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Responsiveness of Two Methods for Measuring Foot and Ankle Volume Nicholas Henschke, Robert Anthony Boland and Roger David Adams Foot Ankle Int 2006 27: 826 DOI: 10.1177/107110070602701013 The online version of this article can be found at: http://fai.sagepub.com/content/27/10/826

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FOOT & ANKLE INTERNATIONAL Copyright  2006 by the American Orthopaedic Foot & Ankle Society, Inc.

Responsiveness of Two Methods for Measuring Foot and Ankle Volume Nicholas Henschke, BAppSc (Physio) Hons; Robert Anthony Boland, Ph.D.; Roger David Adams, Ph.D. Lidcombe, NSW Australia

ABSTRACT

Key Words: Ankle; Swelling; Tape; Volumetry

Background: Measurements of volume are taken in the clinical environment to determine the extent of swelling and to evaluate the effects of treatment interventions. In the research setting, volume measurements are taken to determine experimental outcomes. Water displacement and figure-of-eight methods are highly reliable for measuring foot and ankle volumes, but the responsiveness of the two methods has not been compared. This study was designed to investigate effects of manipulating hydrostatic and blood pressures on foot and ankle volume and responsiveness of the two methods to induced changes in foot and ankle volume. Methods: Intervention effects on volume were compared using water displacement and tape (figureof-eight) methods. Foot and ankle volume was measured in each of the 30 participants while they were supine, sitting, and sitting with a sphygmomanometer cuff inflated around the lower thigh to occlude blood flow into the leg. These variations allowed manipulation of the hydrostatic and blood pressures acting on the foot and ankle. Results: Data from the water displacement method showed that a significant increase in volume of 31 mL (p < 0.002) occurred with the cuff in place, but this was not detected using the figure-of-eight method. No significant difference (p > 0.136) between the sitting and supine positions was detected using either method. Conclusions: Limb dependency while sitting or lying had no effect on measures from either method, but volumetry had a higher responsiveness to changes induced by application of the cuff. This effect was interpreted as arterial leakage past the cuff. Clinical Relevance: The figure-of-eight tape method and the water displacement technique for measuring ankle and foot volume may not be interchangeable. Changes in volume of the ankle and foot are better measured by the water displacement technique, but for measurements of ankle volume alone, the tape method is appropriate. The responsiveness of the tape method to changes in volume is yet to be determined.

INTRODUCTION

Swelling presents as increased volume in or around a body segment and can be measured to provide information about the severity of an injury and the effects of therapy. Immobilization,1 surgery,8,14,18 or injury, such as ankle sprain, can all induce swelling,17,24 and the resulting fibrinous exudation and swelling of capillary endothelial cells can produce scar tissue that impedes rehabilitation.19 For these reasons, various forms of therapy are used to prevent or reduce swelling. Various methods have been described to measure foot and ankle swelling including water displacement (volumetry) and tape methods. Volumetry has been used as the criterion reference for other methods2,5,13 to evaluate treatment interventions17,23 and to evaluate new techniques.12 It provides a direct measure of volume, has high reliability,12,15,17 and can be used for segments with irregular shapes, such as the foot. The water displacement method, however, is time-consuming and not cost-effective in the clinical environment.13,17 A figure-of-eight method can be used instead to efficiently measure ankle swelling by wrapping a tape measure around the ankle twice in a figure-of-eight pattern across the subtalar and talar joints.10 The method is quick because landmarks and positioning of the ankle and foot are standardized. High inter-rater and intra-rater reliabilities have been observed,22 as well as high correlation with water displacement for measurements of ankle edema after lower-limb injury.15,17 While these data imply that the methods are interchangeable, the responsiveness of the methods has not been compared. Responsiveness indicates the extent to which a method can detect that a clinically important change has occurred within the variable of interest.16 Responsiveness to a change in volume of less than 1% has been detected for hand volumetry,5 but the responsiveness of the two methods in the foot and ankle is unclear. The purpose of this study was to compare the responsiveness of the water displacement and figure-of-eight methods under three different conditions that affected foot and ankle

Corresponding Author: Robert Anthony Boland, Ph.D. Faculty of Health Sciences, University of Sydney School of Physiotherapy P.O. Box 170 Lidcombe, NSW 1825 Australia E-mail: [email protected] For information on prices and availability of reprints, call 410-494-4994 X226

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Foot & Ankle International/Vol. 27, No. 10/October 2006

volumes by manipulating the magnitude of hydrostatic and blood pressures acting on the lower leg.

