
`space (Fig. 3). Five scans were of patients who were selected
`
`for PD according to criteria previously described (I). After
`the oral administration of meglumine diatrizoate (Gastrograf(cid:173)
`fin ; E. R. Squibb & Sons, Princeton, New Jersey), these
`abdominal CT scans were obtained with the patient in the
`surgical position (i.e., in the lateral decubitus position). The
`slice selected for analysis was at the level of the L-4, L-5
`intervertebral disc (Fig. 4).
`All 35 scans were subjected to the following anatomical
`analysis. The midpoint of the intervertebral disc or vertebral
`body was approximated and used as the anatomical reference
`point (M). A straight line (H) was drawn through Point M
`dividing the slice into anterior and posterior segments. Next,
`a series of lines was drawn through Point M and tangent to
`the dorsal and ventral margins of each of the following
`abdominal structures: right psoas muscle, right vascular com(cid:173)
`plex, left vascular complex, left psoas muscle. The right vas(cid:173)
`cular complex consisted of either the inferior vena cava (at L-
`4. L-S) or the right common iliac vessels (at L-S , S- J) depend(cid:173)
`ing on the level of the CT slice. The left vascular complex
`consisted of either the aorta or the left common iliac vessels.
`The angle that each line made with Line H was recorded.
`Subsequently, the span (number of degrees between the lines
`tangent to the dorsal and ventral borders) of each structure
`(RPS, R YS. L YS, LPS) relati ve to the midpoint of the disc
`was calculated, and the overlap of muscular and vascular
`structures (RPYD, LPYD) was determined (Fig. 5 and Table
`I).
`In addition to the 3S scans studied as above, 8 abdominal
`CT scans obtained from prospective surgical candidates in
`
` 2
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`

`February 1985
`
`PERCUTANEOUS DISCECTOMY
`
`143
`
`FIG. 3. Abdominal CT scan . approximately at the level of the LS. S- I interspace, obtained with the patient in the supine positio n. The iliac
`vessels (arrowheads). partiall y calcified. co urse along the media l aspect of the psoas muscles (wide arrows) and present an obstruction to a lateral
`approach to the disc space.
`
`the surgical position were analyzed to define the relation of
`the bowel to the path of the size 40 French chest tube (Fig.
`1). This was accomplished by drawing a line through Point
`M and tangent to the dorsal border of the most dorsally
`located segment of bowel. The angle that this line made with
`Line H was recorded .
`
`RESULTS
`
`The data gathered from the 25 abdominal CT scans ob(cid:173)
`tained near the LA, L-5 level with the patient in the supine
`position (supine crest position) are presented in Figure 6. The
`right and left psoas spans were relatively constant among the
`25 patients: mean spans were 60° on the right and 62° on the
`left. Although little overlap between the right psoas muscle
`and the right vascular complex was found , these structures
`were closely apposed. No overlap was noted between the left
`psoas muscle and the left vascular complex. The mean differ(cid:173)
`ence between the ventral border of the right psoas muscle and
`the dorsal border of the right vascular complex was I., whereas
`the comparable value on the left side was 18°.
`The data gathered from the five abdominal CT scans ob(cid:173)
`tained at the L-5, S-1 level with the patient in the supine
`position are presented in Figure 7. The right and left psoas
`spans were relatively constant among the patients: mean spans
`were 4 r on the right and 51° on the left. Considerable overlap
`between the right psoas muscle and the right vascular complex
`was noted on every scan. Considerable overlap was also noted
`between the left muscular and vascular structures.
`
`FIG. 4. Abdominal CT scan. at the level of the L-4. L-S interspace.
`obtained aft er the oral administration of contrast medium with the
`patient in th e surgical position for a right-sided approach to th e
`intervertebral disc. Neither th e major vessels (arrOll"ileads) nor seg(cid:173)
`ments of bowel present a n obstructi on to the retroperitoneal surgical
`path o n the right side. The psoas muscles are indicated by the WTO\\ ·S .
`
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`

