The unsolved problem—How to test the functional value of hand sensibility

(GUES~~-;/~~~/-;LJ The Unsolved Problem-How to Test the Functional Value of Hand Sensibility Erik Moberg, MO, PhD

Orthopedic and Hand Surgery Department, Sahlgrenska University Hospital, G6teborg, Sweden

n spite of all that has been written about the

I subject, our specialty still lacks a tool for the evaluation of the functional sensibility of the hand.

Without such a tool, different methods of nerve suturing and nerve grafting cannot be compared. In the foreword to his last book, Peripheral Nerve Surgery, Sir Herbert Seddon (1975) wrote: "If the recording of sensory recovery can be better defined and generally adopted, it will be a great step forward." At that time Sir Herbert no doubt had contributed more to the development of nerve surgery than had anyone else. His statement actually contradicted his earlier standpoint (1954), when he, like most contemporary workers in the field, still believed that the old neurologic tests with pinprick and cotton wool gave an adequate evaluation of sensory recovery. But he had observed that "academic" recovery, documented by pinprick and cotton wool, was certainly not the same as functional recovery. A hand with normal test results often had poor function. Over time his new view gained more support, 6 and it was agreed that new ways of measuring sensory recovery had to be found. There existed useful tests for motor function, but without adequate sensory function even the best motor function results were found to be of limited value. Such a hand could be described as "blind." Vision has a lot of qualities similar to hand sensory function. A simple reading test-the subject trying to read texts of different sizes-will give a most useful grading of the level of sight. Something similar must be found for assessing hand sensibility, not a multipurpose examination. The following prerequisites must be fulfilled for a hand senSibility test to be used in daily practical work: 1. The results must be measured in numbers. Erik Moberg was formerly head of the Orthopaedic and Hand Surgery Departments, Professor of Orthopaedic and Hand Surgery, University of G6teborg, Sweden. Correspondence and reprint requests to Professor Erik Moberg, Kjellbergsgatan 8, 411 32 G6teborg, Sweden.

2. These numbers must correspond with the

functional value, i.e., with what the hand can do.

3. The results must be repeatable and, with small variations, reproducible among trained testers. 4. The test must be useful for small areas, such as a single digital nerve, because more than 70% of all reported observations of sensory recovery are from single nerves.

A lot of terms, more or less well defined and covering variations of functional reality, are used in this field. First, for our purpose, we can discard the four modalities of sensory quality and the neurologic ways to test them. Seddon found them erratic, just as many other workers did later. Certainly, the desired test must involve a stimulus to the skin. Because we can exclude stimuli causing pain and those with variations in temperature, there will remain, in my opinion, only two variations: 1. Stimuli causing sense of touch without macroscopic skin deformation. 2. Stimuli causing skin deformation also. Neurophysiologists, especially the ones who are working in the field of microneurography, now clearly statel ? that it is impossible to separate the different systems of the four rapidly and slowly adapting receptors (RA I, RA II, SA I, and SA II) by the different kinds of skin deformation tests. All the receptors respond to the tests. They have also shown that the cutaneous receptors have proprioceptive as well as exteroceptive function. 3 ,12,18 Besides those mentioned above, there are other receptors, namely, the free nerve endings, which only rarely can be examined by microneurography and which we know are present in increased percentages during sensory recovery after nerve suture. In this circumstance, the other receptors also can be expected to have changed from their normal function. Actually, there seems to be almost a double set of receptor systems, due to the July-September 1991

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activity through the C-fibers.11 The cornea has practically only C-fibers, whose endings are unmyelinated and still seem able to produce almost the same sensory qualities as skin. In this area of assessing sensory responses, real knowledge is rare and hypotheses frequent. Therefore, the test we want cannot have two goals, one neurophysiologic and the other clinical, as is often proposed. We must stay with the single problem, difficult enough, of finding a simple way to measure functional sensibility. To recapitulate, the result regarding sensory quality obtained from skin stimulation is a synthesis of all available factors, but, after a nerve suture, each of these factors is likely to differ from its normal.

