SANDY CRAFT, BS, DEAN P. CURRIER, PhD, and ROGER M. NELSON, MS
Motor conduction examinations of the left anterior interosseous nerve were performed on 25 healthy women. The purposes of this study were to determine the optimal position for placement of the active recording electrode, and to report normal motor conduction values for the anterior interosseous nerve. The anterior interosseous nerve (branch of the median nerve) was stimulated proximal to the elbow and the evoked responses were recorded from three sites over the flexor pollicis longus. The optimal site for placement of the active recording electrode was over the lateral distal one-third of the anterior surface of the forearm at a point representing the distal 38 percent of the length of the forearm. A latency of 4.0 msec and an amplitude of 2.5 mv may serve as the limits of normal values for motor conduction of the anterior interosseous nerve and for action potentials of the flexor pollicis longus muscle, respectively.
The anterior interosseous nerve, a purely motor branch of the median nerve in the forearm, may be subject to dysfunction from various causes. Al though isolated dysfunction of the anterior interos seous nerve is infrequent, many cases of related muscular paralysis or paresis have been reported. The literature does not reveal any motor conduction studies-4)f the anterior interosseous nerve when re cording from the flexor pollicis longus. The pur poses of this study were to determine the optimal position for placement of the active recording elec trode, to describe a new motor nerve conduction procedure, and to report normal motor conduction values for the anterior interosseous nerve.
ANATOMY The anterior interosseous nerve originates from the posterior surface of the median nerve between 2.3 cm and 8.0 cm distal to the humeral condyles. The nerve then runs distally on the flexor digitorum
Ms. Craft, a student in the Department of Physical Therapy, Medical College of Georgia, when this study was conducted, is now associated with the Warm Springs Hospital, Warm Springs, GA 31830. Dr. Currier is Associate Professor, Department of Physical Therapy, Faculty of Rehabilitation Medicine, The University of Alberta, Edmonton, Alberta, Canada T6G 2G4. Mr. Nelson is Chief, Physical Therapy, US Public Health Ser vice Hospital, San Francisco, CA 94118.
Volume 57 / Number 10, October 1977
profundus and passes between this muscle and the flexor pollicis longus continuing distally along the interosseous membrane. The anterior interosseous nerve typically innervates the flexor pollicis longus, the radial portion of the flexor digitorum profundus, and the pronator quadratus (Fig. I). 1 " 4
REVIEW OF LITERATURE Unexplained paralysis of the three muscles in nervated by the anterior interosseous nerve was first reported in 1948 by Parsonage and Turner. 5 Since that time, many cases have been reported and sev eral reasons offered for dysfunction. Dysfunction of the nerve is sometimes referred to as the KilohNevin syndrome after Kiloh and Nevin who re ported two cases of interstitial neuritis.Thomas described similar cases in which recovery was slow but almost complete. 7 Fearn and Goodfellow were first to suggest surgi cal exploration for fast and complete recovery of the compressed nerve. 8 Stern and his associates, upon surgical intervention in one case found a strong constricting fibrous band where the median and the anterior interosseous nerves traversed deep to the flexor digitorum superficialis. Complete recovery of the nerve was seen within four months. 9 Similar constricting bands have been described in other re ports. 3 - 8 - , 0 -' 4
1143
Downloaded from https://academic.oup.com/ptj/article-abstract/57/10/1143/4558743 by University of Texas at Dallas - McDermott Library user on 04 February 2019
Motor Conduction of the Anterior Interosseous Nerve
Vichare reported the presence of an intramuscu lar tendinous band which pressed on the anterior interosseous nerve during supination. He suggested that intermittent pressure by this band might cause neuritis and the characteristic paralysis. 15 Passerini hypothesized that compression of the nerve might be due to a nonspecific inflammatory process of the pronator teres. 1 6 Partial or complete paralysis of the muscles in nervated by the anterior interosseous nerve have been attributed to 1) thrombosis of the ulnar collat eral vessels, 3 ' 12 2) traction injuries from supracon dylar fractures of the humerus, 1 7 and 3) direct trauma in closed forearm fractures due to the close proximity of the nerve to the radius. 1 8
