RAY HUMPHRIES, BS, and DEAN P. CURRIER, PhD
Motor conduction examinations of the right radial nerve were performed on 25 healthy students. The purposes of this study were to determine the optimum position for placement of the active recording electrode, to determine the optimum position of the elbow during conduction examinations, and to report normal values for radial motor nerve characteristics. The radial nerve was stimulated at the supraclavicular notch, axilla, lateral surface of the brachium, and over the middle third of the forearm. The evoked responses were recorded from the abductor pollicis longus or the extensor pollicis brevis. The optimum site for placement of the active recording electrode was found over the medial aspect of the abductor pollicis longus or the extensor pollicis brevis and at a point that represents 28 percent of the forearm length. The optimum position for the elbow was full extension. The distal latency of 2.6 msec, the velocity of the brachium-forearm segment of 50 meters per second, and amplitude of muscle action potentials of 4.0 mv may serve as the limits of normal values for motor conduction of the radial nerve.
^\ssessment of the motor conduc tion of the radial nerve is occasionally neces sary, although this assessment is not done routinely during an electromyographic exam ination. The radial nerve or its posterior inter osseous branch is subject to injury or disease as a result of several types of pathology. Par tial function or paralysis may result from nod ules, 1 ganglions, 2 fractures of the humerus, 3 , 4 entrapments at the arcade of Frohse in the supinator 5 or at the lateral head of the tri ceps, 4 compression of the nerve by pressure from crutches, tourniquets, or positioning of the arm, 4 or benign tumors. 6 , 7
Mr. Humphries, who was a student in the Department of Physical Therapy, Medical College of Georgia, when this study was conducted, is now associated with the Rehabili tation Services of Columbus, Inc, Columbus, GA 31902. Dr. Currier is assistant professor, Department of Physi cal Therapy, Medical College of Georgia, Augusta, GA 30902. Requests for reprints should be sent to Dr. Currier.
Volume 56 / Number 7, July 1976
The purposes of this study were to deter mine the optimum position for placement of the active recording electrode, to determine the optimum position of the elbow during conduction examinations, and to report nor mal values for radial motor nerve characteris tics.
ANATOMY The radial nerve branches from the poste rior cord of the brachial plexus, passes be tween the medial and long heads of the tri ceps, and descends obliquely over the hu merus to the spiral groove. The nerve sup plies the triceps and the anconeus before descending to the brachioradialis and the lat eral epicondyle where it divides into a super ficial (sensory) and a deep branch (the poste rior interosseous nerve) which is mostly mo tor. The posterior interosseous nerve sup plies the extensor carpi radialis brevis and the
809
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Variables in Recording Motor Conduction of the Radial Nerve
branch
Superficial branch
Abductor pollicis longus Extensor pollicis brevis
Fig. 1. Points of stimulation of radial nerve used in this study: A. supraclavicular area, B. axilla, C. lateral surface of the humerus near the spiral groove, and D. interosseous nerve to the abductor pollicis longus and the extensor pollicis brevis.
supinator before piercing the supinator and dividing into three additional branches to supply other muscles. A lateral branch suplies the abductor pollicis longus and termi nates in the extensor pollicis brevis (Fig. 1). 5,8 The superficial head of the supinator may be tendinous and form a fibrous arch known as the arcade of Frohse, and the posterior inter osseous nerve passes under the edge of the arch which may entrap the nerve. 5
REVIEW OF LITERATURE Gassel and Diamantopoulos described a method for determining motor conduction velocities of the radial nerve by stimulating the nerve at the supraclavicular notch, in the midportion of the brachium, and just proxi mal to the lateral epicondyle of the humerus.
810
METHOD Examinations were performed on 25 healthy students (21 women and 4 men) who had no history of neurological dysfunctions. The students ranged in age from 20 to 30 years (mean = 22 years). The nerve conduction data were collected with the subject lying supine on a treatment table with the right arm resting comfortably at the side, the shoulder abducted about 10 de grees, the elbow extended fully, and the fore arm pronated. A Teca Model B-2 electromy ography was used to perform the nerve con duction examinations. The stimulating elec trodes were bipolar with the tips covered with conductive paste. The induced stimulus was a rectangular pulse of 0.2 msec duration and a frequency of one per second. The fre quency response of the amplifier was 10 to 10,000 Hz. All stimuli were supramaximal. The four sites of stimulation of the right radial nerve were at the supraclavicular notch, the * Teca Corp, White Plains, NY 10603.
