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Neurologic complications after lum-bar spine surgery may be broadly classified by the mechanism of injury and by the time period dur-ing which they occur.. In-direct injuries are due to

Neurologic complications after

lum-bar spine surgery may be broadly

classified by the mechanism of

injury and by the time period

dur-ing which they occur The causes of

injury are generally either indirect

or direct, with the latter including

laceration, compression, traction,

and avulsion injuries to the neural

elements Such direct causes are

most commonly the result of a

tech-nical mishap by the surgeon

In-direct injuries are due to the

disrup-tion of the blood supply to the

spinal cord and nerve roots or to the

gradual compression of the neural

elements, as by correction of

defor-mity or by a postoperative

hema-toma This type of injury is usually

the result of ischemia or the

disrup-tion of axoplasmic flow, which

pro-vides neural nutrition Its causes

are more difficult to define and are

often inexplicable

Neurologic injuries categorized

by the time period during which

the insult occurs may be

intraoper-ative, early postoperative (1 to 14

days), or delayed postoperative

(after 14 days) events

Intraopera-tive events are generally related to

complications arising from anes-thesia, patient positioning, surgical technique, or procedure-specific risks Early in the postoperative period and up to 2 weeks after sur-gery, neurologic injuries are most commonly secondary to direct compression of the neural ele-ments This is often caused by the mass effect of postoperative hema-toma, pseudomeningoceles, and epidural abscesses After partial diskectomy, retained fragments or recurrent herniations may also cause neurologic symptoms in this time period After 14 days from surgery, recurrent disk herniation should be considered more likely, although this may occur earlier

as well

To both minimize and prevent potential neurologic complications that may occur in association with lumbar spine surgery, the surgeon must thoroughly understand the relevant anatomy and must do meticulous preoperative planning

Additionally, a thorough under-standing of the etiology of the com-plications can decrease their inci-dence When complications do

occur, rapid recognition and appro-priate treatment can minimize their effect

Anatomy

Knowledge of the relevant anatomy

is essential to minimizing direct neural injuries The spinal cord ter-minates as the conus medullaris at the level of the inferior border of L1 and the superior border of L2 Spinal cord tissue is much less tol-erant of traction and compression than the nerve roots are Even minimal manipulation of the cord may cause profound neurologic consequences Focal injury to the conus medullaris can cause injury

to the function of the lower sacral roots and result in disturbances in bowel, bladder, or sexual function with or without other obvious neu-rologic deficits in the lower extrem-ities

Dr Antonacci is Assistant Professor of Orthopaedic Surgery and Director, Spine Diagnostic and Treatment Center, MCP Hahnemann University School of Medicine, Philadelphia, Pa Dr Eismont is Professor of Orthopaedic Surgery, University of Miami School of Medicine, Miami, Fla.

Reprint requests: Dr Antonacci, Spine Diagnostic and Treatment Center, Graduate Hospital, 1800 Lombard Street, Philadelphia,

PA 19103.

Copyright 2001 by the American Academy of Orthopaedic Surgeons.

Abstract

With the increasing complexity and number of lumbar spine operations being

performed, the potential number of patients who will sustain perioperative

com-plications, including those that involve neural structures, has also increased.

Neurologic complications after lumbar spine surgery can be categorized by the

perioperative time period during which they occur and by their mechanism of

injury Although the overall incidence of neurologic complications after lumbar

surgery is low, the severity of these injuries mandates careful preoperative

plan-ning, awareness of risk, and meticulous attention to perioperative details.

