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Vol 7, No 2, March/April 1999
101
Nerve injury after total hip arthro-
plasty (THA) can be a devastating
complication. Upper-extremity
nerve-traction palsies related to
positioning have been reported
with a higher incidence of ulnar
nerve damage in arthroplasty pa-
tients with inflammatory arthritis.
1
Obturator nerve injuries are ex-
ceedingly uncommon but have
been the subject of case reports.
Superior gluteal nerve and femoral
nerve injury are relatively rare and
in general have a better prognosis
than sciatic nerve injuries. Most of
the literature focuses on the per-
oneal division of the sciatic nerve.
The physiologic demands as well
as the structural anatomy of the
nerves about the hip predispose
these structures to injury during
surgical procedures. In this article,
we will review clinical studies on
the diagnosis, treatment, and prog-
nosis of this infrequent complica-
tion and focus attention on the
importance of prevention.
Peripheral Nerve Anatomy

and Physiology
Nerves are uniquely designed to
quickly transmit electrical impulses,
or action potentials, over long dis-
tances. Each nerve cell is composed
of four regions (Fig. 1). Dendrites
are the thin processes that collect
signals from other nerve cells. The
cell body contains the nucleus and
organelles, which tend to the meta-
bolic needs of the neuron. A single
axon branches off each cell body
and acts as a transport tube for pro-
teins and a conduit for transmission
of action potentials.
Sensory nerves are afferent
fibers that transmit action poten-
tials from nociceptors or mechano-
receptors toward the dorsal root
ganglia of the central nervous sys-
tem. Motor nerves are efferent
fibers that carry action potentials to
special motor end-plates on muscle
spindles. Presynaptic terminals are
the specialized nerve endings that
transmit information to dendrites
of other nerves or to a neuromus-
cular junction. The model hypoth-
esized for transmission of proteins
and transport of neurotransmitter

vesicles from cell body to axon
involves carrier proteins, micro-
tubules, and an adenosine triphos-
phate (ATP)Ðdependent protein
called kinesin. Retrograde axoplas-
mic transport serves to recycle
empty vesicles and has been linked
to the transmission of herpes sim-
plex, rabies, and polio viruses and
tetanus toxin.
A number of other cell types are
associated with the primary nerve
cells. Glial cells surround nerve cell
bodies and their axons. Microglia
are the phagocytes that mobilize
after injury. Oligodendrocytes and
Schwann cells are macroglia cells
that produce the myelin sheath,
which enhances the speed of signal
transmission. Oligodendrocytes
are found only in the central ner-
vous system; each one myelinates
many different axons. Schwann
Dr. DeHart is Attending Orthopaedic Surgeon,
Huebner Medical Center, San Antonio, Tex;
and Clinical Assistant Professor, Department
of Orthopaedic Surgery, University of Texas
Health Science Center at San Antonio. Dr.
Riley is Professor of Orthopaedic Surgery,
Johns Hopkins University, Baltimore.

Reprint requests: Dr. DeHart, Suite 390, 9150
Huebner Road, San Antonio, TX 78240.
Copyright 1999 by the American Academy of
Orthopaedic Surgeons.
Abstract
Nerve injury occurs in 1% to 2% of patients who undergo total hip arthroplas-
ty and is more frequent in patients who need acetabular reconstruction for dys-
plasia and those undergoing revision arthroplasty. Injury to the peroneal divi-
sion of the sciatic nerve is most common, but the superior gluteal, obturator,
and femoral nerves can also be injured. Nerve injury can be classified as neu-
rapraxia, axonotmesis, or neurotmesis. The worst prognosis is seen in patients
with complete motor and sensory deficits and in patients with causalgic pain.
Prevention is of overriding importance, but use of ankle-foot orthoses and
prompt management of pain syndromes can be useful in the treatment of
patients with nerve injury. Electrodiagnostic studies hold promise in complex
cases; however, their intraoperative role requires objective, prospective, con-
trolled scientific study before routine use can be recommended.
J Am Acad Orthop Surg 1999;7:101-111
Nerve Injuries in Total Hip Arthroplasty
Marc M. DeHart, MD, and Lee H. Riley, Jr, MD
Nerve Injuries in Total Hip Arthroplasty
Journal of the American Academy of Orthopaedic Surgeons
102
Nerve Injury
Seddon classified nerve injuries
into three types (Fig. 5). Neura-
praxia is a conduction block of
anatomically intact nerves caused
by minor injury. A period of loss
of sensation may occur, but recov-

ery is likely to be complete. Axon-
otmesis is a more severe injury in
which axons are disrupted but the
investing connective tissue sur-
vives. Wallerian degeneration is
the process of disintegration of the
axon and myelin sheath over the
entire axon distal to the site of
injury. Preservation of the endo-
neurial supporting structures can
cells are found in the peripheral
nervous system; each provides
myelination for only a 0.1- to 1.0-
mm segment of the axon of one
neuron (Fig. 2).
The spaces between Schwann
cells, or nodes of Ranvier, are the
sites of action potential initiation.
The internal milieu of a resting
nerve cell is electronegative com-
pared with the extracellular fluid.
This electrical difference is main-
tained by energy from ATP and a
sodium-potassium pump that con-
stantly pumps sodium out of the
cell. Chemical, mechanical, or volt-
age changes can cause sodium
gates to open, allowing an influx of
positive sodium ions, a process
known as depolarization (Fig. 3).