PHYSICAL THERAPY
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Radial Nerve
The evoked muscle action potentials were re corded by using needle electrodes inserted into the triceps, anconeus, brachioradialis, or extensor digitorum. 9 In 1966, Jebsen re ported two studies of motor conduction of the radial nerve where the nerve was stimu lated at the supraclavicular notch, above the elbow, and in the distal portion of the fore arm. 10,11 The evoked action potentials were recorded from the extensor indicis proprius using monopolar needle electrodes. In 1972, DiBenedetto improved upon pre vious methods of studying motor conduction of the radial nerve by recording from the ex tensor pollicis brevis or abductor pollicis lon gus with surface electrodes. 12 This method was simple and caused minimal discomfort to the patient. DiBenedetto stated that a followup study was needed to report normal veloci ties of the proximal radial nerve. A thorough search of the literature did not reveal any studies concerning the relation ship between motor conduction characteris tics of the radial nerve and elbow position or the most advantageous area for recording ac tion potentials from the abductor pollicis lon gus or extensor pollicis brevis.
Volume 56 / Number 7, July 1976
-Radial Nerve
Brachioradial: Extensor Carpi Radiali Longus Posterior Interosseous Nerve
Branch
Fig. 2. Posterior interosseous nerve (radial) in forearm; S: stimulation site; 1, 2, and 3: active recording electrode positions and representative action potential forms.
Because the radial nerve was stimulated only over the lateral surface of the brachium for these recordings, the investigators were able to determine the effect of arm positioning on latency and the size of the muscle action po tential when the elbow was flexed. Distance measurements were also taken of the length of the forearm from the most proxi mal dorsal crease of the wrist to the antecubital crease of the elbow and to the recording electrode from which the highest amplitude was recorded. These measurements offer a guide for the placement of the active record ing electrode when the abductor pollicis lon gus or the extensor pollicis brevis are atro phied or when these muscles cannot be con tracted voluntarily. The temperature of the examination room ranged from 21 to 31°C (mean = 25.3°C).
RESULTS Recording electrode site number 1 (Fig. 2) provided the largest muscle action potential
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axilla, the lateral surface of the brachium 6 to 10 cm proximal to the lateral epicondyle, and over the middle third of the forearm between the brachioradialis and extensor digitorum (Fig. 1). Segmental distances between the proximal stimulation point and the distal stimulation points were measured using a steel tape measure. A total of eight observa tions were made on each subject. A multielectrode bank was constructed to house three recording electrodes; silver cups (8 mm in diameter) were mounted in plastic along a straight line with a center-to-center distance of 1.5 cm between them. The re cording electrodes were placed over the ab ductor pollicis longus or the extensor pollicis brevis after the skin was prepared properly to reduce resistance. The proximity of the two muscles made it impossible to isolate each muscle for surface electrode placement. The reference electrode was placed over the ten don of the abductor pollicis longus, and the ground over the radius proximal to the mul tielectrode bank. Similar methods of using electrode banks to map recording territory of muscle have been reported previously. 13-15 Muscle action potentials were recorded from each of the three recording electrodes when the posterior interosseous nerve was stimu lated over the middle third of the forearm. The recording site which yielded the largest muscle action potential for any one subject was used for all subsequent recordings on that subject. Photographs taken of evoked muscle responses appearing on the oscilloscopic face were measured later for calcula tion of conduction latency and amplitude of the action potential. The size of the amplitude of the muscle action potential was measured routinely from the baseline of the oscillo scope to the apex of the negative peak. Re cording only from the site of the largest mus cle action potential and stimulating at the four sites, we calculated velocities later for nerve segments between the supraclavicular notch and the axilla, the axilla and the brach ium, and the brachium and the forearm. Conduction latency and amplitude of mus cle action potentials were also measured with the right elbow flexed to 70 degrees and with the forearm and hand resting on the subject's abdomen and the shoulder rotated internally.