J Am Acad Orthop Surg 2001;9:137-145

M Darryl Antonacci, MD, and Frank J Eismont, MD

The spinal nerve roots, while

more tolerant of mechanical

defor-mation than the spinal cord, are less

tolerant than the peripheral nerves

The intradural nerve rootlets are

covered by only a thin

membra-nous root sheath, which is

perme-able to cerebral spinal fluid for

nu-trition.1 In contrast, peripheral

nerves are protected by an

epineu-rium and a perineuepineu-rium This, in

addition to a more developed

con-nective tissue layer, makes

periph-eral nerves much less susceptible to

injury than the intrathecal nerve

rootlets

The results of experimental

stud-ies in dogs suggest that when the

thecal sac is compressed acutely to

45% of its normal area (i.e., to

ap-proximately 75 of the normal 170

mm2), significant nerve-root

com-pression occurs, with measurable

changes in both motor and sensory

function.2 The motor nerve roots

recover more quickly than the

sen-sory roots after the pressure is

re-leased; thus, transient compression

is more likely to affect the sensory

roots The critical value of 75 mm2

can be used for the radiologic

diag-nosis of central spinal stediag-nosis

Re-ducing the cross-sectional area of the

thecal sac to approximately 65 mm2

generates a pressure level of about

50 mm Hg in the cauda equina

Measurable changes in spinal

nerve-root conduction generally occur

between 50 and 75 mm Hg.3 The

effects of compression are related

not only to the duration of

compres-sion and the pressure itself but also

to the rate of onset.4 In the acute

injury setting, rapid application of

compression to the nerve roots

causes more pronounced tissue

changes than slow application The

application of pressure over

multi-ple spinal levels and the

combina-tion of compression with systemic

hypotension can lower these

thresh-old injury levels

The pedicle is a constant anatomic

landmark that can be used to locate

the exiting nerve root and thus min-imize the likelihood of inadvertent injury to it If the anatomy is aber-rant, the one constant is the relation-ship of the pedicle to the nerve root, which lies along the inferomedial edge of the pedicle In cases with poor visualization of the nerve root, resection of bone until the pedicle is visible will aid in the identification

of the exiting nerve root

During anterior lumbar surgery, the hypogastric nerve plexus and sympathetic chain are at risk of injury The aorta, the vena cava, and collateral vessels are preverte-bral and in close proximity to the hypogastric nerve plexus This nerve plexus is approximately 6 to

8 cm in length along the surface of the aorta and extends from the cephalad aspect of L4 (as the supe-rior hypogastric plexus) to the first sacral vertebra As the plexus en-ters the pelvis, it divides into right and left divisions, which course dis-tally and join the inferior hypogas-tric plexus These fibers innervate the seminal vesicles and vas deferens

in the male; injury to these struc-tures can lead to retrograde ejacu-lation Injury to the hypogastric plexus in approaches to the L5-S1 disk space is minimized by blunt dissection directly on the anterior surface of the disk Sweeping the prevertebral tissues and hypogas-tric nerve plexus laterally, rather than dissecting through these struc-tures, decreases the risk of injury to the nerve fibers The use of bipolar cautery and limited exposure also helps to minimize the risk of injury

The exposure of upper lumbar seg-ments is not associated with as high a risk for retrograde ejacula-tion as the exposure of L5-S1, be-cause the sympathetic fibers in-volved lie on the anterior aortic wall Injury to the sympathetic chain, which lies along the anterior border of the psoas muscle, can manifest as patient complaints of contralateral foot coldness In fact,

vasodilatation secondary to this in-jury causes increased warmth in the ipsilateral foot

Preoperative Planning

Failure to recognize variations in normal anatomy on preoperative studies may predispose to injury (e.g., asymptomatic spina bifida) Such a finding may necessitate a particularly careful dissection or alteration in surgical approach Similar caution is necessary after prior laminectomies or with wid-ened interlaminar spaces It is good practice to review all preop-erative radiographs just prior to surgery, with special attention to the variant anatomy in each indi-vidual case

In other situations, such as in patients with high-grade lumbar or cervical stenosis, preoperative con-sideration of patient positioning may help avoid unexpected injury For example, patients with cervical stenosis should be carefully trans-ferred to the prone position with their heads in a neutral or slightly flexed position, or awake position-ing should be used In severe cases, consideration should also be given

to fiberoptic intubation In patients with high-grade lumbar spinal stenosis, use of large Kerrison ron-geurs should be avoided in favor of the motorized diamond burr Un-der these conditions, placement of cottonoid pledgets within a tightly narrowed epidural space should be avoided

Prior to surgery, patients should

be instructed to discontinue the use

of anti-inflammatory medications (for 2 to 3 days) and aspirin (for 2 to

10 days) to minimize intraoperative and postoperative blood loss Pa-tients should also be questioned about complementary or alternative medications, such as gingko and cayenne, which can have effects on clotting

