Download Evaluation of ventral root reimplantation as a treatment of

ARTICLE ORIGINAL
Evaluation of ventral root reimplantation
as a treatment of experimental avulsion
of the cranial brachial plexus in the dog
° P. MOISSONNIER, °° Y. DUCHOSSOY, ° S. LAVIEILLE and °° J.C. HORVAT
° Service de Chirurgie, École Nationale Vétérinaire d'Alfort. 7 Avenue du Général De Gaulle, F- 94704 Maisons Alfort
°° Laboratoire de Neurobiologie, URA CNRS 1448, UFR Biomédicale des Saints Pères, Université René Descartes, 45 rue des Saints Pères, F-75270 Paris Cedex 06
Corresponding author: Pierre Moissonnier, Service de Chirurgie, École Nationale Vétérinaire d'Alfort, 7 Avenue du Général De Gaulle. F-94704 Maisons Alfort,
Tel: 01 43 96 71 14 ; Fax: 01 43 96 71 17 ; Email: [email protected]
SUMMARY
RÉSUMÉ
This in vivo experimental study was carried out 1/ to evaluate the ability
of dog spinal neuron to grow an axon into reimplanted brachial plexus ventral root, and 2/ to assess the functional outcome after root reimplantation.
The reimplantation of C5, C6 and C7 ventral rootlets was carried out
after their avulsion in 6 dogs (group 1) and three other dogs were used as
sham control (group 2). Axonal regrowth in the roots was assessed by Horse
Radish Peroxidase (HRP) retrograde tracing studies and muscular reinnervation was tested by electrophysiology. Functional recovery was evaluated
by clinical examination and muscle weight (in comparison to 12 normal
dogs cadavers : group 3).
HRP-tracing methods demonstrated axonal regrowth into the reimplanted
roots by (moto)neurons confined in the ipsilateral ventral horn. In group 1,
EMG investigations showed signs of reinnervation and neuronal labelling
was observed. In group 2, there were no signs of reinnervation by EMG and
no neuronal labelling. In addition, amyotrophy was more severe in group 2.
No sign of functional recovery was observed in either of the two groups.
Our findings demonstrate that root reimplantation may promote muscular
reinnervation in the dog after brachial plexus avulsion.
Évaluation de la réimplantation radiculaire ventrale en tant que traitement des avulsions expérimentales de la partie craniale du plexus brachial chez le chien. Par P. MOISSONNIER, Y. DUCHOSSOY, S.
LAVIEILLE et J.-C. HORVAT.
KEY-WORDS : brachial plexus - avulsion - dog.
MOTS-CLÉS : plexus brachial - avulsion - chien.
Introduction
Functionally, the dog brachial plexus can be divided in two
parts [32]. The cranial part of the plexus consists of the C5,
C6 and C7 ventral branches : it controls shoulder and elbow
flexion. The caudal part of the plexus is more complex and
commands elbow extension, and carpus and digit mobility.
Ventral branches of the cervical and thoracic spinal nerves
contribute in a variable manner to the brachial plexus [32].
The suprascapular and subscapular nerves arise from the
union of the ventral branches of the fifth (rarely), sixth and
seventh spinal nerves. The musculocutaneous nerve receives
contributions from the C6, C7 and C8 ventral branches of the
cervical nerves but rarely from T1.
Brachial plexus injuries are occasionally encountered in
the veterinary practice, especially in the dog [14, 27, 32, 37].
Most of them are traction lesions which usually result from
road traffic accidents. Neurological deficits depend on the
severity of brachial plexus damage. The brachial plexus
arises from the ventral branches of C5 to T2 spinal nerves.
These branches contribute in a variable manner to the brachial plexus formation. C5 is incorporated in the plexus in
24.19 % of cases [2].
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Cette étude expérimentale a été réalisée dans le but 1/ de connaître la
capacité des neurones médullaires du chien d’émettre un axone au sein de
la racine ventrale d’un nerf spinal réimplantée dans la moelle épinière et, 2/
d’évaluer le résultat fonctionnel de cette réimplantation.
