Ulnar neuropathies following surgery are common. However, they often go undetected during the early postoperative period, because the patient may be unaware of symptoms related to the neuropathy. Nerve conduction studies are useful in localizing the lesion, but are usually employed only in cases developing signs and symptoms. We undertook this study to determine the incidence, time of onset, and outcome of clinical and subclinical ulnar neuropathies. Electrophysiologicalstudies were carried out preoperativety, immediately following surgery, and 4 to 6 weeks postoperatively in 20 coronary artery bypass patients. Conduction velocity across the elbow was reduced in 3 limbs (8%) postoperatively, all of which were detected irnmediately following surgery. One patient developed conduction block and weakness in ulnar supplied intrinsic hand muscles. Denervation was seen in 2 cases and, in 1 case (5%), a right brachial plexus injury was clinically evident 5 days following surgery. All newly developing ulnar neuropathies were asymptomatic, with most recovering to their preoperative electrophysiological status at follow-up. Key words: ulnar neuropathy nerve conduction studies conduction block coronary artery bypass surgery brachial plexus MUSCLE & NERVE 15:701-705 1992 ~
EARLY POSTOPERATIVE ULNAR NEUROPATHIES FOLLOWING CORONARY ARTERY BYPASS SURGERY BRADLEY V. WATSON, BSc, RT(EMG), RICHARD N. MERCHANT, WID, FRCP(C), and WILLIAM F. BROWN, MD, FRCP(C)
Ulnar neuropathies as a complication of various Our prospective study of patients undergoing surgical procedures are ~ ~ m m ~ n T. h e~ ~ coronary ~ ~ ~ artery ~ ~bypass , ~ surgery ~ - was carried out to determine the incidence of peri- and postoperaprecise time of onset, however, may be difficult to tive ulnar neuropathies, their probable times of ascertain, because sedative analgesics or the disonset, and outcome, as judged by follow-up examcomfort resulting from the operation may mask inations at 4 to 6 weeks and, in a few cases, 5 to 6 symptoms for days or even weeks postoperatively. months. Most of the electrophysiological studies have been retrospective in design and provided little, if any, information about the status of the ulnar METHODS nerve prior to surgery.2,4,5,14,15 In some studies, Controls. Ulnar motor nerve conduction studies identification of the neuropathy depended on were carried out bilaterally on 10 volunteers (6 feclinical criteria alone.""",'6~18T h e latter may submales, 4 males) with a mean age of 28.5 years stantially underestimate the true incidence by ex(range 22 to 37 years). In all cases, there was no cluding electrophysiologically detected ulnar neuclinical evidence of an ulnar neuropathy, nor was ropathies without clinical symptoms. there any history or subsequent findings of a peripheral or mononeuropathy. From the Department of Clinical Neurological Sciences (Mr. Watson and Dr Brown) and Department of Anaesthesia (Dr. Merchant), Unlversity Hospital, London, Ontario, Canada. Address reprint requests lo William F. Brown, MD, Clinical Neurological Sciences, University Hospital, 339 Winderrnere Road, London, Ontario. Canada, N6A 5A5 Accepted for publication October 1. 1991 CCC 0148-639X/92/060701-05 $04 00 0 1992 John Wiley & Sons, Inc.
Early Postoperative Ulnar Neuropathy
With approval from the Human Experimentation Committee of the University of Western Ontario, 20 patients scheduled for coronary artery bypass surgery were examined clinically and electrophysiologically within 1 week prior to their operation. Postoperatively, 14 cases were examined within 24 to 48 hours, and the remainder within 1 week of the operation. Fourteen cases
Patients.
MUSCLE & NERVE
June 1992
701
were reassessed 4 to 6 weeks postoperatively, while 6 were lost to follow-up at this time. Finally, 2 cases, 1 which developed a postoperative ulnar neuropathy, were examined at 6 months. Patients with a history of diabetes or alcoholism, or clinical findings of a peripheral neuropathy prior to the operation, were excluded. Electrophysiological studies were carried out in both arms. They consisted of the following. Motor Conduction Studies. T h e ulnar nerve was supramaximally stimulated with percutaneous electrodes at the wrist, 2 to 5 cm distal to the tip of the medial epicondyle, 3 to 5 cm proximal to the tip of the medial epicondyle, and as proximal in the axilla as possible. T h e maximum compound muscle action potential (M) was recorded with surface belly-tendon electrodes from the hypothenar (HT) muscles. Maximum motor- conduction velocities (MMCVs) were measured across the proximal arm, elbow, and forearm segments. Distances about the elbow were measured with the elbow flexed to 45". T h e MMCV across the elbow was considered abnormal if reduced by more than 20% relative to the forearm. Percent conduction slowing across the elbow relative to the forearm was calculated by: Electrophysiology.