Examinations were performed on 25 healthy women who had no history of neurological disor ders. The subjects ranged in age from 20 to 25 years (mean = 22 years). The nerve conduction data were collected with the subjects lying supine on a treatment table with the left arm resting comfortably at their side; the shoulder was abducted about 10 degrees, the elbow extended fully, and the forearm supinated. A Teca Model B-2 electromyograph* was used to perform the nerve conduction examinations. The stimulating electrodes were bipolar with the tips covered with conductive paste. The stimulus was a rectangular pulse of 0.1 msec duration and was delivered once per second. The frequency response of the amplifier was 10 to 10,000 Hz. All stimuli were supramaxi mal. Pilot motor conduction examinations of a few subjects revealed that placement of active recording electrodes over the lateral distal one-third of the anterior surface of the forearm produced action po tentials. Three sites selected for recording action potentials at 28, 33, and 38 percent, respectively, of the forearm length (measured from the most distal volar crease of the wrist to the antecubital crease of the elbow) consistently produced waveform charac teristics believed to be evoked from the flexor pollicis longus. Anatomical dissection of two forearms confirmed the possibility of evoked potentials and determined the gross structure of the flexor pollicis longus and its position relative to other structures. The recording electrodes were placed over the flexor pollicis longus because this muscle could be more readily palpated and isolated in the forearm
* Teca Corp, 220 Ferris Avenue, White Plains, NY 10603
1144
Digitorum
Dispersive
Downloaded from https://academic.oup.com/ptj/article-abstract/57/10/1143/4558743 by University of Texas at Dallas - McDermott Library user on 04 February 2019
METHOD
Stimulating
Fig. 1. Anterior interosseous nerve in forearm and the muscles it innervates; stimulation site; and active recording electrode positions.
than the pronator quadratus or the flexor digitorum profundus. A multielectrode bank consisting of three surface recording electrodes (12 mm diameter) was con structed from Orthoplast.®t The electrodes were mounted on the Orthoplast® in a straight line with a center-to-center separation of 1.5 cm. The multielectrode bank was placed over the flexor pollicis longus with the middle recording electrode placed over a point representing the distal 33 percent of the forearm length. The dispersive electrode was placed over the tendon of the flexor pollicis longus, and the ground electrode was placed over the radius be tween the stimulating and recording electrodes (Fig. 1). The median nerve was then stimulated just prox imal to the elbow with the negative stimulating elec trode proximal to the antecubital crease of the el bow and just medial to the tendon of the biceps brachii. One recording was taken from each elec trode in the bank (total = 3). The electrode which recorded the highest amplitude (baseline to peak of negative deflection) was considered the optimal site for recording.
t Johnson and Johnson, New Brunswick, NJ 08903
PHYSICAL THERAPY
TABLE 1 Action Potential Amplitude and Latency of Anterior Interosseous and Median Nerves (N = 25)
Amplitude (millivolts) Flexor Pollicis Longus Distal Electrode Middle Electrode Proximal Electrode Abductor Pollicis Brevis Latency (milliseconds) Anterior Interosseous Nerve Distal Electrode Middle Electrode Proximal Electrode Median Nerve (elbow to abd. poll, brev.)
Mean
SD
Range
4.4 5.0 5.6 11.3
1.03 1.21 1.16 2.79
2.5-6.0 3.2-7.5 3.8-7.5 6.0-15.0
3.2 2.9 2.6
0.32 0.39 0.43
2.3-4.0 2.2-3.7 1.8-3.6
7.0
0.51
6.2-7.9
Conduction examinations were also performed on the distal segment of the median nerve for the pur pose of appreciating the differences between the measurements obtained conventionally from the ab ductor pollicis brevis muscle and median nerve, and those obtained from the anterior interosseous branch of the median nerve and the flexor pollicis longus muscle. Conventional techniques of previous studies of motor conduction of the median nerve were used for the former. 19 ' 20 Photographs of all evoked responses appearing on the oscilloscope were taken and measured later for nerve conduction latencies and amplitudes of the muscle action potentials. The temperature of the room in which the examinations were performed remained relatively constant.