La réimplantation des radicelles ventrales des racines C5, C6 et C7 a été
réalisée après leur avulsion chez 6 chiens (groupe 1). Trois autres chiens ont
été opérés selon le même protocole mais sans que la réimplantation soit laissée en place (chiens témoins opérés : groupe 2). La repousse axonale a été
étudiée au moyen d’un marquage rétrograde par la péroxydase du raifort
(HRP) et par étude électrophysiologique. La récupération fonctionnelle a
été appréciée par l’examen clinique et par la pesée des muscles (effectuée
comparativement à des muscles prélevés sur 12 chiens témoins non opérés
: groupe 3).
Le marquage rétrograde a démontré que des (moto)neurones spinaux
situés dans la corne ventrale ipsilatérale étaient capables d’émettre un axone
au sein de la racine réimplantée chez les chiens du groupe 1. Dans ce même
groupe, l’examen électromyographique montrait qu’une reconnexion avec
l’effecteur musculaire s’était produite. Dans le groupe 2, aucune réinnervation n’a pu être observée à l’examen électrophysiologique et aucun neurone
n’a été marqué. Aucun signe de récupération fonctionnelle n’a été observé
quel que soit le groupe. Ces résultats montrent que la réimplantation radiculaire peut promouvoir une réinnervation musculaire après avulsion du
plexus brachial chez le chien.
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The so-called avulsion of the brachial plexus (ABP) is
usually complex with both spinal nerve root neurapraxia or
axonotmesis and avulsion of one or several roots from the
spinal cord [15, 32]. The avulsion can take place in the cranial part, in the caudal part or in both parts of the plexus.
While peripheral nerve neurotmesis can be treated with a
good functional outcome using routine surgical principles for
peripheral nerve injuries [14], root avulsion was until now
beyond repair, not only because of the size of the gap separating the spinal cord from the avulsed rootlets, but also
because of a fundamental lack of axonal regrowth and extension from neurons injured in the central nervous system
(CNS) [1]. Thus, ABP results in permanent paralysis of the
muscles innervated by the avulsed roots and of sensory loss
in the corresponding dermatomes. In the dog [32] and in
mankind [13], its treatment is only palliative.
Recent experiments have shown that CNS neurons can
grow and extend axons if an autologous peripheral nerve segment is grafted in their immediate vicinity [1, 36]. In the
adult dog, this axonal regrowth can reach at least 10-15 cm
within a four-month period [26]. These new data justify a
new surgical strategy in the treatment of ABP : ventral root
reimplantation (VRR). In laboratory animals, motoneurons
of the cervical spinal cord have been shown to reinnervate the
corresponding reimplanted ventral roots [6, 7, 8, 16, 17, 20,
35]. Yet, a number of problems still remain to be solved
before a routine clinical application of VRR can be performed : 1/ the large distance between the cervical spinal cord
and the muscular effectors might be a limiting factor for anatomical and functional restoration, a factor that is less significant in small animals such as rats, 2/ in the experimental
models, roots are generally avulsed just before reimplantation. Thus, this procedure does not take into account the time
between accidental avulsion and surgery, nor its consequences on spinal cord, roots or muscle function. The dog
represents an interesting model for carrying out restorative
strategies for both accidental and experimental nerve root
avulsion. We have demonstrated that axonal regrowth of cervical spinal neurons can occur within the reimplanted roots
[25]. In the same experiment, we have also shown that VRR
procedure resulted in postoperative neurological deficits
consistently observed in the hindlimbs (paraparesia) and sympathetic ocular system (Claude Bernard-Horner's syndrome).
These deficits appear to be the consequence of the development of intraspinal cysts (severing the tracts) occuring secondarily to the ventral root intraspinal reimplantation [25]. They
are observed in naturally occuring cases due to the damage
caused to the spinal cord when the rootlets are avulsed.
In order to determine if the reimplantation technique can be
used routinely in the case of spontaneous BPA seen in clinical practice, the present study was designed :
1) to evaluate axonal regeneration into the reimplanted
ventral roots
2) to demonstrate the re-establishment of functional motor
units via an electrophysiological study
3) to compare the restoration of function after reimplantation with the outcome of untreated root avulsion.