FOOT AND ANKLE VOLUME

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A

MATERIALS AND METHODS

The effects of three conditions on foot and ankle volume were compared using a repeated-measures design so that control data came from each subject. The sample size of 30 was required to give power of 0.80 to detect an effect size of half a standard deviation with a significance level of α = 0.05.9 The Human Ethics Committee of the University of Sydney approved the study, and informed consent was obtained from each participant before testing. Rights of participants were protected throughout the study.

B

Subjects

Participants responded to advertisements around the university campus. The inclusion criterion was that volunteers were healthy. Exclusion criteria were the presence of skin conditions or open wounds below the knee, peripheral neuropathies, cardiovascular instability, history of limb or digit amputation, and conditions that could cause fluid accumulation within the leg. Volunteers also were excluded if they took any medication that affected the cardiovascular system or fluid volume (e.g. steroids, calcium channel, or beta blockers). Fourteen men and sixteen women between 18 and 54 years of age (mean ± SD = 27.4 ± 11.58) participated. The mean height of participants was 169.85 ± 9.11 cm, with a mean weight of 65.7 ± 10.96 kg and mean thigh circumference of 44.77 ± 3.28 cm. Nineteen right and eleven left legs were tested. Mean blood pressure across subjects before testing was 119 ± 8/77 ± 8 mmHg, resulting in a mean sub-systolic inflation pressure of 115 (±9) mmHg.

C

Equipment Volumeter

A rectangular volumeter (Figure 1, A) made from Plexiglas with a capacity of 13.5 L was used. The floor of the tank was angled so that participants’ feet were in 7.5 degrees of plantarflexion during measurements. A spout on one side of the volumeter channeled overflow water into a purpose-built measuring cylinder. Measuring Cylinder

The measuring cylinder (Figure 1, B) was a PVC pipe (Vinidex Tubemakers Pty Ltd, Melbourne, Victoria) fixed vertically in a stand. A clear Plexiglas tube (Cadillac Plastics, Davenport, Iowa) was mounted vertically on the outside of the main cylinder and connected to it via a 90-degree PVC elbow pipe (James Hardie Plumbing and Pipelines Pty Ltd, Sydney, NSW). This arrangement created an open ended manometer when the apparatus was filled with water, since atmospheric pressure maintained water levels at equal heights within the pipe and tube. Two adjustable clamps around the

Fig. 1: A, Water displacement apparatus with obturator. Note the foot resting on the angled base and the heel against the back of the volumeter. B, Vernier calipers used to measure distance on the Plexiglas manometer between the upper border of the lower clamp (level 1), and the lower border of the upper clamp (level 2). C, Figure-of-eight method viewed from medial side.

Plexiglas tube could be moved to mark the level of water in the measuring cylinder before and after interventions. Volume could then be determined by using vernier calipers to measure the distance between the clamps, and then applying simple volume equations based on the dimensions of the two cylinders.


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Obturator

A

An obturator was used to reduce the effects of turbulence during measurements and thereby reduce drainage time.12 The obturator was a plastic container supported in the volumeter by two pieces of wood fixed externally on opposite sides (Figure 1, A). A 0.5-kg weight was placed inside the obturator to counteract buoyancy and to ensure stability during measurements. Sphygmomanometer Cuff

B

A thigh cuff 180 mm wide and 480 mm long was connected to an aneroid pressure gauge inflatable to a maximal pressure of 300 mmHg (Alp K2 Sphygmomanometer, Japan). The apparatus was calibrated before commencing the study.21 C

