Nerve injuries in Total Hip Arthroplasty

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Nerve injuries in Total Hip Arthroplasty

• Presented by Drs. Marc DeHart and Lee Riley
• Reviewed by Nimr Ikram, D.O.
• April 20, 1999

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Introduction

• About 1-2 of those undergoing THA obtain some
  nerve injury
• most common in those undergoing revision THA or
  pts with DDH
• inj to peroneal branch of sciatic is most common,
  but obturator, sup. gluteal, and femoral nerves
  may also be injured
• worst prognosis is complete motor and sensory
  deficits.

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Peripheral nerve anatomy and physiology

• Each nerve cell is composed of 4 regions
  dendrite, cell body, axon, and terminal branches
• dendrite collect signals from other cells
• cell body contains nucleus and cell body dealing
  with metabolism
• axon transports proteins and transmits actions
  pot.
• terminal branches relay messages to other nerve
  cells

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Peripheral nerve anatomy and physiology (cont.)

• sensory nerves are afferent fibers that transmit
  a.p. toward dorsal root ganglia of CNS
• Motor nerves are efferent and carry a.p. to motor
  end-plates on muscle spindles
• oligodendrocytes and Schwann cells produce the
  myelin sheath
• oligodendrocytes only in CNS
• Schwann cells found in peripheral nerv. ystem
• demyelinating diseases include multiple sclerosis
  and Guillain-Barre.

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Nerve Injury

• Seddon classified nerve inj. into 3 types
• neurapraxia - conduction block of anatomically
  intact nerves caused by minor inj. Have a period
  of loss of sensation but recovery is complete
• axonotmesis - axons are disrupted but the
  connective tissue survives. Wallerian degen.
  occurs with disintegration of axon and myelin
  sheath distal to site of inj. Intact endoneurium
  allows slow regen. (1 mm/day)
• neurotmesis - complete disruption of nerve may
  lead to painful neuromas

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Nerve injury (cont.)

• Damage occurs by compression, stretch, ischemia,
  and transection.
• Lundborgs exp. with tourniquets showed normal
  circ. when inflation lt 2 hrs.
• If 4-6 hrs., took 2-3 min. for circ. to return
• at 8-10 hrs., took 5-20 minutes to return evid.
  of microvasc. stasis.
• The amount of stretch a nerve tolerates depends
  on whether it is freely mobile or bound.

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Nerve injury (cont.)

• Histologic changes notices after lengthening
  4-11
• nerve microcirc. impaired after 8 stretch and
  stopped after 15 stretch.
• 4 factors that increase prob. of mech. disruption
• 1. Increased load due to compression or stretch
• 2. Increased rate of loading
• 3. Increased duration of loading
• 4. Uneven application of load to tissues

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Anatomy of peripheral nerves about the hip

• Sup. gluteal nerve arises from L4 - S1 and exits
  sciatic notch to supply gluteus medius, minimus,
  and tensor fascia lata.
• Travels with sup. gluteal art. deep to medius and
  max. but superficial to minimus
• ant branches supplying tensor may be sacrificed
  during ant.lat. approach.
• Also at risk when 3-5 cm safe zone prox. to
  greater troch. is violated with direct lat.
  approach
• Trendelenburg sign or gait indicates damage

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Anatomy of peripheral nerves about the hip (cont.)

• Obturator nerve arises from L2 - L4 within post.
  psoas and emerges medially at sacral ala to
  travel along iliopectineal line.
• Rarely injured
• at risk when cement, screws, or reamers penetrate
  the ant. quadrants of the acetabulum.

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Anatomy of peripheral nerves about the hip (cont.)

• Obturator nerve supplies adductors and a medial
  patch of skin on thigh
• persistent pain in groin or thigh, adductor
  weakness after intrapelvic screws, or cement
  visible on x-rays suggest nerve inj.

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Anatomy of peripheral nerves about the hip (cont.)

• Femoral nerve arises from L2 - L4
• passes thru psoas major muscle and travels b/n
  psoas and iliacus and finally enter femoral
  triangle
• supplies motor to quadriceps and sensation to
  medial thigh and calf.
• Prolonged hyperext can cause nerve traction inj.
• Iliacus hematomas are well-known causes of fem.
  nerve palsy
• most at risk during placement of ant. retractors
  when ant. or ant.lat. approaches used.

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Sciatic nerve injury

• Arises from L4 - S3 and is composed of preaxial
  ant. tibial and postaxial post. peroneal
  divisions
• located deep to the piriformis inside the pelvis
  and travels distally deep to gluteal muscles and
  superficial to ext. rotators at level of hip.
• at risk during placement of post. acet.
  retractors or from ant. or lat. traction on the
  femur

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Sciatic nerve injury (cont.)

• Distal to lesser troch. and ischial tuberosity,
  nerve passes b/n adductor magnus and long head of
  biceps, medial to gluteal sling
• all medial branches arise from tibial division
  and supply hamstrings
• short head of biceps is only thigh muscle supply
  by peroneal division of sciatic.
• At sup. aspect of popliteal fossa, 2 divisions
  split into tibial nerve and common peroneal.

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Sciatic nerve injury (cont.)

