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The Evolution of Foot Morphology in Children Between 6 and 17 Years of Age: A Cross-Sectional Study Based on Footprints in a Mediterranean Population
ORIGINAL RESEARCH
The Evolution of Foot Morphology in Children Between 6 and 17 Years of Age: A Cross-Sectional Study Based on Footprints in a Mediterranean Population Panagiotis Stavlas, MD,1 Theodoros B. Grivas, MD,2 Constantinos Michas, MD,3 Elias Vasiliadis, MD,4 and Vassilios Polyzois, MD5 Footprint evaluation is a widely used method for the determination of foot morphology, but its efficacy and validity are considered controversial. Dynamic footprints were obtained from both feet of 5,866 school-aged children (6-17 years old) to detect any foot changes during growth. The interpretation of the imprint was performed using a classification scheme consisting of 6 types of footprints. In this scheme, footprint types I and II represent the typical and intermediate high-arched foot, respectively. Types III and IV represent normal foot variants, while type V corresponds to the low-arched foot and type VI to the severe flat foot, the latter often encountered in pathological conditions. There was statistically significant difference (P ⬍ .05) in footprint-type frequencies between boys and girls of ages 7, 9, 11, 14, and 15, which probably indicates the difference in growth potential of the foot between sexes. The proportion of high- and low-arched foot types decreased with increasing age in both boys and girls. Even though critical changes of the foot are believed to occur during pre-school development, this study shows that considerable changes also take place during school age and until late adolescence. ( The Journal of Foot & Ankle Surgery 44(6):424 – 428, 2005) Key words: footprint, foot morphology, foot growth, foot growth natural history, footprint classification
T he classification of foot morphology based on its medial longitudinal arch (MLA) height is still a controversial topic for foot and ankle specialists. The variety of techniques that have been used to assess the MLA indicates that a single and reliable method has not been universally adopted. Ink or digital footprints (1, 2) and photographic techniques (3) are
Address correspondence to: Panagiotis Stavlas, MD, 53, Mitropoulou St., TK 12462, Dasos Chaidari, Athens, Greece. E-mail: [email protected] 1 Orthopaedic Fellow, Department of Orthopaedics, University Hospital of Aarhus, Aarhus, Denmark. 2 Consultant Orthopaedic Surgeon, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. 3 Resident, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. 4 Resident, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. 5 Resident, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. Copyright © 2005 by the American College of Foot and Ankle Surgeons 1067-2516/05/4406-0002$30.00/0 doi:10.1053/j.jfas.2005.07.023
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indirect methods of measurement, whereas direct methods include somatometric measurements, clinical assessment (4), radiographic evaluation (5), or ultrasonography quantification (6). There are specific limitations associated with each of these techniques. Radiographic and other imaging methods carry potential health risks, especially for the pediatric population, and are costly and subject to different methods of interpretation. On the other hand, although clinical evaluation is the most applicable method for the assessment of foot shape, it can be subjective. One of the most widely used methods for the study of the MLA is the footprint. A typical footprint consists of the hindfoot (or calcaneus) imprint, the midfoot imprint (with the intelligible foot arch and the isthmus of the foot), and the forefoot imprint (with the metatarsal heads and the toes). Several measurement methods and footprint parameters have been proposed to classify the foot into lower, normal, and higher arch types (1–3, 7–9). These parameters quantify the shape of the foot by considering that the height of the MLA must directly correlate to the shape of the footprint (2, 7).