neously stimulated at the wrist with an intensity sufficient enough to evoke a maximum fourthand fifth-digit antidromic sensory nerve action potential as recorded with ring electrodes. T h e orthodromically conducted volley along the ulnar nerve branch was recorded as high in the axilla as possible by means of a surface electrode positioned over the ulnar nerve. For the latter, a surface electrode positioned over the deltoid served as the reference. T h e cervical potential was recorded by a surface electrode positioned over the C-6 spinous process for which Fz served as the reference. Last, the cortical potential was recorded from C3-4 with Fz as the reference site. Electromyography. Concentric needle electromyography was carried out at 4 to 6 weeks in those patients, in whom the MMCV across the elbow was slowed by 10% or more relative to the preoperative value. Insertional and spontaneous activity was searched for in the abductor digiti minimi, first dorsal interosseous, and, in some cases, the flexor carpi ulnaris muscles. Muscles outside the motor innervation territory of the ulnar nerve were also examined to exclude a more widespread neuropathy. Position of the Arms During Surgery. Both arms were extended to the sides of the body, with the forearm pronated in 3 cases, supinated in 5, and halfway between in the remainder. RESULTS
As reductions in MMCV across the elbow were sometimes present preoperatively, operative or postoperative injury to the ulnar nerve was accepted only where the percent reduction in MMCV across the elbow relative to the forearm exceeded the corresponding preoperative value by more than 20%. In these cases, percutaneous stimulation at 2-cm intervals, both proximal and distal to the tip of the medial epicondyle, was carried out to better localize the site of conduction slowing. 1 In 1 case, a brachial neuropathy became evident in the early postoperative period. Here the spinal roots were stimulated using a D-180 highvoltage stimulator with the cathode positioned between the C7 and T1 spinous processes (anode rostral). This made it possible to directly assess conduction between the axilla and spinal roots. Sensory Conduction Studies. To assess conduction across the brachial plexus and roots, as well as to look for evidence of sensory fiber loss in the ulnar nerve territory, the ulnar nerve was percuta-
702
Early Postoperative Ulnar Neuropathy
In the 20 ulnar nerves in I0 controls, all less than 40 years of age, the mean ? 1 SD limit for the forearm, elbow, and proximal arm were 60.8 -+ 4.0, 58.9 -+ 5.6, and 65.4 -+ 4.2 m/s, respectively. Of these, only 3 exhibited a greater than 10% conduction slowing across the elbow relative to the forearm (11.276, 15.1%, and 16.3%; overall mean 3.8%).
Controls.
The motor conduction status of the 20 cases preoperatively, immediately postoperatively, and at the 4- to 6-week follow-up period are summarized in Table 1. Patients.
In 15 of the 20 cases and 33 of the 40 limbs studied, the MMCV across the elbow relative to the forearm differed by less than 20%. However, in 7 ulnar nerves (18%), the transelbow MMCV relative to the forearm was slowed by more than 20% and by more than 30% in 2 of the 7. Motor conduction across the elbow was slowed unilaterally in 3, and bilaterally in 2 of Preoperative Studies.
MUSCLE & NERVE
June 1992
~~~
~~
Table 1. Percent slowing of conduction velocity across elbow PATIENT
0.20
1 2 3 4 5 6 7 8 9 10
L L L L
11 12
L L
R R R
13 14 15 16 17 18 19 20
L L L L L L L L
R R R R R R R
PRE-OPERATIVE 21-30 31-40
R R R
I
I
L L L
R
NA
R R L
L
R
L L L L L L L
R R R R R A R R R R R
these patients. Despite this conduction slowing, hypothenar maximum M potential sizes and sensory conduction were all within the normal range, and symptoms and signs indicative of an ulnar neuropathy were absent. At this time, the MMCV across the elbow, relative to the forearm, was reduced by more than 20% in excess of preoperative values in 3 of the 33 (9%) preoperatively normal ulnar nerves. In 1 of these cases, the reduction exceeded 30% relative to the preoperative value. However, there were no significant changes in the 7 ulnar nerves in which preoperative conduction across the elbow was slowed. Only 1 of the 3 cases, developing significant conduction slowing across the elbow, postoperatively, showed clinical evidence of an ulnar neuropathy. In this case, weakness in ulnar-supplied intrinsic hand muscles and partial conduction block were present unaccompanied by clinically or electrophysiologically detectable sensory loss (Fig. 1). Early Postoperative Studies.
