Nerve injuries in Total Hip Arthroplasty

1. Nerve injuries in Total Hip Arthroplasty Presented by Drs. Marc DeHart and Lee Riley Reviewed by Nimr Ikram, D.O. April 20, 1999

2. 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.

3. 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

4. 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.

5. 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

6. 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.

7. 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

8. 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

9. 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.

10. 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.

11. 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.

12. 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

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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

21. 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.

22. 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

23. 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

24. 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.

25. 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

26. 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.

27. 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

28. 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”

29. THANK YOU!!