TABLE 1
Velocity (meters/sec) Degrees 70 0 Amplitude (mv) Degrees 70 0 Latency (msec) Degrees 70 0
Mean
SD
Range
64.3 67.0
7.94 9.18
52.2-79.4 50.0-83.1
5.7 5.7
1.69 1.49
3.5-9.0 4.0-9.0
4.4 4.4
0.45 0.45
3.5-5.2 3.5-5.2
in every subject. To ascertain whether the other recording sites would be acceptable for recording muscle action potentials in the event site number 1 could not be located, we treated the amplitudes from the three sites and data obtained when stimulation was over the middle third of the forearm with a onedimensional analysis of variance design with repetition of measurement over the one fac tor, amplitude. The F ratio was highly signifi cant (p < 0.01). Newman-Keuls' method of post hoc analysis showed that the mean am plitude (6.4 mv shown in Table 2) recorded from site number 1, the most medial position, was significantly different (p < 0.01) from the mean amplitudes recorded from sites 2 (X = 3.6 mv) and 3 (X = 2.7 mv) (Fig. 2). The location of site number 1 was calculated as a function of the length of the forearm. The mean distance (68.5 mm) from the dorsal crease of the wrist to site number 1 was 28.4 percent of the total length of the forearm as measured from the dorsal crease of the wrist to the antecubital crease of the elbow. The distances ranged from 39 mm to 86 mm (SD = 10.1 mm). Summarized in Table 1 are the results of the effects of elbow flexion on conduction characteristics. A paired t test was used to determine if the difference between mean ve locities was significant. A highly significant difference was found (p < 0.01) between mean conduction velocities with the elbow at 70 degrees of flexion and full extension. Be cause no difference was found between the mean latencies or the mean amplitudes, a statistical analysis was not performed on
812
these data. The mean distance from the stim ulation site proximal to the elbow to the stim ulation site distal to the elbow with the elbow in 70 degrees of flexion was 143.4 mm; with the elbow in full extension, the mean distance was 153.3 mm. Table 2 summarizes the conduction char acteristics recorded from site number 1 when the radial nerve was stimulated at the supra clavicular notch, the axilla, the brachium, and the forearm when the arm was extended fully. DISCUSSION Establishment of the location where maxi mum amplitude of the response of the abduc tor pollicis longus or extensor pollicis brevis can be obtained should prove useful to the clinician using DiBenedetto's technique. 1 2 Calculating this site as a percentage of the subject's forearm length could assist the ex aminer when performing conduction studies on the radial nerve of a patient who cannot contract the muscle for identification or for placement of the active recording electrode. Recording site number 1, which produced the largest sized action potentials in every subject, was located over the proximal por tion of the muscles and over the medial as pect of the forearm. The shape of the action potentials was always triphasic with an initial deflection from the baseline in the positive TABLE 2 Action Potential Amplitude, Conduction Velocity and Latency at Various Points Along the Radial Nerve (N = 25)
Supraclavicular notch-axilla Velocity" Amplitude* Axilla-brachium Velocity Amplitude Brachium-forearm Velocity Amplitude Forearm Latency Amplitude
Mean
SD
Range
74.3 5.5
15.80 1.39
45.8-80.7 3.5-9.0
65.3 5.5
8.40 1.42
62.4-79.3 3.5-9.0
69.8 5.7
12.90 1.49
50.0-80.7 4.0-9.0
2.0 6.4
0.22 1.70
1.5-2.6 4.0-10.0
" Meters per second. 6 Millivolts. c Milliseconds.
PHYSICAL THERAPY
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Action Potential Amplitude, Conduction Velocity and Latency of Radial Nerve with Elbow in Zero and 70 Degrees of Flexion (N = 25)
Volume 56 / Number 7, July 1976
The values of the conduction characteris tics of the radial nerve recorded in this study are similar to those reported previously. 8 1 1 The ranges of the reported values of the evoked characteristics may serve as the limits of normal values; that is, the distal latency of 2.6 msec, the velocity of the brachium fore arm segment of 50.0 meters per second, and the amplitude of muscle action potentials of 4.0 mv may serve as the limits of normal val ues of motor conduction of the radial nerve. Mean amplitude values of the muscle ac tion potentials reported in Table 2 were mea sured from the oscilloscopic baseline to the apex of the negative peak. The mean ampli tude values resulting from this method of cal culating magnitude constitute 69.2 percent of the mean amplitude size when measured by the peak to peak method.
