Contents

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SECTION III

NEUROSURGERY

CHAPTER IX

ENSORY DISTURBANCES IN PERIPHERAL NERVE LESIONS ^a

For many years it has been noted that total loss of sensation after complete division of a peripheral nerve is limited to a much smaller area than one would expect from its anatomic distribution. Likewise, it has been observed that following injury of a peripheral nerve sensory symptoms may rapidly diminish and at times loss of sensation to pin prick be entirely absent. That severe, widespread anesthesia results only from trauma of several nerve trunks of a plexus, has generally been accepted. Lesions of single nerves result in partial anesthesia, or, if a severe anesthesia be present, the area of complete loss of sensation rapidly shrinks.

Many attempts have been made to explain these phenomena. Some of the older theories were to the effect: (1) That nerve fibers grow from healthy surroundings into the insensitive parts; 1 (2) that after section of a nerve, stimulation of the severed part may pass through an accessory branch into an adjacent nerve and reach the major branch of the injured nerve above the lesion, through a second lateral branch (collateral innervation); ² (3) that numerous anastomoses connect the peripheral ramifications of sensory nerves, many cutaneous areas receiving their innervation from different nerves.³ All these opinions have undergone important changes since the investigations of Head and his coworkers. The results of their studies led Head and Sherren ³ to conclude that the sensory mechanism in the peripheral nerves consists of the following three systems:

 (1) Deep sensibility, capable of answering to pressure and to movement of parts and even capable of producing pain under the influence of excessive pressure, or when the joint is injured. The fibers, subserving this form of sensation, run mainly with the motor nerves, and are not destroyed by division of all the sensory nerves to the skin. (2) Protopathic sensibility, capable of responding to painful cutaneous stimuli, and to extremes of heat and cold. This is the great reflex system, producing a rapid, widely diffused response, unaccompanied by any definite appreciation of the locality of the spot stimulated. (3) Epicritic sensibility, by which we gain the power of cutaneous localization, of discrimination of two points, and of the finer grades of temperature, called cool and warm.

Head and Sherren ⁴ state that in complete division of a mixed nerve, as the median or ulnar, the area it supplied does not become uniformly insensitive. Whereas previous observers have stated that sensation is diminished over the full area usually assigned to the injured nerve and lost completely over a small portion only, they have shown that this diminution of sensation is

^a The statements of fact appearing herein are based on "Overlap of So-Called Protopathic Sensibility as Seen in Peripheral Nerve Lesions." by Maj. Lewis J. Pollock, M. C., Archives of Neurology and Psychiatry, 1919, ii, No. 6, 667.

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in reality a total loss of sensibility to stimulation with cotton wool, to the compass test, to the painless interrupted current, and to temperatures between 22^º C. and 40^º C. In this area are felt only the stimuli affecting the protopathic sensibility, such as the prick of a pin and temperatures below 20^º C. and above 40^º C. The area rendered insensitive to light touch by division of the median or of the ulnar nerve varies little in extent. In sharp contrast to this slight variation is the extreme difference in surface extent of the loss of sensation to a pin prick which follows division of either of these nerves. " The consequence of both division and irritation of these nerves shows that as far as protopathic sensibility is concerned they overlap to an enormous extent."'

It is evident, therefore, that the complete sensory distribution of a peripheral nerve consists of its exclusive supply, or that area in which loss of sensation is produced by its division, and in addition its overlap or the are a determined by the limits of. skin sensitive to stimuli when all the adjacent nerves have been severed. Head and Sherren, employing the method of residual sensibility, were able to determine the complete sensory distribution of some of the nerves. These areas were part of the distribution of the median, the internal saphenous, part of the external popliteal, the external saphenous and part of the posterior tibial nerves.

The purpose of the present chapter is: First, to record the smallest area of loss to prick pain which follows interruption of the various peripheral nerves; second, to point out the relative smallness of this area as compared to the area of loss to touch; third, to show that the preservation or early return of prick pain as compared to tactile sense is due to the assumption of function of adjacent nerves, and not to nerve regeneration, as interpreted by Head; and, fourth, to outline the total sensory distribution of some of the peripheral nerves by residual sensibility.

MATERIAL

Observations were made on 500 patients with peripheral-nerve lesions seen early in base hospitals in France, and 520 patients with peripheral-nerve lesions studied later at United States Army General Hospital No. 28, Fort Sheridan, Ill.

