Vol 9, No 2, March/April 2001
137
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

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,

1
In contrast, peripheral
nerves are protected by an epineu-
rium and a perineurium. 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
mm
2
), 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 mm
2
can be used for the radiologic diag-
nosis of central spinal stenosis. Re-

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

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

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

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

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-
M. Darryl Antonacci, MD, and Frank J. Eismont, MD
Vol 9, No 2, March/April 2001
139
son, the suction tip should be

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

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
Neurologic Complications After Lumbar Spine Surgery
Journal of the American Academy of Orthopaedic Surgeons
140
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

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-

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

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
M. Darryl Antonacci, MD, and Frank J. Eismont, MD
Vol 9, No 2, March/April 2001
141
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

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.

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
Neurologic Complications After Lumbar Spine Surgery
Journal of the American Academy of Orthopaedic Surgeons
142

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-

5
(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-

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

Edema formation in spinal nerve roots
induced by experimental, graded com-
pression: An experimental study on
the pig cauda equina with special ref-
erence to differences in effects between
rapid and slow onset of compression.
Spine 1989;14:569-573.
5. Stambough JL, Simeone FA: Neuro-
logic complications in spine surgery,
in Herkowitz HN, Eismont FJ, Garfin
SR, Bell GR, Balderston RA, Wiesel SW
(eds): Rothman-Simeone: The Spine, 4th
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vol 2, pp 1724-1733.
6. Stevens WR, Glazer PA, Kelley SD,
Lietman TM, Bradford DS: Ophthal-
mic complications after spinal surgery.
Spine 1997;22:1319-1324.
7. Hoyland JA, Freemont AJ, Denton J,
Thomas AM, McMillan JJ, Jayson MI:
Retained surgical swab debris in post-
laminectomy arachnoiditis and peri-
dural fibrosis. J Bone Joint Surg Br
1988;70:659-662.
M. Darryl Antonacci, MD, and Frank J. Eismont, MD
Vol 9, No 2, March/April 2001
145
8. Calancie B, Madsen P, Lebwohl N:
Stimulus-evoked EMG monitoring
during transpedicular lumbosacral

16. Le AX, Rogers DE, Dawson EG, Kropf
MA, De Grange DA, Delamarter RB:
Unrecognized durotomy after lumbar
discectomy: A report of four cases
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