Manual Muscle Strength Testing:

Transcription

1 ( SCIENTIFIC/CLINICAL ARTICLES J Manual Muscle Strength Testing: Intraobserver and Interobserver Reliabilities for the Intrinsic Muscles of the Hand J. Willem Brandsma, PhD Physical Therapist, National Institute for Research and Postgraduate Education in Physical Therapy (SWSF), Amersfoort, the Netherlands Ton A. R. Schreuders* Chief Physiotherapist, McKean Rehabilitation Centre, Chieng Mai, Thailand Jim A. Birke, PhD Chief Physical Therapist, Gillis W. Long Hansen's Disease Center, Carville, Louisiana Angelika Piefer Occupational Therapist, McKean Rehabilitation Centre, Chieng Mai, Thailand Rob Oostendorp, PhD Physical Therapist-Manual Therapist, Professor of Manual Therapy, Free University, Brussels, Belgium Scientific Director, National Institute for Research and Postgraduate Education in Physical Therapy (SWSF), Amersfoort, the Netherlands ABSTRACT: The reliability of manual mu scle strength testing of the intrinsic muscles of the hand is reported. The muscle strengths of 28 patients who had neuropathies of the ulnar nerve or the ulnar and median nerves were graded by two physiotherapists to determine intraobserver and interobserver reliabilities. Muscle strength wa s graded using the numeric scale developed by the Medical Research Council (grades 0 to 5). Reliabilities were established for nine muscles or muscle groups. Intraobserver reliabilities ranged from 0.71 to 0.96 and interobserver reliabilities from 0.72 to It is difficult to isolate, and hence grade, mo st of the intrinsic mu scles of the hand. Therefore, it is suggested that sp e cific movements be tested and graded when assessing and evaluating muscle or nerve function. J HAND THER 8: , T he assessment of nerve function is important in the differential diagnosis and evaluation of peripheral nerve lesions, myopathies, neuropathies, and orthopedic conditions. Manual muscle strength testing (MMST) is one of the methods most commonly used by therapists in the assessment and evaluation of these conditions.1.2 Several studies have reported the reliability of MMST, but they have been Supported by a grant from the Q. M. Gas tmann-wichers Foundation in the Netherlands. Correspondence and reprint requ ests to J. Willem Brandsma, PhD, Physical Therapi st, National Institute for Research and Postgraduate Education in Phy sical Therapy (SWSF), P.O. Box 1161, 3800 BD Arnersfoort, the Netherlands. 'Mr. Schreuders is currently Physical Therapist-Hand Therapist, Univer sity Medi cal Ce nter, Dijkz igt Hospital, Rotterdam, the Neth erland s. Another arliclc about nianual musclcstrength testingappears on page 191 of tbie issue. predominately concerned with the larger muscles or muscle groups.v " Little is known about the reliability of MMST of the intrinsic muscles of the hand. Treatment decisions are often based on and guided by MMST scores. Efficacy of treatment can be evaluated using MMST scores. It is therefore essential to have knowledge of the reliability of MMST. Manual muscle strength testing was first extensively used to follow progression and regression of muscle status and evaluate the prophylactic effectiveness of gamma globulin for poliomyelitis.p-!' Manual muscle strength testing ha s been used to assess the natural progression of and the efficacy of prednisone for Duchenne's dystrophy.v" Kleyweg et al. used MMST, as well as other tests, to assess the effect of high-dose gamma globulin for Guillain Barre syndrome.f'!" Manual muscle strength testing is also a very important assessment technique for leprosy neuropathy. Decisions concerning drug treatment or surgery for leprosy are often based on and guided by the results of MMST JUly-September