MOISSONNIER (P.) AND COLLABORATORS
Material and methods
The surgical, behavioural and electrophysiological procedures were all approved by the scientific committee of our
Institution.
MODEL DESIGN
For this long term study, in order to avoid limb self mutilation, we chose to work on a model in which some roots (and
corresponding nerves and muscles) can be isolated from the
rest of the plexus and thus studied independently. We denervated the cranial part of brachial plexus. For this purpose, we
cut the eventual contributions of C5 or C8 to the suprascapular and subscapular nerves. The C8 and T1 contributions to
the musculocutaneous nerve were left intact to avoid neurological deficits in the caudal part of the plexus. Thus, the axonal regrowth observed in the suprascapular and subscapular
nerves arise only from those roots that were reimplanted.
To evaluate the benefits of VRR, we used 3 groups of dogs.
Group 1 was formed of 6 dogs in which VRR was performed.
Group 2 (3 dogs) was a sham control group. A surgical
approach and VRR was performed but the reimplanted roots
were cut distally to the reimplantation site. The comparison
between these two groups led to an appreciation of the consequences of the surgical approach and VRR trauma, and the
benefits of VRR (group 1) compared to spontaneous healing
after cranial BPA (group 2). The dogs used in group 1 and 2
were female beagle dogs aged of 2 to 3 years with a mean
body weight of 12.3 kg (range 8.5 to 14.8 kg). Group 3 was
made up of 12 fresh mixed-breed dog cadavers with a mean
body weight of 13.4 kg (range 6.2 to 18.9 kg) in which left
and right biceps brachialis, supraspinatus and infraspinatus
muscles mass was measured. Our aim with this control group
was to confirm that the muscle mass of the right and the left
forelimb were identical (that the dog is not right- or left-handed). This would be confirmed if the left/right muscle weight
ratio was statistically identical to 1.
SURGICAL APPROACH TO THE VERTEBRAL COLUMN
The lateral surgical approach was initially developed
through dissection studies and has been previously described
[21, 24].
The 9 female adult beagle dogs used were anaesthetized
and routinely prepared for an aseptic surgery of the left forelimb, shoulder and caudal cervical region. The C5, C6 and
C7 ventral branches, with their corresponding nerve roots
and spinal cord segments, were approached as previously
described [25]. The contribution of the C5 ventral branch to
the plexus and of the C8 ventral branch to the suprascapular
and subscapular nerves were checked by dissection and by
direct electric stimulation. A bipolar electrodea was positioned on the surface of the nerve after it had been isolated from
the surrounding tissue and a 5mA-stimulation was applied.
We considered that the branch contributed to the nerves if
a. Nerve stimulator, Aesculap, Germany.
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EVALUATION OF VENTRAL ROOT REIMPLANTATION AS A TREATMENT OF EXPERIMENTAL AVULSION
macroscopic muscle contraction was observed. If they were
found to contribute to the nerves, the stimulated branche (or
contribution to the nerve) were cut to prevent axonal sprounting from the remaining axons coming from C8 or C5 which
were not subjected to VRR. Hemilaminectomy of the caudal
cervical column gave access to the dura. Before durotomy,
the dogs were given methylprednisolone sodium succinateb
(30 mg/kg intravenously).
ROOT AVULSION AND REIMPLANTATION
The dura was first secured and pulled laterally with four
stay-sutures, then opened longitudinally with micro-scissors
under the dissecting microscope, dorsally to the dorsal roots
(fig 1A). To visualise more clearly the ventral rootlets, a
gentle and limited rotation of the spinal cord was achieved by
placing two stay-sutures into the denticulate ligament and
then exerting mild traction on them. The dorsal and ventral
rootlets of C6 and C7 were avulsed from the cord with a curved microsurgical needle holder. The traction was exerted in
a direction parallel to the course of the spinal root (fig. 1B).
The effect was checked visually to determine whether the
avulsion was total. Immediately after injury, two slits were
made in the meningeal membranes and spinal cord tissue on
the left side, ventrally and dorsally to the denticulate ligament (fig. 1C). This incision extended into the ventral horn of
the gray matter. The dorsal slit involved the white mater only.
