- Email: [email protected]
Reliability of thumb web measurements
Reliability of Thumb Web Measurements Prashant M. Murugkar, MCh, DNB Department of Plastic Surgery Manipal Teaching Hospital Manipal College of Medical Sciences Pokhara, Nepal
J. Wim Brandsma, RPT, PhD Green Pastures Hospital and Rehabilitation Centre International Nepal Fellowship Pokhara, Nepal
A. M. Anderson, PhD RELEASE Project Office International Nepal Fellowship Pokhara, Nepal
ABSTRACT: Two new methods of thumb web space measurement, the intermetacarpal distance (IMD) and the derived intermetacarpal angle (DIMA), were proposed and compared with a conventional method for interrater reliability. Forty subjects (22 normal hands, 18 impaired hands) were measured. Reliability of the measurement was estimated using the intraclass correlation coefficient (ICC) and the Bland and Altman method of 95% limits of agreement. Overall, the IMD method showed an ICC of 0.88 with 95% limits of agreement of ÿ6.9 to 5.6 mm (approximately 6.2 mm). Similarly, for the DIMA method, the ICC was 0.47 with 95% limits of agreement of ÿ11.9 to 5.1 (approximately 8.5 ). The IMD method appears more reliable than the conventional method, which had an ICC of 0.26 and 95% limits of agreement of ÿ17.5 to 9.2 (aproximately 13.3 ). The IMD method is recommended as a reliable method of measuring the thumb web space. J HAND THER. 2004;17:58–63.
Khadka Gurung, RPT Yam Pun, PT Green Pastures Hospital and Rehabilitation Centre International Nepal Fellowship Pokhara, Nepal
In the Fourth Bridgewater Treatise,4 Sir Charles Bell wrote, ‘‘on the length, strength, free lateral motion and perfect mobility of the thumb, depends the power of the human hand.’’ Thumb web contracture is one of the most disabling structural impairments of the hand and is a common problem seen in hand trauma, burns, intrinsic paralysis, and Volkmann ischemic contracture. The structural complexity of the thumb web space does not lend itself easily to measurement; this is evident from the fact that there is not much peerreviewed and published research on this subject. Of the methods that have been described for measuring the thumb web space, none have been subject to any reliability studies. The need to have a standardized method for measuring the thumb web is paramount given its importance to thumb function. If such a method could be described, it would provide the hand therapist and hand surgeons a common platform to evaluate the management of thumb web contracture,
Correspondence and reprint requests to Prashant M. Murugkar, MCh, DNB, 63/4 B, Jai–Vijay Society, Sahar Road, Sahar, Mumbai, India 400099. E-mail:. doi:10.1197/j.jht.2003.10.008
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especially if this method could be used in the intraoperative period to measure the adequacy of release of the web contracture. This will help to assess the severity and the effect of intervention such as exercises, splinting, and surgery of thumb web contracture. The concept that the thumb placed in full palmar abduction represents the maximum spread of the thumb web space has been documented by several authors.5–7 With the thumb placed in this position, Brand8 measured the angle made at the intersection of two lines drawn on the skin overlying the palpable subcutaneous surfaces of the first and second metacarpals. He quoted the normal range of the web angle as being 40–508 . Shrinivasan9 used triangular pieces of wood with known angles (25–558 with a gradation of 58 ), these were placed into the thumb web and tested for a snug fit to derive the appropriate measurement of the web angle. Schwanholt and Stern10 used Dixie Yarn Cones inserted into the thumb web space in full palmar abduction to gauge the thumb web space. Bhattacharya11 described a method using dental compound molded into the web space. When the mold set, it was cut sagittally and smeared with ink, and measurements were taken from the ink impression.
The other concept that has been used to measure the thumb web space is to measure the distance between the plane of the palm and the tip of the thumb placed in full palmar abduction. This method has been used by the American Society of Hand Therapists,12 which describes a procedure for measuring thumb opposition using a ruler to measure the distance from the volar tip of the thumb to the third metacarpal. Cambridge-Keeling13 also recommends using the ruler and placing it between the distal palmar crease of the index finger to the pulp or interphalangeal crease of the thumb. This concept, however, relies on the normalcy of the interphalangeal joint of the thumb and of the length of the thumb, which could pose problems in the clinical setting. There is also very little standardization of these methods and no reliability data to support their use. In our method, the thumb was placed in full palmar abduction, the easily identifiable middorsal points on the subcutaneous surfaces of the first and second metacarpal heads were marked, and the separation between these (in millimeters) was measured to calculate the intermetacarpal distance (IMD). Then, using the tip of the radial styloid process as the third point, we measured the distances from it to the first and second metacarpal heads (middorsal points) and, incorporating the IMD measurement, drew a triangle and then measured the angle at the point representing the radial styloid to arrive at the derived intermetacarpal angle (DIMA). By using these easily identifiable surface markings of skeletal landmarks, we hoped to arrive at more reliable measures of the separation between the first and second metacarpals with the thumb in full palmar abduction. These two methods also lent themselves to being used intraoperatively, an advantage none of the earlier methods possessed. We decided to test these two methods for interrater reliability using the intraclass correlation coefficient (ICC)1 and the Bland and Altman2 methods. We also similarly tested the method described by Brand8 because it was already being used in the physiotherapy department. Using an assistant, we passively put the subject’s thumb into full palmar abduction before measuring the thumb web with the three methods. This was done to enable a comparison between a heterogeneous population of subjects with normal hand function and those with impaired hand function. The focus of this study was to find out which of these three methods had the highest interrater reliability when used in a mixed population of normal and impaired hands. If any of these three methods had an ICC of 0.81 through 1.00 or a perfect reliability rating on the subjective rating scale developed by Landis and Koch,3 it could be recommended as a reliable measure of the thumb web space. The purpose of this study was to examine the interrater
TABLE 1. Segregated Data of Age and Sex Distribution of Impaired and Normal Hands in the Study Age (years)
Gender
Impaired hands 30 60 76 70 68 72 30 70 48 55 58 74 45 45 40 28 30 50 Normal hands 38 45 52 40 42 22 50 39 16 11 45 39 61 33 17 16 30 39 23 40 40 40
Male Male Male Male Male Male Male Male Male Male Male Male Male Male Female Female Female Female Male Male Male Male Male Male Male Male Male Male Male Male Female Female Female Female Female Female Female Female Female Female
reliability of three methods of measuring thumb web space.
