Impact of Imaging Height on Diagnostic Accuracy of the “Too Many Toes” Sign in Flatfoot

ABSTRACT

Objectives:

The “too many toes” sign is a clinical indicator for evaluating flatfoot. However, standardized assessment conditions remain undefined. In rehabilitation settings, this sign is used to monitor alignment, functional progression, and response to interventions such as intrinsic foot muscle training and gait retraining. Despite its widespread use, the height at which images are obtained may affect diagnostic interpretation. This study aimed to clarify the influence of imaging height on the assessment of the “too many toes” sign in patients with flatfoot.

Methods:

In this cross-sectional observational study, 11 patients with flatfoot were evaluated preoperatively. Standing photographs were captured at floor level and at 40-cm height behind the participants. The horizontal distance between the lateral malleolus and the fifth toe was measured using ImageJ. Two board-certified foot-and-ankle surgeons assessed the presence of the “too many toes” sign. Statistical comparisons were performed using t-tests and a McNemar test.

Results:

The mean horizontal distance from the lateral malleolus to the fifth toe significantly increased from 0.47 ± 0.13 cm at floor level to 0.59 ± 0.15 cm at 40-cm height. From the floor-level images, two cases were classified as positive for the “too many toes” sign and nine as negative. Conversely, images obtained at 40-cm height identified ten positive and one negative case.

Conclusions:

Imaging height significantly influences the visibility of the lateral toes and assessment of the “too many toes” sign in flatfoot, highlighting the need to standardize camera height for consistent clinical evaluations.

INTRODUCTION

Flatfoot is a foot alignment disorder characterized by the collapse of the medial longitudinal arch, often accompanied by hindfoot pronation, forefoot abduction, and supination.¹⁾ Although flatfoot is commonly classified according to the life stage—childhood, adolescence, or adulthood—in adults, its etiology is diverse, encompassing posterior tibial tendon dysfunction (PTTD), osteoarthritis, joint trauma, and rheumatoid arthritis.²⁾

Historically, adult flatfoot has been referred to as PTTD.³⁾ In 2020, the concept of progressive collapsing foot deformity (PCFD) was proposed,⁴⁾ providing a unified interpretation and terminology for conditions previously described as PTTD or AAFD (adult-acquired flatfoot deformity).

The “too many toes” sign is a clinical method for evaluating flatfoot deformity, characterized by increased visibility of the lateral toes on the affected side when viewed from behind. This finding is typically associated with hindfoot valgus and forefoot abduction or supination deformities, resulting in greater toe visibility compared to the contralateral and unaffected sides.⁵⁾ Because the “too many toes” sign is a diagnostic criterion for both PTTD and the newly proposed PCFD for detecting forefoot abduction,⁶⁾ its clinical significance is considerable.

From a rehabilitation standpoint, the assessment of foot alignment plays an important role in treatment decision-making, such as determining the need for orthotic intervention, intrinsic foot muscle training, and monitoring functional improvements over time. The “too many toes” sign is frequently incorporated into routine clinical evaluations because it can be performed quickly in a standing, weight-bearing condition. However, despite its frequent use in rehabilitation practice, differences in examiner observation angle may lead to inconsistent diagnostic outcomes.

To our knowledge, no studies have investigated standardized measurement methods for the “too many toes” sign, and no consensus exists regarding its assessment. In our preliminary study with healthy adults, we investigated the effect of imaging height—defined as the vertical distance from the floor to the camera at the time of image acquisition—on toe visibility using images obtained at 10, 20, 30, and 40 cm behind the participant. Consequently, images captured from a higher position allowed for easier observation of the toes. This study aimed to investigate an appropriate method for assessing the “too many toes” sign in patients with flatfoot, focusing on the height of the imaging position, to determine its clinical applicability.

MATERIALS AND METHODS

This was a cross-sectional observational study with a within-subject design. The study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of JCHO Tokyo Shinjuku Medical Center (Approval No. R5-6). Written informed consent was obtained from all participants, who were provided with a comprehensive explanation of the purpose and procedures of the study.

Patients undergoing surgery for flatfoot deformities were included preoperatively. Patients were consecutively enrolled between April 2024 and April 2025. Flatfoot deformity was diagnosed based on a combination of clinical and radiographic findings by a board-certified foot-and-ankle surgeon, including collapse of the medial longitudinal arch, hindfoot valgus alignment, and forefoot abduction. In addition, a lateral talometatarsal angle greater than 4° was used as a radiographic criterion.⁷⁾ Patients unable to maintain a standing position were excluded. Ultimately, 11 patients (2 men and 9 women; mean age 65.4 ± 11.9 years) were included in the analysis. Baseline characteristics, including height, body weight, body mass index (BMI), and underlying diagnosis, are shown in Table 1.