Of the 3 ulnar neuropathies appearing for the first time in the immediate postoperative study, 2 returned to their preoperative status while the case with greater than 30% conduction slowing across the elbow was lost to follow-up. Conduction across the elbow improved in the case characterized by par-
Four- to 6-Week Postoperative Studies.
Early Postoperative Ulnar Neuropathy
R R NA
L L R L
L R R L R L R
R
L R L R
L R L R
POST-OPERATIVE 14-6 Weeks1 0-20 21-30 31-40
L L
R
L L R
I
R R R
R L
I
POST-OPERATIVE IEARLVI 0-20 21-30 31-40
NA
L (42%) L L
R
L L
L L
R R
L L
R R NA NA
L
L
R
L L
R R
NA
tial conduction block, although fibrillation activity had now developed in the ulnar supplied intrinsic hand muscles. One new case developed fibrillation potentials
PREOPERATIVE
% tMMCV x ELBOW
~
_
% t - p A x ELBOW
_
POSTOPERATIVE( 24 hrs) 2 I%
POSTOPERATIVE [ 42 days)
1
1
0
10
I
20
1 30
I 40
TIME ( ms)
FIGURE 1. Ulnar nerve motor conduction study in patient 12 illustrating a 21 YO reduction in the hypothenar maximum M potential negative peak area and a reduction of 24% in the maximum motor conduction velocity across the elbow relative to the forearm (arrow). Evidence of partial conduction block and conduction slowing across the elbow was still present 42 days postoperatively.
MUSCLE & NERVE
June 1992
703
and positive sharp waves in ulnar-supplied intrinsic hand muscles, and a 15% reduction in conduction velocity across the elbow in excess of pre- and early postoperative values. However, there were no accompanying signs or symptoms of an ulnar neuropathy, and sensory conduction studies were normal. SixmMonth Follow-Up. Two patients were available for follow-up at 6 months. The case developing conduction slowing (15%) across the elbow for the first time, and fibrillation activity at the 4- to 6-week mark, had returned to preoperative status. In the other case, conduction across the elbow was normal throughout the study. Localization. In the 3 cases where conduction across the elbow relative to the forearm was slowed by more than 20%, the site of the greatest conduction slowing was across the postcondylar course of the nerve in 2 cases, and across the cubital tunnel in the remaining case.
One patient, seen 5 days following surgery and asymptomatic at that time, had developed clinical signs of a brachial neuropathy, primarily affecting the middle and lower trunks of the brachial plexus. I n this case, motor conduction across the elbow was normal, but there was a 78% reduction in the negative peak area of the hypothenar maximum M potential between the spinal root and axillary stimulus sites. This patient was subsequently lost to follow-up.
Brachial Plexopathy.
DISCUSSION
Ulnar neuropathies are a common complication of surgery, with a reported incidence in retrospective studies4,14,15 between .02% and l.O%, and appreciably higher (0.8% to 38%) in prospective studies.9,12, I(
EARLY POSTOPERATIVE ULNAR NEUROPATHIES FOLLOWING CORONARY ARTERY BYPASS SURGERY BRADLEY V. WATSON, BSc, RT(EMG), RICHARD N. MERCHANT, WID, FRCP(C), and WILLIAM F. BROWN, MD, FRCP(C)
Ulnar neuropathies as a complication of various Our prospective study of patients undergoing surgical procedures are ~ ~ m m ~ n T. h e~ ~ coronary ~ ~ ~ artery ~ ~bypass , ~ surgery ~ - was carried out to determine the incidence of peri- and postoperaprecise time of onset, however, may be difficult to tive ulnar neuropathies, their probable times of ascertain, because sedative analgesics or the disonset, and outcome, as judged by follow-up examcomfort resulting from the operation may mask inations at 4 to 6 weeks and, in a few cases, 5 to 6 symptoms for days or even weeks postoperatively. months. Most of the electrophysiological studies have been retrospective in design and provided little, if any, information about the status of the ulnar METHODS nerve prior to surgery.2,4,5,14,15 In some studies, Controls. Ulnar motor nerve conduction studies identification of the neuropathy depended on were carried out bilaterally on 10 volunteers (6 feclinical criteria alone.""",'6~18T h e latter may submales, 4 males) with a mean age of 28.5 years stantially underestimate the true incidence by ex(range 22 to 37 years). In all cases, there was no cluding electrophysiologically detected ulnar neuclinical evidence of an ulnar neuropathy, nor was ropathies without clinical symptoms. there any history or subsequent findings of a peripheral or mononeuropathy. From the Department of Clinical Neurological Sciences (Mr. Watson and Dr Brown) and Department of Anaesthesia (Dr. Merchant), Unlversity Hospital, London, Ontario, Canada. Address reprint requests lo William F. Brown, MD, Clinical Neurological Sciences, University Hospital, 339 Winderrnere Road, London, Ontario. Canada, N6A 5A5 Accepted for publication October 1. 1991 CCC 0148-639X/92/060701-05 $04 00 0 1992 John Wiley & Sons, Inc.