The result is an action potential Ñ
a brief explosive change in the
nerve cell to a very positive value.
Nodes of Ranvier have high con-
centrations of voltage-gated sodi-
um channels that ease initiation of
action potentials. The insulating
myelin allows action potential cur-
rent to flow quickly with little
attenuation to the next node of
Ranvier. This jumping of the ac-
tion potential down the neuron
from node to node is very effective
in increasing the conduction speed
of the signal down the axon. De-
myelinating diseases, such as mul-
tiple sclerosis and Guillain-BarrŽ
syndrome, interfere with the prop-
agation of the signal, slowing or
completely stopping conduction.
As many as several thousand
axons and their accompanying
Schwann cells are bundled together
by a loose endoneurial connective
tissue into fascicles (Fig. 4). Edema
of this endoneurium is the hallmark
of irreversible nerve damage. Peri-
neurium is the expansion of dense
connective tissue that surrounds
each fascicle. It has high tensile

strength and serves as the major
barrier for endoneurial edema.
Fascicles are bundled together into
nerves by epineurium, which is a
loose meshwork composed of colla-
gen and elastin that protects the
nerve from compressive forces.
Spinal nerves do not have peri-
neurium or epineurium and are
more vulnerable to tensile and com-
pressive forces.
2
Because of the high metabolic
demands of the nerve tissue, blood
supply is crucial for effective signal
transmission. The vascular supply
to the nerves is derived from both a
segmental extrinsic system of
superficial vessels, which give off
perforating branches, and an intrin-
sic system of epineurial, perineu-
rial, and endoneurial plexuses with
their communicating branches.
Fig. 1 A typical neuron. (Adapted with
permission from Bodine SC, Lieber RL:
Peripheral nerve physiology, anatomy, and
pathology, in Simon SR (ed): Orthopaedic
Basic Science. Rosemont, Ill: American
Academy of Orthopaedic Surgeons, 1993,
p 327.)

Cell body
Nucleus
Myelin sheath
Dendrites
Axon hillock
Axon
Node of
Ranvier
Terminal branches
Presynaptic
terminal
Postsynaptic neuron
Nodes of
Ranvier
Nucleus
Inner tongue
Axon
Layers of
myelin
Fig. 2 The Schwann cell wraps lipid-rich
myelin around the axon to enhance con-
duction of electrical impulses. (Adapted
with permission from Bodine SC, Lieber
RL: Peripheral nerve physiology, anatomy,
and pathology, in Simon SR (ed): Ortho-
paedic Basic Science. Rosemont, Ill: Amer-
ican Academy of Orthopaedic Surgeons,
1993, p 328.)
Marc M. DeHart, MD, and Lee H. Riley, Jr, MD
Vol 7, No 2, March/April 1999

103
sis. The effect of ischemia with
compression in the tissue under a
tourniquet was compared with
ischemia alone in more distal tissue.
Evidence of endoneurial edema
was found after 2 to 4 hours of com-
pression.
The amount of stretch a nerve will
tolerate depends on whether the
nerve is freely mobile in supple soft
tissue or whether it is bound down by
osseous prominences, fascia, or scar.
Rabbit sciatic nerve showed conduc-
tion failure with 25% lengthening.
Histologic changes were found after
lengthening of nerves by 4% to 11%.
Nerve microcirculation was found to
be impaired after 8% stretch and
stopped after 15% stretch.
5
The rup-
ture of axon fibers precedes the fail-
ure of fascicles and may occur with
stretch of as little as 4% to 6%.
2
Four major factors that increase
the probability of mechanical dis-
ruption include increased load due
to compression or stretch, increased

rate of loading, increased duration
of loading, and uneven application
of load to tissues. Clinical experi-
ence and LaplaceÕs law (tension is
proportional to the pressure and
radius of a cylindrical structure)
demonstrate that large-diameter
axons are more susceptible to dam-
guide the slow (1 mm per day)
regeneration of sprouts to their
original end-organ. Atrophy and
scarring of muscle can prevent
effective function if axons fail to
reach motor end-plates within 2
years of the time of injury.
3
This
accounts for the variability in de-
gree of recovery. Complete disrup-
tion of the nerve, or neurotmesis,
carries the worst prognosis for
recovery and may lead to abortive
efforts at regeneration, which can
result in painful neuromas.
Damage to nerves and their
blood supply can be caused by var-
ious combinations of compression,
stretch, ischemia, and transection.
Compressive trauma affects both
the structure of the nerve and the