The observations of early peripheral-nerve lesions were in most instances uncontrolled by operative procedures. The major portion of the lesions were partial and frequently complicated by injuries to adjacent small sensory branches. But these observations served a useful purpose. They showed:(1) That in many cases for the first two or three weeks only a very small area within the border of the part insensitive to cotton wool was sensitive to pinprick; (2) that in a few a larger zone sensitive to pin prick appeared within15 days; and (3) that the return of sensitiveness to pin prick in a larger zone, corresponding to the area which was later determined as overlap, usually was found, at times variable from 30 to 100 days. The cases showing return to pinprick over a large area in less than 30 days were predominantly cases of radial and musculospiral lesions.

The material of peripheral-nerve lesions studied later may be divided into two groups: The first, a group of 391 cases uncontrolled by operation, and in

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the majority of instances recovering spontaneously: the second, a group of 129cases controlled by operation, which many be tabulated as follows:

CHART

General impressions relative to the sensory changes in peripheral-nerve lesions were derived from the whole material. The areas of total nerve supply and of overlap were obtained only from cases certified by operation. The cases which have been used in the study of regeneration of nerves likewise were certified by operation. Therefore, although the whole 1,020 cases contributed to the general conclusions concerning these problems, only one group, consisting of the cases coming to operation, was employed in obtaining the data which serve as the basis for the special conclusions contained herein.

METHODS OF INVESTIGATION

The problems under investigation were not studied from a psychological standpoint. The areas of overlap were found in the course of clinical examinations of a large group of cases. The methods of examination, therefore, were those ordinarily used clinically. The sense of touch was tested by a wisp of cotton. The sensation of pain in response to the prick of a pin was ascertained By using a weighed needle sliding within a bit of glass tubing so that with different weighed needles a pressure of from 5 to 35 grains could be applied.

Although in this chapter temperature sense will not be referred to because of the difficulty of standardizing methods and the impossibility of employing the finer methods clinically, it may be stated that for the rough examination of sense of cold, a pledget of cotton twisted to a point and saturated with ether was used. This method permits a less diffuse type of stimulation and has the advantage of case and simplicity. For physiologic research this method is, of course, inapplicable. Light touch with a wisp of cotton to determine sense of touch may be accepted if the exact threshold of sensation is not under investigation, and if exact borders of loss of sense of touch be not insisted on. For the purposes of this investigation, the exact borders of loss of sense of touch need not be insisted on. Only one factor must be considered in this method of examination, namely, return of so-called hair sensibility must not be confused with touch; hence, in testing for touch where an accurate border was to be determined, the parts were closely shaven.

The degree of pressure which it is permissible to employ in determining prick pain without jeopardizing the results by confusion with pressure pain

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remains to be discussed. Although, as pointed out by Head and Sherren, ⁶ deep sensibility may be evoked when testing for touch with a stiff roll of wool, this objection is not valid for determining prick pain within certain limits. A sharp needle was used by Head and Sherren in their early clinical investigation, care being taken to differentiate between sense of deep pressure and true pain. Boring ⁷ says: “In determining the pain threshold it was especially necessary not to exceed pressures of 6 gm. Although at high intensities of stimulus the introspective difficulty of abstracting from pressure was less with pain than with cutaneous pressure, the greater intensities frequently drew blood and therefore were abandoned." As in Boring's work it was necessary to examine a small area of skin repeatedly and at very short intervals for all forms of sensation, his objection is valid. On the other hand, with the World War cases under consideration, it was necessary only to examine sense of prick pain in areas of overlap and not to confuse this pain with pressure pain. In these cases pain was never found to result from 35 gin. of pressure with a blunt object, and since care was taken to obtain from the patient responses only to pain from prick of a sharp point, it is believed that pressure of even 35 gm. is permissible to map out the overlap of sense of prick pain. No exact measurements of threshold to prick pain were made and in the majority of cases pressure did not exceed 30 gm.

EXCLUSIVE NERVE SUPPLY

Recognizing that, following section of a mixed nerve, the loss to prick pain occupies an area much smaller than the loss to touch, it first was necessary to ascertain the smallest area which is insensitive to pin prick following section of various nerves. This would indicate the limits of any possible overlap.

Although only a small portion of the area insensitive to touch is quite insensitive to pin prick, diminution of pain sense is present in a large part of the area insensitive to touch, and if graduated degrees of pressure be employed, concentric rings of analgesia are demonstrated. However, we are concerned not with the question of whether any hypalgesia is present, but whether any portion of the skin is at all sensitive to pain, provided this pain be due to superficial sensibility. If a part of the skin is sensitive to pain, when a nerve is divided, this sensation must be derived from some source other than this nerve.