Early Postoperative Ulnar Neuropathy
With approval from the Human Experimentation Committee of the University of Western Ontario, 20 patients scheduled for coronary artery bypass surgery were examined clinically and electrophysiologically within 1 week prior to their operation. Postoperatively, 14 cases were examined within 24 to 48 hours, and the remainder within 1 week of the operation. Fourteen cases
Patients.
MUSCLE & NERVE
June 1992
701
were reassessed 4 to 6 weeks postoperatively, while 6 were lost to follow-up at this time. Finally, 2 cases, 1 which developed a postoperative ulnar neuropathy, were examined at 6 months. Patients with a history of diabetes or alcoholism, or clinical findings of a peripheral neuropathy prior to the operation, were excluded. Electrophysiological studies were carried out in both arms. They consisted of the following. Motor Conduction Studies. T h e ulnar nerve was supramaximally stimulated with percutaneous electrodes at the wrist, 2 to 5 cm distal to the tip of the medial epicondyle, 3 to 5 cm proximal to the tip of the medial epicondyle, and as proximal in the axilla as possible. T h e maximum compound muscle action potential (M) was recorded with surface belly-tendon electrodes from the hypothenar (HT) muscles. Maximum motor- conduction velocities (MMCVs) were measured across the proximal arm, elbow, and forearm segments. Distances about the elbow were measured with the elbow flexed to 45". T h e MMCV across the elbow was considered abnormal if reduced by more than 20% relative to the forearm. Percent conduction slowing across the elbow relative to the forearm was calculated by: Electrophysiology.
neously stimulated at the wrist with an intensity sufficient enough to evoke a maximum fourthand fifth-digit antidromic sensory nerve action potential as recorded with ring electrodes. T h e orthodromically conducted volley along the ulnar nerve branch was recorded as high in the axilla as possible by means of a surface electrode positioned over the ulnar nerve. For the latter, a surface electrode positioned over the deltoid served as the reference. T h e cervical potential was recorded by a surface electrode positioned over the C-6 spinous process for which Fz served as the reference. Last, the cortical potential was recorded from C3-4 with Fz as the reference site. Electromyography. Concentric needle electromyography was carried out at 4 to 6 weeks in those patients, in whom the MMCV across the elbow was slowed by 10% or more relative to the preoperative value. Insertional and spontaneous activity was searched for in the abductor digiti minimi, first dorsal interosseous, and, in some cases, the flexor carpi ulnaris muscles. Muscles outside the motor innervation territory of the ulnar nerve were also examined to exclude a more widespread neuropathy. Position of the Arms During Surgery. Both arms were extended to the sides of the body, with the forearm pronated in 3 cases, supinated in 5, and halfway between in the remainder. RESULTS
As reductions in MMCV across the elbow were sometimes present preoperatively, operative or postoperative injury to the ulnar nerve was accepted only where the percent reduction in MMCV across the elbow relative to the forearm exceeded the corresponding preoperative value by more than 20%. In these cases, percutaneous stimulation at 2-cm intervals, both proximal and distal to the tip of the medial epicondyle, was carried out to better localize the site of conduction slowing. 1 In 1 case, a brachial neuropathy became evident in the early postoperative period. Here the spinal roots were stimulated using a D-180 highvoltage stimulator with the cathode positioned between the C7 and T1 spinous processes (anode rostral). This made it possible to directly assess conduction between the axilla and spinal roots. Sensory Conduction Studies. To assess conduction across the brachial plexus and roots, as well as to look for evidence of sensory fiber loss in the ulnar nerve territory, the ulnar nerve was percuta-
702
Early Postoperative Ulnar Neuropathy
In the 20 ulnar nerves in I0 controls, all less than 40 years of age, the mean ? 1 SD limit for the forearm, elbow, and proximal arm were 60.8 -+ 4.0, 58.9 -+ 5.6, and 65.4 -+ 4.2 m/s, respectively. Of these, only 3 exhibited a greater than 10% conduction slowing across the elbow relative to the forearm (11.276, 15.1%, and 16.3%; overall mean 3.8%).
Controls.
The motor conduction status of the 20 cases preoperatively, immediately postoperatively, and at the 4- to 6-week follow-up period are summarized in Table 1. Patients.