neural vascular supply. Large,
closely packed fasciculi have less
cushioning epineurium and are
more vulnerable than nerves with
smaller fasciculi and a greater
amount of epineurial tissue.
2
LundborgÕs classic experiments
involving tourniquet application
4
demonstrated that normal circula-
tion returned within seconds when
inflation time was 2 hours or less.
For tourniquet times between 4 and
6 hours, it took 2 to 3 minutes for
the circulation to return, and a peri-
od of hyperemia was observed.
After 8 to 10 hours, blood flow took
5 to 20 minutes to return, and there
was evidence of microvascular sta-
Fig. 3 A, When the cell is at rest, the passive fluxes of Na
+
and K
+
into and out of the cell
are balanced by the energy-dependent sodium-potassium pump. (Adapted with permis-
sion from Bodine SC, Lieber RL: Peripheral nerve physiology, anatomy, and pathology, in
Simon SR [ed]: Orthopaedic Basic Science. Rosemont, Ill: American Academy of
Orthopaedic Surgeons, 1993, p 332.) B, An action potential can be the result of voltage
(top), chemical (center), or mechanical (bottom) changes that open axon sodium channels.

The resulting sodium influx causes an explosive positive change in the nerve cell.
(Adapted with permission from Kandel ER, Schwartz JH, Jessell TM: Principles of Neural
Science, 3rd ed. Norwalk, Conn: Appleton & Lange, 1991, pp 75-76.)
Vessel
Epineurium
Perineurium
Endoneurium
Fascicle
Nerve fiber
Epineurium
Perineurium
Endoneurium
Fig. 4 Cross-sectional anatomy of a nerve. (Adapted with permission from Wilgis EFS,
Brushart TM: Nerve repair and grafting, in Green DP (ed): Operative Hand Surgery. New
York: Churchill Livingstone, 1993.)
A B
Closed
Ligand
binding
Stretch
Open
P
i
∆Vm
Nerve Injuries in Total Hip Arthroplasty
Journal of the American Academy of Orthopaedic Surgeons
104
age than smaller fibers. Clinical
factors, which will be discussed
later, also play a role in nerve injury

and repair.
Anatomy of the Peripheral
Nerves About the Hip
The superior gluteal nerve arises
from the L4, L5, and S1 nerve roots
and exits at the sciatic notch to sup-
ply the gluteus medius, gluteus
minimus, and tensor fascia lata. It
travels with the superior gluteal
artery deep to the gluteus maximus
and medius but superficial to the
gluteus minimus. In one study,
6
subclinical superior gluteal nerve
injury was found in 77% of cases in
which a transtrochanteric lateral or
posterior hip approach was used.
Anterior branches supplying the
distal tensor fascia lata may be sac-
rificed during the anterolateral
approach when dissecting the inter-
val between the gluteus medius
and the tensor. It is also at risk if
the 3- to 5-cm Òsafe areaÓ proximal
to the greater trochanter is violated
during direct lateral approaches to
the hip.
7
When this safe area is
respected, clinical deficits are rare.

8
A positive Trendelenburg sign or
Trendelenburg gait and weak ab-
duction can indicate damage to this
nerve.
The obturator nerve arises from
the L2, L3, and L4 nerve roots
within the posterior psoas and
then emerges medially at the
sacral ala to travel along the ilio-
pectineal line (Fig. 6). It is rarely
injured,
9
but case reports docu-
ment a risk of injury when cement,
screws, or reamers penetrate the
anterior quadrants of the acetabu-
lum (Fig. 7). The obturator nerve
exits the pelvis at the superior
aspect of the obturator foramen,
where it supplies the adductor
muscles and a medial patch of
thigh skin. Persistent pain in the
groin or thigh, adductor weakness
after placement of intrapelvic
screws, or allograft or cement visi-
ble on radiographs after hip arthro-
plasty suggests obturator nerve in-
jury.
10

Hip disease can cause re-
ferred pain to the knee through
the obturator distribution.
The femoral nerve arises from the
L2, L3, and L4 nerve roots; passes
through the psoas major muscle;
and then travels between the psoas
and the iliacus to enter the thigh as
the lateralmost structure of the
femoral triangle. The femoral nerve
supplies motor impulses to the mus-
cles of knee extension (the quadri-
ceps) and sensation to most of the
medial thigh and calf. Prolonged
hyperextension of the thigh can
cause femoral-nerve traction in-
juries. Iliacus hematomas in patients
who have bleeding disorders or are
taking anticoagulants are well-
known causes of femoral nerve
palsy. The femoral nerve is rarely
injured after hip arthroplasty (0.04%
to 0.4% of cases)
1,9,11
; it is most at
risk during placement of anterior
acetabular retractors when anterior
or anterolateral approaches are used
(Fig. 8). Simmons et al
12