2 TABLE 1. Muscle Abductor digiti minimi First dorsal interosseous Abductor pollicis brevis Opponens pollicis Lumbricals/interossei Testing Muscles versus Movements Movement Abduction, little finger Abduction, index finger Abduction, thumb Opposition, thumb Intrinsic-plus position who had had recent "reactional episodes" of the disease were excluded because muscle testing can be painful for these patients and their nerve function status may change rapidly. Likewise, patients who had established deformities of the hand were excluded if these would have affected the test position and movements. In hand therapy, MMST is most commonly used for entrapment neuropathies, nerve lacerations and repairs, and tendon transfer surgery. In many neuropathies and myopathies, the most distal muscles, the intrinsic muscles of the hands and feet, are affected first. This is an important reason to have knowledge of the reliability of tests of the intrinsic muscles. The knowledge of appropriate test positions and interpretations of test results for these muscles is equally important. Electromyographic studies show that most of the thumb and finger movements are not the result of contraction of one specific muscle (i.e., abduction of the little finger is not the result of contraction of the abductor digiti minimi only) An exception is the first dorsal interosseous, which could be considered the sole abductor of the second finger, provided the correct testing position is achieved. It is therefore presumptuous to give the impression, which textbooks about muscle testing give, that individual intrinsic muscles can be graded. 26-2H We prefer to talk about testing movements rather than testing individual muscles (Table 1), as suggested by Florence et al." We support the statement offered in the assessment recommendation manual published by the American Society of Hand Therapists that "... most actions or movements are the product of multiple synergists... and MMST should be interpreted accordingly." 29 Bohannon, Lamb, and Sapega offer further information concerning MMST in general :n The purposes of this study are to describe correct testing positions for some muscles or muscle groups of the intrinsic muscles of the hand, and to present intraobserver and interobserver reliability data of these tests. METHOD Manual muscle strength testing was performed by two assessors. Each assessor had many years of experience (15 years and 7 years) in the evaluation of nerve function for leprosy patients, a population that requires regular monitoring of nerve function FIGURE 1. Abduction of the little finger. The examiner supports the patient's hand in supination. With the fingers of his or her supportillg hand, the tester is able to palpate the hypothenar muscles. In this way. the tester is able to judge for grade 0 or grade 1 in the case of severe paralysis without having to change the test position. The patient is asked to abduct the little finger with the intcrpualangcal (IP) joints straight and the meiacarpophalallgcal (MCP) joint slightly bent to avoid trickmovement from the extensor digiti minimi. Resistance, when indicated. is givell at the lmse of the little fillger. IJ PATIENTS Subjects for the reliability study were patients from the McKean Rehabilitation Centre in Chieng Mai, Thailand. This is a rehabilitation institute to which a large number of patients who have leprosy and who require hospital care (e.g., ulcer treatment, reconstructive surgery, and treatment for leprosy neuropathy) are admitted. Leprosy is a chronic infectious disease mainly of the skin and the peripheral nerves Leprosy neuropathy of the upper extremity may result in weakness and paralysis primarily of the ulnar-nerve-innervated and the mediannerve-innervated intrinsic muscles. A total of 28 patients, 22 men (mean age 44 years, SO 15.2) and 6 women (mean age 41 years, SO 16.1), who had confirmed ulnar and/or median nerve weakness or paralysis comprised the study group. Patients 186 JOURNAL OF HAND THERAPY FIGURE 2. Adduction of the little finger. The patient is asked to keep the little finger adducted against the ring finger. The mctacarpcplmlanoca! (MCP) ioint should be held in neutral positiou, Resistance. when trying to separate the two fingers. is applied at the base of the little fillger.

