Elsevier

The Foot

Volume 18, Issue 4, December 2008, Pages 220-227
The Foot

Effect of using truncated versus total foot length to calculate the arch height ratio

https://doi.org/10.1016/j.foot.2008.06.002Get rights and content

Abstract

Objective

The purpose of this study was to determine the arch height ratio in a large cohort of subjects as well as to assess the reliability and validity of the foot measurements utilized in the study.

Method

Eight hundred and fifty subjects, 393 women and 457 men, consented to participate in the study. The dorsal arch height, total foot length, and the truncated foot length were used to calculate two variations of the arch height ratio. In addition to determining within- and between-rater measurement reliability, radiographs were used to establish validity.

Results

The truncated arch height ratio can be estimated using the total foot length, unless toe deformities are present in the individual being assessed. All foot measurements had high levels of intra- and inter-rater reliability and the validity of measuring the dorsal arch height while standing with equal weight on both feet was established.

Conclusions

This investigation provides normative values from a large cohort of healthy female and male subjects for two variations of the arch height ratio. The arch height ratio is a reliable and valid measurement that may prove useful to clinicians and researchers for the classification of foot posture.

Introduction

The clinical diagnosis of foot disorders is often linked to abnormal foot posture. The assessment of static foot posture requires the use of a simple and minimally invasive technique that can easily be performed in the clinical setting with a high level of consistency and validity. The bony arch index (BAI), also described in the literature as the arch index and the arch height index, has been used as a technique by several authors to describe the posture of the medial longitudinal arch [1], [2], [3], [4], [5], [6]. The bony arch index is different than the “arch index” that was originally described by Cavanagh and Rodgers, which was based on plantar surface contact area [7].

Cowan et al. was one of the first to describe the BAI as a technique to quantify the height of the medial longitudinal arch using linear measurements rather than plantar surface contact area [1]. Cowan et al. defined the BAI as the ratio of navicular height to foot length, with foot length defined as the distance measured from the heel to the metatarsophalangeal joint. In their study, navicular height was defined as the linear distance from the navicular tuberosity to the supporting surface while the subject stood with full body weight on the foot that was being measured [1].

While the BAI has been widely used to assess the bony height of the medial longitudinal arch, different investigators have utilized different subject positions to obtain the measurement as well as to define foot length. Although Cowan et al. originally described the assessment of navicular height with the subject standing with full body weight on the foot being measured, other investigators have used 50% body weight or 90% body weight [2], [5], [6]. With regard to foot length, while Cowan et al. originally described this measurement as the length from the heel to the metatarsophalangeal joint. Other investigators, however, have defined this as the distance from the most posterior aspect of the calcaneus to the end of the head of the first metatarsal or have used the distance from the posterior point on the calcaneus to the medial side of the first metatarsophalangeal joint [2], [5]. These variations in the definition of the foot length used to calculate the BAI as well as the percentage of weight bearing the subject is positioned in for the measurement of navicular height make it very difficult to compare results amongst the various studies as well as to develop a normative database. Another issue related to the BAI is the consistency of measuring navicular height. Evans et al. is one of the few investigators who have reported good levels of reliability for the measurement of navicular height in adults [8]. Using four different raters with between 11 and 15 years of clinical experience, they reported that the within-rater reliability based on intraclass correlation coefficients (ICCs) for the 60 adults ranged from 0.80 to 0.85, with between-rater reliability of 0.76. While Weiner-Ogilvie and Rome reported that navicular height measurements demonstrated the smallest intraobserver and interobserver differences in a group of young adults, the mean differences in navicular height between the two observers who performed the measurements ranged from 17% to 22% [9]. Likewise, Menz and Munteanu found that when assessing navicular height in older adults using multiple raters, the test–retest reliability measured using ICCs was only 0.64 [10]. In a study quite similar to the one performed by Evans et al., Vinicombe et al. reported low to moderate reliability of navicular height measurements using five raters with 3–7 years of clinical experience [11]. The ICC values reported by Vinicombe et al. for within-rater reliability ranged from 0.33 to 0.62 with between-rater reliability between 0.54 and 0.76 over two different measurement sessions. Vinicombe et al. also reported standard error of the measurement (S.E.M.), which is a number in the same units as navicular height that represents how much variation would occur in the measurement if measured more than once [20]. Their S.E.M. results suggested that clinicians could expect a measurement error in the range of 12% to 28% when multiple clinicians are measuring navicular height [11].

One potential factor for the difference in the findings between Evans et al. and Vinicombe et al. could be related to the level of clinical experience of the raters used in the two studies. Evans et al. used raters with 11–15 years of clinical experience, while the raters in the Vinicombe et al. study had only 3–7 years of clinical experience [8], [11]. Other factors that can influence the consistency of measuring navicular height between raters include difficulty in locating the navicular tuberosity secondary to anatomical variations among individuals as well as balance related issues that can occur as subjects intermittently change their standing position when attempting to maintain full or 90% of their body weight on the foot being measured [11], [12].