The avulsed rootlets were reimplanted into the slit with
microforceps and a small piece of Surgicel®c was left in
place to cover them in order to prevent bleeding and in order
to secure the rootlets in position (fig. 1D). The dogs were
then randomized as 1/ reimplanted group (in which reimplantation was left in place) and 2/ sham control group (in which
the reimplanted roots were cut distally to the reimplantation
site). In this group, the distal part of the cut root retracted
(several centimeters) from the cord.
The dura mater was left open. A 0.5-cm free adipose tissue
graft was placed over the hemilaminectomy site and wound
closure was completed in layers.
POSTOPERATIVE TREATMENT
Ketoprofen was choosen for pain control from the analgesics available at the time of this experiment [28]. It was
administrered at the rate of 2 mg/kg IM BID for 4 days together with prednisolone given orally (1 mg/kg) for 4 days.
During the first two weeks, when some of the dogs were
paraplegic, they received post-operative care as described for
spinal neurosurgical patients [22] : perioperative antibiotic
therapy (cefalexine 30 mg/kg per os BID 8 days), management of postoperative pain (as described previously), management of micturition dysfunction (manual compression of
the urinary bladder, intermittent catheterization, bethanechol
5.0 mg per os BID 5 days), supportive care (bedding and
cleaning) and physical therapy (turning the patient every 4
hours, passive motion).
b. Solumedrol, Upjohn Comp.
c. Johnson & Johnson.d. Electrodes concentriques bifilaires 53503®,
Médélec, France.
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589
FUNCTIONAL EVALUATION
Behaviour, gait and neurological function were assessed
every day by one of the authors.
Under general anesthesia, conventional EMG recordings
[10, 34] were made at 1, 2, 4 and 6 months postoperatively,
with concentric needle electrodesd connected to an EMG
devicee. These studies were conducted in all forelimb
muscles and, in particular, in those innervated by the lesioned
roots (supraspinatus, infraspinatus and biceps brachialis).
EMG was also recorded in the corresponding muscles of the
normal (right) forelimb. Spontaneous electrical activity following denervation was quantified using a simple scale :
0 : no spontaneous activity (no recording)
+ : moderate spontaneous activity in some location of the
muscle belly
++ : moderate spontaneous activity in every location of the
muscle belly
+++ : marked spontaneous activity in every location of the
muscle belly
Evoked muscular potentials (EMP) were recorded (in mV)
following supramaximal stimulation of C7 ventral branch by
a 0.45 x 50 mm negative electrode (53508, Médélec, France)
introduced percutaneously, caudally to the transverse process
of the sixth cervical vertebra. The positive electrode was
positioned near the left scapula. The recording needle was
positioned into the muscles (supra and infra- spinatus, biceps
and triceps brachialis, radial carpal extensor, interosseous).
RETROGRADE AXONAL TRACING WITH HRP
Six months after VRR, the dogs were anaesthetized and the
craniomedial region of the left shoulder was approached
[18]. The musculo-cutaneous, suprascapular and subscapular
nerves were isolated from the surrounding connective tissues
and transected before they penetrated into the muscles. The
cut end of the nerves were placed on a plastic sheet and surrounded with petroleum jelly to avoid tracer contamination
of the neighboring tissues. Then, a small pad of gelfoam®f,
soaked in 30 % Horse Radish Peroxidase (HRP)g solution,
was left in contact with the tip of the nerve for one hour [4].
After tracer application, the exposed area was washed out
several times with saline and the wound was closed in layers.
For this second invasive procedure, pain was controlled
again by ketoprofen administration.
MORPHOLOGICAL METHODS
Forty eight hours later, the dogs were sacrificed by barbiturate overdose. The heart was approached via a medial sternotomy and the left ventricle was canulated. The dogs were perfused with 15 liters of an isotonic heparinized saline solution
followed by 8-10 liters of 3 % glutaraldehyde in 0.1 M phosphate buffer at 4° C. The cervical spinal cord was then dis-
d. Electrodes concentriques bifilaires 53503®, Médélec, France.
e. E.M.G. 2001®, Racia s.a., France.
f. Upjohn Comp.
g. Sigma type VI.