Complications Related to

Induction of Anesthesia

and Patient Positioning

The risk of intraoperative

neuro-logic injuries begins with the

in-duction of anesthesia and

position-ing of the patient for surgery The

incidence of significant neurologic

injury, including complete

paraly-sis, secondary to spinal or epidural

anesthesia has been reported to be

approximately 0.02%.5 Injuries

re-lated to these types of anesthesia are

usually secondary to direct

mecha-nisms These include laceration by

inadvertent needle placement and

compression of the neural elements

secondary to postinjection

hema-toma Paralysis can occur in patients

with low-lying spinal cords who

undergo routine epidural or

intra-thecal injections of anesthetic agents

Peripheral nerve injury secondary

to the placement of intravenous

and arterial lines, although

uncom-mon, can also occur

Peripheral nerve injuries after

lumbar spine surgery more typically

occur secondary to malpositioning

or improper padding of the patient

In posterior lumbar surgery, the

patient is usually placed in a prone

position on rolls or on a four-poster

padded frame (e.g., Relton frame)

or Andrews-type table After

posi-tioning, it is important to ensure

that the abdomen hangs free, so as

to minimize intraoperative blood

loss Regardless of the type of frame

used, well-padded support is

neces-sary, with care taken to avoid

exces-sive pressure on the chest wall and

pelvis Extra foam padding of the

posts aids in distributing pressure

uniformly to the patient’s skin and

helps to avoid skin blisters and

burns Every patient should be

positioned and padded as would be

appropriate for a much longer

duration of surgery than projected

Direct compressive or traction

inju-ries of upper- and lower-extremity

nerves can occur In particular,

ex-cessive pressure or stretch at the brachial plexus or femoral nerve can lead to upper- and lower-extremity nerve palsies, respectively In the upper extremity, the ulnar and an-terior interosseous nerves are par-ticularly susceptible to external pressure, as are the peroneal and lateral femoral cutaneous nerves of the lower limbs

In patients with coexistent cervi-cal and lumbar stenosis, careful positioning of the head in neutral or slight flexion is mandatory to avoid cervical myelopathy or spinal cord injury, either while transferring the patient prone or during final posi-tioning A Mayfield three-point head holder provides very reliable positioning for long-duration sur-gical procedures and for high-risk patients This avoids pressure on the face and in particular on the eyes Ophthalmic injuries have been reported secondary to excessive pressure on the eyes, resulting in permanent blindness in rare in-stances.6

Direct and Indirect Surgical Injuries

Direct and indirect injuries related to surgical technique make up the ma-jority of intraoperative neurologic complications Three factors appear

to predispose to iatrogenic injuries:

the relative inexperience of the sur-geon, failure to follow meticulous surgical technique, and a history of prior surgical procedures on the patient In patients with undis-turbed anatomy, the frequency of injury should be very rare If inju-ries are occurring relatively more frequently, it is mandatory that the surgeon reevaluate the surgical techniques employed (Table 1)

Most neurologic injuries from direct trauma are related to either trauma by surgical instruments or placement of pedicle screws or hooks Several principles should be

observed to minimize risks Appro-priately sized rongeurs down to 1

mm with a small foot-plate should

be available When removing bone

or soft tissue, one must always check to see that the dura has been dissected free (especially in patients with rheumatoid arthritis) and that adequate space is available for the Kerrison foot-plate If scarring or adhesions are present, careful dis-section with angled curettes or dural elevators is required If the area is too narrow, bone must be removed from above with either motorized burrs or osteotomes before rongeurs can be safely used Protection of the dura with cot-tonoid pledgets should be avoided

in these conditions Use of magnifi-cation, such as with loupes or an op-erating microscope, can be helpful

in difficult situations In general, Kerrison rongeurs should be directed parallel to the exiting nerve root to avoid transection Motorized burrs are passed from medial to lateral to avoid dural damage Diamond-tipped burrs with copious saline irri-gation can be used safely close to the dura with a lower risk of laceration During diskectomy, the exiting nerve root must be mobilized me-dially to expose the herniation In large herniations, it may not be pos-sible to completely mobilize the root without excessive traction If that is the case, the disk should be removed before complete mobilization Be-fore incising the disk anulus, one should always make sure that the exiting root has been mobilized and protected Meticulous hemostasis is important to avoid mistaking a nerve root for a disk fragment The smallest pituitary rongeurs should