FIGURE 1 Footprint parameters. s, footprint angle; arch index, B/(A ⫹ B ⫹ C); Chippaux-Smirak index, g/f(%)
Schwartz et al proposed the use of the footprint angle in the evaluation of footprints (10). This angle was defined between the line connecting the most medial points of the heel and metatarsal regions, and the line connecting the most lateral point on the medial foot border to the most medial point of the metatarsal region. They assumed that as the arch becomes higher, this arch angle increases. Clarke modified Schwartz’s method slightly and provided additional objective data (8). Cavanagh and Rodgers introduced the arch index and classified footprints in 3 categories (high, normal, and flat arch) using the ratio of the area of the middle third of the toeless footprint to the total toeless footprint area (7). The ChippauxSmirak index is another parameter that has been used in footprint evaluation (11, 12). It describes the ratio of the maximal width of the metatarsal region to the minimal width of the arch region on the footprint. A large index indicates a high width in the arch area (Fig 1). In 1984, the senior author of this study (T.B.G.) proposed a wider footprint classification system (13). According to this method, the main parameters of a footprint can be identified are shown in Fig 2. Six footprint types can be differentiated, depending on the relationship between these parameters. In footprint type I, the longitudinal axis of the calcaneus (LAC) axis lies lateral to the longitudinal axis of the foot (LAF) axis, and there is no isthmus imprint (x ⫽ y). This footprint type represents the typical high-arched foot. The intermediate higharched foot is represented by footprint type II, where y ⬎ x ⱖ 3/4 y. In footprint type III, the isthmus is wider such that 3/4 y ⬎ x ⱖ 2/4 y. This is considered to be a normal footprint type, similar to type IV, where 2/4 y ⬎ x ⱖ 1/4 y. In the latter, the LAC axis lies lateral or on the LAF axis. In type V, the isthmus is very wide. The LAC axis is over or lies medial to the LAF axis and 1/4 y ⬎ x ⱖ 0. This footprint type represents the
FIGURE 2 A typical footprint and the 6 footprint types are shown. The longitudinal axis of the foot (LAF) is the line from the center of hindfoot (or calcaneus) imprint to the second toe. The longitudinal axis of calcaneus imprint (LAC) is the line that dissects the imprint of the hindfoot (the so-called calcaneal oval or calcaneal egg). In every footprint, a line (M) is drawn along the medial border of the foot. A perpendicular line (y) is then drawn, from line (M) to the lateral outline of the isthmus, corresponding to the width of midfoot. An additional line (x), which is parallel to (y), is drawn in the midfoot, corresponding to the width of the arch. As it is clearly seen, the result of y-x is the width of the isthmus of the footprint. According to the relationship between these axes (LAF and LAC) and lines (x and y), 6 footprint types are described (see text for details).
low-arched foot. In type VI, x is greater than y, and the LAC axis lies medial to the LAF axis. This type is found in pathological conditions with severe flat foot (that is, vertical talus, tarsal coalition). It is thought that the development of the MLA of the foot occurs mainly in the pre-school years of life (14, 15). The aim of our study was to analyze the evolution of foot morphology in a large population of school-aged children. These findings can then be correlated to previous studies that have reported MLA development to continue after pre-school age and gradually increase during growth (16 –18). The establishment of reliable criteria to identify specific foot types (that is, flatfoot) that may require management continues to evolve. It is hoped that the results of this survey could contribute to this ongoing discussion (4, 19, 20). Materials and Methods Footprints were analyzed from both feet of 5,866 children (2,935 boys and 2,931 girls) aged between 6 and 17 years. The survey was carried out in 31 elementary and high schools in the area of Western Attica in Greece. Informed consent was obtained from the parents of all children after both a verbal and a written explanation of the study. Children who demonstrated a history of neuromuscular disease or lower-limb injury, abnormal gait and discomfort in walking, or any kind of foot deformity were excluded from the