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MOISSONNIER (P.) AND COLLABORATORS
FIGURE 1. — Semi-schematic representation of the avulsion-reimplantation procedure of one ventral root. The spinal cord is cross sectioned to show the depth of
reimplantation of the ventral rootlet. (A) The dura matter is incised around the dorsal aspect of the dorsal root. (B) The dorsal root is avulsed from the spinal
cord with a needle handler. (C) The avulsed dorsal and ventral rootlets are reimplanted into a slit made in the spinal cord and covered (D) with a small hemostatic sponge (Surgicel®).
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EVALUATION OF VENTRAL ROOT REIMPLANTATION AS A TREATMENT OF EXPERIMENTAL AVULSION
sected out and kept in the same fixative. Each spinal cord
segment (C5 to C8) was cut into 40 µm thick cross sections,
with a cryostat. The sections were processed for HRP histochemistry according to Mesulam [23], then counterstained
with neutral red. In each section, only labeled neurons displaying a nucleolus were counted with a light microscope.
The distribution of the neurons in the ventral horn was plotted.
Left and right supraspinatus, infraspinatus and biceps brachialis muscles were removed before perfusion and weighedh
in groups 1, 2 and 3.
STATISTICAL ANALYSIS
Muscular mass was the only factor statistically analysed
that was thought to be associated with functional recovery.
To rule out individual variations in muscle weight and compensatory muscular hypertrophy which probably depends on
multiple factors including the dog activity, dog weight
amongst others, we calculated "r" : the left to right muscle
weight ratio in the reimplanted (r1 : group 1) sham control
(r2 : group 2) and normal (rn : group 3) groups. "r" data from
all groups were assessed for normality of distribution.
ANOVA test was performed using SAS®i. When the overall
test was significant at 5 percent, we tested the differences between the groups. The comparison error rate was fixed at
0,05 / 3 (= 0.015).
Results
CLINICAL OBSERVATIONS
The clinical data were in accordance with our previous
observations [25]. Immediately after surgery, a flaccid paralysis in the left shoulder appeared in all animals of the group
1 and 2. Regional palpation revealed a severe amyotrophy
which developed within weeks in the muscles supplied by the
avulsed nerve roots (supraspinatus, infraspinatus and partially in biceps brachialis). Clinically, this amyotrophy was
more severe in group 2 in which the muscles were reduced to
a thin streak of elastic tissue, contrasting with the bulky
appearance of the muscle on the right side. During the first
two months after avulsion, none of the dogs used their left
limb which would lie along the thoracic wall. Signs of clinical restoration were difficult to appreciate but gradual improvement in the function of the affected limbs occurred in all
the dogs. Four months after surgery elbow flexion could be
observed but there was no evidence for a difference in the
shoulder function between groups 1 and 2.
Most of the dogs exhibited signs indicating damage to long
fiber tracts of the spinal cord. Motor (paraparesis, generally
left side lateralized), sensory (proprioceptive deficits) and
sympathetic (Cl. Bernard-Horner's syndrome) signs were
observed. Left hindlimb patellar and flexion reflexes were
h. Balance : Mettler P 160®.
i. SAS Institute Inc. SAS Procedures Guide, Release 6.11 Edition. Cary,
NC : SAS Institute Inc., 1996.
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591
increased. Nevertheless, these deficits remained slight, so
that the dogs could move themselves independantly and be
continent 15 days after surgery. Neurological deficits gradually decreased with time but the neurological assessment
remained slightly abnormal (mild proprioceptive left side
lateralized hindlimb deficits) until the end of the protocol, in
all the dogs. There was no Cl. Bernard-Horner’s syndrome at
this time.
ELECTROPHYSIOLOGICAL EVALUATION
Neurophysiological signs of denervation in the left shoulder muscles (spontaneous activity following denervation)
were observed in groups 1 and 2. Subsequent evidence of
reinnervation (evoked muscular potentials) was only observed in group 1.