reported
the highest rate of femoral nerve
palsy after hip arthroplasty (2%);
however, all patients had full func-
tional recovery by 12 months. The
presence of thigh pain, anteromedial
Fig. 5 Spectrum of injury to a nerve as it
is stretched. (Only one axon in its connec-
tive tissue layers is shown.) A = Neura-
praxia, with all anatomic structures intact.
B = Axonotmesis, with disruption of the
axon but intact connective tissues. C =
Neurotmesis, with complete disruption of
all layers. (Adapted with permission from
Sunderland S: Nerve Injuries and Their
Repair: A Critical Appraisal. New York:
Churchill Livingstone, 1991, p 148.)
A
B
C
Fig. 6 Cross section of the pelvis at the level of the hip joint shows location of the obtura-
tor, femoral, and sciatic nerves. (Adapted with permission from Weber ER: Peripheral
neuropathies associated with total hip arthroplasty. J Bone Joint Surg Am 1976;58:66-69.)
Obturator nerve
Femoral nerve
Sciatic nerve
Femoral artery
Femoral vein
Marc M. DeHart, MD, and Lee H. Riley, Jr, MD
Vol 7, No 2, March/April 1999

105
thigh and medial leg numbness,
quadriceps weakness, and difficulty
climbing stairs suggests femoral
nerve injury.
The sciatic nerve arises from the
L4, L5, S1, S2, and S3 nerve roots
and is composed of the preaxial
anterior tibial and postaxial poste-
rior peroneal divisions. These divi-
sions usually travel together in a
single sheath, but in 10% to 30% of
cases they are separate as high as
the greater sciatic notch. The nerve
is located deep to the piriformis
inside the pelvis and then travels
distally deep to the gluteus muscles
and superficial to the external rota-
tors at the level of the hip joint. It
is the nerve most frequently in-
jured during hip arthroplasty and
is at risk for injury either from
placement of posterior acetabular
retractors or from anterior or lateral
traction on the femur.
Distal to the level of the lesser
trochanter and the ischial tuberosi-
ty, the sciatic nerve passes between
the adductor magnus and the long
head of the biceps femoris, just

medial to the insertion of the
gluteal sling. All medial branches
of the sciatic nerve arise from the
tibial division and supply the ham-
strings. The short head of the biceps
is the only thigh muscle supplied
by the peroneal division of the sci-
atic nerve. At the superior aspect
of the popliteal fossa, the two divi-
sions split into the tibial nerve and
the common peroneal nerve. The
peroneal nerve innervates the dor-
siflexors and evertors of the foot
and ankle. The tibial nerve inner-
vates the plantar flexors and inver-
tors. The sural nerve provides sen-
sation to most of the lateral aspect
of the calf and arises from both the
medial sural cutaneous branch of
the tibial nerve and the lateral sural
cutaneous branch of the common
peroneal nerve.
Sciatic Nerve Injury in
THA
As mentioned previously, the sciat-
ic nerve is the nerve most common-
ly injured during THA. It was in-
volved in over 90% of the 53 nerve
injuries reported by Schmalzried et
al

11
in their series of more than
3,000 cases. The incidence of sciatic
nerve injury in primary THA has
been reported to be between 0.6%
and 3.7%, with most large series
citing a rate of about 1.5%.
9,11
Overall rates are elevated by the
relatively higher incidence in revi-
sions (3% to 8%) and in patients
with developmental dysplasia of
the hip (DDH) (5.8%).
11
In uncom-
plicated primary THA, sciatic
nerve injury occurs in fewer than
1% of cases. Weber et al
9
noted
that since only severe injury pre-
sents as a clinical problem, the con-
dition may be more common than
is generally appreciated. They
reported that in a study utilizing
preoperative and postoperative
electromyography, 70% of THA
patients had subclinical sciatic
nerve injury.
The etiology of nerve injury

is protean. Direct trauma from
scalpel, electrocautery, retractors,
wires, reamers, Gigli saw, bone
fragments, or cement protrusion;
constriction by suture, wire, or
cable; heat from the polymeriza-
tion of cement; compression from
dislocation; excessive lengthening;
and subfascial hematoma have all
been reported. However, the cause
of 50% of all sciatic nerve palsies is
unknown.
11,13
Fig. 7 The acetabular-quadrant system
(ASIS = anterosuperior iliac spine). Screws
originating in the anterosuperior quadrant
threaten the external iliac artery and vein.
Screws from the anteroinferior quadrant
threaten the iliac vessels and the obturator
nerve. There is less risk of neurovascular
injury with placement of short (<25 mm)
screws in the posterosuperior quadrant.
(Adapted with permission from Wasielew-
ski RC, Cooperstein LA, Kruger MP,
Rubash HE: Acetabular anatomy and the
transacetabular fixation of screws in total
hip arthroplasty. J Bone Joint Surg Am 1990;
72:501-508.)
ASIS
Postero-