`144
`
`KANTER AND FRIEDMAN
`
`Neurosurgery. Vol. / 6. /'/0. 2
`
`RVD
`
`RPV
`
`H
`
`RPD
`
`LPV
`
`LPD
`
`FIG. 5. Grid used for anatomical analysis superimposed on a drawing of a cross section of the abdomen at the level of the L-4. L-5
`intervertebra l space. The psoas muscles may be see n on either side of the vertebral body. The major vessels are immediately ventral to the
`vertebral bod y. Im portant anatomical landmarks are identified with the appropriate abbreviations (see Table I).
`
`TABLE I
`Ahhrel·ialio//.I Used in AnulOl1Iical A nal,l'I'isfilf PD"
`Descriptive Name
`Abbreviation
`- - - - - - - -
`Midpoint of vertebral body
`M
`Horizontal (line passing through point in the
`H
`coronal plane)
`Right psoas dorsal
`Right psoas ventral
`Right vascular dorsal
`Right vascu lar ventral
`Left vascular ventral
`Left vascu lar dorsal
`Left psoas ventral
`Left psoas dorsal
`Right psoas span
`Right vascul ar span
`Left vascu lar span
`Vascular span
`Left psoas span
`Right psoas-vascul ar difference
`Left psoas-vascular difference
`Right colon dorsal
`Left colon dorsal
`
`RPD
`RPV
`RVD
`RVV
`LVV
`LVD
`LPV
`LPD
`RPS
`RVS
`LVS
`VS
`LPS
`RPVD
`LPVD
`RCD
`LCD
`"See Figure 5.
`
`The data gat hered from the five abdo minal CT sca ns ob(cid:173)
`tai ned at th e level of the L-4. L-S intervertebral disc in th e
`surgical (lateral decubitus) position are presented in Figure 8.
`The mu sc ular-vasc ular relationships illustrated in these graphs
`are similar to th ose desc ribed above for the 25 scans near the
`
`If)
`w
`w
`n::
`<.::J
`w
`0
`
`300
`
`200
`
`100
`
`0
`
`- 100
`
`LPD
`
`LPV
`LVD
`
`5
`
`10
`
`I I I I I I I I I
`20
`25
`
`15
`
`PATIEN T NUMBER
`
`FIG. 6. Graphic relationship of retroperitoneal muscular and vas(cid:173)
`cular structures near the level of the L-4. L·5 interspace with the
`patient in the supine position. The psoas span is shaded. Little or no
`overlap is present between the psoas muscle and the dorsal borders
`of the vascular structures (RVD. LVD) on either side. (See Table I
`for definition of labels.)
`
`L-4. L-S level in the supine position . An important feature of
`the scans obtained in the surgical position is the relationship
`of the bowel to the path of the 40 French chest tube. It is
`inconsequential to analyze the presence and relative location
`of bowel in the supine scans because the bowel may shift
`position when the patient is placed in the surgical position. It
`is of the utm ost utility to perform this analysis on scans
`obtained in the surgical (lateral decubitus) position because
`
` 4
`
`