CONCLUSIONS The results from this study enabled us to conclude that the optimum site for placement of the active recording electrode for radial motor nerve conduction is over the medial aspect of the abductor pollicis longus or ex tensor pollicis brevis at a point that repre sents the distal 28 percent of the forearm length. The elbow should be extended fully during the examination. The conduction val ues obtained in this study were similar to those reported previously and may serve as normal values in clinical examinations. REFERENCES 1. Mulholland RC: Non-traumatic progressive paralysis of the posterior interosseous nerve. J Bone Joint Surg 48[Br]:781 —785, 1966 2. Bowen TL, Stone KH: Posterior interosseous nerve paralysis caused by a ganglion at the elbow. J Bone Joint Surg 48[Br]:774-776, 1966 3. Kettlekamp DB, Alexander H: Clinical review of radial nerve injury. J Trauma 7:424-431, 1966 4. Lotem M, Fried A, Levy M, et al: Radial palsy follow ing muscular effort. J Bone Joint Surg 53[Br]:500506,1971 5. Spinner M: The arcade of Frohse and its relationship to posterior interosseous nerve paralysis. J Bone Joint Surg 50[Br] :809—812, 1968 6. Capener N: The vulnerability of the posterior interos seous nerve of the forearm. J Bone Joint Surg 48[Br]:770-773, 1966 7. Sharrard WJW: Posterior interosseous neuritis. J Bone Joint Surg 48[Br]:777-780, 1966 8. Warwick R, Williams PL (eds): Gray's Anatomy, 35th Brit ed. Philadelphia, W. B. Saunders Co, 1973, pp 1044-1045
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direction. Upon gross inspection of the ex tensor pollicis brevis and the abductor pollicis longus in two dissected cadavers, we found the muscles to be long and flat with unipennate fibers. The motor end plate of each of these muscles is apparently located so that it is not available to recording from surface electrodes. Inspection of an illustra tion of the wave form shown in DiBenedetto's report also revealed an initial positive deflec tion, but the amplitudes were very small. This fact led us to speculate that DiBenedetto's active recording electrode was probably placed over the areas corresponding to our second and third electrode sites. Placement of the active recording electrode over the central and lateral portions of the muscles would have accounted for the recording of action potentials smaller than those recorded over the medial aspect. Statistical analysis indicated that sites numbered 2 and 3 in our study are not acceptable for recording mus cle action potentials of maximal size. Amplitude and shape of the muscle action potential were found more variable when stimulating the radial nerve at the supraclav icular notch and the axilla than when stimu lating over the lateral brachium and the fore arm. These changes may have occurred bymeans of volume conduction resulting in stimulation of adjacent nerve branches which innervated muscles of the forearm. Careful rotation of the stimulating electrodes elimi nated the undesirable changes of amplitude and shape. The four meter per second increase in ve locity with the elbow in full extension is mis leading when determining the effect of arm positioning (Tab. 1). Flexion of the elbow pro duced a mean distance of 9.9 mm less than when the elbow was extended fully. Conduc tion and amplitude measurements were re corded from electrode site number 1 while stimulating over the lateral surface of the brachium with the elbow flexed and ex tended . Since no difference in mean latencies occurred between the two elbow positions, the difference in velocities was attributed solely to a difference in distance. This finding indicates the importance of standardization of an elbow position for all motor conduction studies of the radial nerve.
10. Jebsen RH: Motor conduction velocity of distal radial nerve. Arch Phys Med Rehabil 47:12-16, 1966 11. Jebsen RH: Motor conduction velocity in proximal and distal segments of the radial nerve. Arch Phys Med Rehabil 47:597-602, 1966 12. DiBenedetto M: Posterior interosseous branch of the
radial nerve: Conduction velocities. Arch Phys Med Rehabil 53:266-271, 1972 13. Nelson RM, Currier DP: Motor nerve conduction ve locity of the musculocutaneous nerve. Phys Ther 49:586-590,1969 14. Currier DP: Motor conduction velocity of axillary nerve. Phys Ther 51:503-509, 1971 15. Currier DP: Placement of recording electrode in me dian and peroneal nerve conduction studies. Phys Ther 55:365-370, 1975
Anatomy of the Trunk A Review BARBARA E
KENT, M A
Divided into two parts, this review is presented to help physical therapists evaluate and treat patients who have neck or back problems with greater
understanding and increased effective
ness
Paper, 36 pp, illus, $2.00
Prepayment is required on all orders — price is subject to change without notice. Allow three weeks for delivery. All orders are sent postage paid. Make checks payable to:
American Physical Therapy Association 1 1 56 1 5th St., N.W., Washington, D C. 20005
814
PHYSICAL THERAPY
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9. Gassel MM, Diamantopoulos E: Pattern of conduction times in the distribution of the radial nerve. Neurology 14:222-231, 1964
Motor conduction examinations of the right radial nerve were performed on 25 healthy students. The purposes of this study were to determine the optimum position for placement of the active recording electrode, to determine the optimum position of the elbow during conduction examinations, and to report normal values for radial motor nerve characteristics. The radial nerve was stimulated at the supraclavicular notch, axilla, lateral surface of the brachium, and over the middle third of the forearm. The evoked responses were recorded from the abductor pollicis longus or the extensor pollicis brevis. The optimum site for placement of the active recording electrode was found over the medial aspect of the abductor pollicis longus or the extensor pollicis brevis and at a point that represents 28 percent of the forearm length. The optimum position for the elbow was full extension. The distal latency of 2.6 msec, the velocity of the brachium-forearm segment of 50 meters per second, and amplitude of muscle action potentials of 4.0 mv may serve as the limits of normal values for motor conduction of the radial nerve.