To delineate the area exclusively supplied with pain sense by a given nerve one of two conditions must be present: First, the presence of pain sense having been demonstrated within the area of a nerve's supposed anastomic supply, that nerve is found at operation to be divided, and the ends separated. Second, the nerve having been seen to be divided, presence of pain sense is demonstrated in its distribution within the length of time given for the return of protopathic sensibility (Head, Rivers, and Sherren, 43 days). In the cases under the second condition 28 days was the limit, with the exception of the radial nerve, in which the limit was 37 days.

The relatively small number of cases studied does not warrant an attempt to outline the exclusive supply of peripheral nerves to both epicritic and protopathic sensibilities. Suffice it to say that the results as to the nerves in the

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hand are in general accord with Stopford,⁸ who found in the ulnar nerve some variation from the accepted area of epicritic sense in 20 per cent of the cases and in the median nerve in 38 percent. In three eases of median nerve section anesthesia was present over the dorsal surface of the distal phalanx of the thumb.

FIG. 127.- Sensory changes in ulnar nerve lesions: Diagonal lines, anesthetic to touch; black lines, loss of prick pain and touch sense; continuous line, borders of loss of temperature sense. The same scheme of charting is followed in all of the diagrams. Where duplication of letters occurs, the first is preoperative and the second postoperative sensory chart

In ulnar-nerve lesions superimposing the outlines of complete analgesia, in the cases shown in Figure 127, the smallest area of analgesia was found to occupy the palmar and dorsal surfaces of the little finger, extending over the dorsal surface of the hand in a triangular area over the fifth metacarpal boneto one-third of its length (fig. 128). The area included between the borders

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of the accepted supply of the ulnar nerve and the borders of this analgesia represents the possibly supply of overlapping nerves to pain sense.

The inner border of the smallest area of exclusive supply to pain of the median nerve was obtained in the same way from cases in which the median nerve was subsequently found to be divided (fig. 129, g, h, i, j). The outer border was obtained from these cases and in addition from cases of combined ulnar and median lesions which at operation were likewise found to be anatomic divisions, with the ends separated (fig. 129, a, b, c, d, e, f, k). The exclusive supply of the median nerve to pain sense was found to occupy the dorsal and palmar surfaces of the distal phalanges of the index and middle fingers, the ulnar half of the palmar surface of the second phalanx of the index finger, part of the ulnar portion of the distal half of the second phalanx of the middle finger and the dorsal surface of less than half of the second phalanges of the index and middle fingers. Despite the fact that this small area of total analgesia in median

FIG. 128.- Smallest composite area of analgesia in ulnar nerve lesions nerve lesions

nerve lesions has been recognized, ⁹ it is necessary at this point to call special attention to this observation as from the study of this nerve much evidencerelative to overlap was obtained (fig. 130).

The cases of radial nerve lesions, certified at operation or examined lessthan 37 davs after resection and suture, showed a wide variety of areas of analgesia and in one case no analgesia at all. (Fig. 131, a to m.)

Although not infrequently recorded, no case of radial nerve lesion wasobserved which did not show loss of sensation to touch. Of all the peripheralnerves, the radial shows the greatest variation in the areas of loss of sensationto both epicritic and protopathic sensation. This is due to the fact that sixnerves are concerned with the sensory supply of the dorsum of the hand; themedian, radial, antibrachii, posterior branch of the musculospiral. musculo-cutaneous, and ulnar.

Stopford ⁸ emphasizes, as do Head and Sherren,⁴ the importance of theinusculocutaneous nerve in the supply of the dorsum of the hand, and states

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FIG. 129. – Sensory changes in median nerve lesions: G, H J, radial and mediain; I, ulnar and median: B. E. ulnar, median, and internal cutaneous; A, C, D, E, ulnar median, and musculocutaneous, K

FIG. 130.- Smallest composite area of analgesia in median nerve lesions

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that its terminal branches may extend oil to the dorsum of the metacapus, and “it appears that the extent of its distribution varies inversely with that of the radial."' Although this may be true, it must not be forgotten that the median nerve must be considered in the supply of sensation to the dorsal area over the distal portion of thethumb

FIG. 131.- Sensory changes in radial nerve lesions

One of the reasons for vary ing reports relative to the sensory loss in radial nerve lesions is the hairy nature of the area of skin under investigation. The return of hair sensibility frequently is confused with the presence of settseof touch. The skin must be closely shaved in all cases where examination of touch is contemplated. No area of skin is exclusively supplied by the radial nerve for prick pain.