be used to remove the disk, and they should be opened only after they have been inserted in the disk space Occasionally, the suction tip can become nicked by another instru-ment, such as the burr The sharp edge created can cause a dural or nerve root laceration For this

rea-son, the suction tip should be

checked and discarded if damaged

Other laceration injuries may

occur with the use of osteotomes

during medial facetectomies and

during aggressive bone removal

with the rongeur Tearing or

rip-ping of the ligamentum flavum

should be avoided Particular care

is needed when removing the bone

fragments of the medial facet,

because the capsule of the facet is

often adherent to the ligamentum

flavum or the dura itself Any

movement of the dura while bone

is being removed, either during

facetectomy or when a Kerrison

rongeur is being used, should alert

the surgeon that such an

attach-ment may be present Use of a

Penfield or Woodson probe can

help loosen any attachments to the dura Performing bone removal while leaving the ligamentum flavum intact may also serve as an added measure of protection to the thecal sac

Compression or contusion of the nerve roots or cauda equina is another potential type of neurologic injury related to surgical technique

Excessive thecal sac retraction, especially prior to adequate decom-pression of the spinal canal in pa-tients with lumbar stenosis, can cause ischemic injuries As noted previously, compression of the the-cal sac to less than 45% of its cross-sectional area can cause changes in motor and sensory root conduction

Poorly visualized nerve roots are often subject to such unrecognized

compression Bertrand described the “battered-root” syndrome, in which new-onset numbness after laminectomy or laminotomy strongly suggests intraoperative root injury.5 Excessive compression with cot-tonoid pledgets, gel foam, or mal-positioned fat grafts has also been reported as a source of intraopera-tive neurologic compromise.7 The incidence of nerve-root avul-sion injuries has been reported to

be approximately 0.4%.5 Forceful retraction of a nerve root, especially within a stenotic foramen, can be an inadvertent cause of a nerve-root avulsion This can also occur during aggressive bone removal The inci-dence of conjoined nerve roots in the lumbar spine has been reported

to be between 2% and 14%,5 and probably is more common than is generally acknowledged Failure to recognize a conjoined nerve root can result in excessive compression, laceration, or avulsion Adequately visualizing the nerve-root sleeve and working laterally relative to the nerve root will help to minimize the incidence of this complication In many instances, when the nerve root cannot be identified or mobi-lized, it is better to remove more bone until the pedicle is exposed than to place undue traction on the neural elements

The frequency of dural tears as a complication of lumbar surgery can

be reduced through meticulous technique Although identification

of a dural tear is typically made after the sudden leak of spinal fluid, identification of dural tears that have not yet disrupted the arachnoid layer is also important Most tears can be repaired primarily with 5-0 or 6-0 suture with a run-ning stitch Care must be taken to avoid incorporating any neural ele-ments into the closure After clo-sure, a Valsalva maneuver aids in the identification of a persistent or residual leak In these cases, rein-forcement of the repair is possible

