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Research Reports |
DS Williams, PT, PhD, is Assistant Professor, Department of Physical Therapy, East Carolina University, Greenville, NC 27858-4353 (USA) (blaise{at}udel.edu)
IS McClay, PT, PhD, is Director of Research, Joyner Sportsmedicine Institute, Harrisburg, Pa, and Associate Professor, Department of Physical Therapy, University of Delaware
Submitted December 16, 1999;
Accepted May 10, 2000
| Abstract |
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Key Words: Arch Clinical measurement Foot Reliability Validity
| Introduction |
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In a study of runners with plantar fasciitis, Warren and Jones6 used a discriminant analysis and found that several measurements, including arch height during normal standing and lower-extremity length, were able to correctly predict inclusion in a group of runners without plantar fasciitis 76.1% of the time but were able to predict inclusion in the injured group only 15.6% of the time. James et al7 found that no structural characteristic, including pronated and supinated feet, could be used to predict a specific injury. In contrast, Giladi et al8 demonstrated that subjects with low arches were less likely than subjects with normal or high arches to develop stress fractures in the lower extremity. Some of the controversy in the literature may be due to the many different ways of measuring the medial longitudinal arch. Additionally, researchers often use absolute medial longitudinal arch measures rather than measures scaled to the individual's foot length, for example. Normalizing medial longitudinal arch height to foot length or some other lower-extremity anthropometric measure may result in better classifications of foot types.
There are a number of methods of measuring the medial longitudinal arch.814 Although most of these methods attempt to quantify the arch, some methods are based on observation. Giladi et al8 classified the nonweight-bearing foot as either high-arched or low-arched by a visual assessment alone. Even among experienced clinicians, however, visual categorization of the arch is highly inconsistent.15 Although Dahle et al11 attempted to define classification criteria, the determination of the foot in 50% of weight bearing as pronated or supinated was still based on observation.
Some researchers have incorporated the use of radio-graphs9,13 or photographs10 to classify the medial longitudinal arches of their subjects. Hawes et al12 measured the highest point of the soft tissue along the medial longitudinal arch in full weight bearing. Although this measurement, as well as footprint measurements,16,17 can be easily obtained, we do not believe that these measurements necessarily represent the state of the bony architecture of the foot. The soft tissue on the plantar surface of the foot is thick and variable and can mask the true bony architecture of the foot.
Saltzman et al14 correlated measurements taken at 50% of weight bearing with measurements obtained from radiographs to determine their validity. Intraclass correlation coefficients (ICCs) were used to assess reliability on 45 subjects. Intrarater reliability values were established for talar height (ICC=.90), navicular height (ICC=.92), and arch height (ICC=.91). All 3 values were normalized to footprint length. The authors concluded that the measurements correlated well with the measurements obtained from radiographs, with Pearson correlation coefficients ranging from .51 to .86. Measurements obtained from radiographs of talar height/foot length, calcaneus to first metatarsal angle, and calcaneal inclination were compared with measurements of navicular height/footprint length, arch height/footprint length, and talar height/footprint length. The measurements obtained from radiographs were different from the clinical measurements. Therefore, we do not believe that these measurements had concurrent validity. Dividing navicular height by foot length is important because the height of the navicular may not give an accurate representation of the arch. For example, a 5-cm navicular height on a size 12 foot would be related to a very different arch structure than the same measurement on a size 6 foot.
Although some of these measures (navicular height, talar height, foot length) have been shown to have some reliability or validity, they have not been compared with one another in order to determine which measure is the most useful. Additionally, measurements taken during partial weight bearing and full weight bearing have not been compared. We contend that a foot with an arch ratio that does not change much from 10% of weight bearing to 90% of weight bearing might be considered rigid or without much mobility, whereas a foot with a large change might be considered flexible or more mobile. Establishing reliability in both weight-bearing and nonweight-bearing conditions allows for measurements that can be taken under both conditions and, therefore, may be used to describe foot mobility. A measure that has been proposed for assessing foot mobility uses both weight-bearing and nonweight-bearing conditions.18 Both foot structure and foot mobility may play an important role in predicting injuries. Therefore, the purpose of our study was to compare the reliability and validity of several measurements of the medial longitudinal arch in both 10% and 90% of weight bearing. These reliability and validity measures will provide a rationale for choosing a measure to quantify the arches of individuals with high arches and low arches.
| Method |
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All measurements were taken based on our use of bony landmarks. These measurements were (1) navicular height, (2) height of the dorsum of the foot at 50% of foot length, (3) angle of the first ray, (4) navicular height divided by foot length, (5) navicular height divided by truncated foot length, (6) dorsum height divided by foot length, and (7) dorsum height divided by truncated foot length. The measurement of foot length can be skewed by foot deformities such as hallux valgus and claw toes. Claw toes are sometimes found in individuals with high arches, whereas hallux valgus is often found in individuals with low arches. These deformities have less of an impact on the measurement of truncated foot length. The angle of the first ray was measured between the floor and the long axis of the first metatarsal using a goniometer with a resolution of 2 degrees. Navicular height was measured from the floor to the most anterior-inferior portion of the navicular. Dorsum height was measured from the floor to the top of the foot at 50% of foot length. Foot length was measured from the most posterior portion of the calcaneus to the end of the longest toe. Truncated foot length was measured from the most posterior portion of the calcaneus to the center of the first metatarsophalangeal joint (Fig. 1). Lengths were measured with calipers with a resolution of 1 mm. Dorsum height was established with the same calipers mounted on a Plexiglas* plate (Fig. 2). Finally, arch mobility was assessed using an equation for calculating relative arch deformity (RAD) modified from that described by Nigg et al18:
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In the reliability portion of the study, 2 physical therapists with different levels of experience (3 and 20 years) took 3 blinded measurements of each variable in each weight-bearing condition. Both testers were experienced in taking foot and ankle measurements daily. The specific measures used in this study were practiced together by both testers on approximately 10 subjects before collecting data. For repeated measures, transparent tape was placed over the skin with the bony landmark underneath. A mark was placed on the tape at the level of the bony landmark, the measurement was taken, the tape was removed, and the process was repeated. The process was then repeated for each subsequent measure.