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FIG. 132.- Sensory changes in external popliteal lesions

The area of exclusive supply of pain of the external popliteal nerve was obtained from certified cases of division and cases examined less than 37 days following resection and suture (fig. 132, a to h). The area consists of a narrowband extending from a point a little above the junction of the lower and middle one-third of the outer surface of the leg, diagonally across the dorsum of the foot to a point over the middle of the metatarsal bone of the great toe. It is interrupted at the junction of its lower and middle one-third by an area which is sensitive to pin prick. The area is due to the overlap on one side of the internal saphenous nerve and, on the other side, the internal popliteal nerve. Although a number of cases showing such an interruption in the band of analgesia have been observed, they have not fulfilled the requirements demanded in estimating exclusive supply. One case, Figure 132, e, showed this type of interruption of the band of analgesia 27 days after resection and suture.

FIG. 133.- Smallest composite area of analgesia in external popliteal lesions

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Another case which was examined 53 days after resection and suture is shown in Figure 132, d, but was not used in estimating the isolated supply. The external popliteal nerve has a surprisingly small exclusive area of pain sense(fig. 133).

The area of the sciatic nerve was obtained from cases certified to be anatomic divisions, Figure 134, a to f. This area is illustrated in Figure 135 and need not be described.

Inasmuch as the results above illustrated represent the smallest area of exclusive supply of various nerves for pain, it is necessary to define to what

FIG. 134.- Sensory changes in sciatic nerve lesions

extent they may be used in formulating our ideas relative to nerve overlap. It is recognized that in some instances such small areas may be present only when we are dealing with the group of 25 percent of cases showing unusual distribution of sensory nerves. These areas are used, therefore, only in establishing a certain limit beyond which it is not permitted to go in interpreting return of sensation to pain as a sign of nerve regeneration. Any return of sense of pain in regions without these borders may be due to unusual nerve distribution or sensory overlap, and represents possible areas of overlap. It will be found that the areas of overlap, described below, are not as extensive as these areas would permit us to assume were we to use exclusive pain sensibility as an indication of the borders of overlap.

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NERVE OVERLAP

The return of sensibility to pin prick, which takes place before the return of sensibility to touch, occurs in regions which occupy the areas of nerve overlap, and this return of sensibility to pin prick can not be interpreted as a sign of nerve regeneration.

This view is supported by the facts that no return of sensibility to pain was found when sensibility to touch had not returned, except in an area of overlap; that when a nerve is divided and at the same time one or more adjacent nerves are divided sensation to pin prick does not return in the area of the overlap of these nerves even many months following the injury; that when a nerve adjacent to one which is severed and which supplies an area of overlap to that nerve is sectioned, the preexisting sensibility to pin prick in the overlap area is lost; that when sensibility to pin prick is present within the anatomic sensory distribution of a severed nerve resection and sature has no effect on the general outline of this area of sensibility.

Within two weeks after the occurrence of a peripheral-nerve lesion the area of analgesia usually nearly coincides with the area of anesthesia. Some cases showed an intermediate zone or a shrinkage of the analgesic area within 15 days. In from 30 to 100 days the majority of cases showed the presence of a shrinkage to an extent which was later identified with overlap. It is probable that the cases would have shown the same

FIG. 135.- Smallest composite area of analgesia in sciatic nerve lesions

extent of shrinkage in less than 100 lesions days, but conditions were such that in these cases the first record available was obtained 100 days after the injury. Certainly the majority of cases showed the shrinkage to be well established under 50 days. Some months after the injury had been received the shrinkage was present and the remaining area of analgesia has been described above as the exclusive sensory supply for pain sense in various peripheral nerves.

The shrinkage of the analgesic area can be due to but two conditions: Nerve regeneration, or the assumption of function by adjacent nerves. If any overlapping of peripheral nerves is possible, it becomes necessary to define the extent of this overlap before any return of sensation can be interpreted as a sign of nerve regeneration. So far as it can be ascertained, no evidence has ever been adduced to show that overlapping nerves functionate

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immediately following the injury of an adjacent nerve. Neither have the laws of dual innervation been clearly defined. Until this is accomplished, it is illogical to infer that return of sensation in the area of an overlapping nerve is a sign of nerve regeneration and is not caused by the functioning of this over-lapping nerve. If the shrinkage of the area insensitive to pin prick responsible for the increase in size of the intermediate zone be a sign of nerve regeneration and not a result of overlap, it should occur whether the adjacent nerves be intact or not. This, however, is not the case, as will be shown. In other words, if certain areas of skin become sensitive to pain or are found sensitive to pain following section of a given nerve, and the condition is due to nerve regeneration, then section of the adjacent nerve would have no effect on the appearance of this sensibility.