Table 1.  . Baseline characteristics of participants.

Characteristic	(n = 11)
Sex
Male	2 (18)
Female	9 (82)
Age, years	65.4 ± 11.9
Height, cm	154.2 ± 9.6
Weight, kg	60.6 ± 25.5
BMI, kg/m2	25.5 ± 4.4
PCFD diagnosis	11 (100)

Data presented as number (percentage) or mean ± standard deviation.

To assess the “too many toes” sign, the lower leg and foot were exposed to ensure clear visualization. Participants stood in a natural upright position facing a wall, with their heels aligned along a line marked on the floor 1 m from the camera. To standardize lower-leg rotation, participants were instructed to orient their patella toward the wall. Photographs were obtained from 1 m behind the participants under two imaging conditions: at floor level and at a height of 40 cm above the floor (Figs. 1 and 2). Photographs were captured using a Nikon COOLPIX A900 (Nikon, Tokyo, Japan). The height of 40 cm was selected because it represents a practical level at which the examiner can assess the lower limb from behind while squatting at approximately knee height. Additionally, in our prior investigation capturing images from heights of 10, 20, 30, and 40 cm, imaging at 40 cm yielded the most optimal visualization of the toes from behind.⁶⁾ To ensure consistent positioning, the floor (heel placement point), practice chair (Minato Medical Science, Osaka, Japan), and camera location were pre-marked to prevent any misalignment between the heel and camera center.

Fig. 1.

 Photographs captured from 1 m behind the participants at two heights: floor level and 40 cm above the floor.

Fig. 2.

 A representative case of photographs captured at floor level and 40-cm level. Vertical lines were drawn from the lateral edges of the lateral malleolus and fifth toe, and the horizontal distance between them was measured.

Frontal plane images were analyzed using ImageJ software (National Institutes of Health, Bethesda, MD, USA). The measured value was defined as the horizontal distance on the photograph between the lateral edge of the lateral malleolus and the fifth toe. During image analysis, the line tool in ImageJ was used to draw horizontal and vertical reference lines to avoid measurement bias caused by image tilt. Vertical lines were drawn from the lateral edges of the lateral malleolus and the fifth toe, and the horizontal distance between them was measured (Figs. 2 and 3). Using the same photograph, the measurement was performed three times, and the mean value was used for analysis (Table 2). All measurements were performed by an independent examiner to eliminate the influence of interobserver variability. Inter-rater reliability for the measurement of the horizontal distance between the lateral malleolus and the fifth toe at floor level and at 40 cm was evaluated between two examiners. Intra-rater reliability was assessed by repeated measurements performed by one examiner with a 3-month interval. The intraclass correlation coefficient (ICC [2,1], two-way random-effects model, absolute agreement) was used to assess both intra- and inter-rater reliability for consistency across analyses (Table 3). ICC values were interpreted as follows: less than 0.50, poor; 0.50–0.75, moderate; 0.75–0.90, good; and greater than 0.90, excellent.

Fig. 3.

 Representative photographs of cases of negative and positive “too many toes” sign assessed at floor level and 40-cm level. Vertical lines were drawn from the lateral edges of the lateral malleolus and fifth toe.

Table 2.  . Mean horizontal distance between lateral malleolus and fifth toe in images captured at floor level and at 40 cm above floor.

Case	Mean horizontal distance (cm)
	Floor level	40-cm level
1	0.34	0.40
2	0.43	0.55
3	0.68	0.83
4	0.56	0.68
5	0.60	0.73
6	0.30	0.35
7	0.38	0.59
8	0.51	0.63
9	0.64	0.78
10	0.26	0.45
11	0.47	0.50

Table 3.  Intra- and inter-rater reliability for horizontal distance between lateral malleolus and fifth toe.

Comparison	Imaging condition	ICC (2,1)
Examiner 1 (first vs second)	Floor level	0.855
Examiner 1 (first vs second)	40-cm level	0.888
Examiner 1 vs Examiner 2 (first measurements)	Floor level	0.776
Examiner 1 vs Examiner 2 (first measurements)	40-cm level	0.799

ICC values interpreted as: <0.50, poor; 0.50–0.75, moderate; 0.75–0.90, good; >0.90, excellent.