The data of the anterior interosseous nerve were tested by one-factor analyses of variance with repe tition of measurement over the one factor, effect of recording electrode placement on latency and am plitude. The F ratios were highly significant (P < 0.01) for latencies and for amplitudes (Table 2). Newman-Keuls' method of post hoc analysis showed that the amplitude and latency means differed sig nificantly between all three recording electrodes. The mean amplitude recorded from the proximal recording electrode differed significantly from the mean values recorded from the middle and distal electrodes. The mean amplitude recorded from the middle electrode differed significantly from the mean amplitude recorded from the distal electrode. Differences among the three mean latencies re corded from the three electrode sites also differed significantly.
DISCUSSION The latency recorded from the anterior interos seous nerve necessarily represents conduction over the median nerve as well as the anterior interosseous
RESULTS The amplitudes of the action potential from the flexor pollicis longus and latencies from the anterior interosseous nerve are shown in Table 1. The proxi mal recording electrode was found to consistently produce the optimum waveform and conduction characteristics. The proximal recording site consist ently yielded the smallest possible deflection pre ceding the negative deflection, the fewest phases in the waveform, and the largest amplitude. Also, the proximal recording site yielded optimum latencies compared to the other two recording sites. The mean and standard deviation values for the distance from the proximal electrode to the most distal volar crease of the wrist (38 percent of the length of the forearm) was 9.6 ± 0.32 cm. The values ranged from 9.1 to 10.2 cm. The amplitudes recorded from action potentials of Volume 57 / Number 10, October 1977
TABLE 2 Summary of Analyses of Variance for Amplitude of the Flexor Pollicis Longus Action Potential and Latency of the Anterior Interosseous Nerve (N = 25) Source Treatments Amplitude Latency Subjects Amplitude Latency Interaction Amplitude Latency Total Amplitude Latency a
DF
SS
MS
2 2
16.03 3.49
8.02 1.75
24 24
74.16 8.85
3.09 0.37
48 48
18.47 1.70
0.38 0.04
74 74
108.66 14.04
F
Significant at < 0.01 level.
1145
Downloaded from https://academic.oup.com/ptj/article-abstract/57/10/1143/4558743 by University of Texas at Dallas - McDermott Library user on 04 February 2019
Source
the flexor pollicis longus and abductor pollicis brevis, and the latencies of the anterior interosseous and of the median nerves, respectively, are reported in Table 1. The mean latency of the anterior interos seous nerve from the point of stimulation to the proximal recording site was 37 percent of the mean latency of the median nerve. The mean size of the amplitude from the flexor pollicis longus recorded from the proximal site was 50 percent of the mean size of the amplitude from the abductor pollicis brevis.
1146
A
B
C 2.5
MSEC
Fig. 2. Representative action potential forms recorded from the flexor pollicis longus at A) proximal, B) middle, and C) distal recording positions.