To establish concurrent validity, lateral radiographs were taken of the right foot of each subject in 10% and 90% of weight bearing. The subject stood with the right foot on the scale and the lateral border of the foot against the radiographic film cassette. The source-to-image ratio was held consistent between subjects at 101.6 cm (40 in), and intensities were set at 30 mA and 72 kV peak. The left lower extremity was placed on a step in front of the subject with the knee at an angle that was comfortable to the subject. A Bell-Thompson ruler was also placed against the cassette in an attempt to ensure appropriate scaling during measurement from the films. The same measurement techniques described earlier were used. Essentially, we used the measurements obtained from the radiographs and expected all other measurements to agree with those measurements if validity was present.
Validity was established using the measurements taken by tester 1 compared with measurements of the same bony landmarks taken from the radiograph. Tester 1 was the less experienced therapist, and we used this tester's data because we expected that ICC values may be lower for a less experienced therapist.
| Results |
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| Discussion |
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=0.17, SD=0.02) is more consistent with our value (
=0.164, SD=0.025), which suggests that their absolute value for foot length would be higher. These higher values might suggest a sampling of individuals with larger feet in the study by Cowan et al. In addition, the mean relative arch deformation value in our study was consistent with relative arch deformation values reported previously.18 Within-tester reliability values were excellent, in our opinion, for all measurements taken (ICC=.804.995) (Tab. 3), based on the values recognized by Landis and Koch.22 Other researchers2326 who have assessed within-tester reliability for various foot measures have found varying results. The results of our study show generally higher ICC values for intratester reliability than for intertester reliability. This finding may be due to our testers' wide range of experience (3 years versus 20 years) and previous practice in taking the measurements. Between-tester reliability showed mixed results across the 2 weight-bearing conditions. Reliability dropped considerably from the 10% of weight bearing condition for navicular height (from ICC=.924 to ICC=.608), navicular height divided by foot length (from ICC=.924 to ICC=.565), and for navicular height divided by truncated foot length (from ICC=.909 to ICC=.563). Both testers found palpation of the navicular head to be more difficult in 90% of weight bearing than in 10% of weight bearing. This finding may have occurred because the soft tissue on the medial border of the arch becomes taut in 90% of weight bearing. Although the testers were consistent within themselves, each tester may have been palpating a slightly different landmark in the 90% of weight bearing condition. Tester 2 showed consistently higher values for navicular height, suggesting that perhaps the posterior portion of the navicular was being measured rather than the anterior portion.
The ICC values for first ray angle were consistently low across both weight-bearing conditions. We believe that this finding is most likely due to the difficulty in taking this measurement, which required alignment of the goniometer along the floor and the long axis of the first metatarsal in the sagittal plane. Although there is little soft tissue overlying this bone, the extensor tendons overlying the bone, in our opinion, may have influenced the visualization of the long axis of the first metatarsal itself. No consistent offset was found between testers 1 and 2.
Although higher values for intertester reliability have been reported when measurements were taken in a weight-bearing condition,27 the results of our study suggest that this may not be true for the measure of navicular height. Other researchers11,14 used a 50% of weight bearing condition (with weight evenly distributed on both feet), which may make palpation of the navicular easier. Reliability of measurements is important, in our opinion, because we believe that measurements obtained in 10% and 90% of weight bearing are needed to assess mobility of the arch.
We examined concurrent validity by using a measure of the same thing as was measured on the radiographs. All ICC (2,k) values were
.704 (Tab. 5). The normalized measurements (measurements 47) had high ICCs, with associated low standard errors of measurement (Tab. 2), which, in our view, adds to evidence for validity.28 Normalizing these foot measurements appears to decrease the variability in arch height that is attributed to foot size. The absolute height of the navicular or the dorsum may not accurately reflect the structure of the arch. For example, when using a criterion of 1.5 standard deviations above the mean, 7 arches were classified as high based on measurements of dorsum height divided by truncated foot length. Although 6 arches were classified as high based on measurements of dorsum height, only 2 of these arches were classified as high based on the normalized measurements.
| Summary and Conclusions |
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| Footnotes |
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This work was previously presented at the Combined Sections Meeting of the American Physical Therapy Association; February 37, 1999; Seattle, Wash.
This study was approved by the Institutional Review Board at the University of Delaware.
* Rohm & Haas Co, Independence Mall W, Philadelphia, PA 19105 ![]()
| References |
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