Experimental Protocol

Data about the mid-thigh circumference and blood pressure were collected from each participant before testing to enable calculation of the required pressure for the thigh cuff.11 To achieve an adequate occlusion pressure (Pocc ), the variables of limb circumference, cuff width, and both systolic (Psys ) and diastolic (Pdia ) blood pressures are applied as follows: Pocc = (Psys − Pdia ) × limb circumference + Pdia 3 × cuff width This relationship predicts that the occlusion pressure (Pocc ) will be sub-systolic for a normotensive patient when the cuff width to limb circumference ratio is greater than 0.3:1.11 The experimental limb was selected by coin toss, and bony landmarks were marked with a permanent pen on the ankle and foot before testing for the figure-of-eight method.10 Before testing began and between testing in each condition, subjects rested supine for 20 minutes to establish homeostasis for both blood pressure and distribution of blood volume.21 The three postural conditions that manipulated hydrostatic pressure acting on the foot and ankle were: 1. Sitting with the lower leg vertical and no cuff around the thigh (Figure 2, A) 2. Supine with the lower leg vertical over the bed-end and no cuff around the thigh (Figure 2, B) 3. Sitting with a cuff inflated around the lower thigh and the lower leg vertical (Figure 2, C). These conditions were applied in random order. The examiner made two measurements under each condition, first with the volumetric method and then with the figure-of-eight method. This was because the tape measurements took less than 30 seconds, compared to between 5 and 6 minutes for the volumetric method.12 Thus, any serial effects of the tape method on the volumetric measurements should have been minimal.

Fig. 2: Conditions of testing with subject seated and no cuff around thigh (A), lying and no cuff around thigh (B), seated and cuff around thigh (C).

Method for Volumetry Measurements

The obturator was placed in the volumeter. The measuring cylinder was placed underneath the overflow spout, and the volumeter was filled to the level of the overflow spout with water that had been warmed to 32◦ C (±1 degree).5 Water temperature was controlled for patient comfort, and because upper limb measurements taken at 32◦ C were shown to have high within-session reliability.5 Water was then poured into the measuring cylinder until the meniscus became visible at the bottom of the manometer tube. When water had finished dripping from the volumeter, the lower clamp was set to level 1 to zero the instrument, the obturator was temporarily removed, and the participant lowered his or her foot and ankle into the volumeter. The obturator was replaced, and displaced water overflowed and collected in the measuring cylinder (Figure 1, A). When water had finished dripping from the spout, the limb was withdrawn and the upper clamp on the measuring cylinder was set to level 2. The examiner then measured and recorded the distance between levels 1 and 2 using the vernier calipers (Figure 1, B). This distance was recorded in millimeters; however, the conversion factor for millimeters to milliliters was known to be: 1 mm of vertical displacement = 8.78 mL of volume.12 Thus, by multiplying the measured distance by 8.78, foot and ankle volume could be expressed in milliliters.5


Foot & Ankle International/Vol. 27, No. 10/October 2006 Figure-of-Eight Method

The examiner wrapped the tape around the ankle according to a standardized protocol (Figure 1, C), using the premarked landmarks:10 the tuberosity of the navicular, the base of the fifth metatarsal, the tip of the medial malleolus, the tip of the lateral malleolus, and the anterior tibial tendon. The protocol was as follows: The beginning of the tape was placed midway between the anterior tibial tendon and the tip of the lateral malleolus. The tape was drawn medially across the instep and inferior to the tuberosity of the navicular. The tape was drawn across under the medial longitudinal arch and laterally to just proximal to the base of the fifth metatarsal. The tape was continued around the ankle to the distal tip of the medial malleolus and pulled across the Achilles tendon and towards the tip of the lateral malleolus. The tape was taken back to the starting position. Reliability

Intra-rater reliability for the two methods was determined before testing. A blinded observer repeatedly measured plastic bottles containing different amounts of water with the volumeter, and the ankles of normal asymptomatic subjects were measured twice in random order by the figure-of eight method. The intraclass correlation coefficient (ICC) using the (2,1) form was calculated for each method.20 Reliability of 0.99 (p < 0.001) was observed for volumetric measurements,12 and a value of 0.99 (p < 0.001) also was observed for the tape method. Analyses

Using SPSS for Windows, version 12.01, a planned contrasts analysis within a fully repeated-measures ANOVA was performed for each of the volumetric and figure-ofeight data sets to compare the effects associated with the three experimental conditions.25 Pearson’s product moment correlation coefficient was used to evaluate the relationship between the two methods in each of the three positions. Z-scores were used to compare the relative sensitivity of the two methods, which assessed volume change in different units. All volumetric data were pooled to obtain a grand mean and standard deviation, and this was repeated for figure-ofeight data. The condition means for each method could then be represented as Z scores or deviations from the grand mean in standard deviation units.