METHODS AND SUBJECTS Subjects A mixed population of subjects was recruited from among the staff and patients at the Green Pastures Hospital (Table 1). Verbal informed consent was obtained. Twenty-two subjects had a (clinically) normal hand and 18 subjects had an impaired hand. Of the subjects with impaired hands, ten had combined ulnar and median paralysis of the hand without a contracted thumb web, five had combined ulnar and median paralysis of the hand with a contracted thumb web, two patients with combined ulnar and median paralysis of the hand had undergone January–March 2004
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release of the contracted web, and there was one subject with a history of ulnar collateral ligamentous strain of the thumb. Twenty-six of the subjects were male and 14 were female. The mean age was 43 years, the minimum age was 11 years, and the maximum age was 76 years. Individuals in whom passive stretching of the thumb web was contraindicated were excluded from the study. The sequence of the testing (tester and test) was done according to a randomized table. This study was approved by the Internal Review Board of the Green Pastures Hospital and the International Nepal Fellowship.
Assistant A helper from the physiotherapy department was chosen as the assistant, performing the passive stretching of the thumb web space. He was instructed in this maneuver and took special care not to distort the markings (see ‘‘Method’’) while opening the thumb web. He also wiped off the skin markings after each tester finished his measurements, before the second tester measured.
Methods of Measurement Intermetacarpal Distance
Instrumentation The methods for measuring the IMD and the DIMA used Wernier calipers (Hommel r INOX) to record the distances in millimeters (This device has not been subject to any reliability testing.). The conventional intermetacarpal angle8 used a DeVore goniometer (Hand Therapy Devices, DeVore, Tucson, AZ). This device has been shown to be a valid and reliable tool.14 Groth et al.14 in their study on the goniometry of the proximal and distal interphalangeal joints, stated that the interrater reliability achieved using the DeVore goniometer was 0.99 and 0.86 (ICC 2, 1), respectively, for the dorsal or lateral methods of placement of the goniometer. Using a method similar to that used by Groth et al.14 to check the validity of the DeVore goniometer, five random angles were drawn on a page with a protractor. These angles were then measured with the goniometer by the authors. All goniometer angles were found to be in agreement with the protractor-generated angles. The same two instruments were used by both testers to minimize instrument-related errors.
Testers Two therapists from the physiotherapy department were chosen as the testers. They measured the thumb web by each of the three methods. The testers were introduced to the study and were familiarized with the methods to be used in two orientation sessions one week before the study began. The testers were blinded to all measurements and assessed the patients in separate cubicles. The testers were not examined for their intrarater reliability; the interrater reliability alone was the focus of the study.
The tester used a skin-marking pen to mark the middorsal points of the first and second metacarpal heads. The assistant then passively stretched (palmar-abducted) the thumb web. The tester placed the two points of the calipers against the skin marks (Figure 1). Once the tester was satisfied with the positioning of the calipers, he handed the calipers to an independent recorder who noted the distance in centimeters to the nearest millimeter. This method of recording the IMD and the intermetacarpal angle is different from the way it will be done in the clinical setting, because then the tester himself or herself will record it. The need for the assistant, however, will persist in the examination of the thumb web in a paralyzed hand when the subject cannot actively abduct his or her thumb. Derived Intermetacarpal Angle In addition to the middorsal points, the radial styloid was marked with the wrist in a neutral position. The assistant then passively stretched the thumb web. The tester proceeded to place the points of the calipers against the middorsal points on the first metacarpal head and the styloid and, when satisfied with the placement, handed the calipers to the independent recorder who noted the distance. A similar reading was taken between the middorsal
Recorder One of the authors of the study (PMM) recorded all the measurements, because the testers were blinded to the measurements to prevent tester bias. 60
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FIGURE 1. Method of measuring the intermetacarpal distance.
variation attributable to tester). We have used a subjective rating scale system developed by Landis and Koch3 in which an ICC less than 0.40 indicates slight to fair reliability; 0.41–0.60, moderate reliability; 0.61– 0.80, substantial reliability; and 0.81–1.00, excellent reliability, to determine the reliability of the methods. The second method used was the Bland and Altman2 method of calculating 95% limits of agreement, which gives a range within which two measurements on the same patient could be expected to lie and is therefore useful for assessing the clinical importance of the intertester variation.