3 / FIGURE 3. Abduction of the index finger. With the hand in mid pronation-supination, the patient is asked to abduct the index finger. The interphalangeal OP) joints of the finger are to be kept straight and the metacarpophalangeal (MCP) joint should remain in slight flexion. Resistance, when indicated, is applied at the base of the indexfinger. FIGURE 4. Abduction of the thumb (palmar abduction). The patient's forearm is supinated and the wrist is in extension. The patient is asked to abduct the finger in a plane perpendicular to the plane of the palm of the hand (thumb to nose). Resistance, when indicated, is applied at the base of the thumb at the level of the metacarpopliatangeal (MCP) joint. because of the neuropathies that may result as a complication of the disease. The patients and the assessors, therefore, were familiar with the technique. Only one hand was tested in cases of bilateral involvement. Unilateral study minimizes the testing time and the fatigue of both the tester and the patient, which could compromise reliability, and it allows one data point per variable per subject for statistical analysis. The interobserver reliability study was completed in 1 day. There was sufficient time, 10 to 15 minutes, between assessments to avoid possible fatigue that could influence test results. For the intraobserver reliability study, the patients were reassessed within 3 days of the first assessment. One assessor conducted the intraobserver reliability study. Because the patients were unfamiliar to the assessor, the possibility of the assessor's recalling muscle grades after 3 days would be unlikely. Patients who had known weakness or paralysis of the intrinsic muscles had been selected. In cases of bilateral involvement, the assessors decided, in turn, which hand should be tested. In such cases, preference was given to the hand with involvement of both nerves. In addition, the hand with weak muscles was preferred because there would be agreement on grade in the case of complete paralysis. The test positions were demonstrated for the patients even though all of the patients were familiar with the testing. The second assessor had no knowledge of the scores of the first assessor. Resistance, when indicated, was given in the shortened position of the muscle and maintained for 2 to 3 seconds (isometric contraction). A maximum of three trials were permitted per test to grade muscle strength. The muscle tests were performed in the following order: abduction, little finger; adduction, little finger; abduction, index finger; abduction, thumb; opposition, thumb; and the intrinsic positions of the index, middle, ring, and little fingers separately (Figs. 1-6). FIGURE 5. Thumb in opposition. The same test position as that used for thumbabduction (Fig. 4), but resistance is from the inside of the hand, perpendicular to the resistance applied for thumb abduction. FIGURE 6. Intrinsic-plus position. The patient is asked to put thehand in the intrinsic-plus position. When indicated, resistance is applied at the volar side of the proximal phalanx, pushing the finger into extension. July-September

4 TESTS Grades 0 to 5, as proposed by the Medical Research Council (MRC), were used, with some modifications of the definitions for the different grades (Table 2).15,37 The grades are defined by range of motion and resistance, e.g., grade 4 is full range of motion and less than normal resistance and grade 2 is decreased range of motion and no resistance. Gravity was not taken into consideration for each test position. For the intrinsic position, grade 2 was given when proximal interphalangeal (PIP) joint extension was less than 30 degrees short of full extension while maintaining the metacarpophalangeal (MCP) joints in flexion. This position is often referred to as the intrinsic-plus position, i.e., MCP joints flexed with the interphalangeal (lp) joints extended. Grade 1 was not considered practical for this test. RESULTS Cohen's weighted kappa was used to calculate intraobserver and interobserver reliability coefficients (Table 3). Weighted kappa is an accepted statistic for measurement of observer agreement that has been used in other MMST reliability studies.v" Our study also shows that the coefficients for interobserver reliability are, overall, a little lower than are those for intraobserver reliability. All reliability coefficients, however, show substantial agreement or better.38 DISCUSSION Few studies of the reliability of MMST have been performed. Those that have, have been concerned with larger proximal muscles or muscles groups in the extremities. Our results compare favorably with the results of these studies. In many diseases and conditions, changes in motor function of the peripheral nerves are first observed in the intrinsic muscles. To evaluate motor function in these conditions and to be able to intervene medically or surgically at the appropriate time, it is mandatory to be knowledgeable about the reliability of MMST of the intrinsic muscles of the hand. In a review article about the accuracy of clinical tests for the diagnosis of carpal tunnel syndrome, MacDermid mentions four studies in which a muscle test was used as part of the diagnostic procedure.39 Sensitivities of the MMST for TABLE 2. Modified Medical Research Council Scale" Grade Range of Movement Resistance 5 Normal Normal 4 Normal Reduced 3 Normal None 2 Reduced None 1 None Palpable contraction only o None No palpable contraction "Definitions should be interpreted with caution, e.g., if joint movement is restricted because of "stru ctu ral" problems but resistan ce is norm al, grad e 5 is given. 