^\ssessment of the motor conduc tion of the radial nerve is occasionally neces sary, although this assessment is not done routinely during an electromyographic exam ination. The radial nerve or its posterior inter osseous branch is subject to injury or disease as a result of several types of pathology. Par tial function or paralysis may result from nod ules, 1 ganglions, 2 fractures of the humerus, 3 , 4 entrapments at the arcade of Frohse in the supinator 5 or at the lateral head of the tri ceps, 4 compression of the nerve by pressure from crutches, tourniquets, or positioning of the arm, 4 or benign tumors. 6 , 7
Mr. Humphries, who was a student in the Department of Physical Therapy, Medical College of Georgia, when this study was conducted, is now associated with the Rehabili tation Services of Columbus, Inc, Columbus, GA 31902. Dr. Currier is assistant professor, Department of Physi cal Therapy, Medical College of Georgia, Augusta, GA 30902. Requests for reprints should be sent to Dr. Currier.
Volume 56 / Number 7, July 1976
The purposes of this study were to deter mine the optimum position for placement of the active recording electrode, to determine the optimum position of the elbow during conduction examinations, and to report nor mal values for radial motor nerve characteris tics.
ANATOMY The radial nerve branches from the poste rior cord of the brachial plexus, passes be tween the medial and long heads of the tri ceps, and descends obliquely over the hu merus to the spiral groove. The nerve sup plies the triceps and the anconeus before descending to the brachioradialis and the lat eral epicondyle where it divides into a super ficial (sensory) and a deep branch (the poste rior interosseous nerve) which is mostly mo tor. The posterior interosseous nerve sup plies the extensor carpi radialis brevis and the
809
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Variables in Recording Motor Conduction of the Radial Nerve
branch
Superficial branch
Abductor pollicis longus Extensor pollicis brevis
Fig. 1. Points of stimulation of radial nerve used in this study: A. supraclavicular area, B. axilla, C. lateral surface of the humerus near the spiral groove, and D. interosseous nerve to the abductor pollicis longus and the extensor pollicis brevis.
supinator before piercing the supinator and dividing into three additional branches to supply other muscles. A lateral branch suplies the abductor pollicis longus and termi nates in the extensor pollicis brevis (Fig. 1). 5,8 The superficial head of the supinator may be tendinous and form a fibrous arch known as the arcade of Frohse, and the posterior inter osseous nerve passes under the edge of the arch which may entrap the nerve. 5
REVIEW OF LITERATURE Gassel and Diamantopoulos described a method for determining motor conduction velocities of the radial nerve by stimulating the nerve at the supraclavicular notch, in the midportion of the brachium, and just proxi mal to the lateral epicondyle of the humerus.
810
METHOD Examinations were performed on 25 healthy students (21 women and 4 men) who had no history of neurological dysfunctions. The students ranged in age from 20 to 30 years (mean = 22 years). The nerve conduction data were collected with the subject lying supine on a treatment table with the right arm resting comfortably at the side, the shoulder abducted about 10 de grees, the elbow extended fully, and the fore arm pronated. A Teca Model B-2 electromy ography was used to perform the nerve con duction examinations. The stimulating elec trodes were bipolar with the tips covered with conductive paste. The induced stimulus was a rectangular pulse of 0.2 msec duration and a frequency of one per second. The fre quency response of the amplifier was 10 to 10,000 Hz. All stimuli were supramaximal. The four sites of stimulation of the right radial nerve were at the supraclavicular notch, the * Teca Corp, White Plains, NY 10603.