RESULTS FIGURE 2. Method of measuring the distance between the middorsal point of the second metacarpal and the radial styloid.
points of the second metacarpal and the radial styloid (Figure 2). These two readings and that of the IMD were used to draw a triangle, and the DIMA was calculated to the nearest degree. Conventional Intermetacarpal Angle The conventional method used was that described by Brand.8 The testers drew two lines (using a ruler) on the skin along the lateral sides of the first and second metacarpals and extended them proximally until they intersected, forming an angle. The assistant then passively stretched the thumb web. The tester placed the two arms of the goniometer along the lines marked. When satisfied with the placement, they asked the recorder to verify, and the recorder then noted the readings to the nearest degree (Figure 3).
Statistical Analysis The data for all three tests were analyzed by two methods to assess reliability of the measurements. The ICC (ICC 2,1)1 calculates the proportion of the variability in the data, which can be attributed to genuine between-subject variation and presents the outcome on a scale of reliability from 0 to 1 (1 = no
Reliability of the measurement was estimated using the ICC1 and Bland and Altman2 method of calculating 95% limits of agreement. Because the ICC is the ratio of the between-subject variation to the overall variation in the data, the variability in the hands chosen for the study has an impact on the reliability coefficient calculated. For this reason, the ICC is presented for the two subgroups of clinically normal and abnormal hands. Overall, the IMD method showed an ICC of 0.88 with 95% limits of agreement of ÿ6.9 to 5.6 mm (approximately66.2 mm). Similarly, for the DIMA method, the ICC was 0.47 with 95% limits of agreement of ÿ11.9 to 5.18 (approximately 68.58 ). Although both of these methods (IMD and DIMA) appear more reliable than the conventional method, which had an ICC of 0.26 and 95% limits of agreement of ÿ17.5 to 9.28 (approximately 613.38 ), the IMD method is recommended to assess severity of thumb web contractures and to evaluate the effect of interventions because it has the highest interrater reliability. The ICC of IMD increased to 0.92 in the normal hands with 95% limits of agreement of 64.8 mm, compared with an ICC of 0.81 and 95% limits of agreement of 67.3 mm in the impaired hands (Table 2).
DISCUSSION
FIGURE 3. Method of measuring the thumb web by the conventional method using a DeVore goniometer.
The thumb accounts for more than 40% of hand function.15 A thumb web contracture leaving the thumb adducted will severely impair hand function. A reliable method to measure the thumb web will allow a uniform and standardized technique of evaluating thumb web contracture. It will enable the clinician to grade severity of contracture and to evaluate the effect of intervention. For the measurement of the IMD, the ICC is consistently higher than 0.80, indicating that less than 20% of the observed variability is the result of intertester variability even when the mixed population of normal and abnormal hands is used. This ratio January–March 2004
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TABLE 2. Assessment of Reliability of the Three Methods 95% Limits of Agreement, All ICC Hands (Bland & ICC ICC (Impaired (All Data) (Normal Hands) Hands Only) Altman Method) IMD DIMA* CWA*
0.88 0.47 0.26
0.92 0.68 0.24
0.81 0.34 0.17
ÿ6.9–+5.6 mm ÿ11.9–+5.18 ÿ17.5–+9.28
Expected Range of Two Measurements, All Hands (Bland & Altman Method)
Mean Difference, All Hands (Bland & Altman Method)
66.2 mm 68.58 613.38
+0.7 mm ÿ3.48 ÿ4.18
ICC = intraclass correlation coefficient; IMD = intermetacarpal distance; DIMA = derived intermetacarpal angle; CWA = conventional web angle. *DIMA and CWA measured in degrees.