TESTS AND EVALUATIONS IN PRACTICAL USE It is appropriate here to examine what presently recommended tests can give us for practical use. The two tests that are initially conducted without macroscopic skin deformation are the old von Frey test, performed with either a hair, a light strip of paper, cotton, or a fine nylon thread (used by Seddon), or a variation of the von Frey test, such as the fairly popular Semmes-Weinstein test. 7 After extensive experience with the von Frey test, I found it useless for my purpose and cannot imagine any modification that would make it acceptable. Marsh 5 recently disagreed with this position but has not been able to disprove it. It must be remembered that, after nerve suture, long-lasting and very disturbing hypersensibility usually occurs, which is an important functional decrement. No doubt the von Frey test will continue to be useful in neurology, but it must be remembered that in neurology the problems are of a totally different kind-diagnosis of central lesions, not hand function. The occasionally still-advocated British MRC-scale, based on the von Frey test, has never had a scientific foundation. It was a wartime improvization and is now more of a hindrance than a boom to progress. The Semmes-Weinstein test also starts as a pure "touch" test without skin deformation, and it gives repeatable data that simulate exactness. Very disturbing to me, however, is that when advancing from finer to coarser threads, this method suddenly changes character from a pure touch test to a skin deformation test, and one hardly knows where on the scale this takes place. Another objection is the astonishing fact that the test is never evaluated directly against hand function. Therefore, one does not know what the numbers really mean. How important this is will be clear later in this paper when the ridge tests are discussed. My feeling is that with Semmes-Weinstein, only a limited part of the scale covers useful function, and that is the field we must try to cover with our test. And so we arrive at the pure skin-deformation tests and can start with the letter test of Porter and the ring figure test used in Brescia. Because full details are not published, no lengthly discussion would 106

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be helpful here. The tests are based upon metal letters or symbols, which are pressed against the skin for identification by the patient. None of. them is tested directly against hand function, nor is any directly transferred into numerical measurements. Better known are the ridge tests, one by Renfrew and the other by an American variation; both are pure skin-deformation tests. In the Renfrew test, a 2-mm-wide ridge on a plastic ruler rises from 0 to a maximum height of 1 mm (1.5 and 2 mm in later versions). The ridge must glide with light pressure against the skin area to be tested, and the subject must say when he or she begins to feel the ridge. A millimeter scale from 0 mm to 100 mm indicates the distance on the scale and so, indirectly, the height of the ridge. In principle the American instrument is the same. I have tested both for the assessment of function and compared them with my technique of the twopoint discrimination (2 PO) test, and found that they can crudely separate functional differences. The interesting aspect is that the part of the scale that was of practical interest when evaluating senSibility was in the zone from 1 mm to about 15 mm. The other 85 mm of the scale was beyond the area of practical interest; all the variations obtained were in a field of sensibility too inferior to be of use at all. This illustrates as well as can be done that it is not just numbers we need, it is numbers revealing useful facts. With the existing 2 PO tests, the response to stimulation with skin deformation is given as a synthesis of the responses from all available receptors. This is the same in both test variations, the so-called "moving" 2 P02 and my version?,8,10 The free nerve endings also take part in the response. It must be understood that there can never be a "static" 2 PO test. It is the motion of the prongs that causes the skin deformation and makes an answer possible. The motion in the Oellon type is different and will, depending on how well the test is performed, give lower values and more easily cause errors, especially when the instrument is jumping over creases in the skin and if there is, on the paperclip instrument (as some brands have), a nub left from the cutting procedure. This is of no importance in my version of the 2 PO test. That this version gives repeatable results is seen in Tables 1 and 2. It must be mentioned that what the patient feels is not always one or two prongs. Often the patient's response is based upon a feeling of a more narrow or a broader application. This is of no practical importance. Another point to stress, and an area in which mistakes often are made, is that the subject has not two but three alternatives for an answer: "One prong," "Two prongs," and "I can't tell." A very important point is that the 2 PO test is useful only when the technique is perfect. There are similarities between this test and microsurgery. Both are delicate procedures during which the working hand must be braced exactly, just like the hand part you are examining. Every vibration or disturbing extra motion is to be avoided. My own technique has become better and better through the years. Training

TABLE 1.