PHYSICAL THERAPY
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Radial Nerve
The evoked muscle action potentials were re corded by using needle electrodes inserted into the triceps, anconeus, brachioradialis, or extensor digitorum. 9 In 1966, Jebsen re ported two studies of motor conduction of the radial nerve where the nerve was stimu lated at the supraclavicular notch, above the elbow, and in the distal portion of the fore arm. 10,11 The evoked action potentials were recorded from the extensor indicis proprius using monopolar needle electrodes. In 1972, DiBenedetto improved upon pre vious methods of studying motor conduction of the radial nerve by recording from the ex tensor pollicis brevis or abductor pollicis lon gus with surface electrodes. 12 This method was simple and caused minimal discomfort to the patient. DiBenedetto stated that a followup study was needed to report normal veloci ties of the proximal radial nerve. A thorough search of the literature did not reveal any studies concerning the relation ship between motor conduction characteris tics of the radial nerve and elbow position or the most advantageous area for recording ac tion potentials from the abductor pollicis lon gus or extensor pollicis brevis.
Volume 56 / Number 7, July 1976
-Radial Nerve
Brachioradial: Extensor Carpi Radiali Longus Posterior Interosseous Nerve
Branch
Fig. 2. Posterior interosseous nerve (radial) in forearm; S: stimulation site; 1, 2, and 3: active recording electrode positions and representative action potential forms.
Because the radial nerve was stimulated only over the lateral surface of the brachium for these recordings, the investigators were able to determine the effect of arm positioning on latency and the size of the muscle action po tential when the elbow was flexed. Distance measurements were also taken of the length of the forearm from the most proxi mal dorsal crease of the wrist to the antecubital crease of the elbow and to the recording electrode from which the highest amplitude was recorded. These measurements offer a guide for the placement of the active record ing electrode when the abductor pollicis lon gus or the extensor pollicis brevis are atro phied or when these muscles cannot be con tracted voluntarily. The temperature of the examination room ranged from 21 to 31°C (mean = 25.3°C).
RESULTS Recording electrode site number 1 (Fig. 2) provided the largest muscle action potential
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axilla, the lateral surface of the brachium 6 to 10 cm proximal to the lateral epicondyle, and over the middle third of the forearm between the brachioradialis and extensor digitorum (Fig. 1). Segmental distances between the proximal stimulation point and the distal stimulation points were measured using a steel tape measure. A total of eight observa tions were made on each subject. A multielectrode bank was constructed to house three recording electrodes; silver cups (8 mm in diameter) were mounted in plastic along a straight line with a center-to-center distance of 1.5 cm between them. The re cording electrodes were placed over the ab ductor pollicis longus or the extensor pollicis brevis after the skin was prepared properly to reduce resistance. The proximity of the two muscles made it impossible to isolate each muscle for surface electrode placement. The reference electrode was placed over the ten don of the abductor pollicis longus, and the ground over the radius proximal to the mul tielectrode bank. Similar methods of using electrode banks to map recording territory of muscle have been reported previously. 13-15 Muscle action potentials were recorded from each of the three recording electrodes when the posterior interosseous nerve was stimu lated over the middle third of the forearm. The recording site which yielded the largest muscle action potential for any one subject was used for all subsequent recordings on that subject. Photographs taken of evoked muscle responses appearing on the oscilloscopic face were measured later for calcula tion of conduction latency and amplitude of the action potential. The size of the amplitude of the muscle action potential was measured routinely from the baseline of the oscillo scope to the apex of the negative peak. Re cording only from the site of the largest mus cle action potential and stimulating at the four sites, we calculated velocities later for nerve segments between the supraclavicular notch and the axilla, the axilla and the brach ium, and the brachium and the forearm. Conduction latency and amplitude of mus cle action potentials were also measured with the right elbow flexed to 70 degrees and with the forearm and hand resting on the subject's abdomen and the shoulder rotated internally.