translates to 95% limits of agreement for the IMD method of 66.2 mm. This study did not document the exact factors contributing to the lower reliability of the conventional method and the DIMA when compared with the IMD method. However, the reliability of the IMD method could stem from the fact that marking the midpoint of the dorsal aspect of the first and second metacarpal heads is easier than marking the entire lateral lengths of the first and second metacarpal shafts, as required with the conventional method. The other reason for the lower reliability of the conventional method could be the distortion of the straight lines when the thumb is abducted, thus making placement of the goniometer and measuring the exact angle difficult. The skin markings of the middorsal points are also displaced during thumb abduction, but the displacement is far less and therefore contributes less to measurement errors. In the method of measuring the DIMA, the logic of using the radial styloid was that it was easier to locate by palpation than a point at the anatomic snuffbox. A relative angle is measured in both methods because neither corresponds with the true axis of abduction and opposition. The snuffbox is often more difficult to locate in a patient unable to actively extend his or her thumb (as in the intraoperative setting). Instead of drawing lines to join the points and have the same problem of warping, we decided to measure the distances between the two middorsal points and the radial styloid, and then draw the triangle. The DIMA was then measured from this triangle (the angle opposite the side representing the IMD). This seems to have made a difference in terms of increasing the reliability of the method over the conventional method, despite the fact that the intersection of the lines in the conventional intermetacarpal angle is closer to the carpometacarpal joint, although the gains in reliability are insufficient to make the test appropriate for routine use. The two new methods described in this study have the advantage of not being affected by the normalcy of the interphalangeal joint of the thumb or its length. They have the added advantage of allowing passive measurements of the thumb web space. The methods of measuring the intermetacarpal angle and IMD can 62
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also be used intraoperatively, which will allow the surgeon to measure the effect of the surgical release of the thumb web space. This has not been practiced with any of the methods described previously. In all three methods, we were able to identify a difference in the reliability of the methods when applied in the normal versus the impaired hands. We had assumed this, because it seems easier to measure normal hands. In the preferred method of measuring the IMD, the ICC increases to 0.92 in the normal hands with 95% limits of agreement of 64.8 mm compared with an ICC of 0.81 and 95% limits of agreement of 67.3 mm in the impaired hands. An interesting finding of this study is that in the clinically contracted thumb webs, the average angle (both the conventional and DIMA) was approximately 518 , which falls within the normal range of 40– 508 mentioned for the conventional intermetacarpal angle.8 This finding is also relevant in the context of Shrinivasan’s9 and Brand’s16 suggestion that an excessive release of intermetacarpal angles of greater than 50–558 should be avoided because it will functionally weaken the thumb. The mention of these angles is, however, not supported by any study of the normal range of thumb web. Our study suffered from several limitations. We did not compare the new methods with a gold standard measurement such as a radiograph of the hand with the thumb in full palmar abduction. It would be interesting to study how the IMD and DIMA correlate with radiography. This will also throw light on how basing the fulcrum of the angle at the styloid relates to the actual fulcrum at the carpometacarpal joint. We studied the dimensions of the thumb web with the thumb held passively; we need to test the reliability of the new methods in the active setting. The exact functional implication of the different measures obtained from the new methods was not studied. The exact reason for the greater reliability of the IMD method versus the conventional method and the DIMA was not studied. Although applicable to an intraoperative setting, the new methods need to be tested in such a setting for their reliability. It is recommended that a future study of these two methods will look into normal thumb web measurements, and then evaluate the functional implications
of the measurements and their sensitivity in detecting thumb web contracture. In this study of measuring the thumb web, the web was stretched by a second person. The test–retest reliability of the method of measuring the IMD also needs to be tested in a further study. A ‘‘handy’’ therapist could possibly stretch and measure without the help of an assistant. Reliability of this method needs to be determined. Normative age-related data from a large study population need to be established. Alternatively, in a clinical situation, one could use the thumb web distance/angle of the unaffected hand as a reference value.
CONCLUSION A study of reliability of measurements of the thumb web space has shown that measuring the IMD has an excellent interrater reliability of ICC more than 0.80 and a clinically useful test–retest range (difference \= approximately66.2 mm). The test has practical technical properties in that it can be performed intraoperatively and on hands with abnormal interphalangeal joints of the thumb and abnormal thumb length. A study to estimate the normal range for the measurement is recommended.
Acknowledgments This study was performed in the Physiotherapy Department of Green Pastures Hospital & Rehabilitation Centre, Pokhara, Nepal, with the approval of the International Nepal Fellowship. The assistance of Friedberg Herm, MD, the Superintendent of the Green Pastures Hospital, and the support of Man Bahadur (Technician, Physiotherapy Department, Green Pastures Hospital) are gratefully acknowledged. The authors also thank Atul Shah, MCh (Plastic
Surgery), for his guidance in the very early stages of this project.
