Intraoperative radial nerve injury during coronary artery surgery – report of two cases

Marianna Papadopoulou, Konstantinos Spengos*, Apostolos Papapostolou, Georgios Tsivgoulis and Nikolaos Karandreas
*
Corresponding author: Konstantinos Spengos [email protected] Author Affiliations
University of Athens School of Medicine, Department of Neurology, Eginition Hospital, Athens, Greece
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Journal of Brachial Plexus and Peripheral Nerve Injury 2006, 1:7 doi:10.1186/1749-7221-1-7The electronic version of this article is the complete one and can be found online at: http://www.JBPPNI.com/content/1/1/7 Received:30 July 2006 Accepted:5 December 2006 Published:5 December 2006 © 2006 Papadopoulou et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
AbstractPeripheral nerve injury and brachial plexopathy are known, though rare complications
of coronary artery surgery. The ulnar nerve is most frequently affected, whereas radial
nerve lesions are much less common accounting for only 3% of such intraoperative injuries.
Two 52- and 50-year-old men underwent coronary artery surgery. On the first postoperative
day they both complained of wrist drop on the left. Neurological examination revealed
a paresis of the wrist and finger extensor muscles (0/5), and the brachioradialis
(4/5) with hypoaesthesia on the radial aspect of the dorsum of the left hand. Both
biceps and triceps reflexes were normoactive, whereas the brachioradialis reflex was
diminished on the left. Muscles innervated from the median and ulnar nerve, as well
as all muscles above the elbow were unaffected. Electrophysiological studies were
performed 3 weeks later, when muscle power of the affected muscles had already begun
to improve. Nerve conduction studies and needle electromyography revealed a partial
conduction block of the radial nerve along the spiral groove, motor axonal loss distal
to the site of the lesion and moderate impairment in recruitment with fibrillation
potentials in radial innervated muscles below the elbow and normal findings in triceps
and deltoid. Electrophysiology data pointed towards a radial nerve injury in the spiral
groove. We assume external compression as the causative factor. The only apparatus
attached to the patients’ left upper arm was the sternal retractor, used for dissection
of the internal mammary artery. Both patients were overweight and lying on the operating
table for a considerable time might have caused the compression of their left upper
arm on the self retractor’s supporting column which was fixed to the table rail 5
cm above the left elbow joint, in the site where the radial nerve is directly apposed
to the humerus.
Although very uncommon, external compression due to the use of a self retractor during
coronary artery surgery can affect – especially in obese subjects – the radial nerve
within the spiral groove leading to paresis and should therefore be included in the
list of possible mechanisms of radial nerve injury.
BackgroundPeripheral nerve injury and brachial plexopathy are known, though rare complications
of coronary artery surgery. The true incidence of nerve injury during general anesthesia
remains unclear and probably is underestimated [1]. The ulnar nerve is most frequently affected accounting for one third of all nerve
damages, whereas radial nerve lesions are much less common accounting for only 3%
of such intraoperative injuries [2]. We report two cases of left radial nerve lesion during coronary artery surgery,
presumably due to an external compression caused by a sternal retractor that is used
for dissection of the internal mammary artery.
Case presentationsA 52-year old obese man with known ischemic heart disease but no history of any neurological
disease underwent coronary artery bypass surgery. Preoperative routinely performed
diagnostic workup revealed no significant findings. During surgery he was laid supine
on the operating table with both arms fully adducted to his side, fixed in the neutral
position. Intraoperative monitoring included electrocardiography, pulse oxymetry and
automatic blood pressure monitoring using a standard-size adult cuff affixed to the
patient’s right upper arm. No particular events occurred during anesthesia or surgery
and recovery was good so that patient was transferred within a day from the intensive
care unit to the normal ward.