Table 1

Basic Spine Surgery Technique

1 Ensure adequate exposure and lighting

2 Do not pass instruments over the open wound

3 Avoid overaggressive bone removal

4 Use the Kerrison rongeur with foot-plate oriented parallel to thecal sac

5 Use Kerrison rongeur without upward or downward pressure

6 Leave ligamentum flavum intact to protect thecal sac

7 Do not pull or tear ligamentum flavum

8 Release all tissue attachments to dura

9 Use disposable and undamaged suction tips around thecal sac

10 Be aware of conjoined nerve roots

11 Use knife to incise anulus only vertically

12 Open mouth of pituitary rongeur within disk space

13 Avoid use of electrocautery near the dura

14 Use cottonoid pledgets cautiously

15 Use burr in medial-to-lateral direction under direct visualization

16 Never manipulate thecal sac above L2

17 Never retract thecal sac more than 50%

18 Consider neurologic monitoring

19 Do not leave spikes of bone after decompression

20 Control bleeding with bone wax, hemostatic agents, and cautery

prior to closure

21 Use drains when appropriate

22 Have anesthesiologist do Valsalva maneuver before closure

with muscle or fat grafts sutured

over the repair to the dura The

use of fibrin glue, which is derived

from equal volumes of thrombin

and cryoprecipitate, may add to the

reinforcement of tenuous repairs

Larger defects in the dura may

re-quire patch grafting with a

seg-ment of fascia from the

paraverte-bral muscles Once the repair has

been made, a watertight closure

without wound drains is required

for the overlying fascia,

subcuta-neous tissue, and skin

Postopera-tively, patients are typically kept

supine for several days to reduce

the hydrostatic pressure on the

dural repair

Persistent or residual dural leaks

at the time of initial repair may be

treated by the percutaneous

place-ment of a subarachnoid drain

im-mediately after the procedure The

placement of a subarachnoid drain

above the dural tear allows

diver-sion of spinal fluid and a decrease in

hydrostatic pressure at the repair

site Patients should be kept supine

after surgery for as long as 5 days,

and prophylactic antibiotic coverage

should be maintained Continuous

drainage at a rate of 10 to 15 mL/hr

is recommended In addition, close

monitoring of spinal fluid levels of

protein, glucose, and cell count is

important until the drain is

discon-tinued Daily Gram stains and

cul-tures of the collected spinal fluid

should also be obtained

Complications Due to

Changes in Spinal

Alignment

Neurologic complications

some-times occur without an obvious

intraoperative cause These indirect

injuries are usually the result of

dis-ruption of the vascular perfusion of

the spinal cord or nerve roots More

commonly associated with scoliosis

surgery, cord ischemia can occur

secondary to application of

exces-sive distraction forces to a relatively rigid spinal deformity It can also occur secondary to excessive hypo-tension Any change in neurologic monitoring signals during these maneuvers should alert the surgeon

to possible neurologic injury The degree of correction of the spinal deformity should be lessened or completely released, and a return to baseline of the evoked potentials should occur before further reduc-tion is attempted In some instances, the removal of the posterior instru-mentation is indicated Ischemic events involving the spinal cord and neural elements are estimated to occur in approximately 1 of every 3,000 surgical procedures for sco-liosis.5

Another procedure with high risk for neural deficit is reduction of spondylolisthesis Decompression

of the neural foramina (especially

at L5) before instrumentation and avoidance of nerve-root comsion from manual downward pres-sure during the process of drilling, tapping, and insertion of pedicle screws or the placement of rods reduces the risk of neurologic in-jury However, root injury is prob-ably secondary to effective length-ening of the root associated with deformity reduction or to release of reduction or resection of the sacral dome (sacral shortening)

Injuries Due to Instrumentation

The risk of neural injury secondary

to aberrant pedicle-screw place-ment has been reported.5 A num-ber of principles should be adhered

to in order to minimize that risk

The proper starting point should be identified by using osseous land-marks or, in cases of severe de-formity, by directly palpating the pedicle through a laminotomy

Once the pedicle has been probed,

it should be checked for inadvertent

perforations After tapping, the hole should be checked again for perforations Radiography or fluo-roscopy should be used to evaluate the placement of screws and the overall alignment after insertion of hardware Intraoperative pedicle-screw stimulation with electromyog-raphy is commonly used to ensure proper pedicle-screw placement.8 Stimulation of the pedicle screw that results in nerve-root conductivity below a certain threshold stimula-tion can be indicative of screw breakout or pedicle fracture Re-orientation or redrilling of the screw hole is warranted Fractures of the pedicle secondary to screw mis-placement can also cause direct nerve-root impingement by the frag-ment of bone

Patients noted to have postoper-ative neurologic deficits or leg pain after the placement of instrumenta-tion should be evaluated with com-puted tomography (CT) This is preferable to magnetic resonance (MR) imaging because it accurately demonstrates screw placement Questionable screw placement in the clinical setting of new-onset leg pain or neurologic deficit is best managed by reoperation to remove

or replace the device and to ensure adequate neural foraminal decom-pression (Fig 1)