superior
Postero-
inferior
Antero-
superior
Antero-
inferior
Fig. 8 The close proximity of the femoral
nerve and vessels to an anteriorly placed
acetabular retractor. (Adapted with permis-
sion from Shaw JA, Greer RB: Compli-
cations of total hip replacement, in Epps CH
[ed]: Complications in Orthopaedic Surgery.
Philadelphia: JB Lippincott, 1994, p 1035.)
Nerve Injuries in Total Hip Arthroplasty
Journal of the American Academy of Orthopaedic Surgeons
106
The peroneal division of the sci-
atic nerve is more susceptible to
injury than the tibial division.
Schmalzried et al
11
found that 94%
of the sciatic nerve injuries in their
study involved the peroneal divi-
sion. The tibial division was only
rarely involved by itself (2% of
cases). The superficial position of
the common peroneal nerve as it
wraps around the neck of the fibula

makes it vulnerable to compres-
sion. The peroneal division may be
more susceptible to stretch injuries
because it is relatively more fixed
between the sciatic notch and the
fibular head. Another explanation
is based on morphologic differences
between the tightly packed fascicles
of the peroneal division and those
of the tibial division, which has
relatively more connective tissue
(Fig. 9). The fact that the peroneal
division is more lateral may also
increase its vulnerability to trauma.
Generally accepted risk factors
for sciatic nerve injuries include
THA in patients with DDH and
revision THA. Johanson et al
13
noted increased blood loss and time
of surgery in their patients with
nerve injury and considered all fac-
tors to be related to the level of diffi-
culty of the case. Whether the risk
is higher in women and to what
degree leg lengthening increases
risk remain controversial. Some
hypothesize that the increased risk
in women is due to less soft-tissue
mass,

9
while others believe that the
increased risk is related to the
prevalence of DDH.
3
Pritchett
14
suggests that a Òdouble crushÓ phe-
nomenon, as described in carpal
tunnel syndrome, may play a role in
hip arthroplasty patients who also
have spinal stenosis. Of 16 spinal
stenosis patients with footdrop of
unknown cause diagnosed after hip
arthroplasty, 12 had improvement
of the nerve palsy after spinal
decompression with laminectomy.
The role of leg lengthening in
cases of nerve injury is unclear.
Nerves will tolerate only a finite
amount of acute stretch. A soft-
tissue bed that is scarred and has
compromised vascularity should in-
crease the potential for injury with
lengthening. Both the presence of
scar from previous operations and
the desire to increase leg length must
be considered in revisions and DDH
cases. Edwards et al
15

noted that 6 of
10 patients with nerve palsy had leg
lengthening of more than 3 cm.
Lengthening of less than 3.8 cm
was associated with only peroneal-
division palsies; lengthening by more
than 3.8 cm was associated with both
peroneal- and tibial-division palsies.
A Mayo Clinic review of DDH pa-
tients who underwent THA demon-
strated a 13% incidence of sciatic
nerve palsy.
16
Of those patients with
lengthening of 4 cm or more, 28%
had palsy. No nerve injuries oc-
curred in those with lengthening of
less than 4 cm. Kennedy et al
17
de-
monstrated acute progressive wors-
ening of somatosensory evoked
potential (SSEP) changes when
reduction of the femoral head was
achieved after increasing the neck
length. All four patients in whom
causalgia developed postoperatively
had SSEP reductions in amplitude
greater than 75% after component
reduction. Nercessian et al

18
report-
ed on 66 patients with lengthening
between 2.0 and 5.8 cm without neu-
rologic deficit. They calculated the
amount of lengthening as a percent-
age of the length of the femur and
concluded that lengthening of up to
10% was safe.
Diagnosis
Clinical assessment alone underesti-
mates the true incidence of nerve
injury after hip arthroplasty.
6,9,19
The diagnosis of significant nerve
Transection
Fig. 9 Multifascicular nerves with abundant connective tissue (as seen in the tibial divi-
sion) are less vulnerable to transection or compression than nerves with tightly packed fas-
cicles (as seen in the peroneal division). (Adapted with permission from Bodine SC, Lieber
RL: Peripheral nerve physiology, anatomy, and pathology, in Simon SR (ed): Orthopaedic
Basic Science. Rosemont, Ill: American Academy of Orthopaedic Surgeons, 1993, p 361.)
Tibial Division Peroneal Division
Marc M. DeHart, MD, and Lee H. Riley, Jr, MD
Vol 7, No 2, March/April 1999
107
injuries is usually not challenging
and should begin with adequate pre-
operative documentation of motor
strength and sensation. Thorough
evaluation of patients before revision