ORIGINAL 2 PD VALUES

Validity of the Two-Point Discrimination Test in Normal Individuals* NO. OF DIFFERENCES OVER 1 MM FOUND IN SECOND TEST

NO. OF TESTS

3-5 mm 6-8 mm 9-10 mm

190

126 24

2mm

3mm(+or-)

2 11

o

1

1

3

'The same areas were tested twice by the author. The interval between the two tests was at least 48 hours. Hard manual work can in a few days raise values from normal by 2 mm; quite exceptional, 3 mm. Differences between transverse and longitudinal applications, about 1 mm, of no practical interest. From: Moberg E: Two-point discrimination test. Scand J Rehabil Med 22, 1990.

TABLE 2.

ORIGINAL 2 PD VALUES

3-5 mm 6-9 mm 10-15 mm

fiGURE 1. When, as often advertised, the test is performed in the way shown here, no reliable results can be obtained. Examiner and examinee will both produce disturbing motions. From: Moberg E: Two-point discrimination test. Scand I Rehabil Med 22, 7990.

Validity of the Two-Point Discrimination Test in Tetraplegic Patients*

NO. OF TESTS

54

13 15

NO. OF DIFFERENCES OVERIMM FOUND IN SECOND TEST 2mm 3mm 4 mm (+ or -) 4 4 2

1

2

2

'The same areas were tested twice by three different physicians, not by the author. The interval between the two tests was at least 48 hours. Hard manual work can in a few days raise values from normal by 2 mm; quite exceptional, 3 mm. Differences between transverse and longitudinal applications about 1 mm, of no practical interest. From: Moberg E: Two-point discrimination test. Scand J Rehabil Med 22, 1990.

is a must. A short period of instruction cannot make you a good microsurgeon, or a reliable tester. The instrument must be small and almost weightless. Every instrument I have seen with a millimeter scale is too clumsy. Today I totally refuse instruments with long handles (calipers) along with all the "stars" on the market. One of them that is advertised over and over in a hand journal shows a picture of both the examiner's hand and that of the examinee in free space, without any stabilization at all (Fig. 1). Such an examination is useless but is described as easy and reliable . Figure 2 shows the stabilization that I consider necessary. The application force should be 10-15 g. An excellent survey of possible errors is given by Bell and Buford.! Forty-five years ago I discovered my technique, and it was my great error that I did not describe the technique in detail at that time. While touring the world in subsequent years I witnessed many inadequate technical variations that destroyed the value of the 2 PO test. When manufacturers of the test instrument can make mistakes as described, how can one expect helpers without much instruction and training to get good results? By moving and by pressing one can obtain almost any results wanted, and the patient can assist by wriggling the digit. We can see such results from examinations everywhere. And so the great majority of published results are without

fiGURE 2. In order to avoid every unwanted and di sturbing motion or vibration, the part of the hand to be examined must be steadily immobilized on a firm support. The same is true for the examiner's hand. Only small and almost weightless instruments must be used. Long-arm instruments must be discarded. From: Moberg E: Two-point discrimination test. Scand I Rehabil Med 22, 7990 .

value. Because in general nothing is said about the technique used or about the experience behind it, there is no way to pick out the few studies of value. Again and again I have examined cases for which results of, say, 6 mm were claimed or published . With my technique I found values of about 18 mm in the same cases. As a typical example, the plantar pulp of the great toe has normally, when examined by me, a 2 PO of 15 mm. When it is transferred to replace a lost thumb, about half of all axons, even with the best microsurgery, miss contact with their ordinary receptors. A number of receptors, even if reconnected, never reach normal status again. The projection of the big toe on the brain is, in size, just about 1% of the projection of a thumb. This reveals much of how inferior the nerve supply and receptor system are in July-September 1991