`

`Februwy 1985
`
`200
`
`100
`
`0
`
`(j) w
`w
`a::
`<.:l w
`
`0
`
`RP V
`
`7
`
`RVD
`RPD
`
`- 10 0~--.-----~----~----~----~
`2
`3
`5
`4
`
`PAT IENT NUMBER
`
`FIG, 7, Graphic relationshi p of retroperitoneal muscular and vas(cid:173)
`cular structu res near the level of the L-S. S-l interspace with the
`patient in the supine positi on. The psoas span is shaded. Considerable
`overlap is prese nt betwee n the psoas muscle and the dorsal borders
`of the vascu lar structures (RV D. LVD) on both sides. (See Table I
`for defin ition of labels.)
`
`PERCUTANEOUS DISCECTOMY
`
`145
`
`Percutaneous
`Discectomy
`Performed
`
`TABLE 2
`Position o/'Most Dorsal BOlld Segment in Candidatesjor PD
`Angle between
`Symptomatic H and Dorsal Free Psoas
`Border of
`Path"
`Side"
`Bowelh
`Yes
`+S
`3S
`L
`42
`+2
`Yes
`L
`34
`+0
`Yes
`L
`40
`Yes
`*
`+8
`No
`12
`- 21
`R
`-2
`R
`No
`3S
`-1 4
`21
`No
`L
`12
`- 20
`No
`L
`a Asterisk indicates central disc herniation with bilateral symptoms.
`b Positive numbers indicate that the bowel lies ventral to H. Neg(cid:173)
`ative numbers indicate that a segment of bowel lies dorsal to H.
`C Free psoas path was calculated as the absolute value of the
`difference between the dorsal border of the most dorsally located
`segment of bowel and the dorsal border of the psoas muscle.
`
`300
`
`200
`
`100
`
`0
`
`(j)
`w
`w
`a::
`<.:l
`W
`0
`
`LPD
`
`LP V
`L VD
`
`RVD
`RPV
`
`RPD
`
`,,.
`'ill,
`
`Ih'~
`
`itrn"
`J
`'.
`
`m
`
`• M
`
`~"
`
`- I OO,-L---r-----r-----.-----r----~
`2
`5
`4
`3
`
`PATIENT NUMBER
`FIG. 8. Graphic relati onship of retroperitoneal muscular and vas(cid:173)
`cular struct ures near the L-4. L-S interspace with the patient in the
`surgical position. (See Table I for definiti on of labels.)
`
`the informatio n will be vital in determining whether the
`surgical path is clear.
`The data gath ered fro m the eight abdominal CT scans
`obtained fro m prospecti ve surgical ca ndidates in the surgical
`positio n are presented in Table 2. Four patients were unac(cid:173)
`ceptable candidates because a loop of bowel was too close to
`the path of the 40 French chest tu be by subjecti ve evaluati on.
`Retrospective ly. the angle between line H and the dorsal
`border of the bowel was determined in these eight sca ns. A
`posi ti ve number indi cates that the dorsal border of th e bowel
`is ve nt ral to l in e H: a negati ve number indicates that the
`dorsal border of the bowel is dorsal to line H. In accepted
`candidates. the a ngle was ze ro or positi ve (Fig. 9) a nd. in
`unaccepted ca ndidates. the angle was negative (Fig. 10). Al(cid:173)
`though individ ua l \'alues provided little use ful informati on.
`
`FIG. 9. Abdominal CT scan in the surgical position of a patient
`acceptable fo r PD. Note that the dorsal border of the bowel is ventral
`to Line H. (See Table I fo r defi niti on of labels.)
`
`the mean free psoas path (the absolute valu e of the difTere nce
`between the dorsal border of the most dorsall y located seg(cid:173)
`ment of bowel and the dorsal border of the psoas muscle) in
`accepted ca nd idates was 38°: the sa me value in unaccepted
`ca ndidates was 20° degrees.
`
` 5
`
`

`

`146
`
`KANTER AND FRIEDMAN
`
`AeliroslIIgety. I 'o/. 16. Ao. 2
`
`retical possibilities include retroperitoneal malignancy. psoas
`abscess. and congenital renal anomaly. The psoas minor
`muscle. in a young muscular indi vidual. can mimic a para(cid:173)
`spinous mass.
`The abdominal CT scan obtained in the surgical position
`is a valuable screening technique for PD candidates. Analysis
`of the surgical position abdominal CT scans should eliminate
`the possibility of catastrophic complications with this proce(cid:173)
`dure.
`
`ACKNOWLEDGMENT
`
`The authors recognize Dr. Robert Jacobson , who developed
`this methodology.
`
`Received for publicati o n, April II . 1984: accepted. September 22.
`1984.
`Reprint requests: Steven L. Kanter, M.D. , Department of Neuro(cid:173)
`logical Surgery, Box J-265. J. Hillis Miller Health Center, University
`of Florida, Gainesville, Florida 326 10.
`
`REFERENCE
`
`I. Friedman WA: Percutaneous discectom y: An alternative to
`chemonucleolysis? Neurosurgery 13:542-547 . 1983.
`
`COMMENTS
`
`This paper must be considered in its overall context rather
`than as a method of analysis for an already proven operative
`technique. Kanter and Friedman admit that they have per(cid:173)
`formed percutaneous discectomies on only IS patients. They
`do not list their visceral, vascular, or neurological complica(cid:173)
`tions, nor do they tell us of the complications in the even
`fewer surgical candidates who had prospective preoperative
`computed tomographic scans.
`Citing only one reference, a paper written by one of the
`authors, Kanter and Friedman have avoided controversy
`about the procedure itself and focused on an anatomical
`analysis of how certain complications can be avoided. Until
`the actual incidence of these complications is known, the
`effectiveness of their preoperative CT scanning regimen re(cid:173)
`mains unclear. The potential for the visceral, vascular and
`neurological injuries mentioned by the authors makes me
`doubt whether percutaneous discectomy has any advantages
`over microdiscectomy, in which a similar tiny incision is
`made. Microdiscectomy offers the distinct advantages of di(cid:173)
`rect visualization of the offending disc and compressed nerve
`roots. Also, removal of a herniated disc under magnification
`can be performed at all lumbar levels.
`Although this paper does help us to understand the com(cid:173)
`puted tomographic anatomy involved in percutaneous discec(cid:173)
`tomy at L-4, L-S , it raises even more questions about the
`safety of the operation itself.
`
`Frederick A. Simeone, M.D.
`Philadelphia. Pennsylvania
`
`In late 1982, I traveled to Miami and observed Dr. Robert
`E. Jacobson perform percutaneo us discectomy. It seems to
`have all the advantages of chemonucleolysis without the
`major disadvantage of potential allergic reaction. [ came away
`impressed with the ease of entering the L-4, L-5 disc percu(cid:173)
`taneously. but learned that this procedure is prohibitively
`difficult at L-S. S-I. I was also concerned about the possibility
`of damage to the nerve root. Now this paper warns of other
`potential serious complications of this procedure.
`
`FIG. 10. Abdominal CT scan in the surgical position ofa patient
`unacceptable for PD. Note that the dorsal border of the bowel is
`dorsal to Line H. (See Table I for definition of labels.)
`
`DISCUSSION
`
`PO is a proced ure that, in carefully selected patients, rep(cid:173)
`resents a viable alternative to other lumbar disc techniques.
`The potential advantages of PO are very similar to those of
`chemonucleolysis. Because there is no lumbar incision, mus(cid:173)
`cle stripping, bone removal. or nerve root retraction , postop(cid:173)
`erative wound pain is minimal. This generally means a greatly
`shortened hospital stay and an early return to full activities.
`Unlike chemonucleolysis, there is no risk of anaphylaxis. In
`addition. the incidence of postoperative back pain and spasm
`may be lower with PO (I).
`The foregoing anatomical study suggests that the risk of
`vascular injury is negligible at the L-4. L-S level, but is
`substantial at the L-S. S-I level. In addition. segments of
`bowel may lie in the retroperitoneal surgical path. In fact ,
`approximately one-third of our patients who were otherwise
`suitable for PO were found upon evaluation with post-Gas(cid:173)
`trograffin surgical position abdominal CT scans to have seg(cid:173)
`ments of bowel obstructing the path through which the 40
`French chest tube would pass. This estimation includes pa(cid:173)
`tients whose CT scans were performed after completion of
`this anatomical stud y.
`As more abdominal CT scans are obtained in the surgical
`position on patients otherwise suitable for PD. a variety of
`anatomical and pathological structures obstructing the retro(cid:173)
`peritoneal surgical path are likely to be encountered. Theo-
`
` 6
`
`