procedures may help demonstrate
minor nerve damage caused by prior
procedures. Complaints of weak-
ness, numbness, or paresthesias may
indicate a compromised nerve that is
at increased risk during the next
operation. Electrodiagnostic tests
can indicate nerve impairment and
the presence of preexisting neu-
ropathies of diabetes, chronic alcohol
abuse, or hypothyroidism.
Weakness of the muscles of ankle
dorsiflexion can indicate damage to
the peroneal division of the sciatic
nerve. Its sensory distribution in-
cludes the dorsum of the foot, with
the deep peroneal nerve supplying
the web space between the first and
second toes. The short head of the
biceps is the only muscle above the
knee that is supplied by the peroneal
division. Electromyographic (EMG)
recordings of this muscle can show
whether peroneal division injury is
at the level of the hip or at another
site of vulnerability, the fibular head.
Damage to only the tibial division is
rare and results in weakness of all
knee flexors except the short head of
the biceps. Weakness of the posteri-

or muscles of ankle and toe plantar
flexion should also be seen.
Prognosis
The prognosis of a nerve injury is
related to factors specific to the
injury and clinical factors related to
the patient (Table 1). In the case of
nerve injuries related to THA, the
patient is often elderly, with multi-
ple concurrent medical problems.
The damaged nerve is large, and the
distance from the end-organ is great.
In revision surgery, the previous
operation may leave binding scar
tissue and an altered vascular sup-
ply to the nerve. All these factors
decrease the likelihood of successful
nerve regeneration. In a large series
of primary THA procedures, as
many as 2% of patients had tran-
sient neurologic problems, and 0.5%
had permanent nerve damage.
20
Although 80% of patients with
nerve injuries have some persistent
neurologic dysfunction,
11,13
causal-
gic pain most highly predicts major
disability.

13
Edwards et al
15
found
that patients who had palsy of only
the peroneal division did well, but
that patients with injury to both the
tibial and the peroneal divisions
had less optimal recovery of func-
tion. In a review of over 3,100 hip
arthroplasty operations, Schmalz-
ried et al
11
found that patients who
recovered neurologic function usu-
ally did so by 7 months. All pa-
tients who had evidence of some
motor function immediately after
the operation or who recovered
some motor function during their
hospital stay had a good recovery.
No patient with dysesthesias had
satisfactory recovery of function.
Treatment
If no specific cause is identified,
often no immediate treatment to
decrease compression or stretch of
the nerve is indicated. Serial exam-
inations may demonstrate nerve
recovery. An advancing Tinel sign

distal to the site of injury signifies
regeneration of axons and at least
partial nerve continuity. Electro-
myograms and nerve conduction
velocity measurements may pro-
vide a more objective measure of
the level of injury, the degree of
injury, and evidence of recovery of
motor function.
When transection of the nerve is
discovered intraoperatively, an
attempt at nerve repair seems war-
ranted. Sunderland et al
21
reported
a single case of a sharply transected
sciatic nerve in a young patient that
was repaired early with a good
result. The results of nerve repair in
elderly patients are not promising.
In the rare case in which a mechani-
cal source of compression can be
identified, it should be removed.
Removal of long-skirted femoral
heads or more superior placement
of the acetabular component can
relieve tension on the nerve; how-
ever, this may require trochanteric
advancement to restore soft-tissue
tension. Delayed onset of progres-

sive neurologic symptoms after a
normal postoperative check should
alert the physician to consider evac-
uation of a subfascial hematoma. In
patients who have received anti-
coagulation therapy, motor and sen-
sory deterioration with increasing
thigh circumference demands cor-
rection of coagulation status and
surgical decompression.
Motor deficits can often be man-
aged with physical therapy to
strengthen ankle dorsiflexors and
stretch antagonist muscles so as to
prevent joint contractures. Ankle-
foot orthoses can be used to treat
footdrop, allowing clearance dur-
ing the swing phase and prevent-
Table 1
Clinical Factors in Nerve Injury
and Repair
Injury factors
Nerve injured
Degree of injury
Size of zone of injury
Distance of zone of injury from
an end-organ
Local tissue condition at injury
site (tension, vascularity,
presence of scar and infection)

Patient factors
Age
Preexisting neuropathies (e.g.,
those due to diabetes, alco-
holism, hypothyroidism,
spinal stenosis)
General medical condition (e.g.,
history of smoking or cortico-
steroid use)
Nerve Injuries in Total Hip Arthroplasty
Journal of the American Academy of Orthopaedic Surgeons
108
ing the steppage gait indicative of
weak dorsiflexors. Orthoses may
also help prevent equinus defor-
mity.
The presence of sensory deficits
requires diligence from the patient
in preventing inadvertent trauma
to the extremity, as may occur in
patients with diabetic neuropathy.
Dysesthesia and causalgic pain
postoperatively are best treated
with antidepressants as well as
with early and repeated sympa-
thetic nerve blocks as needed.
13
Surgical correction of late equino-
varus deformities may be necessary
in rare cases to provide stability of