Table 1: Observed volumes for each condition using water displacement method

Condition

Mean volume (mL)

Standard deviation (mL)

Supine Sitting Cuff in sitting

1040.81 1038.16 1069.32

±169.46 ±162.27 ±165.32

∗ Significant

at p < 0.003.

in volume. The range was from 703.72 mL to 1465.38 mL. Volumetric data for each condition are displayed in Table 1. There was no significant difference (F1,29 = 0.107, p = 0.746) between measurements taken in the sitting position compared to measurements taken in the supine position. The mean volume when the sphygmomanometer cuff was wrapped around the lower thigh was significantly greater by 25 mL than the mean volume obtained in the supine condition (F1,29 = 10.63, p < 0.003) and by 31 mL than the volume obtained in the sitting condition (F1,29 = 12.503, p < 0.002). Data for Figure-of-eight Method

From 90 measurements of ankle and foot circumference the mean was 521 (±31) mm, with a range from 455 to 585 mm. Results for circumference measures taken with the figure-of-eight method are shown in Table 2. There was no significant difference (F1,29 = 1.647, p = 0.209) in circumferences taken in the supine and sitting positions. The mean circumference for the cuff condition was not significantly different from either the sitting position (F1,29 = 2.352, p = 0.136) or the supine position (F1,29 = 0.011, p = 0.209). Correlations

A Pearson’s coefficient of r = 0.931 (p < 0.001) was obtained when volumetric and figure-of-eight data from the sitting position were inter-correlated. A correlation between the two methods of r = 0.921 (p < 0.001) was obtained for Table 2: Observed circumference for each condition using figure-of-eight method

RESULTS

Condition

Data for Volumetric Method

Drainage time for all volume measurements averaged 3 mins 11 sec (±38 sec). The mean of the 90 measurements of ankle and foot volume was 119.53 (±18.83) mm of displaced water, which equated to 1049.21 (±165.33) mL

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Supine Sitting Cuff in sitting


Circumference (mm)

Standard Deviation (mm)

522 520 522

±31 ±31 ±31

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0.15

0.1

Z Score

0.05

0

-0.05

-0.1

-0.15 Sitting

Lying

Cuff

Condition of Testing Legend Water displacement method Figure-of-eight method Fig. 3: Changes detected for each condition according to measurement method expressed as Z scores (with standard errors).

the supine condition, and a value of r = 0.943 (p < 0.001) was obtained for the cuff condition. Responsiveness

Data for sensitivity to change for each method are shown in Figure 3, where standardized deviation units for change allow comparison between methods. Data for the cuff condition obtained by the volumetric method indicated that segment volume was significantly greater than the grand mean by >0.1 of a standard deviation. In comparison, the tape method indicated that circumference was unchanged for the same condition. For the supine and sitting conditions, volume and circumference were unchanged, respectively. DISCUSSION

From our observations that no increase in volume was associated with the sitting and lying conditions without the cuff, we concluded that hydrostatic effects during these conditions were too brief to influence lower leg volume. However, one potentially significant weakness of our study was that we hypothesized that the greatest change in volume would occur during the sitting condition when hydrostatic and blood pressure effects were least, and the smallest change would occur when the occlusive cuff was inflated around the thigh. In fact, our data indicated that the greatest change occurred under the cuff condition. The volumetric method detected these changes, but the tape method did not. Therefore, the issue to resolve before considering the

responsiveness of each method is the source of the observed increase under the cuff condition. Comparisons with data from recent studies in the upper limb indicate that the observed volume increase resulted from insufficient pressure in the thigh cuff to occlude arterial flow. This would imply that the formula used to calculate occlusion pressure11 did not predict a sufficiently high pressure. Previous research indicated that low cuff pressures occluded blood flow if a wide cuff was used.11 Those authors measured flow using Doppler ultrasound when they determined the relationship between limb girth, blood pressure, and cuff pressure. Our observations with volumetry, however, were that segment volumes increased despite applying a sub-systolic pressure predicted to occlude flow. This paradoxical result can be explained by referring to other data derived from sub-systolic occlusive pressures. In a series of studies using a high pressure of 220 mmHg with a narrow cuff to occlude flow into and from the arm,3,6,7 sub-diastolic cuff pressures were found to induce volume increases within the forearm and hand segment.4,7 The proposed mechanism was that volume increased at sub-diastolic cuff pressures because venous flow was significantly occluded but leakage occurred past the cuff with each arterial pulse at higher cuff pressures. This interpretation was supported by data that showed volume increases were progressively larger as cuff pressures were raised (and therefore progressively occluded venous leakage) over repeated testing at 30 mmHg below, 15 mmHg below, and then 5 mmHg above diastolic pressure.7 Our data were consistent with this effect using the same