REFERENCES 1. Streiner DL, Norman GR. ICC Health Measurement Scales. Oxford: Oxford University Press, 1984:104–27. 2. Bland PW, Altman D. Practical Statistics for Medical Research. London: Chapman Hall, 1991, p 396. 3. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics. 1977;33:159–74. 4. Bell C. The Hand—Its Mechanism and Vital Endowments as Evincing Design. London: William Pickering, 1833, p 107. 5. Howard LD. Contracture of the thumb web. J Bone Jt Surg [Am]. 1950;32:267–73. 6. Littler JW. Architectural principles of reconstructive hand surgery. Surg Clin North Am. 1951;31:463–76. 7. Sharpe C. Tissue cover for the thumb web. Arch Surg. 1972;104:21–5. 8. Brand PW. Deformity in leprosy. In:Chocrane RG (ed). Leprosy in Theory and Practice. (ed 2). Bristol UK: John Wright & Sons Ltd, 1964, pp 485–96. 9. Shrinivasan H. Reconstructive surgery in treatment of deformities of hand. In: Dharmendra (ed). Leprosy. Bombay: Kothari Medical Publishing House, 1978:567–617. 10. Schwanholt C, Stern P. Brief or new: measuring cone for thumb abduction/extension. Am J Occup Ther. 1984;38:263–4. 11. Bhattacharya S. Documentation of the first web space angle. J Hand Surg [Br]. 1989;14:298–300. 12. American Society of Hand Therapists. Clinical Assessment and Recommendations, (2nd ed). Chicago, IL: American Society of Hand Therapists, 1992, p 65. 13. Cambridge-Keeling CA. Range of motion measurement of the hand. In: Hunter JM, Mackin EJ, Callahan AD (eds). Rehabilitation of the Hand 4th ed. Philadelphia, PA: C V Mosby Co, 1995, pp 93–107. 14. Groth GN, VanDeven KM, Phillips EC, Ehretsman RL. Goniometry of the proximal and distal interphalangeal joints, part II: placement preferences, interrater reliability, and concurrent validity. J Hand Ther. 2001;14:23–9. 15. Winzeler S, Rosenstein BD. Occupational injury and illness of the thumb. Am Assoc Occup Health Nurs J. 1996;44: 487–492. 16. Brand PW. Tendon transfer reconstruction of radial, ulnar, median and combination paralysis: principles & techniques. In: McCarthy JG (ed). Plastic Surgery (vol. 8 part 2) Philadelphia, PA: WB Saunders Co, 1990, pp 49–59.
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J. Wim Brandsma, RPT, PhD Green Pastures Hospital and Rehabilitation Centre International Nepal Fellowship Pokhara, Nepal
A. M. Anderson, PhD RELEASE Project Office International Nepal Fellowship Pokhara, Nepal
ABSTRACT: Two new methods of thumb web space measurement, the intermetacarpal distance (IMD) and the derived intermetacarpal angle (DIMA), were proposed and compared with a conventional method for interrater reliability. Forty subjects (22 normal hands, 18 impaired hands) were measured. Reliability of the measurement was estimated using the intraclass correlation coefficient (ICC) and the Bland and Altman method of 95% limits of agreement. Overall, the IMD method showed an ICC of 0.88 with 95% limits of agreement of ÿ6.9 to 5.6 mm (approximately 6.2 mm). Similarly, for the DIMA method, the ICC was 0.47 with 95% limits of agreement of ÿ11.9 to 5.1 (approximately 8.5 ). The IMD method appears more reliable than the conventional method, which had an ICC of 0.26 and 95% limits of agreement of ÿ17.5 to 9.2 (aproximately 13.3 ). The IMD method is recommended as a reliable method of measuring the thumb web space. J HAND THER. 2004;17:58–63.
Khadka Gurung, RPT Yam Pun, PT Green Pastures Hospital and Rehabilitation Centre International Nepal Fellowship Pokhara, Nepal
In the Fourth Bridgewater Treatise,4 Sir Charles Bell wrote, ‘‘on the length, strength, free lateral motion and perfect mobility of the thumb, depends the power of the human hand.’’ Thumb web contracture is one of the most disabling structural impairments of the hand and is a common problem seen in hand trauma, burns, intrinsic paralysis, and Volkmann ischemic contracture. The structural complexity of the thumb web space does not lend itself easily to measurement; this is evident from the fact that there is not much peerreviewed and published research on this subject. Of the methods that have been described for measuring the thumb web space, none have been subject to any reliability studies. The need to have a standardized method for measuring the thumb web is paramount given its importance to thumb function. If such a method could be described, it would provide the hand therapist and hand surgeons a common platform to evaluate the management of thumb web contracture,
Correspondence and reprint requests to Prashant M. Murugkar, MCh, DNB, 63/4 B, Jai–Vijay Society, Sahar Road, Sahar, Mumbai, India 400099. E-mail:
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especially if this method could be used in the intraoperative period to measure the adequacy of release of the web contracture. This will help to assess the severity and the effect of intervention such as exercises, splinting, and surgery of thumb web contracture. The concept that the thumb placed in full palmar abduction represents the maximum spread of the thumb web space has been documented by several authors.5–7 With the thumb placed in this position, Brand8 measured the angle made at the intersection of two lines drawn on the skin overlying the palpable subcutaneous surfaces of the first and second metacarpals. He quoted the normal range of the web angle as being 40–508 . Shrinivasan9 used triangular pieces of wood with known angles (25–558 with a gradation of 58 ), these were placed into the thumb web and tested for a snug fit to derive the appropriate measurement of the web angle. Schwanholt and Stern10 used Dixie Yarn Cones inserted into the thumb web space in full palmar abduction to gauge the thumb web space. Bhattacharya11 described a method using dental compound molded into the web space. When the mold set, it was cut sagittally and smeared with ink, and measurements were taken from the ink impression.