TABLE 1
Velocity (meters/sec) Degrees 70 0 Amplitude (mv) Degrees 70 0 Latency (msec) Degrees 70 0
Mean
SD
Range
64.3 67.0
7.94 9.18
52.2-79.4 50.0-83.1
5.7 5.7
1.69 1.49
3.5-9.0 4.0-9.0
4.4 4.4
0.45 0.45
3.5-5.2 3.5-5.2
in every subject. To ascertain whether the other recording sites would be acceptable for recording muscle action potentials in the event site number 1 could not be located, we treated the amplitudes from the three sites and data obtained when stimulation was over the middle third of the forearm with a onedimensional analysis of variance design with repetition of measurement over the one fac tor, amplitude. The F ratio was highly signifi cant (p < 0.01). Newman-Keuls' method of post hoc analysis showed that the mean am plitude (6.4 mv shown in Table 2) recorded from site number 1, the most medial position, was significantly different (p < 0.01) from the mean amplitudes recorded from sites 2 (X = 3.6 mv) and 3 (X = 2.7 mv) (Fig. 2). The location of site number 1 was calculated as a function of the length of the forearm. The mean distance (68.5 mm) from the dorsal crease of the wrist to site number 1 was 28.4 percent of the total length of the forearm as measured from the dorsal crease of the wrist to the antecubital crease of the elbow. The distances ranged from 39 mm to 86 mm (SD = 10.1 mm). Summarized in Table 1 are the results of the effects of elbow flexion on conduction characteristics. A paired t test was used to determine if the difference between mean ve locities was significant. A highly significant difference was found (p < 0.01) between mean conduction velocities with the elbow at 70 degrees of flexion and full extension. Be cause no difference was found between the mean latencies or the mean amplitudes, a statistical analysis was not performed on
812
these data. The mean distance from the stim ulation site proximal to the elbow to the stim ulation site distal to the elbow with the elbow in 70 degrees of flexion was 143.4 mm; with the elbow in full extension, the mean distance was 153.3 mm. Table 2 summarizes the conduction char acteristics recorded from site number 1 when the radial nerve was stimulated at the supra clavicular notch, the axilla, the brachium, and the forearm when the arm was extended fully. DISCUSSION Establishment of the location where maxi mum amplitude of the response of the abduc tor pollicis longus or extensor pollicis brevis can be obtained should prove useful to the clinician using DiBenedetto's technique. 1 2 Calculating this site as a percentage of the subject's forearm length could assist the ex aminer when performing conduction studies on the radial nerve of a patient who cannot contract the muscle for identification or for placement of the active recording electrode. Recording site number 1, which produced the largest sized action potentials in every subject, was located over the proximal por tion of the muscles and over the medial as pect of the forearm. The shape of the action potentials was always triphasic with an initial deflection from the baseline in the positive TABLE 2 Action Potential Amplitude, Conduction Velocity and Latency at Various Points Along the Radial Nerve (N = 25)
Supraclavicular notch-axilla Velocity" Amplitude* Axilla-brachium Velocity Amplitude Brachium-forearm Velocity Amplitude Forearm Latency Amplitude
Mean
SD
Range
74.3 5.5
15.80 1.39
45.8-80.7 3.5-9.0
65.3 5.5
8.40 1.42
62.4-79.3 3.5-9.0
69.8 5.7
12.90 1.49
50.0-80.7 4.0-9.0
2.0 6.4
0.22 1.70
1.5-2.6 4.0-10.0
" Meters per second. 6 Millivolts. c Milliseconds.
PHYSICAL THERAPY
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Action Potential Amplitude, Conduction Velocity and Latency of Radial Nerve with Elbow in Zero and 70 Degrees of Flexion (N = 25)
Volume 56 / Number 7, July 1976
The values of the conduction characteris tics of the radial nerve recorded in this study are similar to those reported previously. 8 1 1 The ranges of the reported values of the evoked characteristics may serve as the limits of normal values; that is, the distal latency of 2.6 msec, the velocity of the brachium fore arm segment of 50.0 meters per second, and the amplitude of muscle action potentials of 4.0 mv may serve as the limits of normal val ues of motor conduction of the radial nerve. Mean amplitude values of the muscle ac tion potentials reported in Table 2 were mea sured from the oscilloscopic baseline to the apex of the negative peak. The mean ampli tude values resulting from this method of cal culating magnitude constitute 69.2 percent of the mean amplitude size when measured by the peak to peak method.