Downloaded from https://academic.oup.com/ptj/article-abstract/57/10/1143/4558743 by University of Texas at Dallas - McDermott Library user on 04 February 2019
nerve. Since the anatomical position of the anterior interosseous nerve is deep in the forearm, the nerve is not readily accessible to surface electrical stimula tion or to obtaining conduction velocity. For this reason, the median nerve was stimulated proximal to the elbow where it is easily accessible to electrical stimulation. Until latencies from a larger number of subjects are reported, the latency of 4.0 msec might be used as the upper limit for "normal" latency of the anterior interosseous nerve. This latency value would allow for error in recording electrode place ment, since the latency of 4.0 msec was recorded from the middle and distal recording electrodes. The proximal recording electrode site provided the most favorable recording location apparently because of its position being closest to the motor end-plate region. The recordings from the proximal electrode consistently yielded the smallest initial positive deflection or least time away from the mo tor point. An action potential recorded directly over the motor end-plate region of a muscle should yield only an abrupt negative deflection from the baseline of the oscilloscopic display 21 and yield the shortest time from stimulus to response. The proximal re cording electrode site in this study nearly met both requirements and was considered the optimal loca tion for recording conduction of the anterior inter osseous nerve and waveform characteristics over the flexor pollicis longus. When recording from the flexor pollicis longus, diphasic and multiphasic waveforms were obtained. No waveform had more than four phases and all exhibited characteristic bimodal peaks (Fig. 2). When action potentials are recorded outside of the motor end-plate regions of muscle, different shapes and sizes of action potentials can be expected. In the present study recording from the proximal electrode provided the largest sized action potentials ranging from 3.8 to 7.5 mv (Tab. 1). Analyses indicated that the middle and distal recording electrode positions were not acceptable for recording optimum conduc tion characteristics of the anterior interosseous nerve because the latencies were longer and the amplitudes smaller than those recorded from the proximal recording electrode. In order to allow for error in electrode placement, however, the smallest amplitude recorded (2.5mv) must be used as the low limit of "normal." The characteristic waveform when recording from the abductor pollicis brevis. unlike the flexor pollicis longus. was diphasic and exhibited no initial positive deflections. The waveforms deflected from the base line acutely in a negative direction. The amplitude of the action potentials of the abductor pollicis
brevis ranged from 6.0 to 15.0 mv in contrast to that recorded from the proximal electrode over the flexor pollicis longus which ranged from 3.8 to 7.5 mv. Latency measurements of the median nerve ranged from 6.2 to 7.9 msec in contrast to those of the anterior interosseous nerve which ranged from 1.8 to 3.6 msec (Tab. 1). The flexor pollicis longus consists of a unipennate fiber arrangement and all muscular fibers are unidi rectional to the radial side of the tendon. 22, 23 Coers and Woolf have shown that motor end-plates in human muscles form a narrow band always located at the center of the fiber equidistant from the origin and insertion. 24 Christensen found that in unipen nate muscles, the end-plates form a transverse band through the middle of the muscular fibers. 25 The motor end-plates of the flexor pollicis longus are apparently located so that they are not readily avail able to recording from surface electrodes. Since the recording electrodes could not be placed over the motor end-plate region of the muscle, the initial positive deflection preceding the major negative phase of the action potential (Fig. 2) probably rep resents conduction time over muscle between the active recording electrode and the motor end-plate region. These initial positive deflections were noted to be of greater magnitude from the distal recording electrode than any other electrode site. Because of the initial positive deflection, latency was measured
PHYSICAL THERAPY
as the time from the point of stimulation to the initial deflection from the baseline.