Posterior interbody grafts, or cages, used during posterior-lumbar interbody fusions potentially can dislodge and impinge on the nerve roots or cauda equina, causing seri-ous neurologic sequelae The inci-dence of this complication is in the range of 0.3% to 2.4%.9 Another problem with such procedures is the wide exposure required for graft insertion, with resultant traction injury or development of instability Anterior interbody devices carry similar risks with regard to incor-rect placement and dislodgment With the placement of anterior in-terbody fusion devices, injury to the hypogastric plexus secondary to the

traumatic exposure can result in

retrograde ejaculation in men The

incidence of injury to the plexus has

been reported to be in the range of

1% to 5% with the use of these

de-vices, especially when utilizing a

laparoscopic approach.10 The risk of

such an injury after open anterior

lumbar fusion surgery has been

reported to be 0.42%.11 Additionally,

malplacement of anterior interbody

devices themselves or expulsion of

disk material posteriorly into the

spinal canal can cause neurologic

compromise, with an incidence of

2% to 4%.10

Bone Graft–Related

Neurologic Injury

The site from which bone graft is

harvested is often the origin of

post-operative pain Kurz et al12noted a

15% incidence of pain in the first 3

postoperative months Frymoyer et

al13noted this problem in up to 37%

of patients as long as 14 years after

surgery In many instances, the

postoperative pain was part of a

general pain syndrome Persistent

pain was more common in patients

in whom the grafts had been taken from the same side as their preoper-ative sciatica

Donor-site pain can also be spe-cifically related to peripheral nerve injury This may be secondary to involvement of the lateral femoral cutaneous nerve (meralgia pares-thetica) during harvesting of ante-rior iliac crest bone Nerve symp-toms may result from entrapment secondary to scar formation, hema-toma, or laceration The variant anatomy of this nerve as it crosses the anterior ilium mandates careful dissection The incidence of this complication is reportedly between 1% and 14%.14 Beginning the inci-sion at a point 3 cm posterior to the anterior superior iliac spine lessens the chance of this complication

When taking a bone graft from the posterior iliac crest, one should

be aware of the location of the su-perior cluneal nerves and the sciatic nerve.12 The risks associated with bone-graft harvesting from this area can be significant The incision should be parallel to the midline, as the incidence of superior cluneal

nerve injuries increases with exten-sion of the inciexten-sion more than 8 cm lateral to the posterior superior iliac spine The superior cluneal nerves are cutaneous branches of the proxi-mal three lumbar nerves and sup-ply sensation to a large portion of the buttock after piercing the lum-bodorsal fascia Although there is a large degree of cross-innervation, numbness or painful neuromas may develop after laceration Pal-pation of the sciatic notch may aid the surgeon in establishing land-marks for taking the graft and avoiding injury to the sciatic nerve

or superior gluteal artery The direction of use of the osteotome or gouge should always be cephalad and tangential to the notch

Complications in the Early Postoperative Period

A careful neurologic assessment when the patient awakens from surgery provides an index exami-nation to distinguish a deficit that may have occurred intraoperatively from one that occurs in the early postoperative period Anatomic correlation of the neurologic deficit noted on examination with intraop-erative events often facilitates early diagnosis This is often more valu-able than attempts at postoperative imaging with CT, MR imaging, or plain radiography Evaluation of perineal sensation and sphincter tone is also essential, particularly after high lumbar surgery when the possibility of spinal cord injury exists The development of neuro-logic symptoms in a patient who awakened from lumbar surgery neurologically intact should alert the surgeon to the possibility of the development of new neural ele-ment compression The importance

of an early accurate baseline exami-nation cannot be overemphasized,

as diagnostic imaging of the neural elements with MR imaging or CT

Figure 1 Lateral (A) and anteroposterior (AP) (B) radiographs of a 46-year-old man who

underwent anterior diskectomy with bone grafting and posterior fusion with pedicle

screws 4 years previously The patient awakened from surgery with severe left leg pain

extending to the dorsum of his foot and was subsequently seen by several physicians.

Radiographs demonstrate misplacement of three of the four pedicle screws.

