SPINE Volume 28, Number 5. PP 423-428
`©2003, Lippincott W'illi:ims EV \1(7ilkins, Inc.
`
`An Anatomic Study of the Lumbar Plexus with Respect
`to Retroperitoneal Endoscopic Surgery
`
`Takatomo Moro, MD,* Shin—ichi Kikuchi, MD, PhD,* Shin—ichi Konno, MD, PhD,* and Hiroyul<i Yaginuma, MD, PhDT
`
`Study Design. The distribution of the lumbar plexus
`was analyzed using cadavers.
`Objective. To clarify the safety zone to prevent nerve
`injuries with respect to retroperitoneal endoscopic surgery.
`Summary of Background Data. Surgical approaches to
`the retroperitoneal space vary among surgeons. Recently,
`retroperitoneal endoscopic surgery has been applied to
`various spinal disorders. When the psoas major muscle is
`separated during retroperitoneal endoscopic surgery,
`there is a potential risk of injury to the lumbar plexus or
`nerve roots. However, there is sparse knowledge regard-
`ing the relationship between the greater psoas muscle
`and the lumbar plexus.
`Methods. A total of 30 cadavers were analyzed. Six lum-
`bar spines of the cadavers were cut in parallel with the
`lumbar disc space. Each axial section was photographed
`and captured into a computer. The distribution of the lum-
`bar plexus was analyzed using computer images. The posi-
`tions where the genitofemoral nerve emerged on the ab-
`dominal surface of the psoas major muscle were analyzed
`using 24 cadavers.
`Results. L2/3 and above, all parts of the lumbar plexus,
`and nerve roots were located from the dorsal fourth of the
`vertebral body and dorsally. The genitofemoral nen/e de-
`scends obliquely forward through the psoas major muscle,
`emerging on the abdominal surface between the cranial
`third of the L3 vertebra and the caudal third of the L4 verte-
`bra. The safety zone of the psoas major muscle to prevent
`nerve injuries, excluding the genitofemoral nerve, is at L4JL5
`and above.
`Conclusions. The safety zone, excluding the genito-
`femoral nerve, is at L4-L5 and above. [Key words: anat-
`omy, endoscopic surgery, genitofemoral nerve] Spine
`2003:28:423—428
`
`Since laparoscopic discectoniy was reported, endoscopic
`surgery has been applied to various kinds of lumbar
`spine diseases.3’7‘w Retroperitoneal endoscopic surgery
`has been applied to anterior interbody fusion for disc
`herniation, anterior decompression and interbody fusion
`for burst fracture, and discectomy for extreme lateral
`
`From the "Department of Orthopaedic Surgery and the 'jDepartment
`of Armloriiy, Fiikushiiiiri Medical University, Sclioril of \/lerlicirie,
`Fukushima City, Japan.
`Acknowledgement date: February 4, 2002. First revision date: June 3,
`1002.
`Acceptance date: August 14, 2002.
`Device status/drug statement: This report does not contain information
`about medical LleVice(s)/driiglsl.
`Conflict ofinterest: No funds were received in support ofthis work. No
`benefits in any form have been or will be received from a commercial
`party related directly or indirectly to thc suhicct of this report.
`Address reprint requests to Takatomo Moro, MD, Department of Or-
`thopaedic Surgery, Fukushima Medical University School of Medicine,
`1 Hikarigaoka, Fukushima City, Fukushima 960-1295, japan. E-mail:
`1nom@fn1u.ac.ip.
`
`Page 1
`
`disc herniation.l’” When the psoas major muscle is sep-
`arated during retroperitoneal endoscopic surgery, there
`is a potential risk of injury to the lumbar plexus or nerve
`roots. McAfee etalg reported on 18 patients who under-
`went endoscopic retroperitoneal interbody fusions. In
`that study, there were three patients with postoperative
`coniplications. There was sepsis in one case, a bone
`dowel partial fracture in one case, and temporary geni-
`tofemoral nerve palsy in one case. llowever, there is little
`knowledge regarding the relationship between the
`greater psoas muscle and the lumbar plexus in light of
`endoscopic surgery.1‘”‘ The aim of this study is to clarify
`
`5/3
`
`S
`
`s: superior
`i: inferior
`
`Figure 1. Cut levels of the lumbar spine of a cadaver and their
`abbreviated names. The cranial third of the L3 vertebral body is
`referred to as L33 lL3 superior), and the caudal third of the L3
`vertebral body is referred to as L3i (L3 inferior).