measuring process and a lower limb volumeter demonstrated to have high reliability.12 It is likely, therefore, that the discrepancy between the effects of cuff occlusion in this study and the earlier study11 is caused by a higher sensitivity of volumetry to changes in volume than Doppler ultrasound. The figure-of-eight method is used because it is quick, reliable, and has good correlation with volumetric measures in patients with ankle sprains.15 In this study however, the criterion reference volumetric method and the tape method yielded conflicting data for the cuff condition, despite high correlation between methods. Two factors might account for this. The tape method may not be as responsive as the water displacement method, or methods may not be interchangeable and reflect different features of the foot and ankle segment. The order of testing introduced a bias that should have favored the responsiveness of the tape method because it always was the second of the testing procedures. Thus, there always was up to 30 seconds longer for volume to accumulate in the foot and ankle before tape measurements were completed. Our data, however, showed that only the volumetric method detected the increase in foot and ankle volume after application of the cuff. This could be interpreted as evidence for the superior sensitivity of the volumetric method in detecting volume change. However, our data may reflect instead that the two methods measure different phenomena. While the volumetric method detected leakage past the inflated cuff, the extra volume might have accumulated in the large capacity vessels of the lower limb but had not yet reached the ankle. It is possible then that while fluid had accumulated in the shank, it had not yet accumulated within the ankle joint capsule or surrounding extra-cellular tissues during the 3 to 4 minutes of cuff occlusion. If this were the case, then data from the tape method could, in fact, be accurate and reflect stable ankle and heel volumes, and the volumetric method only detected large vessel changes elsewhere, probably in the lower calf. If so, the observed high correlation between the tape and volumetric methods is misleading. Certainly, the Z-scores highlight this possibility, and it is difficult to argue from those data that the two methods are interchangeable. Further research should investigate whether the responsiveness of the two methods would be more similar if tape measurements were compared with foot volumes immersed to the level of the malleoli. In the meantime, a clinician or researcher should define the area of interest and probably should refer to changes in foot and ankle segment volume during water displacement measurements and changes in ankle and heel volume during tape measurements. Finally, our data and the demonstrated responsiveness of the water displacement method in the upper and lower limb raise the issue of whether the method of Graham et al.11 was sensitive enough to detect leakage under the cuff. We applied their formula to predict occlusive pressures but instead detected leakage using instrumentation that has demonstrated