can be difficult to interpret in the

early postoperative period

Neurologic deficits that develop

in the early postoperative period (1

to 14 days) usually occur secondary

to retained disk fragments after

diskectomy, postoperative

hema-toma, pseudomeningocele,

hernia-tion of a fat graft, or (rarely) an

epidural abscess Acute

spondy-lolisthesis secondary to iatrogenic

instability may also present with a

new neurologic deficit This is more

likely to occur in the late

postopera-tive period; when it does occur in

the early postoperative period, it is

more likely to occur after aggressive

lateral decompressions with

viola-tion of the pars or facet joints Plain

radiography and CT may be helpful

in the evaluation of this problem

Recurrent Disk Herniation

After diskectomy for disk

hernia-tion, the incidence of neural

com-pression by a retained or missed

fragment of disk is approximately

0.2%.15 The patient typically

awak-ens from surgery and reports

unre-lieved symptoms of radiculopathy

Because early postoperative

imag-ing is difficult to interpret,

reexplo-ration based on the clinical

exami-nation findings and symptoms may

be indicated to ensure the removal

of any remaining disk fragment

Of course, more than one fragment

may be causing residual

compres-sion At the time of the index

proce-dure, suspicion that a fragment of

disk may have been missed should

be raised by the presence of friable

disk material or multiple fragments

Epidural Hematoma

The development of a postoperative

epidural hematoma may be

associ-ated with excessive or poorly

con-trolled intraoperative bleeding

Pa-tients often have few complaints

initially, but significant increasing back pain subsequently develops

This may progress to unremitting leg pain or even cauda equina syn-drome in severe cases Patients with increasing back or leg pain require careful monitoring A complete neurologic assessment is mandatory, including a rectal examination and a check for perianal pin-prick sensa-tion If neurologic deterioration oc-curs, a spinal imaging study, such as CT-myelography or MR imaging, should be performed In obvious cases, the patient can be immediately taken to the operating room for evacuation without imaging The presence of an epidural hematoma is

a surgical emergency, requiring decompression

Epidural Abscess

In the 2- to 4-week period after sur-gery, epidural abscess (Fig 2) be-comes a potential cause of new-onset neurologic deficits, although this is a rare complication Epidural abscesses, like hematomas, require urgent decompression

Pseudomeningocele

Dural tears that occur during sur-gery and that are not recognized and repaired or are inadequately repaired can result in the formation

of a pseudomeningocele5(Fig 3)

With the increased number of oper-ations for stenosis being performed, this complication may be more fre-quent than previously suspected

The incidence of pseudomeningo-cele formation is estimated to be between 0.07% and 2%.8 The prev-alence of incidental durotomy is higher, at approximately 4%.8 In-cidental durotomy is the second most common cause of lawsuits after lumbar spine surgery and the most common complication of re-peat laminectomy.8

The formation of pseudomenin-goceles is more common after lum-bar spine surgery than after cervi-cal spine surgery Although small dural tears can close spontaneously, many continue to leak and form pseudomeningoceles The use of agents such as Adcon-L may pre-cipitate continued leakage of unrec-ognized dural lacerations.16 These can be noted as a slowly expanding fluid mass or soft-tissue bulging on physical examination Patients usu-ally present with a progressively worsening headache Both the mass and the headache may in-crease in magnitude on standing Diagnosis is readily made early by using myelography followed by

CT Magnetic resonance imaging may also be helpful in the diagno-sis, but it may be difficult to

differ-Figure 2 T2-weighted MR image of a 50-year-old man who underwent posterior laminectomy Approximately 3 to 4 weeks after surgery, severe, unremitting back pain developed The image demonstrates enhanced signal in the disk space with enhancement anterior to the thecal sac extending cephalad, consistent with an epidural abscess Treatment included irri-gation and debridement and intravenous antibiotic therapy.

entiate a pseudomeningocele from

a postoperative hematoma with

this modality The onset of

neuro-logic symptoms may present either

insidiously or acutely with pain,

headache, and sudden neurologic

deficit A neurologic deficit may

occur when one or more nerve

roots herniate out of the dural tear

and become trapped within the

pseudomeningocele

Treatment of pseudomeningoceles

includes surgical exploration and

repair Careful dissection is required

Excision of the cyst is not necessary, but opening of the cyst to avoid in-jury to the trapped roots is usually required before closure and repair

Summary

Neurologic complications after lumbar spine surgery are neither common nor necessarily foresee-able With the increasing number

of lumbar spine operations being performed, the number of patients who will sustain neurologic injury can be expected to increase Be-cause of the often irreversible and dramatic nature of these injuries, as well as the lack of definitive treat-ments once they have occurred, it

is obviously best to prevent these in-juries through use of meticulous op-erative technique, awareness of risk, and close attention to perioperative details

Figure 3 Lateral (A) and axial (B) MR images of a 55-year-old man approximately 4 to 5 weeks after lumbar laminectomy He reported a

sudden sharp pain with coughing, and a fluctuant mass was noted in his low back The images demonstrate a large pseudomeningocele.

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