`
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`424 Spine - Volume 28 - Number 5 - 2003
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`anterior margin of vertebral body
`
`psoas major muscle
`
`IV fllcégéala
`
`P
`
`posterior margin of vertebral body
`
`Figure 2. Zone definition of the localization of the lumbar plexus and nerve roots at each image. The area between the anterior edge of
`the vertebral body and the posterior edge of the vertebral body was divided into four zones. The most anterior zone was defined as zone
`I, the second anterior zone was zone II, the third anterior area was zone Ill, and the most posterior area was zone IV. The area posterior
`to the posterior edge of the vertebral body was defined as zone P, and the area anterior to the anterior edge of the vertebral body was
`defined as zone A.
`
`the safety zone of the psoas major muscle during retro-
`peritoncal endoscopic surgery using cadavers.
`
`I Materials and Methods
`
`Localization of the Lumbar Plexus and Nerve Roots.
`Lumbar spines were removed from six embalmed human ca-
`davers and immediately frozen at -80 C. From the I.l—l.5
`vertebral body, each specimen was cut in parallel with the lum-
`bar disc space and the lumbar vertebra at the cranial third and
`caudal third of the each lumbar vertebral body (Figure 1). The
`distribution of the lumbar plexus and nerve roots in each axial
`section was photographed. Each image was captured into a
`computer. The relationship between the greater psoas muscle
`and the lumbar plexus was analyzed using computer images.
`The area between the anterior and posterior edges of the ver—
`tebral body was divided into zones I, II, III, and IV (Figure 2).
`The area anterior to the anterior edge of the vertebral body was
`defined as zone A, and the area posterior to the posterior edge
`of the vertebral body was defined as zone P. The relationship
`between the localization of the lumbar plexus and nerve roots
`and each zone was examined.
`
`I Results
`
`The Relationship Between the Localization of the
`Lumbar Plexus and Nen/e Boots and the
`Vertebral Body
`All parts of the lumbar plexus and nerve roots were
`found in zones IV and P at L2—L3 and above (Figure 3A).
`All of the lumbar plexus, except for the genitofemoral
`nerve, and all nerve roots were found it1 zone ll and
`abdomin-ally at L4-—L5 and above (Figure 3B).
`A typical case is presented. The nerve tissue was found
`in zone IV and dorsally at L2—L3 (Figure 4A). At L33 (L3
`superior) and caudally,
`the genitofemoral nerve was
`found in zone II on the right side and in zone III on the
`left side (Figure 4B). At L3i (L3 inferior) on both sides,
`the genitofemoral nerve was found in zone I (Figure 4C).
`At L5—S, the genitofemoral nerve was found in zone A;
`the L4 nerve root, L5 nerve root, femoral nerve, and
`obturator nerve were found in zones II, III, and IV (Fig-
`ure 4D). Intraobserver reliability was 0.87.
`
`The Relationship Between the Greater Psoas Muscle and
`the Genitofemoral Nerve. The positions where the genito-
`femoral nerve emerges on the abdominal surface of the psoas
`major muscle were analyzed using 24 enibalrned cadavers. The
`three characteristics used to identify the genitofemoral nerves
`are piercing the psoas major muscle at its upper medial portion,
`piercing the fascia transversalis to enter the abdominal wall
`around the deep inguinal ring, and not having a lateral cutane—
`ous branch.
`
`The Relationship Between the Psoas Major Muscle
`and the Genitofemoral Nerve
`
`As for the level to which the genitofemoral nerve passes
`the psoas major muscle among the 24- examples (48
`sides) investigated in this study, I.3—I.4 had1S sides and
`L4s had 14 sides. The level of the positions where all of
`the genitofemoral nerve passed through the psoas major
`muscle was between L35 and L4i (95% confidence inter-
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`An Anatomic Study for Endoscopic Surgery - Moro et al 425
`
`Figure 3. A. The number with which the lumbar plexus and the nerve roots by the 12 sides existed. B. The number with which the lumbar
`plexus and nerve roots, excluding the genitofemoral nerve, existed.