• Most commonly injured nerve during THA
• Schmalzried et al had a sutdy of 3000 pts with 53
  nerve injuries
• 90 involved the sciatic nerve
• incidence in primary THA is b/n 0.6 - 3.7
• Weber et al noted that only severe injuries
  present as clinical problem so may occur more
  often then documented.
• With pre and post op EMGs, 70 had subclinical
  sciatic nerve inj.

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Sciatic nerve injury (cont.)

• Etiology
• Direct trauma - scalpel, cautery, retractors,
  wires, reamers, bone fragments, or cement
  protrusion
• Constriction - suture, wire, or cable
• Heat - from polymerization of cement
• Compression - from dislocation
• Excessive lengthening
• Subfascial hematoma
• cause of gt 50 of nerve palsies unknown.

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Sciatic nerve injury (cont.)

• Peroneal division more susceptible
• Schmalzried found that 94 of sciatic nerve inj
  involved peroneal division
• superficial position at fibular head makes it
  vulnerable to compression
• relatively more fixed at sciatic notch and at the
  fibular head so susceptible to stretch.

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Sciatic nerve injury (cont.)

• Risk factors include revision THA, DDH, and
  lengthening
• Johanson et al noted increased blood loss and
  time of surgery in pts with nerve inj.
• nerves will tolerate only a finite amount of
  acute stretch
• Mayo Clinic review of DDH pts who underwent THA
• 13 had sciatic nerve palsies
• no nerve inj. occurred in those with lengthening
  lt 4 cm.
• Nercessian reported on 66 pts length 2-5.8 cm s
  deficit
• calculated amount of lengthening as a of length
  of the femur and concluded up to 10 was safe.

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Diagnosis

• Clinical assessment alone underestimates the true
  incidence of nerve injury
• proper preop documentation of neurovasc status
• if weakness of ankle dorsiflexion, damage to
  peroneal division of sciatic
• EMG recording of short head of biceps tells if
  peroneal division affected at hip or fibular
  head.

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Prognosis

• Related to factors specific to the injury and
  clinical factors related to patient
• causalgic pain most highly predicts major
  disability
• Schmalzried found that pts who recovered neuro
  fxn did so by 7 months.
• Pts with some motor fxn during hosp stay had a
  good recovery.

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Treatment

• If no specific cause is identified, no immediate
  tx is indicated.
• EMGs and NCS may provide an objective measure of
  the level of injury, the degree of injury, and
  evidence of recovery of motor fxn.
• If intraop transection of nerve occurs, an
  attempt at repair is warranted
• delayed onset of prog neuro symptoms after a
  normal postop check, should consider evacuation
  of subfascial hematoma

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Treatment (cont.)

• Motor deficits can be managed with P.T.
• AFOs can be used to treat foot drop
• Dysesthesias and causalgic pain are best treated
  with antidepressants and early and repeated
  sympathetic nerve blocks.

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Prevention

• The best treatment of any complication is
  prevention
• most important to identify the pt who is most at
  risk
• revision THA, DDH, and excessive leg lenghtening
• there is no strong evidence favoring any one
  approach for prevention of nerve injury

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Prevention (cont.)

• Technical factors include
• wide exposure and meticulous hemostasis to
  ensure visualization
• constant attention to nerve position
• careful placement and replacement of retractors
• careful placement of fixation screws and
  attention to drill-bit depth are essential
• avoid anterior quadrant screws
• proper placement of components minimize
  dislocations and need for revision surgery

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Electrodiagnostic studies

• Several studies have used evoked potentials and
  EMG to warn surgeons of impending damage to
  peripheral nerves during surgery.
• Evoked potentials are voltage changes in sensory
  fibers after stimulation of peripheral nerves
• damage alters electrical signals by dec size
  (amplitude) or increasing transmission time
  (latency)
• dec of gt50 in amplitude or an inc of gt10 in
  latency suggests neurologic compromise
• amplitude change can be influenced by pt. temp.,
  blood pressure, PCO2, level of anesthesia, and OR
  noise.

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Electrodiagnostic studies (cont)

• Stone et al used SSEP monitoring of peroneal
  nerve and found 20 incidence of intraop signal
  changes
• noted with retractor placement, leg positioning
  for femoral reaming and cement removal, ant. or
  lat. retraction of femur, and hip reduction
• valuable method for use in revisions and
  reoperations
• Black et al found no reduction in sciatic nerve
  palsy in monitored vs unmonitored pts

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Electrodiagnostic studies (cont)

• Rasmussen et al compared revision cases, found no
  statistical significance b/n groups
• also reported 2 pts who had postop palsies had no
  SSEP changes during the procedure.
• Another method to monitor nerve fxn is intraop
  EMG responses
• no studies have been done on this.

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Summary

• Nerve injury in THA is uncommon, occurring in
  1-2 of all pts who undergo primary THA.
• Peroneal division of sciatic nerve is most
  frequently injured
• risk factors include revision THA, DDH, and limb
  lengthening
• lengthening of gt 4cm or gt 10 of femur length
  predispose to nerve injury

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Summary (cont.)

• Complete loss of neuro fxn or severe causalgic
  pain carries the worst prognosis
• importance of prevention is best summarized by
  Schmalzried
• No amount of preoperative discussion or
  postoperative consultation decreased the high
  degree of dissatisfaction that was expressed by
  these patients

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THANK YOU!!