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Interest of peripheral anesthetic blocks as a diagnosis and prognosis tool in patients with spastic equinus foot: A clinical and electrophysiological study of the effects of block of nerve branches to the triceps surae muscle
Clinical Neurophysiology 116 (2005) 1596–1600 www.elsevier.com/locate/clinph
Interest of peripheral anesthetic blocks as a diagnosis and prognosis tool in patients with spastic equinus foot: A clinical and electrophysiological study of the effects of block of nerve branches to the triceps surae muscle Kevin Buffenoira,b,c,d, Philippe Decqa,c, Jean-Pascal Lefaucheurb,c,* b
a Service de Neurochirurgie, Hoˆpital Henri Mondor, Assistance Publique—Hoˆpitaux de Paris, Cre´teil, France Service de Physiologie—Explorations Fonctionelles, Centre Hospitalier Universitaire Henri Mondor, Assistance Publique—Hoˆpitaux de Paris, 51 avenue du Mare´chal de Lattre de Tassigny, 94010 Cre´teil, France c INSERM E00.11, Faculte´ de Me´decine de Cre´teil, Cre´teil, France d Service de Neurochirurgie, Hoˆpital La Mile´trie, Poitiers, France
See Editorial, pages 1491–1492
Abstract Objective: To evaluate clinically and electrophysiologically the effects of selective anesthetic blocks of motor nerve branches to the triceps surae muscle on lower limb stretch reflex in patients with spastic equinus foot. Methods: Eleven patients were assessed before and after selective anesthetic block of the superior soleus nerve or the gastrocnemius nerves, performed by lidocaine injection. The stretch reflex (SR) of the ankle with the knee flexed or extended and the Achilles tendon reflex (TR) were scored clinically. Additionally, the direct M response and the H reflex to tibial nerve stimulation were recorded on the three heads of the triceps surae muscle. The ratio of H reflex to M response of maximal amplitudes (Hmax/Mmax) was calculated. Results: The SR and TR mean scores were significantly reduced after soleus nerve block but not after gastrocnemius nerve block. Electrophysiologically, Hmax and Hmax/Mmax ratios were significantly reduced for the soleus muscle after soleus nerve block and for the lateral (but not medial) gastrocnemius muscle after gastrocnemius nerve block. Conclusions: Soleus nerve block appeared more appropriate than gastrocnemius nerve block to relieve spasticity clinically. In addition, the decrease in Hmax/Mmax ratio suggested that lidocaine preferentially blocked proprioceptive Ia fibers rather than A-alpha motor fibers. Significance: Selective anesthetic blocks of nerve branches to the triceps surae muscle are useful in the assessment of lower limb spasticity and can benefit from H reflex investigation. H reflex recordings showed a preferential susceptibility of muscle spindle afferents to local anesthetics and supported the hypothesis of a prominent role of the soleus muscle in spastic ankle. The clinical and electrophysiological effects induced by anesthetic blocks may help to guide therapeutic interventions, such as neurotomy, neurolysis or botulinum toxin injection. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: H-reflex; Lidocaine; Local anesthesia; Motor block; Proprioceptive fibers; Soleus muscle; Spasticity; Stretch reflex
1. Introduction
* Corresponding author. Address: Service de Physiologie—Explorations Fonctionelles, Centre Hospitalier Universitaire Henri Mondor, Assistance Publique—Hoˆpitaux de Paris, 51 avenue du Mare´chal de Lattre de Tassigny, 94010 Cre´teil, France. Tel.: C33 1 4981 2694; fax: C33 1 4981 4660. E-mail address: [email protected] (J.-P. Lefaucheur).
Liljestrand and Magnus (1919) first showed spasticity relief following local anesthetic block in an animal model. Later, Walsche (1924) developed the technique of procaine injection in human spastics. Finally, Tardieu and Hariga (1964) proposed anesthetic block as a prognosis test before treatment of spasticity by alcohol neurolysis. The injection of local anesthetics into the motor nerve branch innervating
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2004.11.024
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a spastic muscle relieves spasticity focally and transiently. Spasticity being relieved, the retraction of tendons and the force of antagonist muscles can be tested. This evaluation may help to therapeutic decisions. Thus, the value of anesthetic blocks for the assessment of spastic patients has been recently emphasized (Esquenazi, 2004; Filipetti and Decq, 2003). Myotatic reflex hyperexcitability, causing exaggeration of stretch and deep tendon reflexes, defines spasticity (Lance, 1980). The respective effects of local anesthetics on proprioceptive Ia fibers and alpha-motoneuron fibers, which compose the afferent and efferent pathways of the myotatic reflex, remain unknown. This prospective study was designed to evaluate clinically and electrophysiologically the effects of lidocaine injection into motor nerve branches to the triceps surae muscle on ankle reflexes in 11 spastic patients.