`
`val; range, 924 00%) (Table 1 ). lntraobserver reliability
`was 0.82.
`
`I Discussion
`
`Safety Zone of the Lumbar Plexus and Nerve Rants
`Nerve damage is one of the complications that should be
`avoided during retroperitoneal endoscopic surgery.
`From the results of this study, it was thought that the
`safety zone may be at L2—L3 and above. Between the
`cranial third of the L3 vertebral body and L4—L5 , only
`the genitofeinoral nerve was located in the abdominal
`zone rather than the center of the vertebral body. If the
`possibility of damaging the genitofemoral nerve is not
`considered, the safety zone should be at L4—L5 and
`above. \When spreading the psoas major muscle at L2—L3
`and below, start from the abdominal edge of the verte-
`bra, because nerves are not located in the abdominal
`surface of the vertebra. The lumbar plexus and nerve
`roots were contained in the psoas major muscle. There-
`fore, split between the psoas major muscle and vertebral
`body without dissecting the psoas major muscle.
`L5—S1 is located on the caudal side from the abdon1i—
`nal aortic bifurcation. Therefore, during the method of
`
`spreading the psoas major muscle posteriorly for ex—
`treme lateral L5—S1 lumbar disc herniation, there is a risk
`of iliac artery and vein damage. At L5—S1, the space be-
`tween the psoas major muscle and the lumbar quadrate
`muscle is wide as compared with 1.4-1.5 and above.
`Therefore, the lateral surface of the vertebral body can be
`reached fron1 the gap of these muscles. The method of
`retracting the psoas major muscle anteriorly and reach-
`ing to the lateral surface of the vertebral body may be
`useful2 (Figure 5). However, according to the present
`study, it is the danger zone, where the lumbar plexus and
`nerve roots were included in the center of the vertebral
`body and dorsally, that is to be operated in the case of
`this approach. At L5—b1, there is the L4 nerve root, L5
`nerve root, femoral nerve, and obturator nerve between
`the psoas major muscle and the lumbar quadrate muscle.
`Therefore, those nerve tissues must be checked and pro-
`tected with endoscope.
`
`The Possibility of Genitnfemaral Nerve Damage
`The genitofemoral nerve forms the lumbar plexus to sup-
`ply the abdominal wall with the ilioinguinal nerve, ilio—
`hypogastricus nerve, and subeostalis nerve. The distribu-
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`426 Spine - Volume 28 - Number 5 - 2003
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`Figure 4. A, Cut image at L2-L3 (down shot) displays the L1 and L2 nerve roots that exist in zone IV. B, Cut image at L3s (down shot)
`displays the L1 and L2 nerve roots that exist in zones P and IV.
`shows the genitofemoral nerve that exists in zones II and III. C, Cut
`image at L3i (down shot) displays the L1 and L2 nerve roots that exist in zone IV. Allows heads to show L3 nerve roots that exist in zone
`P.
`show genitofemoral nerves that exist in zone I. D, Cut image at L5-S (down shot) displays white frames that show the L4 and L5
`nerve roots that exist in zones II,
`III, and IV. Displays obturator nerves and femoral nerves that exist in zones II and Ill.
`shows
`genitofemoral nerves that exist in zone A.