the ankle joint, to release contrac-
tures, or to provide active dorsi-
flexion.
Prevention
The best treatment of any complica-
tion is prevention. The first step in
prevention is to identify the pa-
tients who are most at risk. Patients
with hip dysplasia and those who
will undergo revisions are clearly at
increased risk. Minimizing the
amount of leg lengthening during
preoperative planning and using
leg-length measurement techniques
may decrease the risk to the nerve.
There is no strong evidence favor-
ing any one approach for prevent-
ing nerve injury.
Whether it is prudent to expose
the nerve in high-risk cases is still
debated. Stillwell
22
performed
neurolysis to free the sciatic nerve
from binding scar and to allow
mobilization during revision cases.
Simon et al
23
recommend exposure,
macroneurolysis, and protection

routinely in every posterior ap-
proach and noted only one instance
of sensory loss in 400 cases. In-
creased intraoperative attention
with palpation of the nerve before
and after arthroplasty and limited
sciatic neurolysis of nerves that are
tethered or difficult to locate may
help to decrease the prevalence of
nerve injury.
24
However, direct
exposure of the nerve may damage
the anastomotic blood supply and
can lead to increased scarring.
Technical factors that may help
decrease the incidence of nerve
damage include wide exposure and
meticulous hemostasis to ensure
visualization of the anatomy, con-
stant attention to nerve position,
and careful placement and replace-
ment of retractors. Deliberate con-
trol of scalpels and reamers is
essential to avoid unwanted injury
to soft tissue. Careful placement of
fixation screws and attention to
drill-bit depth are essential. Use of
anterior-quadrant screws predis-
poses to nerve injury (Fig. 7).

Internal rotation of the femur dur-
ing placement of cerclage wires
and cables is recommended to help
visualize the soft tissue of the pos-
terior femur.
25
Proper placement of compo-
nents helps minimize dislocations
and the need for revisions that put
the nerve at increased risk. Black et
al
26
recommend extreme care when
revising only the acetabular com-
ponent in patients with monolithic
stems, which can rest directly on
the sciatic nerve. When cementing
the cup in acetabular revision
cases, the use of bone graft may
help prevent intrapelvic extravasa-
tion of cement.
Electrodiagnostic Studies
Several studies have reported the
use of electrodiagnostic tools, such
as evoked potentials (Fig. 10) and
electromyography (Fig. 11), to warn
surgeons of impending damage to
peripheral nerves during surgery.
Evoked potentials, first described in
1875 by Caton, are voltage changes

in sensory fibers after stimulation
of peripheral nerves. Damage or
irritation of nerves can alter electri-
cal signals by decreasing the size
Fig. 10 Examples of SSEP recordings. A, Baseline. B, Increased latency and decreased
amplitude associated with retractor compression of the sciatic nerve. C, Recovery of trac-
ing when the retractor is removed. (Reproduced with permission from Stone RG, Weeks
LE, et al: Evaluation of sciatic nerve compromise during total hip arthroplasty. Clin
Orthop 1985;201:26-31.)
Postincision
P1 = 39.2 msec
N1 = 46.4 msec
P1−N1 = 1.5 µV
Retractor on sciatic nerve
P1 = 46.4 msec
N1 = 54.4 msec
P1−N1 = 0.7 µV
Retractor removed
P1 = 40.8 msec
N1 = 52.0 msec
P1−N1 = 1.2 µV
A
B
C
1.5 µV
10 msec
+
−
Marc M. DeHart, MD, and Lee H. Riley, Jr, MD
Vol 7, No 2, March/April 1999

109
(amplitude) or increasing the trans-
mission time (latency) of the evoked
potential. Somatosensory evoked
potentials (SSEPs) are recorded
over the somatosensory cortex and
are monitored by an electroen-
cephalographlike device to give
feedback to the operating surgeon.
Somatosensory potentials are used
commonly in spine surgery. The
American Electroencephalographic
Society guidelines recommend
using a decrease of 50% or more in
amplitude or an increase of 10% or
more in latency to identify neuro-
logic compromise. In an animal
study,
27
statistically significant
SSEP changes were seen prior to
damage that caused postoperative
motor changes. However, com-
plete motor palsy in one division
can be caused while normal SSEP
tracings are seen in the other divi-
sion.
Amplitude changes can be influ-
enced by changes in patient tem-
perature, blood pressure, P

CO
2
,
level of anesthesia, and the electri-
cal noise in the operating room.
Cortical SSEPs cannot be recorded
during spinal anesthesia. For these
reasons, Kennedy et al
17
recom-
mend placing the monitoring elec-
trode directly on the most proximal
extent of the sciatic nerve.
Stone et al
28
first used SSEP
monitoring of the peroneal nerve
during total hip arthroplasty and
found a 20% incidence of intraoper-
ative signal changes. Changes in
SSEPs have been noted with retrac-
tor placement, leg positioning for
femoral reaming and cement re-
moval, anterior or lateral retraction
of the femur, and hip reduction.
29,30
In a nonrandomized, unmonitored
control group,
31
2 of 35 patients