2. Patients and methods Eleven patients with spastic equinus foot gave their informed consent to participate in the study. They were 6 males and 5 females with a mean age of 39 years (range: 12–71 years). Spastic equinus foot affected the right side in 6 patients and the left side in 5 patients. The etiology of spasticity was stroke (ischemia, nZ5, or hemorrhage, nZ1), head injury (nZ4), or postnatal hemiplegia (nZ1). The superior nerve branch innervating the soleus muscle and the nerve branches innervating the medial and lateral heads of the gastrocnemius muscle were selectively blocked. The two types of block were performed in a random order, during two sessions separated by more than a week. Clinical and electrophysiological parameters were assessed before and 20 min after each block by the same examiner (KB), blinded for the type of block. 2.1. Peripheral nerve block technique The motor nerve branches were blocked as they were leaving the tibial nerve trunk, before entering the muscle body. A CT-scan was first performed to identify the nerve pedicles. The patient was placed on the CT table in the prone position, corresponding to the same position as for the block. Two metal markers were placed on the leg: a horizontal marker in the flexion crease of the knee and a vertical marker corresponding to the midline of the leg, used as the reference system for target determination. The motor nerve branches innervating the triceps surae muscle were identified on 2.5 mm-thick CT slices, acquired from the flexion crease of the knee to the middle third of the leg. Then, their coordinates (distance to the flexion crease of the knee, distance to the midline, and depth) were determined to guide lidocaine injection. After skin anesthesia by injection of 1 mL of 1% lidocaine, a 50 mm-long needle (Stimuplexw needle,
Fig. 1. Anatomic landmarks for block approach of the nerve branch to medial gastrocnemius (GM), lateral gastrocnemius (GL) and soleus (SOL) muscles, as defined by CT-scan coordinates.
B. Braun, Melsungen, Germany) connected to a current stimulator (Neurostim LA II, Hugo Sachs Elektronik, March, Germany) was inserted according to the anatomic landmarks corresponding to the CT-scan target coordinates (Fig. 1). Current was delivered at 1 Hz, the needle being moved until a selective contraction of the target muscle was obtained for stimulus intensity lower than 0.2 mA. At this emplacement, 0.5–1.5 mL of 2% lidocaine was injected, after gentle aspiration to ensure the absence of vessel at the tip of the needle. Lidocaine was chosen instead of longacting local anesthetics because patients were ambulatory, and in our experience, spasticity relief is more consistently obtained with 2% than with 1% concentration. 2.2. Clinical assessment The stretch reflex (SR) of the triceps surae muscle was tested by manual stretching with the knee extended or flexed. The SR was scored on a 0–4 scale previously proposed by Tardieu et al. (1954), with 0: absence of stretch reflex, 1: perception of a jerk, 2: fatigable clonus, 3: unfatigable clonus, 4: unfatigable clonus triggered at slow speed. The reflex obtained by Achilles tendon percussion (tendon reflex, TR) was scored as 0: absent, 1: present, 2: brisk.
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2.3. Electrophysiological assessment The electrophysiological recordings were performed on a Keypoint EMG machine (Medtronic France S.A.S., Boulogne-Billancourt, France). The patients were lying in prone position on the spastic side, with the knee flexed to an angle of 208 and the ankle free. Electrical 1 ms-duration pulses were delivered to the tibial nerve with the active electrode applied onto the popliteal fossa and the reference on the patella. Selective recordings were performed on the three muscle heads of the triceps surae, i.e. the medial and the lateral gastrocnemius muscles and the soleus muscle, using adhesive surface electrodes and a belly-tendon montage. Bandpass ranged from 20 Hz to 2 kHz. The total time analysis was 50 ms. Stimulus intensity was progressively increased to determine the maximal peak-to-peak amplitude of the H reflex (Hmax) and of the direct M response (Mmax), for each of the three muscle heads of the triceps surae. The Hmax/Mmax ratios were also calculated. 2.4. Statistics Repeated measures analyses of variance with Bonferroni’s multiple comparison post-tests were performed with StatView 5.0 software (SAS Institute, Inc., USA). A value of P!0.05 was considered as significant.