The optimal site for placement of the active re cording electrode was over the lateral distal onethird of the anterior surface of the forearm at a point
REFERENCES
1. Sunderland S: The innervation of the flexor digitorum profun dus and lumbrical muscles. Anat Rec 93:317, 1945 2. Sunderland S, Ray LJ: Metrical and non-metrical features of the muscular branches of the median nerve. J Comp Neurol 85:191, 1946 3. Spinner M: The anterior interosseous nerve syndrome. J Bone Joint Surg [Am] 52:84-94, 1970 4. Hollinshead WH: Anatomy for Surgeons: The Back and the Limbs. New York, Hoeber and Harper, 1958, vol 3, p 421 5. Parsonage MJ, Turner JW: Aneuralgic amyotrophy: Shoulder girdle syndrome. Lancet 1:973-978, 1948 6. Kiloh L, Nevin S: Isolated neuritis of anterior interosseous nerve. Br Med J 1:850-851, 1952 7. Thomas DF: Kiloh-Nevin. J Bone Joint Surg [Br] 44:962, 1962 8. Fearn CB D'A, Goodfellow JW: Anterior interosseous nerve palsy. J Bone Joint Surg [Br] 47:91-93, 1965 9. Stern MB, Rosner LJ, Blinderman EE: Kiloh-Nevin syn drome: Report of a case and review of the literature. Clin Orthop 53:95-98, 1967 10. Sharrard WJW: Anterior interosseous neuritis. J Bone Joint Surg [Br] 50:804-805, 1968 11. Schmidt H, Eiken O: The anterior interosseous nerve syn drome. Scand J Plast Reconstr Surg 5:53-56, 1971 12. Esposito GM: Peripheral entrapment neuropathies of upper extremity. NY State J Med 72:717-724, 1972 13. Selnitsky O: Pronator syndrome: Compression neuropathy of the median nerve at level of pronator teres muscle. George town Med Bull 13:232-238, 1960 14. Lippino T, Celli L, Monteleone M: Paralisi dissociata del
15. 16. 17. 18. 19. 20. 21.
22. 23. 24. 25.
nervo mediano all 'avambraccio da compressione del nervo interosseo anteriore. Chir Organi Mov 61:89-94, 1972 Vichare NA: Spontaneous paralysis of the anterior interos seous nerve. J Bone Joint Surg [Br] 50:806-808, 1968 Passerini D, Valli G: Contributo alia conosconza della sindrome del nerve interossoe anteriore (Kiloh e Nevin). Riv Patol Nerv Ment 89:1-11, 1968 Spinner M, Schrieber SN: The anterior interosseous nerve paralysis as a complication of supracondylar fractures in chil dren. J Bone Joint Surg |Am] 51:1584-1590, 1969 Warren JD: Anterior interosseous nerve palsy as a complica tion of forearm fractures. J Bone Joint Surg [Br] 45:511-512, 1963 Jebsen RH: Motor conduction velocities in the median and ulnar nerves. Arch Phys Med 48:185-194, 1967 Mayer RF: Nerve conduction studies in man. Neurology 13:1021-1030,1963 Currier DP: Placement of recording electrode in median and peroneal nerve conduction studies. Phys Ther 55:365-370, 1975 Grant JCB: An Atlas of Anatomy. Baltimore, Williams and Wilkins Co, 1972, pp 59-62 Woodburne RT: Essentials of Human Anatomy. New York, Oxford University Press, 1973, pp 100-102 Coers C, Woolf AL: Innervation of Muscle. Oxford, Blackwell Scientific Publishers, 1959 Christensen E: Topography of terminal motor innervation in striated muscles from stillborn infants. Am J Phys Med 38:6578,1959
Now available from APT A. . . SPASTICITY: ITS PHYSIOLOGY AND MANAGEMENT I. II. III. IV.
Neurophysiology of Spasticity: Classical Concepts Neurophysiology of Spasticity: Current Concepts Identifying and Assessing Mechanisms Underlying Spasticity Current and Projected Treatment Procedures for Spasticity
By Beverly Bishop, PhD. Reprinted from PHYSICAL THERAPY , April 1977. Paper, 32pp, $2.00 ppd. Make check payable to APTA, 1156 15th Street NW, Washing ton, DC 20005.
Volume 57 / Number 10, October 1977
1147
Downloaded from https://academic.oup.com/ptj/article-abstract/57/10/1143/4558743 by University of Texas at Dallas - McDermott Library user on 04 February 2019
CONCLUSIONS
representing the distal 38 percent of the length of the forearm when the median nerve was stimulated just proximal to the elbow. A latency of 4.0 msec and an amplitude of 2.5 mv may serve as the limits of normal values for motor conduction of the anterior interosseous nerve and for action potentials of the flexor pollicis longus, respectively.