FIG. 136.- Sensory changes in combined lesions of the ulnar, median, and internal cutaneous nerves

SECTION OF NERVES

SECTION OF ADJACENT NERVES

Although in isolated lesions of the ulnar nerve sensibility to pain is frequently seen on the ulnar half of the ring finger, this is never observed when the median nerve is divided at the same time (fig. 136, a, f). Although isolated lesions of the ulnar and of the internal cutaneous nerves always show that the distal end of the analgesia resulting from a lesion of the internal cutaneous and the proximal end of the analgesia resulting from a lesion of the ulnar, do not

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meet, no instance is found in combined lesions of the ulnar, median, and internal cutaneous nerves where an area between the borders of the analgesia of the internal cutaneous and ulnar nerves is sensitive to pain (fig. 136, b, c, d, e, h, i, j).

When the ulnar, radial, and median nerves are divided, a year may follow their division and no shrinkage of analgesia be found on the palmar or dorsal surface of the hand except on the proximal portion of the analgesia where the musculocutaneous and the antibrachii posterior areas adjoin the analgesic area (fig. 137, a, b, d). When a radial lesion is combined with a median, analgesia is always present on the radial part of the palm. When a median lesion or a radial lesion alone is present, this part of the palm is usually sensitive to pin prick (fig. 137, d, e, f, g).

FIG. 137.- Sensory changes in combined lesions of the ulnar, radial, and median nerves, A, B, C, and of the median and radial, D, E, F, G

Isolated lesions of the external popliteal nerve (which corresponds closely to the fifth lumbar root) may show only a small area of analgesia, but when the internal popliteal as well as the external popliteal is severed, there is never found any shrinkage of analgesia or reappearance of sensibility to prick pain in the zone where the supply of the external popliteal meets that of the internal popliteal (fig. 138, a to g).

It can be definitely stated that when nerves supplying adjoining areas are severed, sensation to pain is at no time present in the border areas where it is uniformly observed when either nerve is divided alone. Inasmuch as a large number of the cases observed had resections and sutures performed at least three months prior to the last examination, it may be stated likewise that no

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sensation to pain returns in such areas in the time given for the beginning of regeneration of protopathic sensibility.

EFFECT OF SECTION OF AN OVERLAPPING NERVE

When return to sensibility to pain or presence of sensibility to pain is found in the area of overlap of an adjacent nerve, analgesia will result if this nerve is severed. This is well illustrated in the case shown in Figure 129, g, page 924. This patient had a partial ulnar lesion combined with a complete section of the median. Prick pain was preserved in the radial portion of the

FIG. 138.- Sensory changes in combined lesions of internal and external popliteal portions of sciatic nerve palm and the index finger. When at operation the superficial radial nerve was resected for use as a cable transplant, this part of the palm became analgesic (fig. 137, e).

EFFECTS OF RESECTION AND SUTURE ON EXISTING OVERLAP

Following resection and suture when sensibility to pain is present in an area of overlap, although some change in the outline of this area occurs, in general the area remains the same. At times the borders show some increase in analgesia; much more frequently they show a shrinkage of the analgesia. Slight changes in the borders of an area of analgesia can not be used in arriving

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at a hard and fast conclusion. Frequentlv these borders chance in an astonishing manner for pain produced by higher degrees of pressure by a sharp point not sufficient to produce pressure pain.   

The laws governing dual innervation have not been clearly ascertained. What effect, if any, the handling of nerves or freshening of their ends may have on inhibition is unknown. Another fact in support of the statement that return of sensation in an area of possible overlap can not be ascribed to the regeneration of a nerve is that this area is not generally changed by resection and suture of a severed nerve.

FIG. 139.- Sensory changes before and after resection and suture or the ulnar, and median nerve

The conditions necessary to study profitably the effect of resection and suture of nerves on return of sensibility to pain are: First, that the nerve ends be separated, and, second, that the examination subsequent to the operation be made within the period of time ascribed to the return of protopathic sense. Some difficulty is encountered in meeting the second condition inasmuch as frequently the wide separation of the ends of the nerves makes it necessary to place the extremity in a position which will permit approximation, and to fix it in such a position by means of a case. This often prevents an examination before six weeks have elapsed. None of the cases under consideration were examined later than 50 days after operation, one in less than 1a days. Although some objection may be made to the cases examined over 45 days after operation on the grounds of beginning return of protopathic sense due to regeneration,

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the similarity of the areas unaffected by operation in cases examined under 45 days and those between 45 and 50, coupled with the facts that the ends of the nerves were separated in all of these cases, makes it reasonable to admit them into the group.