`

`Februar.r 1985
`
`We never have performed this operation for several reasons.
`Special instruments are required. Chymopapain became avail(cid:173)
`able. By the time one eliminates all noncandidates for this
`proced~re (extruded discs. spinal stenoses. unacceptable ab(cid:173)
`dominal computed tomographic scan. L-5. S-I discs), very
`few patients rem ain.
`Now. with evidence that chymopapain seems to be only
`50% effective (I) and especially with recent reports of the
`delayed onset of paraplegia after chymopapain injection. per(cid:173)
`haps this procedure will be reconsidered. However. we have
`become quite comfortable with the procedure of microlumbar
`discectom y. In this procedure. all of the maneuvers of stan(cid:173)
`dard partial hemilaminecto my can be done through a 2-cm
`midline incision. which is about the same size as the lateral
`flank incision I observed for percutaneous discectomy (2).
`As far as I know. Dr. Jacobson. who must have performed
`percutaneous discectomies on hundreds of patients, has never
`published his results. I would be surprised if those results are
`any better than the results of chymopapain injection. With
`
`PERCUTANEOUS DISCECTOMY
`
`147
`
`microdiscectomy. we have a failure rate of only 5%. Eighty(cid:173)
`five per cent of patients get sufficient relief to return to work
`or usual activities without medications.
`I predict that microlumbar discectomy will become the
`procedure of choice for ruptured lumbar discs. It requires no
`abdominal computed tomographic scan, treats all types of
`disc herniations. opens up the spinal canal and nerve root
`canal. and requires only a 24-hour hospital stay for most
`patients.
`
`W. Robert Hudgins, M.D.
`Dallas, Texas
`
`I. Crawshaw C Frazer A, Merriam W. Mulholland R. Webb J: A
`comparison of surgery and chemonudeolysis in the treatment of
`sciatica: A prospec tive randomized trial. Spine 9: 195- 197, 1984 .
`2. Hudgins W: The role of microdiscectomy: Symposium o n eval(cid:173)
`uation and care of lumbar spine problems. Orthop Clin North
`Am 14:589-603. 1983 .
`
` 7
`
`