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the toe. After being joined, myelinated fibers never reach the same diameter as before. Still, in no fewer than three papers with different authors it is claimed that the big toe, after this transfer, had a 2 PO of 6 mm! I have examined such cases and found, of course, values less than what a normal big toe in place should show. The conclusions are obvious. One author reported that after World War I there was a race on to determine who could bridge the largest nerve gap without grafting. He concluded: "Of course the Americans won." In the subject under discussion the "winners" are spread all over the globe. And so, the 2 PO test has totally failed to be the instrument by which results from different services or from different surgical variations could be compared. And I have no hope whatsoever that we will see a change in this sad fact. On the other hand, a 45-year experience has shown me that, performed in the right way, this test is a most useful way to evaluate sensory function and sensory recovery. It has also provided a solid foundation for my major handarm reconstructions. This work would not have been possible without the 2 PO, and it includes cases of pure nerve lesions of all kinds-severe trauma, plexus lesions, stroke cases, and tetraplegia. In the latter group, more than 200 hands have been operated on. One could say that cases could be operated on based only on motor function. But without sensory evaluation, including proprioception, neither surgeon nor patient would have any insight before surgery about the expected result and, therefore, any awareness of whether a planned operation would be worthwhile. Tetraplegia cases, especially, with their enormous functional losses, have clearly demonstrated this problem. Even for the diabetic foot my version of the 2 PO test is most useful in identifying in time the patients in danger of getting pressure sores from their shoes. The scale, however, is different. Although the 2 PO test cannot be used as a "gold standard" for comparing the results obtained by different workers, in your own work this test can assist you in managing your patients. It is important to underline that the 2 PO test cannot identify the initial small losses in sensory quality. Therefore, one can never say that a patient with a normal 2 PO has no loss. The different kinds of vibration tools4 now evolving are much better in finding small losses, but so far not useful for the other purposes discussed here. Marsh, in his recently published thesis,s has provided a good survey of these tests. Of course, I have in my work obtained and evaluated every new variation of sensory testing found in the literature. But I have to state that I just have not found that they provide any new useful information, and so I gave them up and stayed with the 2 PO-a crude test, very far from what we want, but useful. The 2 PO test also tells about the presence and absence of finger proprioception, as I have elaborated recently.lO A few words must be said about batteries of tests. When examining the eye, there is no doubt that acuity should be tested. Color tests are the most 108

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important for some situations; tests that assess the field of vision and vision in severely reduced light can be important. But for acuity, which is the problem most often encountered, a test for acuity is crucial-all the other tests are of scarcely any help. In my opinion the same is true when testing hands. For the gripping function, no extra test-no batteryseems important or of real help. Only a direct function test, such as the sensory so-called pick-up test, can in my opinion be a worthwhile addition. There is another comparison that should be made between vision and hand tests. With tests of vision, we know almost exactly what every different test means from functional points of view. With different hand battery tests, this is not so. Therefore, how can we then, in a practical sense, use data of unknown value? In normal cases the 2 PO test can usually be graded only between 4 and 10 mm and an error of 1-2 mm must be accepted. We know that endless variations in sensibility occur but hardly more than a few levels can be defined. It shows how far we are from what we want! The main problem with identification tests is the difficulty in excluding information from other sources, usually nerve regions other than the one tested. Some have tried to get rid of such information by putting surgical gloves over areas to be kept out of the field. Because identification of objects is mainly dependent on skin deformation, and this remains unchanged under gloves, this method will fail. In our own experiments with as many as six pairs of gloves on the index fingers of five normal subjects, the 2 PO test remained at 4 mm, just as before the gloves were put on. The only difference was a fall from ten correct answers in each test to only eight or nine. In my opinion the only way to exclude information from other nerve regions is by blocking them with local anesthesia. The problem here is to avoid an anesthetic spread to the region to be tested. The prerequisites for useful blocking are: 1) small quantities of fairly strong solutions, 2) adrenaline added to prevent the spread, 3) injection as proximal as possible, and 4) experience. As OTs and PTs usually are not permitted to use this technique, they can hardly perform identification tests of value in these circumstances. Even if individual workers may have found useful methods in their own practices, the goal Seddon gave us-to make the recording of sensory recovery better defined and generally accepted-is still over the horizon. After 45 years of work in this area I have to admit our insufficiency.