To describe again the areas sensitive to pin prick in the lesions examined. or to attempt by description to show the sensory changes following operation, is needless. They are clearly indicated by Figures 139 and 140. It is sufficient to state that the following nerves were studied: Ulnar, examined 42 days after operation (fig. 139 a); median, 8 days after operation (fig. 139 f); ulnar and median, 45, 36, 40, 46, 48, and 14 days after operation (fig. 139, b, c, d, e, q, h); external popliteal, 48, 36, 20, and 26 days after operation (fig. 140 a, b, c, d); sciatic, 50and 36 days after operation (fig. 140 f, h).

FIG. 140.- Sensory changes before and after resection of external popliteal and sciatic nerves

RESIDUAL SENSIBILITY

If we assume the relatively early return of sensibility to pin prick to be due to overlap it becomes possible by the method of residual sensibility to outline the borders of overlap of the various peripheral nerves.

The method of residual sensibility is based on the assumption that following section of a given nerve, the area of skin, in its anatomic distribution in which sensation remains, is subserved by the intact adjoining nerves distributed to that area. For example, four nerves supply the palmar surface of the hand: The ulnar, median, musculocutaneous, and radial. If two--the ulnar and

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median-are severed, what sensibility remains is subserved by the musculocutaneous and radial.  If then the borders of the musculocutaneous be determined, that which remains is radial.

In employing this method certain precautions must be observed. For example, we can not take the outer border of the analgesia on the dorsal surface of the hand in an ulnar section to be any part of the border of the overlap of the median unless we may observe the effect of a combined ulnar and musculospiral so that the overlap of the latter nerve be not included. Similarly, we can not outline the border of the overlap of the median on to the radial unless

FIG. 141.- Sensory changes in lesions of median, internal cutaneous, combined median and radial nerves, B, G, M, from which the residual sensibility of the ulnar nerve was obtained and of the ulnar and internal cutaneous radial, combined radial and median nerves, H, J, M, from which the residual sensibility of the median nerve was obtained

we have had a combined lesion of the ulnar and radial to indicate the distribution of the ulnar; or the overlap of the radial to the median on the palm unless we have had a combined median and musculocutaneous lesion, or the overlap of the internal popliteal to the external popliteal unless we have had a combined lesion of the external popliteal with the internal saphenous. The necessity for these combinations reduces the number of cases available for conclusions to a very few. As a result the areas of overlap as outlined probably were smaller than the real overlap. However, the extent of overlap was sufficiently large to prove that it is within such an area that return of sensibility to pin prick occurs soon after injury of peripheral nerves.

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It is hardly necessary to state that the cases studied must have nerves recently resected or he examined prior to an operation which reveals the ends of the nerves separated.

In illustrating the areas of overlap the space between the borders of the overlapping to adjacent nerves has been blocked out with black. The black area therefore represents the total supply to pain of the various nerves studied. The area of actual overlap would be that part of the total sensory supply to pain which extends beyond the accepted sensory limit of the adjacent nerves. The restrictions of the methods necessary to obtain these areas are responsible for an indicated area of total supply, which in some instances is smaller than is actually present, as may be seen in the case of the outer border of the ulnar on the dorsal surface of the hand and the inner border of the external popliteal on the back of the leg (figs. 143, p. 9,36, and 147, p. 938).

FIG. 142.- Residual sensibility to prick pain of the ulnar nerve

 The area of total supply to pain of the ulnar nerve was obtained by the method of residual sensibility from a median lesion, an internal cutaneous lesion, and a combined median and radial (fig. 141, b, g, m). It occupies the ulnar portion of the palm to a line which is a continuation of the ulnar border of the abducted index finger, the palmar surface of the fingers except the terminal phalanx and one-third of the ulnar part of the second phalanx of the middle finger. On the dorsal surface it occupies the ring, little, and more than the ulnar half of the proximal, one and a half phalanges of the middle finger, and the dorsum of the hand to the radial border of the fourth metacarpal bone, ending proximally 1 inch above the wrist (fig. 142).