3. Results 3.1. Clinical assessment All patients completed the study. No immediate or delayed complication of peripheral nerve blocks was observed. Clinical results are presented in Fig. 2. In summary, the mean SR and TR scores were significantly reduced after soleus nerve block but not after gastrocnemius nerve block. Individually, the SR and/or TR scores were reduced in 8 patients after the soleus nerve block and in two patients after the gastrocnemius nerve block. 3.2. Electrophysiological assessment Electrophysiological results are presented in Fig. 3. In summary, Hmax and Hmax/Mmax were significantly reduced for the lateral gastrocnemius muscle after gastrocnemius nerve block, while Hmax, Mmax and Hmax/Mmax were significantly reduced for the soleus muscle after soleus nerve block. The Hmax/Mmax ratio was greater than 0.50 in the soleus muscle for all the patients (but not in the gastrocnemius muscles) and was systematically reduced below 0.50 after soleus nerve block.
Fig. 2. Mean (Gs.e.m.) scores of the ankle stretch reflex (SR) examined with the knee flexed or extended, and of the Achilles tendon reflex (TR), assessed before (white bars) and after (hatched bars) anesthetic block of the gastrocnemius nerves or of the soleus nerve. Significant P values regarding the Bonferroni’s post-tests are indicated.
4. Discussion The present study showed that soleus nerve block was more appropriate than gastrocnemius nerve block to relief spastic equinus foot. In addition, anesthetic nerve blocks lead to significant reduction of Hmax/Mmax ratios. Two main conclusions can be drawn from these results: the preferential susceptibility of Ia fibers to lidocaine and the prominent role of the soleus muscle in spasticity. 4.1. Selective nerve fiber type susceptibility to local anesthetic agents The local anesthetic agents act mainly on voltage-gated sodium channels involved in nerve action potential mechanisms. Nerve fiber susceptibility to the action of
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of the large myelinated Ia fibers remained unknown. Bremer and Titeca (1930) suggested a particular susceptibility of Ia fibers to procaine, but the rapid abolition of muscle spindle afferent activity after lidocaine or procaine application was later explained by preferential blockade of A-gamma fibers (Gokin et al., 2001; Matthews and Rushworth, 1957). In the present study, the injection of lidocaine into motor nerve branches induced a more marked amplitude reduction for the H reflex than for the M response, leading to a decrease in the Hmax/Mmax ratio. This suggests that the susceptibility to lidocaine was greater for the proprioceptive Ia fibers than for the alpha-motoneuron fibers. Higher firing rates presented by muscle spindle afferent fibers compared to alpha-motoneuron fibers could explain preferential effects of local anesthetics on Ia fibers (Filipetti and Decq, 2003). Experiments on animal models need to be performed to confirm this hypothesis. 4.2. Prominent role of the soleus muscle in spastic equinus foot
Fig. 3. Mean (Gs.e.m.) values of H reflex or M response maximal amplitude, and of Hmax/Mmax ratio recorded in the soleus muscle (SOL) and in the lateral or medial gastrocnemius (LG, MG) muscles, assessed before (white bars) and after (hatched bars) anesthetic block of the gastrocnemius nerves or of the soleus nerve. Significant P values regarding the Bonferroni’s post-tests are indicated.