THE FUTURE It is even difficult to suggest approaches for further research. Recently, a very serious worker in the field believed that a localization test could be refined enough to give the answer. It also has been suggested that some variations of the old von Frey test could

be the way. I have a hard time believing it. In my work, I am trying to go further with an analysis of the technical errors in the 2 PD (my version), having made a small tool (Fig. 3) by which vibrations of the examining hand can be eliminated. With the help of this instrument it is also possible to check the application force. It was found that, if an index pulp has a 2 PD of 3 mm, a load of 6 g for both one and two prongs was the minimum that could make the test possible. If the 2 PD was 4 mm, it was necessary to go up to 10 g for the two prongs, 6 g for one. A useful test is possible with more than twice this load, but of course a higher load will bring in receptors from a larger field and is therefore not desirable. If the application force increases still more, it will be difficult to separate between one and two prongs, and errors will increase. To facilitate progress in clinical fields, it is often useful to find an experimental model, easily obtainable, that can be standardized. For our testing needs it has always been difficult to find suitable cases with different degrees of sensory loss in which test methods or results could be compared with respect to function. With rubberband pressure around the index and the thumb, such a system can be obtained. This is useful also if one wants to add the pick-up test in the same conditions of sensory loss. It is still better to obtain the pressure on the nerves by the now commercially obtainable small aircuffs (Fig. 4). With them the pressure and the time of its appreciation can both be standardized. Sensibility goes down slowly and can be totally lost in about 30 min. So the variations in sensory function as well as the function in different parts of the grip can be studied with different methods. It is interesting to know that even

fiGURE 4. An experimental model to produce, in normal subjects, different degrees of sensory loss, here with the help of now commercially available inflatable minikits. To the cutaneous measurements can be added the pick-up test. Beware! Important source of error! See text.

with total loss of cutaneous finger sensibility, quite a bit of identification power remains due to the information obtained from the skin moving over the active thenar muscles and even around muscles higher up in the forearm. This identification power is present only when sideways movements of the two digits occur, but not in a pure tong grip. Most of this identification power can be eliminated with a pressure cuff or with compression by a rubberband placed around the wrist. When placed around the digits this compression is easily tolerable; it soon starts to be painful when it is placed around the wrist. Finally, now long will we have to wait before a kind of "gold standard" arrives? Without it, lots of basic research remains undone and many practical clinical problems remain unsolved.

Selected Bibliography Of the enormous literature only a few important references can be given here. In the recent "Rehabilitation of the Hand," Hunter 1M, Schneider LH, Mackin EJ, et al (eds.), C. V. Mosby, St. Louis, 1990, several chapters with up-to-date references are written by Bell-Krotoski, Callahan, etc. FIGURE 3. My tool for the study of application forces in 2 PO tests. The vibrations from the two human hands' are eliminated. The tool is used only for scientific studies; its use is unnecessarily time-consuming in clinical work.

1. Bell JA, Buford WL: The force-time relationship of clinically used sensory testing instruments. J Hand Ther 1:76, 1988. 2. Dellon AL: The moving two-point discrimination test: Clinical evaluation of the quickly-adapting fiber/receptor system. J Hand Surg 3:474, 1978. 3. Johansson RS, Westling G: Signals in tactile afferents from the

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4. 5. 6. 7. 8. 9. 10.

fingers eliciting adaptive motor responses during precision grip. Exp Brain Res 66(1):141-154, 1987. Lundborg GL, Stenstrom AK, Sollerman C, et al: Digital vibrogram: A new diagnostic tool for sensory testing in compression neuropathy. J Hand Surg llA:693-699, 1986. Marsh D: The measurement of peripheral nerve function in the upper limb. MD thesis, University of Cambridge, 1990. Moberg E: Objective methods of determining the functional value of sensibility in the hand. J Bone Surg 40B:454-466, 1958. Moberg E: Criticism and study of methods for examining sensibility in the hand. Neurology 12:8-19, 1962. Moberg E: Reconstructive hand surgery in tetraplegia, stroke and cerebral palsy: Some basic concepts in physiology and neurology. J Hand Surg 1:29-34, 1976. Moberg E: The role of cutaneous afferents in position sense, kinaesthesia and motor function of the hand. Brain 101:1-19, 1983. Moberg E: Two-point discrimination test. A valuable part of

11. 12. 13. 14. 15. 16. 17. 18.