The area of the median nerve was obtained from an ulnar and internal cutaneous lesion, a radial, a combined radial and median lesion, and cases of combined radial and ulnar lesions (fig. 141, h, j, m). The inner border on the palmar surface was obtained by the method of residual sensibility from an ulnar and internal cutaneous lesion. As to the dorsal surface it was necessary to employ another method, as the cases of combined ulnar and radial lesions were too recent to have had return of prick pain due to overlap. The border

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of overlap of the musculocutaneous to the radial was obtained by means of residual sensibility in a ease of combined radial and median lesion. Inasmuch as the radial has no isolated supply to prick pain, this border separates the musculocutaneous from the median overlap. Therefore, this border was used as the proximal border of the median overlap to the radial nerve, especially in such cases as showed an area of analgesia between the areas of overlap of the median and musculocutaneous nerves (fig. 141). Part of the inner border of the over-lap on the dorsum of the hand is hypothetical and shown as a rough border (fig. 143).

The total supply of the musculospiral nerve was obtained from cases of combined ulnar and median nerve lesions, a ease of combined ulnar, median, and musculocutaneous lesions and a ease of combined ulnar and internal cutaneous lesions (fig. 141, a, d, e, f, h, i, k, 1, m, n). An overlap onto the palm was found to an extent heretofore undescribed. In median nerve lesions the sensibility

FIG. 143.- Residual sensibility to prick pain of the median nerve

to pain in the palm has frequently been ascribed to ulnar overlap. But. Athanassio-Bénisty ⁹recognized the importance of the musculospiral and the musculocutaneous nerves in this condition.

The area of overlap on the palm of the musculospiral nerve extends over the radial part of one and a half phalanges of the index finger, the radial part of the proximal phalanx of the middle finger, and the web between the middle and ring fingers, all of that part of the hand external to a line continuous with the radial border of the middle finger. Internally, it extends from the middle of this line to the middle of the base of the first phalanx of the ring finger and proximally to the middle of the outer surface of the wrist, from which point the border extends in a line to a point 1 inch proximal to the base of the metacarpal bone of the thumb on the radial border of the wrist. This area occupies the entire dorsal surface of the hand with the exception of a strip one-half the width of the little finger on the ulnar border, the little finger, the distal two phalanges of the ring finger, most of the distal two phalanges of the middle

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finger and a little more than the distal phalanx of the index finger. The area on the forearm need not be described (fig. 144).

The inner border of the pain area of the musculoeutaneous nerve on the anterior surface of the forearm was obtained from the residual sensibility following section of the internal cutaneous nerve; the inner border on the dorsal surface of the forearm, from a musculospiral division. The distal border on the palm was obtained from radial lesions, a combined radial and median lesion, and from lines obtained in combined ulnar and median lesions where an area of analgesia existed between the areas of overlap of the musculospiral and the musculocutaneous (fig. 141, e, f, k ). On the dorsal surface of the hand combined sections of ulnar, radial, and median and a case of combined radial and median

FIG. 144.- Residual sensibility to prick pain of the musculospiral nerve

FIG. 145.- Residual sensibility to prick pain of the musculocutaneous nerve

were employed (fig. 137, a, b, e, f; fig. 141, m, h, j). The area of total sensory supply to pain of this nerve can be better appreciated by viewing the illustration than by description (fig. 145). The proximal limits of both the musculocutaneous and musculospiral nerves are hypothetical.

Fortunately two cases were obtained from which the overlap of the internal and external popliteal nerves could be observed according to the method of residual sensation. One was the case in which the internal saphenous and internal popliteal nerves were injected with alcohol for causalgia, producing anesthesia, the residual sensibility about which permitted the outlining of the total supply for pain of the external popliteal nerve (fig. 146, f). The upper border of this area is hypothetical and merges on the outer surface with the external cutaneous, on the posterior surface with the small sciatic, and on the inner side with the obturator nerve.

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The overlap on the sole seen in Figure 147, b, is probably smaller than that which actually exists, as may be seen from the presence of sensibility to pain in the blank area of the sole in a ease of complete interruption of the internal

FIG. 146.- Sensory changes of combined lesions of internal saphenous and internal popliteal nerves, F; small sciatic, external popliteal and internal saphenous and sciatic nerve lesions from which the residual sensibility of the external and internal popliteal nerves was obtained

FIG. 147.- Residual sensibility to prick pain of external poplitoal nerve, B; sensory changes in an uncertified case of complete interruption of the internal popliteal, A

popliteal nerve, a case which, because it was not certified by operation, is not included in the present series (fig. 147, a).