local anesthetics depends on various physical and chemical properties of the drug (lipid solubility, tissue diffusion, molecular weight, binding affinity, concentration) and on functional or anatomic characteristics of the nerve fibers (firing rate, membrane potential level, intra-fascicular localization) (Eledjam et al., 1996). Nevertheless, a significant order of nerve fiber susceptibility to local anesthetics was found. It concerns first the small myelinated A-gamma motor fibers and A-delta sensory fibers, then the large myelinated A-alpha motor fibers and A-beta sensory fibers, and finally the very small myelinated B fibers and unmyelinated C fibers (Gokin et al., 2001; Huang et al., 1997). Proprioceptive and motor functions are known to be depressed earlier than nociception after lidocaine injection (Thalhammer et al., 1995). However, the specific sensitivity
The clinical and electrophysiological effects of anesthetic blocks observed in this study confirm previous studies, which reported, only on clinical grounds, the efficacy of alcohol neurolysis of tibial nerve branches to treat ankle spasticity (Chua and Kong, 2001; Jang et al., 2004). One of these studies showed the effectiveness of tibial neurolysis of nerve branches to the gastrocnemius muscle (Jang et al., 2004). In contrast, it appeared functionally important to us to preserve the gastrocnemius motor nerve branches during tibial neurotomy (Decq et al., 1998, 2000). In the present study, we found that anesthetic blocks reduced the Hmax/Mmax ratio in the soleus muscle, but also for the lateral gastrocnemius muscle, while it remained unchanged for the medial gastrocnemius muscle. Similar behaviors of H reflex amplitude changes in the lateral gastrocnemius and the soleus muscles, differing from that of the medial gastrocnemius muscle, were previously found during fatiguing exercise (Loscher et al., 1996) or following transcutaneous electrical nerve stimulation (Goulet et al., 1997). Nevertheless, the present study gave further evidences for the prominent role of the soleus muscle in spastic equinus foot. Firstly, the Hmax/Mmax ratio was higher than 0.50 only in the soleus muscle, and not in the lateral or medial gastrocnemius muscles. The Hmax/Mmax ratio appraises the excitability of the spinal motoneuron pool and correlates positively with spasticity for values higher than 0.50 (Angel and Hoffmann, 1963; Delwaide et al., 1978; Guiheneuc, 1983; Sehgal and McGuire, 1998). Secondly, soleus nerve blocks, but not gastrocnemius nerve blocks, were able to reduce clinical parameters of spasticity, i.e. the SR and TR scores. These observations fully confirm the previous conclusions drawn from H reflex recordings performed in spastic patients treated by selective tibial neurotomy (Fe`ve et al., 1997; Roujeau et al., 2003).
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As for anesthetic blocks, neurotomy confined to fibers supplying the soleus muscle was sufficient to relieve spastic equinus foot. 4.3. Conclusions With a delay of action of 3 min and a duration of action of several hours, the injection of lidocaine into the superior soleus nerve is able to reduce transiently spasticity in lower limbs, both clinically and electrophysiologically. The present study illustrates the interest of peripheral nerve anesthetic blocks as a diagnostic tool (effects on the stretch reflex, but also differentiation between the consequences of spasticity and tendon retraction, action of antagonistic muscles, etc.). In addition, anesthetic blocks simulate the results of a definitive treatment and could serve as a prognosis tool to predict the long-term outcome of various therapeutic possibilities, such as surgical neurotomy, chemical neurolysis or intramuscular injection of botulinum toxin (Filipetti and Decq, 2003).
References Angel RW, Hoffmann WW. The H reflex in normal, spastic and rigid subjects. Arch Neurol 1963;8:591–6. Bremer F, Titeca J. Du me´canisme de l’action de la novocaı¨ne sur le tonus musculaire. CR Soc Biol Paris 1930;105:873–5. Chua KS, Kong KH. Clinical and functional outcome after alcohol neurolysis of the tibial nerve for ankle–foot spasticity. Brain Inj 2001; 15:33–9. Decq P, Cuny E, Filipetti P, Keravel Y. Role of soleus muscle in spastic equinus foot. Lancet 1998;352:118. Decq P, Filipetti P, Cubillos A, Slavov V, Lefaucheur JP, Nguyen JP. Soleus neurotomy for treatment of the spastic equinus foot. Neurosurgery 2000;47:1154–61. Delwaide PJ, Cordonnier M, Gadea-Ciria M. Excitability relationships between lower limb myotatic arcs in spasticity. J Neurol Neurosurg Psychiatry 1978;41:636–41. Eledjam JJ, Viel E, Bruelle P, De La Coussaye J. Pharmacologie des anesthe´siques locaux. Encycl Med Chir 1996;36-320-A-10:1–16. Esquenazi A. Evaluation and management of spastic gait in patients with traumatic brain injury. J Head Trauma Rehabil 2004;19:109–18.