However, on the first postoperative day he complained of wrist drop on the left. Neurological
examination revealed a severe decrease in muscle power of the wrist and finger extensor
muscles (0/5 MRC) and a slight brachioradialis paresis (4/5 MRC) accompanied by hypoaesthesia
on the radial aspect of the dorsum mani. Biceps and triceps reflexes on the affected
left arm were normoactive whereas the brachioradialis reflex was diminished. All muscles
innervated from the median and ulnar nerve, as well as all the muscles above the elbow
remained unaffected. The clinical diagnosis of radial nerve injury was set and rehabilitation
therapy was recommended.
After hospital discharge and about three weeks after surgery the patient was referred
for neurophysiological evaluation. In the meanwhile the extensor muscles had already
begun to improve. Nerve conduction studies of both radial nerves were performed using
surface electrodes. Compound muscle action potentials (CMAP) were recorded from the
extensor digitorum communis muscle. The opposite radial nerve was examined for comparison.
Supramaximal nerve stimulation was achieved by gradually increasing the stimulation
power until the point where the amplitude of the waveform did no longer increased
was reached. Electrical stimulation at the elbow, below and above the spiral groove,
revealed an amplitude decline of the CMAP that was indicative of a partial conduction
block of the left radial nerve along the spiral groove, whereas CMAP recordings of
the right radial nerve were normal (Table 1). Moreover, motor axonal loss due to wallerian degeneration distal to the site of
the lesion was suggested by the low distal CMAP. Needle electromyography enhanced
this finding by revealing moderate impairment in recruitment with fibrillation potentials
in radial innervated muscles below the elbow and normal findings in both triceps and
deltoid muscles. The motor unit potentials were normal, a finding that is consistent
with a recent nerve injury. In conclusion, all electrophysiological findings were
indicative of a radial nerve injury in the spiral groove. The involvement of the brachioradialis
muscle and the fact that both deltoid and triceps muscles remained unaffected practically
excluded the differential diagnostic alternative of a posterior interosseus neuropathy
and a posterior cord brachial plexus lesion respectively.
Table 1. Electrophysiological studies performed in both cases on radial nerves bilaterally
indicative of a partial conduction block of the left radial nerve along the spiral
groove with additional distal motor axonal loss due to wallerian degeneration.
Another 50-year-old obese man was referred for neurological and neurophysiological
evaluation one month after having undergone coronary artery bypass surgery. He also
reported suffering from a left wrist drop since the first postoperative day. Similarly
to the previous case no incidents occurred during anaetshesia and surgery, during
which exactly the same procedures were followed. Electromyography and nerve conduction
studies were conducted and revealed identical findings suggestive of an injury of
the left radial nerve in the spiral groove.
DiscussionThe similarity of these two cases is impressive. In both cases, there was no direct
injury of the nerve during surgery; no neurotoxic material was injected; no event
predisposing to nerve palsy (hypotension, hypoxia, electrolyte disturbances) occurred
during or after anesthesia [3]; no malposition of the left arm on the operating table or later on the intensive
care unit bed that may cause ischemic nerve injury was documented [4] and no stretch of the brachial plexus could have occurred [5], since the left arm was comfortably attached to the patients’ body. Predisposing
conditions such as arthritis or elbow instability were also excluded [6]. We therefore assume external compression as the causative factor.
The radial nerve is the largest nerve in the upper extremity, arising as an extension
of the posterior cord of the brachial plexus. In the upper arm lies medially to the
humerus, passes obliquely behind the humerus between the lateral and medial heads
of the triceps and then enters the spiral groove to exit into the anterior compartment
of the arm piercing the lateral intermuscular septum below the deltoid insertion.