188 JOURNAL OF HAND THERAPY TABLE 3. Intraobserver and Interobserver Reliabilities of Manual Muscle Strength Testing for the Intrinsic Muscles of the Hand Movement Abduction, little finger Adduction, little finger Abduction, ind ex finger Abduction, thumb Opposition, thumb Intrin sic-plu s position Index finger Middle finger Ring finger Little finger Intraobserver Reliability Interobserver Reliability abduction of the thumb ranged from 29% to 53%. In the study by Florence et al., 18 muscle groups were graded, of which 3 were in the upper extremities." Wrist extension, wrist flexion, and thumb abduction had the lowest reliability coefficient (0.69, 0.65, and 0.71, respectively in that study). Our study shows higher coefficients for muscles or muscle groups in the hand, but, admittedly, with a less detailed scale. Besides adhering to standardized test positions and standard points of application for resistance in order to get repeatable and reliable results, it is essential that the tester be aware of "trick" movements and anomalous innervation patterns.pr' " Clinically,?nomalous innervation can be expected when there IS an uncommon pattern of paralysis with definite damage to a specific nerve. Howell et al. have shown that, when testing the extensor pollicis longus and flexor pollicis brevis, test positions have an influence on the generated force." If test positions and trick movements are not taken into account, the results of MMST may lead to erroneous conclusions and a change in treatment policies that may not be indicated. We selected the tests described for two reasons: (1) if the cause of intrinsic weakness is proximal to the wrist, the tests will give sufficient information; and (2) some muscles or movements can be readily substituted by other muscles or movements and, therefore, are prone to erroneous grading. For example, the flexor pollicis brevis may have an ulnar, a median, or a dual innervation and the mobility of the MCP joint varies a lot, which may make it difficult to test thumb MCP joint flexion; or adduction of the thumb can be accomplished by the extensor pollicis longus and flexor pollicis longus. Only if there are traumatic conditions distal to the wrist might there be indications to test other movements or muscles, in addition to those tested here, to assess the status of the terminal motor branches. When testing the strength of intrinsic muscles in the intrinsic position, the examiner is primarily assessing the strength of the interosseous muscles. With an isolated ulnar lesion, the index and middle fingers will show weakness or may even claw, whereas with an isolated median nerve lesion there will be no perceptible weakness of these two fingers in the intrinsic position." Future research should be directed at determin-

5 ing reliability with an ll-point scale such as that used by Florence et al. 6 In our study the MRC scale was refined. This is especially important because research has shown that with 5% to 30% of muscle force a limb segment can be moved through its full range. against gravity, depending on muscle (group).46a 7 A refined scale, between MRC grades 3 and 5, would help to indicate changes sooner and could be more sensitive in the evaluation of the natural courses of certain diseases or in showing efficacy in treatment interventions. However, reliability may be affected, as shown by Florence et al. Furthermore, the role of experience in the reliability of MMST should be investigated. How much training and experience is needed to reliably grade muscle strength? Possible relationships between MMST scores and dynamometry scores should be determined. We recommend that neuromuscular disorders affecting grip and pinch strengths be assessed at the same time MMST is performed;" The Jamar dynamometer and Preston pinch gauge are instruments for which reliability studies have been conducted.49,5o Further research is needed to determine which of the muscle tests might be the most sensitive for indicating true changes in muscle strength in order to evaluate motor function of the ulnar and median nerves, or the roots or the plexus branches from which they are derived, or muscle strength in pure muscular diseases and disorders. CONCLUSION This study has shown that experienced testers using a standardized protocol can reliably assess the strengths of some intrinsic muscle groups of the hand on a 6-point scale. Manual muscle strength testing is a very useful and valuable technique for the assessment and evaluation of neuromuscular disorders.v'" Ackn owledgment The authors thank H. 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