`
`tion and origin of these nerves have been sufficiently
`examined.” The genitofemoral nerve mainly branches
`from the L1 and L2 nerve root, pierces through the psoas
`major muscle toward the anterior side from the posterior
`side, and subsequently descends in accordance with the
`abdominal surface of the psoas major.6’” However, the
`authors paid no attention to the level of the genitofemo—
`ral nerve emerging on the surface of the psoas major
`muscle. From the results of this study, it was found that
`the level where the genitofemoral nerve passes the psoas
`major muscle ranges from the cranial third of the L3
`
`Table 1. The Positions Where the Genitofemoral Nenre
`Emerges on the Abdominal Surface of the Greater Psoas
`Muscle, Except lor One Side, Which Has No
`Genitolemoral Nerve
`
`Cut Level of Lumbar Spine
`L3s
`L3i
`L3—L4
`L4s
`L4i
`
`Genitofemoral Nerves That
`Had Pierced Through the
`Psoas Major Muscle (n)
`5
`11]
`15
`14
`3
`
`vertebral body to the caudal third of the 1.4 vertebral
`body. That is, in the case of spreading the psoas major
`muscle, it is thought that at the more caudal level the
`genitofemoral nerve may be damaged. In fact, a case of
`transitory genitofemoral nerve paralysis after anterior
`fusion of the I_3—L4 vertebral body with the retroperito—
`neal endoscope has been reported.9 On the other hand,
`
`vertebral body
`
`ala of sacrum
`
`Figure 5. Cut image at L5/S1 displays the course of the retroperi-
`toneoscopic lateral lumbar approach.
`
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`
`entrapment neuralgia of the genitofemoral nerve is
`<nown as one of the complications of inguinal hernior—
`rhaphy. However, reports of having succeeded in reinit-
`-ing the symptoms (pain and paresthesia) without a seri-
`ous problem, even if neurectomy of the genitofemoral
`nerve is done as medical treatment of these complica-
`'ions, have also been made.4 If such a conventional re-
`oort is considered when the genitofemoral nerve is dam-
`aged, there is the possibility that a sensory disturbance
`will arise at the scrotum and medial thigh, which is the
`innervation area of the genitofeinoral nerve. It is thought
`‘hat genitofemoral nerve palsy rarely becomes a serious
`oroblem. However, before an operation accompanied by
`‘he spreading of the psoas major muscle at the L3 verte-
`aral body and below, the patient must be informed of the
`oossibility of sensory disturbance by genitofemoral nerve
`damage, and it is considered necessary to obtain compre-
`iension beforehand.
`
`I Key Points
`
`0 The muscle should be split more anteriorly than
`the dorsal fourth of lumbar vertebral body from
`the cranial third of the L3 vertebral body and above
`to prevent nerve injuries.
`0 \When the psoas major muscle is split at the L3 or
`L4 vertebral body, there is a risk of injury to the
`genitofemoral nerve.
`
`An Anatomic Study for Endoscopic Surgery - Mathews 427
`
`References
`
`. Akdemir G, Misra M, Dujobny M, et al. Micro anatomy of thoracic spine
`iI')l';]l11ll11] and ligaments.
`In: I)iclm1;m (lA, Rosenilinl D], Perin NI, eds.
`Thoracoscopic Spine Surgery. New York: Thieme Medical Publishers, 1999;
`69 —78.
`. Dezawa A, Yan1ane T, Mikami H, et al. Retroperitoneal laparoscopic lateral
`;ipprn;n:li lo ihe lumbar spine: .1 new ;ipproacli_ iecl1niqiie_ and clinical irinl.
`_] Spinal Disord 2[l()L|;1.5 58-43.
`. Foley KT, Smith MM. Microendoscopic disceixomy. Tech Neurosurg 1997;
`31301-7.
`. James RS, Bruce r\H, l\/Inrlx F5, ei nl. I)i;igi1osis and irenlmenl olgeniioienr
`oral and ilioinguinal entrapment neuralgia. Surgery 1987;1U2:581—6.
`. Kasai T. Pri la abdomenmuraj brangoj de la lumba plekso. I Anat I957;3Z:
`262-77.
`. Iyinrrin B, Lawrence HB, Susan MS. The spinal nerves. In: Peiei LW’, ed.
`(Jray’s Anatomy, 28th ed. London: Churchill Livingstone, 1995;1258—92.
`. Mathews HH, Evans MT, Bolligan HI, et al. Laparoscopic discectomy with
`anterior lumbar interbody fusion. Spine 1995
`1797-802.
`. Moriknwa R. Course, distribution and their variety of [lie nerves derived
`from the lumbar plexus to supply the abdominal wall. J Anat 1971,46:
`3 l2—33.
`. McAfee PC, Regan J], Geis WP, et al. Minimally invasive anterior retroper—
`iiouenl gipprogich lo Ihe lumbar‘ spine. Spine 1 '998;23:1476—84.