Fe`ve A, Decq P, Filipetti P, Verroust J, Harf A, Nguyen JP, Keravel Y. Physiological effects of selective tibial neurotomy on lower limb spasticity. J Neurol Neurosurg Psychiatry 1997;63:575–8. Filipetti P, Decq P. L’apport des blocs anesthe´siques dans l’e´valuation du patient spastique. A propos d’une se´rie de 815 blocs moteurs. Neurochirurgie 2003;49:226–38. Gokin AP, Philip B, Strichartz GR. Preferential block of small myelinated sensory and motor fibers by lidocaine: in vivo electrophysiology in the rat sciatic nerve. Anesthesiology 2001;95:1441–54. Goulet CG, Arsenault AB, Bourbonnais D, Levin MF. Effects of transcutaneous electrical nerve stimulation on the H-reflex of muscles of different fibre type composition. Electromyogr Clin Neurophysiol 1997;37:335–42. Guiheneuc P. The use of monosynaptic reflex responses in man for assessing the different types of peripheral neuropathies. Adv Neurol 1983;39:927–49. Huang JH, Thalhammer JG, Raymond SA, Strichartz GR. Susceptibility to lidocaine of impulses in different somatosensory afferent fibers of rat sciatic nerve. J Pharmacol Exp Ther 1997;292:802–11. Jang SH, Ahn SH, Park SM, Kim SH, Lee KH, Lee ZI. Alcohol neurolysis of the tibial nerve motor branches to the gastrocnemius muscle to treat ankle spasticity in patients with hemiplegic stroke. Arch Phys Med Rehabil 2004;85:506–8. Lance JW. The control of muscle tone, reflexes, and movement. Robert Wartenberg lecture. Neurology 1980;30:1303–13. ¨ ber die wirkung des novocaine auf den Liljestrand G, Magnus R. U normalen und den tetanusstarren skelettmuskel und u¨ber die enstehung des muskelstaue beim wundstarrkampf. Pflugers Arch 1919;176: 168–208. Loscher WN, Cresswell AG, Thorstensson A. Excitatory drive to the alphamotoneuron pool during a fatiguing submaximal contraction in man. J Physiol (London) 1996;491:271–80. Matthews PCB, Rushworth G. The relative sensitivity of muscle nerve fibres to procaine. J Physiol (London) 1957;135:263–9. Roujeau T, Lefaucheur JP, Slavov V, Gherardi R, Decq P. Long term course of the H reflex after selective tibial neurotomy. J Neurol Neurosurg Psychiatry 2003;74:913–7. Sehgal N, McGuire JR. Beyond ashworth. Electrophysiologic quantification of spasticity. Phys Med Rehabil Clin N Am 1998;9:949–79. Tardieu G, Hariga J. Traitement des raideurs musculaires d’origine centrale par infiltration d’alcool dilue´ (re´sultats de 500 injections). Arch Fr Pediatr 1964;21:25–41. Tardieu G, Shentoub S, Delarue R. A la recherche d’une technique de mesure de la spasticite´. Rev Neurol (Paris) 1954;91:143–4. Thalhammer JG, Vladimirova M, Bershadsky B, Strichartz GR. Neurologic evaluation of the rat during sciatic nerve block with lidocaine. Anesthesiology 1995;82:1013–25. Walsche FRM. Procaine injection for spasticity. Brain 1924;47:159–72.
Interest of peripheral anesthetic blocks as a diagnosis and prognosis tool in patients with spastic equinus foot: A clinical and electrophysiological study of the effects of block of nerve branches to the triceps surae muscle Kevin Buffenoira,b,c,d, Philippe Decqa,c, Jean-Pascal Lefaucheurb,c,* b
a Service de Neurochirurgie, Hoˆpital Henri Mondor, Assistance Publique—Hoˆpitaux de Paris, Cre´teil, France Service de Physiologie—Explorations Fonctionelles, Centre Hospitalier Universitaire Henri Mondor, Assistance Publique—Hoˆpitaux de Paris, 51 avenue du Mare´chal de Lattre de Tassigny, 94010 Cre´teil, France c INSERM E00.11, Faculte´ de Me´decine de Cre´teil, Cre´teil, France d Service de Neurochirurgie, Hoˆpital La Mile´trie, Poitiers, France
See Editorial, pages 1491–1492
Abstract Objective: To evaluate clinically and electrophysiologically the effects of selective anesthetic blocks of motor nerve branches to the triceps surae muscle on lower limb stretch reflex in patients with spastic equinus foot. Methods: Eleven patients were assessed before and after selective anesthetic block of the superior soleus nerve or the gastrocnemius nerves, performed by lidocaine injection. The stretch reflex (SR) of the ankle with the knee flexed or extended and the Achilles tendon reflex (TR) were scored clinically. Additionally, the direct M response and the H reflex to tibial nerve stimulation were recorded on the three heads of the triceps surae muscle. The ratio of H reflex to M response of maximal amplitudes (Hmax/Mmax) was calculated. Results: The SR and TR mean scores were significantly reduced after soleus nerve block but not after gastrocnemius nerve block. Electrophysiologically, Hmax and Hmax/Mmax ratios were significantly reduced for the soleus muscle after soleus nerve block and for the lateral (but not medial) gastrocnemius muscle after gastrocnemius nerve block. Conclusions: Soleus nerve block appeared more appropriate