EMG recordings made 1 month p.o. revealed fibrillation
potentials (++ to +++) in all left frontlimb muscles normally
innervated by the cranial part of the brachial plexus in groups
1 and 2. These potentials decreased at 4 months (+ to +++)
and even more at 6 months (0 to +) in both groups. A weak
spontaneous activity was also recorded in all muscles of the
left forelimb. These potentials had disappeared at 4 months.
This observation could not be statistically analysed.
EMPs were measurable in all muscles (group 1) and in all
muscles except the supra and infra-spinatus (group 2).
In the supraspinatus and infraspinatus muscles of the group
1 dogs, the evoked muscular potentials were generally of low
amplitude. They increased with time, in particular between
the second and third EMG examinations. The maximum
EMP response in the reinnervated muscles was recorded in
the infraspinatus muscle (amplitude was 80% of right side
recording which was considered as normal).
No late potentials were recorded. Table I gives the complete results of electrophysiological examinations and figure
2 shows 1 month and 6 month EMP recording in the left
supraspinatus muscle of dog 4 (group 1) and dog 9 (group 2).
MORPHOLOGICAL STUDY
In group 1 dogs, reimplanted C6 and C7 roots appeared, in
cross sections, to be embedded in scar tissue and were seen
penetrating into the gray matter. In the group 2 dogs, the
same roots were found outside the vertebral canal.
Cavitation of the spinal cord (micro and macro cyst formation) was a constant histological finding in both groups.
These cysts were located in the gray matter near the intraspinal tip of the reimplanted root as well as at some distance
from it (1 to 10 millimeters). They were surrounded by an
acellular, amorphous lining membrane. The nerve cells located beside the cysts seemed to be unaffected.
HRP-retrograde axonal tracing resulted in the labeling of
left cervical spinal neurons which were located close to the
intraspinal tip of the reimplanted roots (figure 3). With regard
to their location, size and morphology, most of these labeled
cells, dispersed through the ipsilateral ventral horn, were
assumed to be motoneurons. In some instances, axons of the
labeled cells could be traced towards the implanted root.
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MOISSONNIER (P.) AND COLLABORATORS
Dogs : number and (group). Group 1 (reimplantation) or group 2 (control) ; The dogs were randomized in the groups ; Electroeexam : electophysiological examination ; EMG (ElectroMyoGraphic examination) : spontaneous activity is quantified by the following scale : 0 : no spontaneous activity (no recording), + :
moderate spontaneous activity in some location of the muscle belly, ++ : moderate spontaneous activity in every location of the muscle belly, +++ : marked spontaneous activity in every location of the muscle belly, NE : Non Explored (for technical reasons such as postoperative muscle edema) ; EMP (Evoked Muscular
Potential) data are given in mV.
TABLE I. — Results of left forelimb electrophysiological examinations.
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593
FIGURE 2. — Comparison of Evoked Muscular Potential recorded in the infraspinatus muscle at 1 and 6
months in a reimplanted (number 4) and a control (number 9) dog. There is no potential recorded in
dog 9. EMP were recorded in dog 4. They increased with time.
There were no labeled neurons in the control group. The
number of neurones labeled in these experiments is shown in
table II.
MUSCLES
The left supra and infraspinatus muscle amyotrophy was
more severe in group 2 than in group 1. Biceps brachialis
amyotrophy was not obvious during macroscopic examination.
In the normal dogs, rn was close to 1 (biceps brachialis :
0.99 ± 0.06, supraspinatus : 0.97 ± 0.05 and infraspinatus :
1.02 ± 0.06).
In the control dogs (group 2), r2 was low (biceps brachialis :
0.38 ± 0.11, supraspinatus : 0.13 ± 0.05 and infraspinatus :
0.10 ± 0.04).
In the reimplanted dogs (group 1), r1was inferior to rn, but
superior to r2 (biceps brachialis : 0.44 ± 0.15, supraspinatus :
0.30 ± 0.09 and infraspinatus : 0.30 ± 0.15). The differences
between r1 and r2 are significant for the infraspinatus
(p = 0.05) and supraspinatus (p = 0.01) muscles but not significant for the biceps muscle. The differences between r1 and
rn, and, r2 and rn were highly significant for all muscles.