`. Obenchain Th. Laparoscopic lumbar discectomy: case report. _] Laparoen—
`dosc Surg 1991;1:1-15—9.
`. Olinger A, Hildebrandt U, Mutschler W, et al. First clinical experience with
`an endoscopic retroperitoneril zipproricb for anterior fusion of lunibzir spine
`fractures fron1 levels 112 to L5. Surg Endosc 1999;1.5:1215—9.
`. Pait TG, Ture U, Arna utovic KI, et al. Surgical anatomy of the thoracic spine.
`In: Dickman CA, Rosenthal D], Perin NI, eds. Thoracoscopic Spine Surgery.
`New Yorl<:Thien1e .\/Iediczil Publishers, 1999;\'7—67.
`. Romanes G]. The peripheral nervous systeri1. In. Romans G], ed. Cunning—
`ham‘s Textbook of Anatomy. 12th ed. Tront:0xford University Press, I 981;
`739-826.
`
`Point of View
`
`Hallett Holmes Mathews, MD
`From the Virginia Commonwealth University Medical College, and MidAt|antic Spine Specialists,
`Richmond, Virginia.
`
`As surgeonsl have become increasingly aware of surgical
`morbidity for anterior lumbar spine surgery, new tech-
`niques and approaches have been devised to access the
`anterior column of the lumbar spine less invasively and
`with less surgical morbidity. Transperitoneal endoscopic
`surgery has provided predictable access to the L5 —S1 in-
`tervertebral space; however, L4—L5 and above has been
`less predictable in obtaining predictable access without
`the risk of significant intraoperative complications. The
`location of the great vessels anteriorly and their ana-
`
`Device status/drug statement: This report does not contain information
`about medical device(s}/drugls).
`Conflict ofinterest: No funds were received in support of this work. No
`benefits in any form have been or will be received from a commercial
`party related directly or indirectly to the subject of this report.
`Address reprint requests to Hallett I-I. N1-athews, I\/ID, MidAtlantic
`Spine Specialists, 7650 I’-arham Road, Suite 200, Richmond, VA
`23294. E-mail: masshriiatl1ews@aol.cori1
`
`tomic variations have provided less favorable access
`compared with a more lateral transpsoatic approach to
`the anterior vertebral column. The lumbar plexus repre-
`sents the most important structure in the psoas that
`could be injured, and the anatomic variations and loca—
`tions of these structures have yet to be clearly defined
`“An Anatomic Study of the Lumbar Plexus with Re-
`spect to Retroperitoneal Endoscopic Surgery” by Moro
`el al is an important anatomic study that describes the
`important relationship of the lumbar plexus to the
`greater psoas muscle when considering anterior lumbar
`surgical intervention. \X/hether using an endoscopic or
`mini—open technique, it is important to conceptualize the
`most common locations of lumbar plexus structures be-
`fore dissecting the psoas muscle to obtain access to the
`vertebral body or intervertebral disc space. Injuries to the
`genitofemoral nerve and other lumbar plexopathies have
`
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`428 Spine - Volume 28- Number 5 - 2003
`
`been described when a more lateral approach is obtained
`for decompression or device implantation, as great vessel
`dissection is avoided anteriorly.
`Past morbidity of the anterior surgical approach to the
`lumbar spine has often dictated whether spinal surgeons
`would even use such an approach for the treatment of
`spinal disorders. It has becon1e increasingly apparent
`that anterior techniques offer tremendous biomechanical
`and kinematic advantages during surgical reconstruction
`for various spinal disorders. Part of the morbidity has
`been that of dissecting and mobilizing the great vessel at
`
`L4—T,5 in both index and revision surgical techniques.
`The lateral transpsoatic approach is thought by many to
`be the least invasive endoscopically at L4-—L5 and above;
`however, surgeons have not felt comfortable with dis-
`secting the psoas because of the presence of the lumbar
`plexus. This study has offered tremendous assistance in
`planning lateral access to the lun1bar spine and also de-
`ciding vvhether this is the appropriate access for a specific
`surgical pathology. The authors have described very con-
`cise surgical anatomy, which will be helpful for all spine
`surgeons in the future who plan this approach.
`
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