CONCLUSIONS The results from this study enabled us to conclude that the optimum site for placement of the active recording electrode for radial motor nerve conduction is over the medial aspect of the abductor pollicis longus or ex tensor pollicis brevis at a point that repre sents the distal 28 percent of the forearm length. The elbow should be extended fully during the examination. The conduction val ues obtained in this study were similar to those reported previously and may serve as normal values in clinical examinations. REFERENCES 1. Mulholland RC: Non-traumatic progressive paralysis of the posterior interosseous nerve. J Bone Joint Surg 48[Br]:781 —785, 1966 2. Bowen TL, Stone KH: Posterior interosseous nerve paralysis caused by a ganglion at the elbow. J Bone Joint Surg 48[Br]:774-776, 1966 3. Kettlekamp DB, Alexander H: Clinical review of radial nerve injury. J Trauma 7:424-431, 1966 4. Lotem M, Fried A, Levy M, et al: Radial palsy follow ing muscular effort. J Bone Joint Surg 53[Br]:500506,1971 5. Spinner M: The arcade of Frohse and its relationship to posterior interosseous nerve paralysis. J Bone Joint Surg 50[Br] :809—812, 1968 6. Capener N: The vulnerability of the posterior interos seous nerve of the forearm. J Bone Joint Surg 48[Br]:770-773, 1966 7. Sharrard WJW: Posterior interosseous neuritis. J Bone Joint Surg 48[Br]:777-780, 1966 8. Warwick R, Williams PL (eds): Gray's Anatomy, 35th Brit ed. Philadelphia, W. B. Saunders Co, 1973, pp 1044-1045
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direction. Upon gross inspection of the ex tensor pollicis brevis and the abductor pollicis longus in two dissected cadavers, we found the muscles to be long and flat with unipennate fibers. The motor end plate of each of these muscles is apparently located so that it is not available to recording from surface electrodes. Inspection of an illustra tion of the wave form shown in DiBenedetto's report also revealed an initial positive deflec tion, but the amplitudes were very small. This fact led us to speculate that DiBenedetto's active recording electrode was probably placed over the areas corresponding to our second and third electrode sites. Placement of the active recording electrode over the central and lateral portions of the muscles would have accounted for the recording of action potentials smaller than those recorded over the medial aspect. Statistical analysis indicated that sites numbered 2 and 3 in our study are not acceptable for recording mus cle action potentials of maximal size. Amplitude and shape of the muscle action potential were found more variable when stimulating the radial nerve at the supraclav icular notch and the axilla than when stimu lating over the lateral brachium and the fore arm. These changes may have occurred bymeans of volume conduction resulting in stimulation of adjacent nerve branches which innervated muscles of the forearm. Careful rotation of the stimulating electrodes elimi nated the undesirable changes of amplitude and shape. The four meter per second increase in ve locity with the elbow in full extension is mis leading when determining the effect of arm positioning (Tab. 1). Flexion of the elbow pro duced a mean distance of 9.9 mm less than when the elbow was extended fully. Conduc tion and amplitude measurements were re corded from electrode site number 1 while stimulating over the lateral surface of the brachium with the elbow flexed and ex tended . Since no difference in mean latencies occurred between the two elbow positions, the difference in velocities was attributed solely to a difference in distance. This finding indicates the importance of standardization of an elbow position for all motor conduction studies of the radial nerve.
10. Jebsen RH: Motor conduction velocity of distal radial nerve. Arch Phys Med Rehabil 47:12-16, 1966 11. Jebsen RH: Motor conduction velocity in proximal and distal segments of the radial nerve. Arch Phys Med Rehabil 47:597-602, 1966 12. DiBenedetto M: Posterior interosseous branch of the
radial nerve: Conduction velocities. Arch Phys Med Rehabil 53:266-271, 1972 13. Nelson RM, Currier DP: Motor nerve conduction ve locity of the musculocutaneous nerve. Phys Ther 49:586-590,1969 14. Currier DP: Motor conduction velocity of axillary nerve. Phys Ther 51:503-509, 1971 15. Currier DP: Placement of recording electrode in me dian and peroneal nerve conduction studies. Phys Ther 55:365-370, 1975
Anatomy of the Trunk A Review BARBARA E
KENT, M A
Divided into two parts, this review is presented to help physical therapists evaluate and treat patients who have neck or back problems with greater
understanding and increased effective
ness
Paper, 36 pp, illus, $2.00
Prepayment is required on all orders — price is subject to change without notice. Allow three weeks for delivery. All orders are sent postage paid. Make checks payable to:
American Physical Therapy Association 1 1 56 1 5th St., N.W., Washington, D C. 20005
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PHYSICAL THERAPY
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9. Gassel MM, Diamantopoulos E: Pattern of conduction times in the distribution of the radial nerve. Neurology 14:222-231, 1964