In 15 of the 20 cases and 33 of the 40 limbs studied, the MMCV across the elbow relative to the forearm differed by less than 20%. However, in 7 ulnar nerves (18%), the transelbow MMCV relative to the forearm was slowed by more than 20% and by more than 30% in 2 of the 7. Motor conduction across the elbow was slowed unilaterally in 3, and bilaterally in 2 of Preoperative Studies.
MUSCLE & NERVE
June 1992
~~~
~~
Table 1. Percent slowing of conduction velocity across elbow PATIENT
0.20
1 2 3 4 5 6 7 8 9 10
L L L L
11 12
L L
R R R
13 14 15 16 17 18 19 20
L L L L L L L L
R R R R R R R
PRE-OPERATIVE 21-30 31-40
R R R
I
I
L L L
R
NA
R R L
L
R
L L L L L L L
R R R R R A R R R R R
these patients. Despite this conduction slowing, hypothenar maximum M potential sizes and sensory conduction were all within the normal range, and symptoms and signs indicative of an ulnar neuropathy were absent. At this time, the MMCV across the elbow, relative to the forearm, was reduced by more than 20% in excess of preoperative values in 3 of the 33 (9%) preoperatively normal ulnar nerves. In 1 of these cases, the reduction exceeded 30% relative to the preoperative value. However, there were no significant changes in the 7 ulnar nerves in which preoperative conduction across the elbow was slowed. Only 1 of the 3 cases, developing significant conduction slowing across the elbow, postoperatively, showed clinical evidence of an ulnar neuropathy. In this case, weakness in ulnar-supplied intrinsic hand muscles and partial conduction block were present unaccompanied by clinically or electrophysiologically detectable sensory loss (Fig. 1). Early Postoperative Studies.
Of the 3 ulnar neuropathies appearing for the first time in the immediate postoperative study, 2 returned to their preoperative status while the case with greater than 30% conduction slowing across the elbow was lost to follow-up. Conduction across the elbow improved in the case characterized by par-
Four- to 6-Week Postoperative Studies.
Early Postoperative Ulnar Neuropathy
R R NA
L L R L
L R R L R L R
R
L R L R
L R L R
POST-OPERATIVE 14-6 Weeks1 0-20 21-30 31-40
L L
R
L L R
I
R R R
R L
I
POST-OPERATIVE IEARLVI 0-20 21-30 31-40
NA
L (42%) L L
R
L L
L L
R R
L L
R R NA NA
L
L
R
L L
R R
NA
tial conduction block, although fibrillation activity had now developed in the ulnar supplied intrinsic hand muscles. One new case developed fibrillation potentials
PREOPERATIVE
% tMMCV x ELBOW
~
_
% t - p A x ELBOW
_
POSTOPERATIVE( 24 hrs) 2 I%
POSTOPERATIVE [ 42 days)
1
1
0
10
I
20
1 30
I 40
TIME ( ms)
FIGURE 1. Ulnar nerve motor conduction study in patient 12 illustrating a 21 YO reduction in the hypothenar maximum M potential negative peak area and a reduction of 24% in the maximum motor conduction velocity across the elbow relative to the forearm (arrow). Evidence of partial conduction block and conduction slowing across the elbow was still present 42 days postoperatively.
MUSCLE & NERVE
June 1992
703
and positive sharp waves in ulnar-supplied intrinsic hand muscles, and a 15% reduction in conduction velocity across the elbow in excess of pre- and early postoperative values. However, there were no accompanying signs or symptoms of an ulnar neuropathy, and sensory conduction studies were normal. SixmMonth Follow-Up. Two patients were available for follow-up at 6 months. The case developing conduction slowing (15%) across the elbow for the first time, and fibrillation activity at the 4- to 6-week mark, had returned to preoperative status. In the other case, conduction across the elbow was normal throughout the study. Localization. In the 3 cases where conduction across the elbow relative to the forearm was slowed by more than 20%, the site of the greatest conduction slowing was across the postcondylar course of the nerve in 2 cases, and across the cubital tunnel in the remaining case.
One patient, seen 5 days following surgery and asymptomatic at that time, had developed clinical signs of a brachial neuropathy, primarily affecting the middle and lower trunks of the brachial plexus. I n this case, motor conduction across the elbow was normal, but there was a 78% reduction in the negative peak area of the hypothenar maximum M potential between the spinal root and axillary stimulus sites. This patient was subsequently lost to follow-up.
Brachial Plexopathy.
DISCUSSION
Ulnar neuropathies are a common complication of surgery, with a reported incidence in retrospective studies4,14,15 between .02% and l.O%, and appreciably higher (0.8% to 38%) in prospective studies.9,12, I(