than gastrocnemius nerve block to relieve spasticity clinically. In addition, the decrease in Hmax/Mmax ratio suggested that lidocaine preferentially blocked proprioceptive Ia fibers rather than A-alpha motor fibers. Significance: Selective anesthetic blocks of nerve branches to the triceps surae muscle are useful in the assessment of lower limb spasticity and can benefit from H reflex investigation. H reflex recordings showed a preferential susceptibility of muscle spindle afferents to local anesthetics and supported the hypothesis of a prominent role of the soleus muscle in spastic ankle. The clinical and electrophysiological effects induced by anesthetic blocks may help to guide therapeutic interventions, such as neurotomy, neurolysis or botulinum toxin injection. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: H-reflex; Lidocaine; Local anesthesia; Motor block; Proprioceptive fibers; Soleus muscle; Spasticity; Stretch reflex
1. Introduction
* Corresponding author. Address: Service de Physiologie—Explorations Fonctionelles, Centre Hospitalier Universitaire Henri Mondor, Assistance Publique—Hoˆpitaux de Paris, 51 avenue du Mare´chal de Lattre de Tassigny, 94010 Cre´teil, France. Tel.: C33 1 4981 2694; fax: C33 1 4981 4660. E-mail address: [email protected] (J.-P. Lefaucheur).
Liljestrand and Magnus (1919) first showed spasticity relief following local anesthetic block in an animal model. Later, Walsche (1924) developed the technique of procaine injection in human spastics. Finally, Tardieu and Hariga (1964) proposed anesthetic block as a prognosis test before treatment of spasticity by alcohol neurolysis. The injection of local anesthetics into the motor nerve branch innervating
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2004.11.024
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a spastic muscle relieves spasticity focally and transiently. Spasticity being relieved, the retraction of tendons and the force of antagonist muscles can be tested. This evaluation may help to therapeutic decisions. Thus, the value of anesthetic blocks for the assessment of spastic patients has been recently emphasized (Esquenazi, 2004; Filipetti and Decq, 2003). Myotatic reflex hyperexcitability, causing exaggeration of stretch and deep tendon reflexes, defines spasticity (Lance, 1980). The respective effects of local anesthetics on proprioceptive Ia fibers and alpha-motoneuron fibers, which compose the afferent and efferent pathways of the myotatic reflex, remain unknown. This prospective study was designed to evaluate clinically and electrophysiologically the effects of lidocaine injection into motor nerve branches to the triceps surae muscle on ankle reflexes in 11 spastic patients.
2. Patients and methods Eleven patients with spastic equinus foot gave their informed consent to participate in the study. They were 6 males and 5 females with a mean age of 39 years (range: 12–71 years). Spastic equinus foot affected the right side in 6 patients and the left side in 5 patients. The etiology of spasticity was stroke (ischemia, nZ5, or hemorrhage, nZ1), head injury (nZ4), or postnatal hemiplegia (nZ1). The superior nerve branch innervating the soleus muscle and the nerve branches innervating the medial and lateral heads of the gastrocnemius muscle were selectively blocked. The two types of block were performed in a random order, during two sessions separated by more than a week. Clinical and electrophysiological parameters were assessed before and 20 min after each block by the same examiner (KB), blinded for the type of block. 2.1. Peripheral nerve block technique The motor nerve branches were blocked as they were leaving the tibial nerve trunk, before entering the muscle body. A CT-scan was first performed to identify the nerve pedicles. The patient was placed on the CT table in the prone position, corresponding to the same position as for the block. Two metal markers were placed on the leg: a horizontal marker in the flexion crease of the knee and a vertical marker corresponding to the midline of the leg, used as the reference system for target determination. The motor nerve branches innervating the triceps surae muscle were identified on 2.5 mm-thick CT slices, acquired from the flexion crease of the knee to the middle third of the leg. Then, their coordinates (distance to the flexion crease of the knee, distance to the midline, and depth) were determined to guide lidocaine injection. After skin anesthesia by injection of 1 mL of 1% lidocaine, a 50 mm-long needle (Stimuplexw needle,
Fig. 1. Anatomic landmarks for block approach of the nerve branch to medial gastrocnemius (GM), lateral gastrocnemius (GL) and soleus (SOL) muscles, as defined by CT-scan coordinates.