The other concept that has been used to measure the thumb web space is to measure the distance between the plane of the palm and the tip of the thumb placed in full palmar abduction. This method has been used by the American Society of Hand Therapists,12 which describes a procedure for measuring thumb opposition using a ruler to measure the distance from the volar tip of the thumb to the third metacarpal. Cambridge-Keeling13 also recommends using the ruler and placing it between the distal palmar crease of the index finger to the pulp or interphalangeal crease of the thumb. This concept, however, relies on the normalcy of the interphalangeal joint of the thumb and of the length of the thumb, which could pose problems in the clinical setting. There is also very little standardization of these methods and no reliability data to support their use. In our method, the thumb was placed in full palmar abduction, the easily identifiable middorsal points on the subcutaneous surfaces of the first and second metacarpal heads were marked, and the separation between these (in millimeters) was measured to calculate the intermetacarpal distance (IMD). Then, using the tip of the radial styloid process as the third point, we measured the distances from it to the first and second metacarpal heads (middorsal points) and, incorporating the IMD measurement, drew a triangle and then measured the angle at the point representing the radial styloid to arrive at the derived intermetacarpal angle (DIMA). By using these easily identifiable surface markings of skeletal landmarks, we hoped to arrive at more reliable measures of the separation between the first and second metacarpals with the thumb in full palmar abduction. These two methods also lent themselves to being used intraoperatively, an advantage none of the earlier methods possessed. We decided to test these two methods for interrater reliability using the intraclass correlation coefficient (ICC)1 and the Bland and Altman2 methods. We also similarly tested the method described by Brand8 because it was already being used in the physiotherapy department. Using an assistant, we passively put the subject’s thumb into full palmar abduction before measuring the thumb web with the three methods. This was done to enable a comparison between a heterogeneous population of subjects with normal hand function and those with impaired hand function. The focus of this study was to find out which of these three methods had the highest interrater reliability when used in a mixed population of normal and impaired hands. If any of these three methods had an ICC of 0.81 through 1.00 or a perfect reliability rating on the subjective rating scale developed by Landis and Koch,3 it could be recommended as a reliable measure of the thumb web space. The purpose of this study was to examine the interrater
TABLE 1. Segregated Data of Age and Sex Distribution of Impaired and Normal Hands in the Study Age (years)
Gender
Impaired hands 30 60 76 70 68 72 30 70 48 55 58 74 45 45 40 28 30 50 Normal hands 38 45 52 40 42 22 50 39 16 11 45 39 61 33 17 16 30 39 23 40 40 40
Male Male Male Male Male Male Male Male Male Male Male Male Male Male Female Female Female Female Male Male Male Male Male Male Male Male Male Male Male Male Female Female Female Female Female Female Female Female Female Female
reliability of three methods of measuring thumb web space.
METHODS AND SUBJECTS Subjects A mixed population of subjects was recruited from among the staff and patients at the Green Pastures Hospital (Table 1). Verbal informed consent was obtained. Twenty-two subjects had a (clinically) normal hand and 18 subjects had an impaired hand. Of the subjects with impaired hands, ten had combined ulnar and median paralysis of the hand without a contracted thumb web, five had combined ulnar and median paralysis of the hand with a contracted thumb web, two patients with combined ulnar and median paralysis of the hand had undergone January–March 2004
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release of the contracted web, and there was one subject with a history of ulnar collateral ligamentous strain of the thumb. Twenty-six of the subjects were male and 14 were female. The mean age was 43 years, the minimum age was 11 years, and the maximum age was 76 years. Individuals in whom passive stretching of the thumb web was contraindicated were excluded from the study. The sequence of the testing (tester and test) was done according to a randomized table. This study was approved by the Internal Review Board of the Green Pastures Hospital and the International Nepal Fellowship.
Assistant A helper from the physiotherapy department was chosen as the assistant, performing the passive stretching of the thumb web space. He was instructed in this maneuver and took special care not to distort the markings (see ‘‘Method’’) while opening the thumb web. He also wiped off the skin markings after each tester finished his measurements, before the second tester measured.
Methods of Measurement Intermetacarpal Distance
Instrumentation The methods for measuring the IMD and the DIMA used Wernier calipers (Hommel r INOX) to record the distances in millimeters (This device has not been subject to any reliability testing.). The conventional intermetacarpal angle8 used a DeVore goniometer (Hand Therapy Devices, DeVore, Tucson, AZ). This device has been shown to be a valid and reliable tool.14 Groth et al.14 in their study on the goniometry of the proximal and distal interphalangeal joints, stated that the interrater reliability achieved using the DeVore goniometer was 0.99 and 0.86 (ICC 2, 1), respectively, for the dorsal or lateral methods of placement of the goniometer. Using a method similar to that used by Groth et al.14 to check the validity of the DeVore goniometer, five random angles were drawn on a page with a protractor. These angles were then measured with the goniometer by the authors. All goniometer angles were found to be in agreement with the protractor-generated angles. The same two instruments were used by both testers to minimize instrument-related errors.
Testers Two therapists from the physiotherapy department were chosen as the testers. They measured the thumb web by each of the three methods. The testers were introduced to the study and were familiarized with the methods to be used in two orientation sessions one week before the study began. The testers were blinded to all measurements and assessed the patients in separate cubicles. The testers were not examined for their intrarater reliability; the interrater reliability alone was the focus of the study.