In an attempt to circumvent the anatomical variability when attempting to palpate the navicular tuberosity as well as clinical experience issues that could effect the consistency of the navicular height measurement, Williams and McClay proposed measuring the height of the dorsum of the foot at 50% of foot length and dividing by either total foot length or truncated foot length [12]. Williams and McClay reported that the dorsum foot height divided by either total or truncated foot length had the highest ICC values of the seven measurements they evaluated. In their study, Williams and McClay assessed dorsal foot height in 10% and 90% weight bearing.

Several other researchers have used the dorsal height at 50% foot length divided by the truncated foot length as a way to characterize arch height and have termed the measurement as the arch height ratio or arch height index [13], [14], [15], [16], [17]. While both within- and between-rater reliability for the arch height ratio or index has been reported to be high, inconsistencies in the way different researchers have defined the “truncated foot length” as well as the percentage of weight bearing used to obtain the dorsum foot height make comparison of the results from these various studies extremely difficult. Williams and McClay originally defined the truncated foot length as the distance from the most posterior portion of the calcaneus to the center of the first metatarsophalangeal joint, but Franettovich et al. and Vicenzino et al. defined the measure as the distance from the posterior heel surface to the first metatarsophalangeal joint line [12], [15], [16]. In large feet the difference between measuring to the first metatarsophalangeal joint line versus the center of the joint could be greater than a centimeter, which would affect the calculated ratio. With regard to percentage of weight bearing for measuring dorsal height, Williams and McClay performed the measurement in both 10% and 90% weight bearing and used radiographs to substantiate the validity of these two positions [12]. Several investigators have also reported measuring dorsal foot height with the subject in a relaxed standing position, assuming 50% body weight on each foot [15], [16], [17]. Franettovich et al. and Vinicombe et al. have suggested that performing foot measurements in 50% weight bearing improves measurement reliability by decreasing balance related issues that can occur as subjects intermittently change their foot position while attempting to stand with a partial amount of their body weight on the foot being assessed [11], [17].

It would be logical to assume that measuring dorsal foot height in 50% weight bearing could affect the height measured in comparison to values obtained in 10% or 90% weight bearing. Unfortunately, Williams and McClay only validated the dorsal height measurement using radiographs in 10% and 90% weight bearing.

The arch height ratio or index, using dorsal foot height measured at 50% of foot length, would appear to provide the clinician with a more reliable measurement than navicular height as a result of not having to palpate a bony landmark. The consistency and validity of the dorsal height measurement obtained in different weight-bearing conditions, however, warrants further investigation. Furthermore, the largest group for whom the arch height index or ratio has been reported to date is 145 subjects. In their study, Zifchock et al. assessed 68 men and 77 women, using 10% and 50% weight bearing but did not validate the 50% weight-bearing condition [15]. Thus, descriptive data for a large cohort of subjects, including both women and men, would appear to be warranted in order to establish normative values for the arch height index or ratio.

The purposes of this study were to (1) determine the reliability and validity of the arch height ratio when measured in bilateral resting standing posture, (2) determine the arch height ratio in a large cohort of subjects using both total foot length and truncated foot length, and (3) determine if extremity differences exist for dorsal arch height and foot or ball length measurements. For this study, the arch height ratio (AHR) was defined as the dorsal arch height at 50% of the total foot length, measured in bilateral resting standing posture, divided by either total foot or truncated foot length.

Section snippets

Subjects

The left and right feet of 850 subjects, 393 women and 457 men, were assessed to establish a mean and standard deviation for a reference population of convenience. All subjects were recruited using advertisements throughout university and military communities. Each participant met the following inclusion criteria: (1) no history of congenital deformity in the lower extremity or foot; (2) no previous history of lower extremity or foot fractures; (3) no systemic diseases that could effect lower

Results

Descriptive statistics for all measurements are listed in Table 2. The intra- and inter-rater ICC and S.E.M. values for all three raters are shown in Table 3. The within-rater reliability ICC for HTL, HBL, and DAH for all raters ranged from 0.98 to 0.99 with S.E.M. values ranging from 0.03 to 0.05 cm. Between-rater reliability ICC for the same measurements ranged from 0.98 to 0.99 with S.E.M. values ranging from 0.04 to 0.07 cm. The mean values for DAH and HBL obtained from the radiographs were

Discussion

The purposes of this study were threefold. They included (1) determine the reliability and validity of the arch height ratio when measured in bilateral resting standing posture, (2) determine the arch height ratio in a large cohort of subjects using both total foot length and truncated foot length, and (3) determine if extremity differences existed for dorsal arch height and foot or ball length measurements.

Our first concern in interpreting the results was the reliability and validity of the

Conclusions

In summary, the findings of the current study provide normative values for the Trun-AHR and the TFL-AHR for the left and right foot in a large cohort of healthy male and female subjects. While all three foot measurements assessed in this study were found to have excellent levels of intra- and inter-rater reliability, the validity of measuring DAH and the truncated foot length (HBL) while asking the subject to stand and place equal weight on both feet was also established. Based on these

Conflict of interest

None.

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