Each photograph was independently evaluated by two board-certified foot-and-ankle surgeons for the presence of the “too many toes” sign. The “too many toes” sign was identified if more than the fifth and fourth toes were visible from behind. Preoperative outpatient evaluation of the “too many toes” sign was also demonstrated in Table 4. In cases of disagreement, the final judgment was determined through discussion and consensus between the two evaluators. Intra-rater reliability was assessed by repeated measurements performed by a board-certified foot-and-ankle surgeon with a 3-month interval (Table 5). Inter-rater reliability for the assessment of the “too many toes” sign was evaluated using Cohen’s kappa coefficient (Tables 5 and 6). For statistical analysis, a t-test was performed to compare the horizontal distance between the lateral malleolus and the fifth toe at different photographing heights (floor level and 40-cm level). In addition, a McNemar test was used to examine the consistency of the “too many toes” sign diagnosis by the foot-and-ankle surgeons at each height. No formal sample size calculation was performed because this study was designed as an exploratory pilot investigation.

Table 4.  Evaluation of "too many toes" sign by board-certified foot-and-ankle surgeons in floor-level and 40-cm-height images.

Case	Image height		Preoperative outpatient evaluation
	Floor level	40-cm level
1	Negative	Positive	Positive
2	Negative	Positive	Positive
3	Positive	Positive	Positive
4	Negative	Positive	Positive
5	Negative	Positive	Positive
6	Negative	Negative	Negative
7	Negative	Positive	Positive
8	Negative	Positive	Positive
9	Positive	Positive	Positive
10	Negative	Positive	Positive
11	Negative	Positive	Positive
Total
Positive	2	10	10
Negative	9	1	1

Table 5.  Intra- and inter-rater reliability for "too many toes" sign by imaging height based on Cohen's kappa.

Comparison	Imaging condition	Cohen’s kappa
Surgeon 1 (first vs second)	Floor level	1.00
Surgeon 1 (first vs second)	40-cm level	1.00
Surgeon 1 vs Surgeon 2 (first measurements)	Floor level	0.00
Surgeon 1 vs Surgeon 2 (first measurements)	40-cm level	1.00

Kappa values interpreted as: <0.20, poor; 0.21–0.40, fair; 0.41–0.60, moderate; 0.61–0.80, good; >0.80, excellent.

Table 6.  Inter-rater agreement for "too many toes" sign by imaging height based on Cohen's kappa.

Imaging condition	Surgeon 1 negative/ Surgeon 2 negative	Surgeon 1 positive/ Surgeon 2 positive	Discordant cases	Cohen’s kappa
Floor level	9	0	2	0.00
40-cm level	1	10	0	1.00

Kappa values interpreted as: <0.20, poor; 0.21–0.40, fair; 0.41–0.60, moderate; 0.61–0.80, good; >0.80, excellent.

Statistical analyses were performed using SPSS Statistics (Version 29.0; IBM, Armonk, NY, USA). Statistical significance was set at P <0.05.

RESULTS

The horizontal distance between the lateral edge of the lateral malleolus and the fifth toe for each participant, as well as the evaluation results of the “too many toes” sign, are shown in Tables 2 and 4. The mean horizontal distance on the image between the lateral edge of the lateral malleolus and the fifth toe was 0.47 ± 0.13 cm at floor level and 0.59 ± 0.15 cm at 40-cm height (mean ± standard deviation), demonstrating a statistically significant difference between the two conditions (P = 0.037) (Figs. 3 and 4). The measurements of the horizontal distance between the lateral edge of the lateral malleolus and the fifth toe demonstrated good intra- and inter-rater reliability across imaging conditions (Table 3).

Fig. 4.

 The mean horizontal distance (n = 11) between the lateral edges of the lateral malleolus and fifth toe (*P <0.05).

From floor-level images, two cases were classified as positive and nine as negative. In contrast, from 40-cm-height images, ten cases were classified as positive and one as negative (Table 4). The proportion of positive “too many toes” sign by board-certified foot-and-ankle surgeons differed significantly between imaging conditions (P = 0.0078), with a higher detection rate at 40-cm height than at floor level. The 40-cm imaging level showed a high level of agreement with preoperative outpatient evaluation. Inter-rater agreement differed markedly between imaging conditions. Agreement was poor at floor level (κ = 0.00), with no concordant positive cases and two discordant cases, whereas perfect agreement was observed at 40 cm (κ = 1.00), with complete concordance between evaluators (Tables 5 and 6).

DISCUSSION

This study is the first to systematically investigate the impact of imaging height on the diagnostic assessment of the “too many toes” sign in patients with flatfoot. In our preliminary study involving healthy adults, we investigated how toe visibility changed when photographs were taken from heights of 10, 20, 30, and 40 cm behind the participants.⁶⁾ The results demonstrated that images captured from higher positions facilitated easier observation of the toes. Consistent with these findings, the results of the present study showed that increasing the photographing height to 40 cm significantly increased the visibility of the lateral toes and the positive rate of the “too many toes” sign compared with images captured at floor level.