The tester used a skin-marking pen to mark the middorsal points of the first and second metacarpal heads. The assistant then passively stretched (palmar-abducted) the thumb web. The tester placed the two points of the calipers against the skin marks (Figure 1). Once the tester was satisfied with the positioning of the calipers, he handed the calipers to an independent recorder who noted the distance in centimeters to the nearest millimeter. This method of recording the IMD and the intermetacarpal angle is different from the way it will be done in the clinical setting, because then the tester himself or herself will record it. The need for the assistant, however, will persist in the examination of the thumb web in a paralyzed hand when the subject cannot actively abduct his or her thumb. Derived Intermetacarpal Angle In addition to the middorsal points, the radial styloid was marked with the wrist in a neutral position. The assistant then passively stretched the thumb web. The tester proceeded to place the points of the calipers against the middorsal points on the first metacarpal head and the styloid and, when satisfied with the placement, handed the calipers to the independent recorder who noted the distance. A similar reading was taken between the middorsal
Recorder One of the authors of the study (PMM) recorded all the measurements, because the testers were blinded to the measurements to prevent tester bias. 60
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FIGURE 1. Method of measuring the intermetacarpal distance.
variation attributable to tester). We have used a subjective rating scale system developed by Landis and Koch3 in which an ICC less than 0.40 indicates slight to fair reliability; 0.41–0.60, moderate reliability; 0.61– 0.80, substantial reliability; and 0.81–1.00, excellent reliability, to determine the reliability of the methods. The second method used was the Bland and Altman2 method of calculating 95% limits of agreement, which gives a range within which two measurements on the same patient could be expected to lie and is therefore useful for assessing the clinical importance of the intertester variation.
RESULTS FIGURE 2. Method of measuring the distance between the middorsal point of the second metacarpal and the radial styloid.
points of the second metacarpal and the radial styloid (Figure 2). These two readings and that of the IMD were used to draw a triangle, and the DIMA was calculated to the nearest degree. Conventional Intermetacarpal Angle The conventional method used was that described by Brand.8 The testers drew two lines (using a ruler) on the skin along the lateral sides of the first and second metacarpals and extended them proximally until they intersected, forming an angle. The assistant then passively stretched the thumb web. The tester placed the two arms of the goniometer along the lines marked. When satisfied with the placement, they asked the recorder to verify, and the recorder then noted the readings to the nearest degree (Figure 3).
Statistical Analysis The data for all three tests were analyzed by two methods to assess reliability of the measurements. The ICC (ICC 2,1)1 calculates the proportion of the variability in the data, which can be attributed to genuine between-subject variation and presents the outcome on a scale of reliability from 0 to 1 (1 = no
Reliability of the measurement was estimated using the ICC1 and Bland and Altman2 method of calculating 95% limits of agreement. Because the ICC is the ratio of the between-subject variation to the overall variation in the data, the variability in the hands chosen for the study has an impact on the reliability coefficient calculated. For this reason, the ICC is presented for the two subgroups of clinically normal and abnormal hands. Overall, the IMD method showed an ICC of 0.88 with 95% limits of agreement of ÿ6.9 to 5.6 mm (approximately66.2 mm). Similarly, for the DIMA method, the ICC was 0.47 with 95% limits of agreement of ÿ11.9 to 5.18 (approximately 68.58 ). Although both of these methods (IMD and DIMA) appear more reliable than the conventional method, which had an ICC of 0.26 and 95% limits of agreement of ÿ17.5 to 9.28 (approximately 613.38 ), the IMD method is recommended to assess severity of thumb web contractures and to evaluate the effect of interventions because it has the highest interrater reliability. The ICC of IMD increased to 0.92 in the normal hands with 95% limits of agreement of 64.8 mm, compared with an ICC of 0.81 and 95% limits of agreement of 67.3 mm in the impaired hands (Table 2).
DISCUSSION
FIGURE 3. Method of measuring the thumb web by the conventional method using a DeVore goniometer.
The thumb accounts for more than 40% of hand function.15 A thumb web contracture leaving the thumb adducted will severely impair hand function. A reliable method to measure the thumb web will allow a uniform and standardized technique of evaluating thumb web contracture. It will enable the clinician to grade severity of contracture and to evaluate the effect of intervention. For the measurement of the IMD, the ICC is consistently higher than 0.80, indicating that less than 20% of the observed variability is the result of intertester variability even when the mixed population of normal and abnormal hands is used. This ratio January–March 2004
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TABLE 2. Assessment of Reliability of the Three Methods 95% Limits of Agreement, All ICC Hands (Bland & ICC ICC (Impaired (All Data) (Normal Hands) Hands Only) Altman Method) IMD DIMA* CWA*
0.88 0.47 0.26
0.92 0.68 0.24
0.81 0.34 0.17
ÿ6.9–+5.6 mm ÿ11.9–+5.18 ÿ17.5–+9.28
Expected Range of Two Measurements, All Hands (Bland & Altman Method)
Mean Difference, All Hands (Bland & Altman Method)
66.2 mm 68.58 613.38
+0.7 mm ÿ3.48 ÿ4.18
ICC = intraclass correlation coefficient; IMD = intermetacarpal distance; DIMA = derived intermetacarpal angle; CWA = conventional web angle. *DIMA and CWA measured in degrees.