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The area of total supply for pain of the internal popliteal nerve was obtained from the residual sensibility in a case of a combined lesion of the small sciatic, the internal saphenous, and the external popliteal nerves, and a case of

FIG. 148.- Residual sensibility to prick pain of the internal popliteal nerve

external popliteal section (fig. 146, d, e). The upper border of this area is hypothetical and merges with the borders of the small sciatic and obturator nerves (fig. 148).

FIG. 149.- Residual sensibility to prick pain of internal saphenous nerve

The area of total pain supply of the internal saphenous nerve was obtained from the residual sensibility of a combined lesion of the small and great sciatica and eases of sciatic section (fig. 146, a, b, d). The upper border here is likewise hypothetical, merging with the borders of the anterior crural, the external cutaneous, and the obturator nerves (fig. 149).

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CONCLUSIONS

1. The area of prick pain supplied exclusively by an individual nerve is far less than the accepted sensory distribution of that nerve.
2. The area between the border of exclusive supply of prick pain of an individual nerve and the border of its accepted sensory supply constitutes the area of algesic nerve overlap.
3. When nerves serving adjacent areas are severed, sensibility to prick pain between these areas is not present after injury, nor does it return before the sense of touch.
4. When a region in the area of sensory distribution of a severed peripheral nerve is sensitive to prick pain, and this region is adjacent to another nerve area, if this second nerve be severed, complete analgesia results in the previous sensitive region.
5. When sensibility to prick pain is present or returns in the area of possible overlap on to the sensory distribution of a severed nerve, subsequent resection and suture of this nerve does not change the general extent of this sensitive area. although the borders may at times be slightly enlarged or diminished; that is, the pain sense returned or present before the operation was not due to partial regeneration.
6. The laws governing the assumption of function by nerves adjacent to a severed nerve are unknown.
7. Handling and resection and suture of previously divided nerves changes the condition governing the function of overlapping nerves, often initiating greater function.
8. Evidence of the assumption of function by nerves adjacent to a severed nerve is not present immediately following the nerve injury, but gradually shows itself at a later date.
9. The early return of sense of prick pain before the return of sense of touch is not due to temporal dissociation of epicritic and protopathic sensibilities, but is due to the assumption of function by adjacent overlapping nerves.
10. The areas of overlap may be determined with fair accuracy and the early return of sense of prick pain in those areas can not be interpreted as a sign of regeneration of the divided nerve.
11. The changes in prick pain following division of a single nerve are not a safe basis for conclusions regarding regeneration of that nerve.
12. Only when a group of nerves is divided at the same time can the studies of sensation be used in the interpretation of regeneration of these nerves. Under these conditions only that part of the analgesic area may profitably be studied which is removed from the effect of overlap from adjacent nerves. On the other hand, if return to sensibility to prick pain occurs on the border of an uninjured adjacent nerve, this return to sensibility does not indicate regeneration of a nerve.
13. Return of sensibility to prick pain can be used clinically for the determination of nerve regeneration only when it is accompanied by return of tactile sense or when it occurs outside the area of possible overlap of adjacent nerves.

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REFERENCES

(1) Oppenheim, Hermann: Text-book of Nervous Diseases. Translated by Alexander Bruce. Edinburgh, Otto Schulze and Company, 1911, i, 5th Edition, 408.
(2) Létiévant, E.: Traité des sections nerveuses. J. B. Baillière et fils, Paris, 1873, 41.
(3) Head, Henry, Rivers, W. H. It., and Sherren, James: The Afferent Nervous System from a New Aspect. Brain, London, 1905, xxviii, part 2, 99.
(4) Head, Henry, and Sherren, James: The Consequences of Injury to the Peripheral Nerves in Man. Brain, London, 1905, xxviii, part 2, 117.
(5) Ibid., 295.
(6) Ibid., 120.
(7) Boring, Edwin G.: Cutaneous Sensation after Nerve-Division. Quarterly Journal of Experimental Physiology, London, 1916, x, No. 1, 1.
(8) Stopford, John S. B.: The Variation in Distribution of the Cutaneous Nerves of the Hands and Digits. Journal of Anatomy, Cambridge, October, 1918, liii, part 1, 14.
(9) Athanassio-Bénisty, Mme.: Treatment and Repair of Nerve Lesions. University of London Press, Ltd., London, 1918, 32: 117.
Also: Head and Sherren, Brain, London, 1905, xxviii, 135.