Figure 4 gives a schematic representation of these differences.
ported retrogradely through the peripheral nerve and labels,
spinal and dorsal root ganglia neurons [23]. It gives the
opportunity to know where the neuronal soma corresponding
to a given axon is located. In other words, the retrogradely
HRP-labeled neurons are those nerve cells which have grown
an axon into the nerve root at least up to the site of tracer
application. Therefore the present study indicates that root
reimplantation into the spinal cord results in axonal regrowth
from spinal motoneurons close to the lesion and reimplantation site. This can be explained by the results of experiments
previously carried out in rodents [14, 31] where it was established that grafted roots (made of peripheral nerve tissue)
act by providing a new microenvironment which appears to
be much more permissive to axonal regrowth and elongation
than the surrounding injured CNS tissue. Furthermore,
HORVAT et al. [19] have shown that these regenerating
Discussion
This attempt to use ventral root reimplantation (VRR) as a
treatment of brachial plexus avulsion (BPA) in the dog
clearly demonstrates a reinnervation of the reimplanted roots.
The axonal-tracing technique confirms that the regenerating
axons come from the cervical spinal neurons. HRP is transRevue Méd. Vét., 2001, 152, 8-9, 587-596
TABLEAU II. — Number of HP-labeled neurons in the two groups.
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MOISSONNIER (P.) AND COLLABORATORS
FIGURE 3. — Cross section of the cervical spinal cord segment 7 after retrograde neuronal labeling and HRP histochemistry using tetramethyl benzidine (TMB) and counterstaining with neutral red.
A. The reimplanted ventral rootlet (large arrow) penetrates into the ventral horn (VH) of the spinal cord gray matter and is surrounded by large cystic cavities (stars) ; B and C, HRP lebeled neurons (small arrows) are those that
have grown an axon through the reimplanted ventral rootlet at least up to the site of tracer application. They are
located near the intraspinal tip of the reimplanted rootlet and have small black vesicles into their cytoplasm. Scale
bars : A = 200 µm ; B and C = 50 µm.
axons could reform specific connections with a peripheral
muscular target by generating new motor endplates. Our
electrophysiological data are in full agreement with these findings.
FUNCTIONAL RECOVERY
Unlike partial (1 or 2 roots) BPA, complete BPA results in
a significant neurological deficit such that root reinnervation
can be evaluated by clinical tests. Functional recovery, follo-
wing complete BPA, has been observed in small laboratory
animals such as rats [35] or small monkeys [6, 8]. In
constrast, functional recovery following partial BPA performed in cats [17], dogs [20] or sheep [16] was difficult or even
impossible to assess. However, in our dog model, the cranial
part of the plexus can be isolated from the rest of the BP. In
these conditions, functional recovery of the infraspinatus and
supraspinatus muscles depends exclusively on the reimplantation of the C6 and C7 roots, whereas recovery of the biceps
brachial muscle could also be the result of collateralization of
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FIGURE 4. — Comparison of biceps brachii, supraspinatus and infraspinatus muscle weight in group 1 (reimplanted), group
2 (sham control) and group 3 (normal).
«r» is the left to right muscle weight ratio in the reimplanted (r1), sham control (r2) and normal (rn) dogs.
remaining axons originating from the C8 root. Clinical tests
have to be developed to appreciate the mobility of the shoulder in the dog. In this study, we have assumed that the presence of electrophysiological signs of reinnervation does not
neccessarily mean that there is functional recovery, but the
repaired motor units we have described, have been shown to
connect with the descending pattern of the spinal cord in the
rat after electromagnetic cortical stimulation [5] and, thus, to
create a functional motor pathway.