B. Braun, Melsungen, Germany) connected to a current stimulator (Neurostim LA II, Hugo Sachs Elektronik, March, Germany) was inserted according to the anatomic landmarks corresponding to the CT-scan target coordinates (Fig. 1). Current was delivered at 1 Hz, the needle being moved until a selective contraction of the target muscle was obtained for stimulus intensity lower than 0.2 mA. At this emplacement, 0.5–1.5 mL of 2% lidocaine was injected, after gentle aspiration to ensure the absence of vessel at the tip of the needle. Lidocaine was chosen instead of longacting local anesthetics because patients were ambulatory, and in our experience, spasticity relief is more consistently obtained with 2% than with 1% concentration. 2.2. Clinical assessment The stretch reflex (SR) of the triceps surae muscle was tested by manual stretching with the knee extended or flexed. The SR was scored on a 0–4 scale previously proposed by Tardieu et al. (1954), with 0: absence of stretch reflex, 1: perception of a jerk, 2: fatigable clonus, 3: unfatigable clonus, 4: unfatigable clonus triggered at slow speed. The reflex obtained by Achilles tendon percussion (tendon reflex, TR) was scored as 0: absent, 1: present, 2: brisk.
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2.3. Electrophysiological assessment The electrophysiological recordings were performed on a Keypoint EMG machine (Medtronic France S.A.S., Boulogne-Billancourt, France). The patients were lying in prone position on the spastic side, with the knee flexed to an angle of 208 and the ankle free. Electrical 1 ms-duration pulses were delivered to the tibial nerve with the active electrode applied onto the popliteal fossa and the reference on the patella. Selective recordings were performed on the three muscle heads of the triceps surae, i.e. the medial and the lateral gastrocnemius muscles and the soleus muscle, using adhesive surface electrodes and a belly-tendon montage. Bandpass ranged from 20 Hz to 2 kHz. The total time analysis was 50 ms. Stimulus intensity was progressively increased to determine the maximal peak-to-peak amplitude of the H reflex (Hmax) and of the direct M response (Mmax), for each of the three muscle heads of the triceps surae. The Hmax/Mmax ratios were also calculated. 2.4. Statistics Repeated measures analyses of variance with Bonferroni’s multiple comparison post-tests were performed with StatView 5.0 software (SAS Institute, Inc., USA). A value of P!0.05 was considered as significant.
3. Results 3.1. Clinical assessment All patients completed the study. No immediate or delayed complication of peripheral nerve blocks was observed. Clinical results are presented in Fig. 2. In summary, the mean SR and TR scores were significantly reduced after soleus nerve block but not after gastrocnemius nerve block. Individually, the SR and/or TR scores were reduced in 8 patients after the soleus nerve block and in two patients after the gastrocnemius nerve block. 3.2. Electrophysiological assessment Electrophysiological results are presented in Fig. 3. In summary, Hmax and Hmax/Mmax were significantly reduced for the lateral gastrocnemius muscle after gastrocnemius nerve block, while Hmax, Mmax and Hmax/Mmax were significantly reduced for the soleus muscle after soleus nerve block. The Hmax/Mmax ratio was greater than 0.50 in the soleus muscle for all the patients (but not in the gastrocnemius muscles) and was systematically reduced below 0.50 after soleus nerve block.
Fig. 2. Mean (Gs.e.m.) scores of the ankle stretch reflex (SR) examined with the knee flexed or extended, and of the Achilles tendon reflex (TR), assessed before (white bars) and after (hatched bars) anesthetic block of the gastrocnemius nerves or of the soleus nerve. Significant P values regarding the Bonferroni’s post-tests are indicated.
4. Discussion The present study showed that soleus nerve block was more appropriate than gastrocnemius nerve block to relief spastic equinus foot. In addition, anesthetic nerve blocks lead to significant reduction of Hmax/Mmax ratios. Two main conclusions can be drawn from these results: the preferential susceptibility of Ia fibers to lidocaine and the prominent role of the soleus muscle in spasticity. 4.1. Selective nerve fiber type susceptibility to local anesthetic agents The local anesthetic agents act mainly on voltage-gated sodium channels involved in nerve action potential mechanisms. Nerve fiber susceptibility to the action of
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of the large myelinated Ia fibers remained unknown. Bremer and Titeca (1930) suggested a particular susceptibility of Ia fibers to procaine, but the rapid abolition of muscle spindle afferent activity after lidocaine or procaine application was later explained by preferential blockade of A-gamma fibers (Gokin et al., 2001; Matthews and Rushworth, 1957). In the present study, the injection of lidocaine into motor nerve branches induced a more marked amplitude reduction for the H reflex than for the M response, leading to a decrease in the Hmax/Mmax ratio. This suggests that the susceptibility to lidocaine was greater for the proprioceptive Ia fibers than for the alpha-motoneuron fibers. Higher firing rates presented by muscle spindle afferent fibers compared to alpha-motoneuron fibers could explain preferential effects of local anesthetics on Ia fibers (Filipetti and Decq, 2003). Experiments on animal models need to be performed to confirm this hypothesis. 4.2. Prominent role of the soleus muscle in spastic equinus foot
Fig. 3. Mean (Gs.e.m.) values of H reflex or M response maximal amplitude, and of Hmax/Mmax ratio recorded in the soleus muscle (SOL) and in the lateral or medial gastrocnemius (LG, MG) muscles, assessed before (white bars) and after (hatched bars) anesthetic block of the gastrocnemius nerves or of the soleus nerve. Significant P values regarding the Bonferroni’s post-tests are indicated.