Then the nerve passes through the radial tunnel and divides into its terminal branches,
the superficial radial, a pure sensory branch and posterior interosseus nerve, a pure
motor branch. The most common cause of radial nerve injury is compression in the spiral
groove which is a shallow groove formed deep to the lateral head of the triceps, where
the nerve lies in close contact with the humerus. The radial nerve is compressed most
often after piercing the lateral intermuscular ligament, where it lies unprotected
by the triceps against the humerus. Patients with lesions of radial nerve in the spiral
groove need to be differentiated from lesions of the posterior interosseus nerve and
of the posterior cord of the brachial plexus. In the first case no sensory deficit
is present and brachioradialis muscle escapes damage. In the second case, deltoid
and triceps muscles are affected. Another differential diagnostic alternative that
needs to be excluded is severe C7 and C8 radiculopathy that is characterized by a
different sensory deficit (index, middle, ring and little finger) and a motor deficit
in wrist flexion and forearm pronation as well. In both reported cases clinical and
electrophysiological evidence establishes a radial nerve injury within the spiral
groove. Finally, the differential diagnostic alternative of cerebral lesion imitating
the clinical features of radial nerve palsy needs to be excluded. However in such
a case the weakness is never limited solely to radial-innervated muscles and generally
alterations in muscle tone and in the deep tendon reflexes of the limb are apparent.
Moreover, when a patient with wrist drop caused by an upper motor neuron lesion grasps
an object, involuntary synkinesis produces wrist extension as well. Since none of
these features were present, central nervous system affection as cause of both cases
of wrist drop could be clinically excluded.
Assuming an external compression as cause of such a lesion, we have to consider that
the only apparatus attached to the patients’ left upper arm was the sternal retractor,
which is being used for the dissection of the internal mammary artery. Both patients
were overweight and lying on the operating table for a considerable time might have
caused the compression of their left upper arm on the self retractor’s supporting
column which is usually fixed to the table rail 5 cm above the left elbow joint, in
the site where the radial nerve is unprotected directly apposed to the humerus.
Similar radial nerve compression has been attributed to an automatic blood pressure
monitoring cuff [7] and a Kent retractor used for upper abdominal surgery [8]. There have been only three further reports of radial nerve palsy due to the use
of a self retractor for the dissection of the left internal mammary artery for coronary
artery surgery [9-11]. Similarly to our cases where symptoms ceased within two months, in all reported
cases the lesion was reversible.
Transient neurologic symptoms result from action potential propagation failure caused
by ischemia. The most widely used classification of peripheral nerve injury is the
one introduced by Seddon and Sunderland [12,13]. Focal pressure, when brief and modest, distorts the myelin producing segmental conduction
block without wallerian degeneration. This is termed neurapraxia. With increasing
pressure, the axon is interrupted, resulting in secondary wallerian degeneration distally.
If supporting structures, e.g. basal lamina and Schwann cells, remain intact this
injury is termed axonotmesis. Severe injury that results in complete disruption of
the nerve and all the supporting structures is termed neurotmesis. Conduction block
is reversible whereas wallerian degeneration and axonal loss may have a poorer prognosis
with slow and incomplete recovery [14]. Wallerian degeneration is completed within 7–10 days. Spontaneous activity, generated
by denervated muscles, appears approximately during the second week, first proximally
and then more distally. It becomes widespread after the third week and is most prominent
after the fourth week. Thus repeated neurophysiological studies are needed to confirm
the diagnosis and follow the process of reinnervation.
Although very uncommon, external compression due to the use of a self retractor during
coronary artery surgery can cause – especially in obese subjects – radial nerve palsy
and should probably be included in the list of possible mechanisms of radial nerve
injury. Considering the small number of reported similar cases and the fact that symptoms
are reversible, it could be assumed that the frequency of such intraoperative complications
is probably underestimated. Prospective studies or even retrospective evaluation might
be helpful in order to estimate the true incidence of intaoperative nerve injuries,
understand the causative mechanism and eventually find effective preventing strategies.
Competing interestsThe author(s) declare that they have no competing interests.Authors’ contributionsMP performed in both cases the electromyographic studies in both cases and drafted
the manuscript together with KS, who also made the appropriate literature review.
AP performed the conduction studies whereas GT examined clinically both patients.
NK coordinated the work for this paper and also helped drafting the manuscript with
his critical remarks. All authors read and approved the final manuscript.
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