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responsiveness and accuracy for this task. While Doppler ultrasound may detect movement of red blood cells, it is possible that it may not be sensitive enough to detect bulk flow of associated blood constituents such as plasma. It is unlikely that the observed volume changes were random, since the volumetric method has demonstrated reliability, accuracy, and sensitivity across a range of volumes.5 In summary, the figure-of-eight method is quicker to use than volumetry, but the methods may not be interchangeable. The figure-of-eight method may be the method of choice for measuring volume changes around the foot and ankle, but the responsiveness of this method needs to be evaluated further. It might not detect small changes in volume that are clinically significant. In contrast, the volumetric method is responsive to small volume changes, but these could include changes within the foot and lower leg. REFERENCES 1. Airaksinen, O; Partanen, K; Kolari, PJ; Soimakallio, S: Intermittent pneumatic compression therapy in posttraumatic lower limb edema: computed tomography and clinical measurements. Arch. Phys. Med. Rehabil. 72:667 – 670, 1991. 2. Bednarczyk, JH; Hershler, C; Cooper, DG: Development and clinical evaluation of a computerized limb volume measurement system (CLEMS). Arch. Phys. Med. Rehabil. 73:60 – 63, 1992. 3. Boland, R; Adams, R: Acute angles of head-up tilt do not affect forearm and hand volume. Aust. J. Physiother. 46:123 – 131, 2000. 4. Boland, R; Adams, R: Vascular factors in carpal tunnel syndrome. J. Hand Ther. 15:22 – 30, 2002. 5. Boland, RA; Adams, RD: Development and evaluation of a precision forearm and hand volumeter and measuring cylinder. J. Hand Ther. 9:349 – 358, 1996. 6. Boland, RA; Adams, RD: The effects of arm elevation and overnight head up tilt on forearm and hand volume. J. Hand Ther. 11:180 – 190, 1998. 7. Boland, RA; Adams, RD: Sphygmomanometer-induced increases in forearm and hand volume. J. Hand Ther. 12:275 – 283, 1999. 8. Christie, AD; Willoughby, GL: The effect of interferential therapy on swelling following open reduction and internal fixation of ankle fractures. Physiother. Theory Pract. 6:3 – 7, 1990. 9. Cohen, J: Introduction to power analyses. In: Welkowitz, J; Ewen, RB; Cohen, J (eds.). Introductory statistics for the behavioral sciences. 5th edition. Harcourt Brace College Publishers, Fort Worth, pp. 204222, 2000. 10. Esterson, P: Measurement of ankle joint swelling using a figure of eight. J. Orthop. Sports Phys. Ther. 1:51 – 52, 1979. 11. Graham, B; Breault, MJ; McEwen, JA; McGraw, RW: Occlusion of arterial flow in the extremities at subsystolic pressures through the use of wide tourniquet cuffs. Clin. Orthop. 286:257 – 261, 1993. 12. Henschke, N; Boland, RA; Adams, RD: An obturator reduces time for volumetric measurements of the foot and ankle. J. Orthop. Sports Phys. Ther. 34:800 – 804, 2004. 13. Kaulesar Sukul, DM; den Hoed, PT; Johannes, EJ; van Dolder, R; Benda, E: Direct and indirect methods for the quantification of leg volume: comparison between water displacement volumetry, the disk model method and the frustum sign model method, using the correlation coefficient and the limits of agreement. J. Biomed. Eng. 15:477 – 480, 1993. 14. Liehr, P; Todd, B; Rossi, M; Culligan, M: Effect of venous support on edema and leg pain in patients after coronary artery bypass graft surgery. Heart Lung 21:6 – 11, 1992.


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15. Mawdsley, RH; Hoy, DK; Erwin, PM: Criterion-related validity of the figure-of-eight method of measuring ankle edema. J. Orthop. Sports Phys. Ther. 30:149 – 153, 2000. 16. Peat, J: Health science research. A handbook of quantitative methods. Allen and Unwin, Sydney, 2001. 17. Petersen, EJ; Irish, SM; Lyons, CL; et al.: Reliability of water volumetry and the figure of eight method on subjects with ankle joint swelling. J. Orthop. Sports Phys. Ther. 29:609 – 615, 1999. 18. Ross, M; Worrell, TW: Thigh and calf girth following knee injury and surgery. J. Orthop. Sports Phys. Ther. 27:9 – 15, 1998. 19. Safran, MR; Benedetti, RS; Bartolozzi, AR, 3rd ; Mandelbaum, BR: Lateral ankle sprains: a comprehensive review: part 1: etiology, pathoanatomy, histopathogenesis, and diagnosis. Med. Sc. Sport Exerc. 31:S429-437, 1999. 20. Shrout, P; Fleiss, J: Intraclass correlations: Uses in assessing rater reliability. Psych. Bull. 86:420 – 428, 1979.

21. Sixth report of the Joint National Committee on prevention, detection, evaluation, and treatment of high blood pressure. Arch. Intern. Med. 157:2413 – 2446, 1997. 22. Tatro-Adams, D; McGann, SF; Carbone, W: Reliability of the figureof-eight method of ankle measurement. J. Orthop. Sports Phys. Ther. 22:161 – 163, 1995. 23. Thordarson, DB; Ghalambor, N; Perlman, M: Intermittent pneumatic pedal compression and edema resolution after acute ankle fracture: a prospective, randomized study. Foot Ankle Int. 18:347 – 350, 1997. 24. van Dijk, C; Mol, B; Lim, L; Marti, R; Bossuyt, P: Diagnosis of ligament rupture of the ankle joint: physical examination, arthrography, stress radiography and sonography compared in 160 patients after inversion trauma. Acta Orthop. Scand. 67:566 – 570, 1996. 25. Winer, B: Statistical principles in experimental design. 2nd ed., McGraw-Hill, New York, 1971.