(6%) had postoperative incomplete
sciatic nerve palsy, while none of
the 25 patients in the monitored
group had neurologic compromise.
Intraoperative monitoring was con-
sidered to be a valuable method for
use in revisions and reoperations.
Black et al
26
found no reduction
in sciatic nerve palsy in monitored
patients compared with an unmon-
itored historical control group from
the same institution. They felt that
monitoring may be more appropri-
ate in selected high-risk groups. In
a follow-up study, Rasmussen et
al
29
found no difference in the inci-
dence of sciatic nerve injury be-
tween 290 monitored patients and
a historical control group of 450
unmonitored patients (2.8% vs
2.7%). When they compared only
revision cases, no statistically sig-
nificant difference between groups
was found (6.7% vs 5.3%). They
concluded that SSEP monitoring
was not effective in predicting or

preventing nerve injuries. They
also reported that 2 patients who
were found to have postoperative
palsies had no SSEP changes dur-
ing the procedure.
Another method for monitoring
nerve function is to record EMG
responses. Intraoperative electro-
myography has been used to moni-
tor nerve function during opera-
tions that place the recurrent laryn-
geal nerve, facial nerve, spinal
nerves, and sciatic nerves at risk.
Electromyographic responses can
be recorded either as an averaged
motor evoked potential or as the
individual contraction of a muscle.
If an averaged motor evoked poten-
tial is recorded, either the spinal
cord or the nerve must be stimulat-
ed proximal to the site of surgery.
After changes through the site of
surgery, the elicited neurologic
activity is recorded as an EMG trac-
ing from a peripheral muscle.
Multiple stimulations are made,
and the muscle responses are aver-
aged by a computer.
Yet another technique is the
mechanically elicited, or sponta-

neous, electromyogram. Mechan-
ical irritation of the nerve results in
an action potential that produces a
muscle contraction measured by an
EMG response. The EMG response
elicited by mechanical irritation
provides the surgeon immediate
real-time feedback of exploration.
Muscle relaxation must be kept to a
minimum of two twitches of a
train-of-four stimulation for EMG
recording to be possible.
Because the site of hip surgery
and the site of calf muscle recording
Fig. 11 Example of EMG tracings during hip arthroplasty. Baseline is on the left. Repetitive firing of anterior tibialis muscle is represent-
ed during compression of the peroneal division of the sciatic nerve.
LT ANT TIB
LT GASTROC
Nerve Injuries in Total Hip Arthroplasty
Journal of the American Academy of Orthopaedic Surgeons
110
are both peripheral, anesthetic
effects on the brain and spinal cord
do not interfere with the perfor-
mance of mechanically elicited elec-
tromyography. This allows use of
spinal or epidural anesthesia with-
out signal interference. Sutherland
et al
32

used spontaneous electro-
myography in 44 consecutive revi-
sion and complex hip arthroplasty
procedures. In 5, intraoperative
EMG activity resolved with retrac-
tor or limb adjustments. None of
the patients in that study had post-
operative nerve deficits.
Intraoperative electromyography
may be a helpful adjunct in the pre-
vention of nerve palsy in high-risk
patients. However, larger prospec-
tive trials are necessary to demon-
strate a reduction in the overall rate
of sciatic nerve palsy between mon-
itored and unmonitored patients.
Summary
Preservation of neurologic struc-
tures is important to maintain high
levels of limb function and patient
satisfaction after hip arthroplasty.
Fortunately, nerve injury in THA is
an uncommon complication, occur-
ring in only 1% to 2% of patients
who undergo primary hip arthro-
plasty.
The peroneal division of the sci-
atic nerve is the nerve most fre-
quently injured during revision
cases and in the treatment of

demanding cases of hip dysplasia.
There is a trend in the literature that
supports an increase in sciatic nerve
injuries when the leg is lengthened
by more than 4 cm or by more than
10% of the length of the femur.
Postoperative footdrop or weakness
of ankle dorsiflexors results from
peroneal division palsy and causes
a steppage gait. Often, an ankle-
foot orthosis is all that a patient
requires to manage the deficit.
Complete loss of neurologic
function or severe causalgic pain
carries the worst prognosis. The
role of electrodiagnostic studies
intraoperatively requires further
study before recommendations for
routine use can be made. The
importance of prevention is best
summarized by Schmalzried et al,
11
who stated, ÒNo amount of preop-
erative discussion or postoperative
consultation decreased the high
degree of dissatisfaction that was
expressed by these patients.Ó
Acknowledgments:The authors would
like to thank Taryn Tuinstra, Kym Palatto,
PAC, and Jeffery H. Owen, PhD, for their

valuable assistance in preparing this manu-
script.
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