translates to 95% limits of agreement for the IMD method of 66.2 mm. This study did not document the exact factors contributing to the lower reliability of the conventional method and the DIMA when compared with the IMD method. However, the reliability of the IMD method could stem from the fact that marking the midpoint of the dorsal aspect of the first and second metacarpal heads is easier than marking the entire lateral lengths of the first and second metacarpal shafts, as required with the conventional method. The other reason for the lower reliability of the conventional method could be the distortion of the straight lines when the thumb is abducted, thus making placement of the goniometer and measuring the exact angle difficult. The skin markings of the middorsal points are also displaced during thumb abduction, but the displacement is far less and therefore contributes less to measurement errors. In the method of measuring the DIMA, the logic of using the radial styloid was that it was easier to locate by palpation than a point at the anatomic snuffbox. A relative angle is measured in both methods because neither corresponds with the true axis of abduction and opposition. The snuffbox is often more difficult to locate in a patient unable to actively extend his or her thumb (as in the intraoperative setting). Instead of drawing lines to join the points and have the same problem of warping, we decided to measure the distances between the two middorsal points and the radial styloid, and then draw the triangle. The DIMA was then measured from this triangle (the angle opposite the side representing the IMD). This seems to have made a difference in terms of increasing the reliability of the method over the conventional method, despite the fact that the intersection of the lines in the conventional intermetacarpal angle is closer to the carpometacarpal joint, although the gains in reliability are insufficient to make the test appropriate for routine use. The two new methods described in this study have the advantage of not being affected by the normalcy of the interphalangeal joint of the thumb or its length. They have the added advantage of allowing passive measurements of the thumb web space. The methods of measuring the intermetacarpal angle and IMD can 62
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also be used intraoperatively, which will allow the surgeon to measure the effect of the surgical release of the thumb web space. This has not been practiced with any of the methods described previously. In all three methods, we were able to identify a difference in the reliability of the methods when applied in the normal versus the impaired hands. We had assumed this, because it seems easier to measure normal hands. In the preferred method of measuring the IMD, the ICC increases to 0.92 in the normal hands with 95% limits of agreement of 64.8 mm compared with an ICC of 0.81 and 95% limits of agreement of 67.3 mm in the impaired hands. An interesting finding of this study is that in the clinically contracted thumb webs, the average angle (both the conventional and DIMA) was approximately 518 , which falls within the normal range of 40– 508 mentioned for the conventional intermetacarpal angle.8 This finding is also relevant in the context of Shrinivasan’s9 and Brand’s16 suggestion that an excessive release of intermetacarpal angles of greater than 50–558 should be avoided because it will functionally weaken the thumb. The mention of these angles is, however, not supported by any study of the normal range of thumb web. Our study suffered from several limitations. We did not compare the new methods with a gold standard measurement such as a radiograph of the hand with the thumb in full palmar abduction. It would be interesting to study how the IMD and DIMA correlate with radiography. This will also throw light on how basing the fulcrum of the angle at the styloid relates to the actual fulcrum at the carpometacarpal joint. We studied the dimensions of the thumb web with the thumb held passively; we need to test the reliability of the new methods in the active setting. The exact functional implication of the different measures obtained from the new methods was not studied. The exact reason for the greater reliability of the IMD method versus the conventional method and the DIMA was not studied. Although applicable to an intraoperative setting, the new methods need to be tested in such a setting for their reliability. It is recommended that a future study of these two methods will look into normal thumb web measurements, and then evaluate the functional implications
of the measurements and their sensitivity in detecting thumb web contracture. In this study of measuring the thumb web, the web was stretched by a second person. The test–retest reliability of the method of measuring the IMD also needs to be tested in a further study. A ‘‘handy’’ therapist could possibly stretch and measure without the help of an assistant. Reliability of this method needs to be determined. Normative age-related data from a large study population need to be established. Alternatively, in a clinical situation, one could use the thumb web distance/angle of the unaffected hand as a reference value.
CONCLUSION A study of reliability of measurements of the thumb web space has shown that measuring the IMD has an excellent interrater reliability of ICC more than 0.80 and a clinically useful test–retest range (difference \= approximately66.2 mm). The test has practical technical properties in that it can be performed intraoperatively and on hands with abnormal interphalangeal joints of the thumb and abnormal thumb length. A study to estimate the normal range for the measurement is recommended.
Acknowledgments This study was performed in the Physiotherapy Department of Green Pastures Hospital & Rehabilitation Centre, Pokhara, Nepal, with the approval of the International Nepal Fellowship. The assistance of Friedberg Herm, MD, the Superintendent of the Green Pastures Hospital, and the support of Man Bahadur (Technician, Physiotherapy Department, Green Pastures Hospital) are gratefully acknowledged. The authors also thank Atul Shah, MCh (Plastic
Surgery), for his guidance in the very early stages of this project.
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