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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. Introduction. About 1-2% of those undergoing THA obtain some nerve injury most common in those undergoing revision THA or pts with DDH
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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
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.
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
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.
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
Nerve injury (cont.) • Damage occurs by compression, stretch, ischemia, and transection. • Lundborg’s exp. with tourniquets showed normal circ. when inflation < 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.
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
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
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.
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.
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.
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
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.
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 EMG’s, 70% had subclinical sciatic nerve inj.
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 > 50% of nerve palsies unknown.
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.
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 < 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.
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.
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.
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
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.
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
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
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 >50% in amplitude or an inc of >10% in latency suggests neurologic compromise • amplitude change can be influenced by pt. temp., blood pressure, PCO2, level of anesthesia, and OR noise.
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
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.
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 > 4cm or > 10% of femur length predispose to nerve injury
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”