local anesthetics depends on various physical and chemical properties of the drug (lipid solubility, tissue diffusion, molecular weight, binding affinity, concentration) and on functional or anatomic characteristics of the nerve fibers (firing rate, membrane potential level, intra-fascicular localization) (Eledjam et al., 1996). Nevertheless, a significant order of nerve fiber susceptibility to local anesthetics was found. It concerns first the small myelinated A-gamma motor fibers and A-delta sensory fibers, then the large myelinated A-alpha motor fibers and A-beta sensory fibers, and finally the very small myelinated B fibers and unmyelinated C fibers (Gokin et al., 2001; Huang et al., 1997). Proprioceptive and motor functions are known to be depressed earlier than nociception after lidocaine injection (Thalhammer et al., 1995). However, the specific sensitivity
The clinical and electrophysiological effects of anesthetic blocks observed in this study confirm previous studies, which reported, only on clinical grounds, the efficacy of alcohol neurolysis of tibial nerve branches to treat ankle spasticity (Chua and Kong, 2001; Jang et al., 2004). One of these studies showed the effectiveness of tibial neurolysis of nerve branches to the gastrocnemius muscle (Jang et al., 2004). In contrast, it appeared functionally important to us to preserve the gastrocnemius motor nerve branches during tibial neurotomy (Decq et al., 1998, 2000). In the present study, we found that anesthetic blocks reduced the Hmax/Mmax ratio in the soleus muscle, but also for the lateral gastrocnemius muscle, while it remained unchanged for the medial gastrocnemius muscle. Similar behaviors of H reflex amplitude changes in the lateral gastrocnemius and the soleus muscles, differing from that of the medial gastrocnemius muscle, were previously found during fatiguing exercise (Loscher et al., 1996) or following transcutaneous electrical nerve stimulation (Goulet et al., 1997). Nevertheless, the present study gave further evidences for the prominent role of the soleus muscle in spastic equinus foot. Firstly, the Hmax/Mmax ratio was higher than 0.50 only in the soleus muscle, and not in the lateral or medial gastrocnemius muscles. The Hmax/Mmax ratio appraises the excitability of the spinal motoneuron pool and correlates positively with spasticity for values higher than 0.50 (Angel and Hoffmann, 1963; Delwaide et al., 1978; Guiheneuc, 1983; Sehgal and McGuire, 1998). Secondly, soleus nerve blocks, but not gastrocnemius nerve blocks, were able to reduce clinical parameters of spasticity, i.e. the SR and TR scores. These observations fully confirm the previous conclusions drawn from H reflex recordings performed in spastic patients treated by selective tibial neurotomy (Fe`ve et al., 1997; Roujeau et al., 2003).
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As for anesthetic blocks, neurotomy confined to fibers supplying the soleus muscle was sufficient to relieve spastic equinus foot. 4.3. Conclusions With a delay of action of 3 min and a duration of action of several hours, the injection of lidocaine into the superior soleus nerve is able to reduce transiently spasticity in lower limbs, both clinically and electrophysiologically. The present study illustrates the interest of peripheral nerve anesthetic blocks as a diagnostic tool (effects on the stretch reflex, but also differentiation between the consequences of spasticity and tendon retraction, action of antagonistic muscles, etc.). In addition, anesthetic blocks simulate the results of a definitive treatment and could serve as a prognosis tool to predict the long-term outcome of various therapeutic possibilities, such as surgical neurotomy, chemical neurolysis or intramuscular injection of botulinum toxin (Filipetti and Decq, 2003).
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