Although the difference in horizontal distance between the lateral malleolus and the fifth toe across imaging heights was small (approximately 0.12 cm), it may not be negligible relative to the width of the fifth toe. Importantly, this difference corresponded to a substantial change in diagnostic classification of the “too many toes” sign, underscoring that even minor measurement variations may affect clinical assessment. This pattern likely results from the morphological overlap of the lateral hindfoot and toes when imaging from ground level, whereas imaging from a height of 40 cm, corresponding to an approximate inclination angle of 21.8° relative to the foot, provided improved visualization of the toes. In the present cohort, the 40-cm imaging level showed a high level of agreement with routine preoperative outpatient evaluation, which may be explained by the fact that our board-certified foot-and-ankle surgeons typically assess the “too many toes” sign from a viewing height of approximately 40 cm in routine clinical practice. The marked improvement in inter-rater reliability at 40 cm suggests that imaging height not only influences diagnostic interpretation but also substantially enhances assessment consistency. At floor level, the absence of concordant positive cases resulted in low reliability, likely reflecting limited visibility of the lateral toes. In contrast, the 40-cm imaging height enabled consistent identification of the sign between evaluators, indicating that appropriate imaging height may improve both diagnostic accuracy and reproducibility in clinical assessment. Unlike previous studies emphasizing the reliability of the “too many toes” sign as a subjective clinical marker,⁵⁾ this study demonstrates that observation conditions, specifically camera angle and height, can significantly affect assessment outcomes. These findings suggest that even in cases of clinically severe flatfoot, the “too many toes” sign may appear negative, depending on the imaging height. Although false-positive interpretation of the “too many toes” sign may theoretically occur, it is likely to be less common than false-negative findings, because increased imaging height primarily enhances the visibility of the lateral toes rather than artificially exaggerating their appearance. From a rehabilitation perspective, this variability underscores the need for consistent observational environments during physical therapy evaluations. Given that lower-extremity alignment screening is routinely performed in rehabilitation settings, standardizing the camera height or examiner viewpoint may enhance inter-rater reliability and contribute to more accurate treatment planning. This highlights a potential flaw in the conventional evaluation method, which vaguely describes the observation as “from behind in the standing position” without specifying the imaging conditions—potentially compromising diagnostic accuracy.

The “too many toes” sign, reflecting both hindfoot pronation and forefoot abduction, is an important clinical indicator of PCFD. Therefore, improving the reliability of image-based assessments can play a crucial role in accurate disease classification and informed therapeutic decision-making. A key strength of this study is the use of quantitative distance measurements, providing an objective anatomical basis for a traditionally subjective assessment. Using digital analysis software and standardizing the imaging distance and height, we enhanced reproducibility and minimized observer variability. The high intra- and inter-rater reliability observed in this study supports the reproducibility of the quantitative measurement method. This methodological approach offers a promising path toward developing quantitative tools that can augment traditional clinical signs in both pre- and post-surgical interventions.

This study had several limitations. First, the imaging height was limited to two conditions, leaving it unclear whether 40 cm represents the optimal height or simply an improvement over ground-level observations. Second, the sample size was relatively small, which limits the generalizability of the results. Third, potential confounding factors, such as knee valgus alignment, were not fully controlled. Knee valgus has been reported to influence foot alignment and gait mechanics.^8,9) Although participants were instructed to keep the patella facing forward during image acquisition to standardize lower-leg rotation, this approach may not have ensured complete control of foot alignment or eliminated the influence of such confounding factors. Fourth, the measured distance may be influenced by individual differences in foot size; therefore, normalization (e.g., relative to foot length) may help reduce inter-individual variability, although absolute measurements were used in this study to reflect routine clinical practice. Fifth, this study included only patients undergoing surgery for flatfoot, which may introduce a selection bias toward more severe deformities; therefore, the findings may not be fully generalizable to patients with mild or asymptomatic flatfoot. Lastly, although the horizontal distance from the lateral edge of the lateral malleolus to the fifth toe was measured in this study, measurements based solely on images cannot exclude the potential influence of subcutaneous fat thickness. Future studies should address these limitations by controlling for participant BMI, standardizing camera-to-toe distance, and evaluating a broader range of imaging conditions and patient populations to determine the optimal imaging protocol for “too many toes” sign assessment. Furthermore, the development of quantitative and objective evaluation methods incorporating three-dimensional assessment is warranted.

CONCLUSION

Variations in camera height significantly influenced the diagnosis of the “too many toes” sign in patients with flatfoot. An elevated imaging height (40 cm) improved visibility and diagnostic consistency. These findings underscore the need to standardize observation conditions, long ambiguous in conventional assessment methods, and may contribute to the establishment of a more consistent evaluation approach in future clinical practice.