hand surgical rehabilitation, e.g. in tetraplegia. Scand J Rehabil Med 22:127-134, 1990. Mount castle VB: Medical Physiology, 12th ed. St. Louis, CV Mosby, 1968. Phillips CH: Movements of the Hand. Liverpool, Liverpool University Press, 1986. Renfrew S: Finger tip sensation: A routine neurological test. Lancet 1:369-370, 1969. Seddon HF & coworkers: Peripheral Nerve Injuries. London, Her Majesty's Stationary Office, 1954. Seddon HJ: Surgical Disorders of the Peripheral Nerves. Edinburgh, Churchill Livingstone, 1975. Weinstein S: Tactile sensitivity of the phalanges. Percept Mot Skills 14:351, 1962. Vallbo AB, Johansson RB: The tactile sensory innervation of the glabrous skin of the human hand. In Gordon G (ed.): Active Touch. Oxford, Pergamon Press, 1978. Westling GK: Sensory-motor Mechanism during Precision Grip in Man. Umea, Umea Univ Med Diss, New Series 171, 1986.

CLET;E~-T~-~HE EDITOR] To the Editor: I would like to make several comments about the article entitled "A Study of the Accuracy of a Commercially Available Volumeter" written by Janet Waylett-Rendall, OTR, and Deborah S. Seibly, OTR, in the JanuaryMarch 1991 issue of the Journal of Hand Therapy. Having extensively utilized the Hand Volumeter in my practice at a community hospital, I have these concerns about their study: Figure I(a) is a photograph of a hand being immersed into the volumeter with the thumb away from the spout. The photograph does not depict the proper placement of the hand immersed in the water, with the thumb toward the spout. This makes the observant reader a little cautious about the authors' data collection technique. The four examiners were implied to be registered occupational therapists (OTRs), but the fourth was an experienced hand center aide. An experienced hand center aide is not an OTR. In the Discussion the authors commented about "topping off" the volumeter with a "beaker rather than a spray hose." This statement made me wonder whether some of the beakers had been topped off with a spray hose. As indicated by numerous texts, the leveling or topping off should be done by a beaker or a faucet that does not have a spray. The rationale for this is that the spray hose or faucet aerator

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introduces an inconsistent amount of air into the water, thus not standardizing the reading. I greatly appreciated the authors' efforts and research to provide clinical statistics to back up the stated claims of volumeter accuracy. - Margaret Sood, OTR, Rancocas Hospital, Willingboro, New Jersey

Reply: Thank you for calling our attention to the errors in our article. Let us attempt to clarify. Our original photos were lost during the review process (with the exception of the rubber hand, shown in Figure 2). Figure 1A was provided by the publisher and does show the thumb oriented away from the spout of the volumeter. However, the principle of fluid (volume) displacement as first conceived by Archimedes remains reliable and valid provided that the position of the hand and forearm in the container are always consistent and the position of the fingers on the dowel remains constant. The method of placing the thumb on the spout side was conceived by the manufacturer for consistency's sake. As we stated, we did adhere to this method during our study. The Method section in our article defines the proper placement of the hand as given by the manufacturer. No studies have been performed that indicate that the orienta-

lion of the thumb within the volumeter would effect the accuracy of the measurement, providing that positioning was consistent. The second error is an omission, one that, unfortunately, we did not correct. We in no way wished to imply there were four OTRs as examiners. The three words omitted are italicized in the sentence that follows: "Three of the four examiners were registered occupational therapists, of which two were specialists in hand treatment, one was a generalist in physical disabilities and the fourth examiner an experienced hand center aide." Concerning your last comment regarding the topping off of the volumeter: When the literature review was conducted in 1980-1981, there was only one text that addressed the method of conducting the test-the first edition of Rehabilitation of the Hand. Use of an aerated hose was not specifically addressed. Looking at the second (1984) and third (1990) editions of Rehabilitation of the Hand, use of an aerated hose was mentioned as reducing reliability of the volumeter. However, the source quoted for the information was our paper, which was presented at the annual meeting of ASHT in 1981. We are glad that our article was so carefully read by Ms. Sood and appreciate her comments.-Janet Waylett-Rendall, OTR, and Deborah Seibly, OTR, Hand Rehabilitation Center, Lorna Linda University Medical Center, Lorna Linda, California.