RESTORATION OF MUSCLE FUNCTION
The condition of the muscle at the time of reinnervation is
crucial for VRR success. Skeletal muscle can substantially
recover its ability to contract when it is reinnervated following transection and resuture of its peripheral nerve but a
prolonged period of denervation is thought to make denervation changes irreversible [12]. Muscle weight is directly
related to muscle function [12]. Muscle paralysis leads to
severe muscular fibrosis and complete degeneration [3]. In a
frog model it has been shown that a nerve does not loose its
ability to reinnervate a muscle but, in contrast, a muscle
rapidly looses its ability to become reinnervated [12]. The
strength produced by a reinnervated muscle depends on the
time elapsed since the muscle was denervated. It has been
suggested that following target reinnervation some neurons
acquire the capacity to branch and to form large motor units.
After a two year period of permanent denervation, the
muscle belly becomes phagocytosed and if reinnervation is
performed at this time, there is no possibility of success [30].
The extent to which the duration of denervation influences
the ability of the neuron and muscle to recover has not been
established in the dog. Nevertheless, the re-establishment of
appropriate connections following surgery implies axonal
regrowth from spinal neurons and to the muscular effectors,
through the site of injury. The maximum speed of outgrowth
Revue Méd. Vét., 2001, 152, 8-9, 587-596
recorded experimentally in the rat, 4.83 mm per day
[Earlanger], never seems attainable in man. There is a
consensus of opinion as to the range of regeneration speed in
man, from 0.5 mm [33] to 2 mm per day [29]. No data is
available in the dog but the distance separating the spinal
cord and the muscle might be a limiting factor for anatomical and functional restoration. Therefore, we think that reimplantation has to be performed as soon as possible and that
functional rehabilitation (with neuromuscular stimulation)
has to be planned immediately after surgery to maintain
muscle function [9].
RELIABILITY OF THE SURGICAL PROCEDURE
Spinal cord cysts and neuronal death are lesions due to
avulsion itself and to the VRR procedure. The functional
outcome of the dogs depends on the severity of these lesions.
The destruction of the ventral horn of the spinal cord and the
replacement of the neuropile by cysts means there is no hope
for axonal outgrowth. In our study, there exists a correlation
between the severity of the lesions, the number of marked
neurons, the intensity of the evoked muscular potentials and
the muscle weight. Twenty four neuronal somata were labeled in dog 6 (group 1) which showed the most severe histological spinal cord lesion including large cysts. In this dog,
the amplitudes of the evoked muscular potentials were
weak, and muscle weight was reduced. We observed that the
greater the number the regenerating neurons, the higher are
the EMP. The improvement of the reimplantation technique
(limitation of haemorrhage, deepness control of root introduction into the gray matter) is expected : 1/ to reduce spinal
cord lesion and subsequent postoperative deficits, 2/
increase the number of regenerating axons, 3/ enhance functional recovery.
The current treatment of BPA is only palliative and limb
amputation is often proposed [15, 32, 37]. Our results suggest
596
that an active therapeutic approach for BPA could enhance
the functional outcome of this dramatic condition. Therefore,
root reimplantation appears to be a very attractive candidate
for cranial BPA treatment. For a correct evaluation of gait
and functional recovery after VRR, avulsion of the whole
brachial plexus studies must be studied. This would correspond more clearly to the clinical presentation where a complete (or caudal part) avulsion of the plexus is observed. It
would be then possible to know if the function of the extensor muscles, without which the function of the whole of the
member is compromised, can be restored.
However, before it can be used routinely, many problems
have to be solved such as : 1/ reinnervation does not necessarily result in a functional recovery, 2/ muscle function has
to be monitored 3/ the reimplantation technique has to be
improved.
Acknowledgments
This study was supported by a grant from the DGER,
Agriculture Ministry and the CNVSPA. The authors
thank Mrs. L. KLUKVINE for her photographs, Mr. A.
PERIGNON for his invaluable assistance with the drawings,
Dr. A.A. PONTER for his critical reading of the manuscript
and Dr. M. SANAA for his assistance in the statistical evaluation.
Reprint requests should be sent to : Pierre MOISSONNIER, Service de Chirurgie, École Nationale Vétérinaire
d'Alfort, 7 Avenue du Général De Gaulle. 94704 Maisons
Alfort, France. Tel : 33 01 43 96 71 14 ; Fax : 33 01 43 96 71
17 ; Email : [email protected]
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