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TABLE 1 Age group
6 7 8 9 10 11 12 13 14 15 16 17 Total
TABLE 2 Age group
6 7 8 9 10 11 12 13 14 15 16 17 Total
Footprint type values of right feet among boys and girls, with respective percentages in parentheses n
110 312 326 430 466 466 626 626 626 626 626 626 5866
Boys
Girls
I
II
III
IV
V
I
II
III
IV
V
1 (1.8) 6 (3.8) 8 (4.8) 9 (4.1) 11 (4.7) 11 (4.7) 15 (4.8) 9 (2.8) 1 (0.3) 1 (0.3) 3 (0.9) 5 (1.6)
12 (21.8) 24 (15.3) 31 (18.7) 31 (14.4) 43 (18.4) 46 (19.7) 36 (11.5) 47 (15) 25 (8) 22 (7) 27 (8.6) 24 (7.6)
29 (52.7) 94 (60.2) 96 (58.1) 137 (63.7) 150 (64.3) 130 (55.8) 221 (70.6) 203 (64.8) 233 (74.4) 258 (82.4) 255 (81.4) 264 (84.3) 2935
8 (14.5) 14 (8.9) 19 (11.5) 29 (13.4) 21 (9) 28 (12) 25 (8) 27 (8.6) 36 (11.5) 19 (6) 22 (7) 18 (5.7)
5 (9) 18 (11.5) 11 (6.6) 9 (4.1) 8 (3.4) 18 (7.7) 16 (5.1) 27 (8.6) 18 (5.7) 13 (4.1) 6 (1.9) 2 (0.6)
2 (3.6) 9 (5.7) 6 (3.7) 15 (6.9) 11 (4.7) 13 (5.5) 13 (4.1) 6 (1.9) 1 (0.3) 4 (1.2) 4 (1.2) 3 (0.9)
12 (21.8) 29 (18.5) 28 (17.3) 46 (21.4) 40 (17.1) 42 (18) 41 (13) 28 (8.9) 40 (12.7) 34 (10.8) 24 (7.6) 27 (8.6)
30 (54.5) 97 (62.1) 108 (67) 132 (61.4) 161 (69) 157 (67.3) 231 (73.8) 236 (75.4) 251 (80.1) 256 (81.7) 265 (84.6) 264 (84.3) 2931
7 (12.7) 17 (10.8) 10 (6.2) 10 (4.6) 10 (4.3) 17 (7.3) 17 (5.4) 26 (8.3) 14 (4.4) 14 (4.4) 18 (5.7) 14 (4.4)
4 (7.2) 4 (2.5) 9 (5.6) 12 (5.5) 11 (4.7) 4 (1.7) 11 (3.5) 17 (5.4) 7 (2.2) 5 (1.6) 2 (0.6) 5 (1.6)
Footprint type values of left feet among boys and girls, with respective percentages in parentheses n
110 312 326 430 466 466 626 626 626 626 626 626 5866
Boys
Girls
I
II
III
IV
V
I
II
III
IV
V
1 (1.8) 1 (0.6) 10 (6) 6 (2.8) 14 (6) 10 (4.3) 13 (4.1) 9 (2.8) 3 (0.9) 2 (0.6) 2 (0.6) 3 (0.9)
13 (23.6) 23 (14.7) 29 (17.5) 44 (20.4) 48 (20.6) 45 (19.3) 38 (12.1) 54 (17.2) 31 (9.9) 28 (8.9) 33 (10.5) 31 (9.9)
29 (52.7) 103 (66) 96 (58.1) 127 (59) 148 (63.5) 135 (57.9) 223 (71.2) 196 (62.6) 235 (75) 249 (79.5) 242 (77.3) 257 (82.1) 2935
6 (10.9) 14 (8.9) 20 (12.1) 27 (12.5) 15 (6.4) 31 (13.3) 21 (6.7) 29 (9.2) 25 (8) 22 (7) 26 (8.3) 17 (5.4)
6 (10.9) 15 (9.6) 10 (6) 11 (5.1) 8 (3.4) 12 (5.1) 18 (5.7) 25 (8) 19 (6) 12 (3.8) 10 (3.2) 5 (1.6)
2 (3.6) 7 (4.4) 5 (3.1) 12 (5.5) 15 (6.4) 12 (5.1) 12 (3.8) 6 (1.9) 1 (0.3) 3 (0.9) 3 (0.9) 2 (0.6)
12 (21.8) 35 (22.4) 26 (16.1) 54 (25.1) 44 (18.8) 49 (21) 43 (13.7) 35 (11.1) 43 (13.7) 40 (12.7) 31 (9.9) 34 (10.8)
31 (56.3) 93 (59.6) 111 (69) 127 (59) 155 (66.5) 151 (64.8) 227 (72.5) 234 (74.7) 243 (77.6) 250 (79.8) 257 (82.1) 257 (82.1) 2931
7 (12.7) 17 (10.9) 10 (6.2) 11 (5.1) 7 (3) 15 (6.4) 17 (5.4) 16 (5.1) 16 (5.1) 14 (4.4) 17 (5.4) 14 (4.4)
3 (5.4) 4 (2.5) 9 (5.6) 11 (5.1) 12 (5.1) 6 (2.5) 14 (4.4) 22 (7) 10 (3.2) 6 (1.9) 5 (1.6) 6 (1.9)
study. The sample was divided into 12 different age groups at 1-year intervals, and every age group was subdivided into male and female subgroups. The Harris and Beath footprinting mat (Apex Foot Health Industries, South Hackensack, NJ) was used to obtain dynamic (walking) bilateral footprints in every child (21). Prior to use, the mat was lightly and evenly inked on its ridged side with oil-soluble print ink with a printer’s roller. A sheet of slightly absorbent paper was carefully placed over the inked mat, and the child was instructed to walk over the mat using the length of the walkway. The ink footprint was then retrieved, and the border of the acquired image was immediately outlined with a pencil to ensure that any future distortion or spread of the ink could be easily recognized. The interpretation of the footprints was done by the first 2 authors of this study (P.S. and T.B.G.) with Grivas’ classification method (13). Statistical analysis of a total of 11,732 footprints was done using the Wilcoxon signed-rank test for matched pairs to determine if there was any differ426
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ence in morphology between right and left foot among groups. The Mann-Whitney 2-sample rank-sum test was performed to identify any difference in the frequency of footprint types between boys and girls in each age group. Finally, the chi-square for trend test was used to determine if there was any tendency for change of the frequency of the observed footprint types during growth. P values of less than .05 were considered to be significant.
Results Tables 1 and 2 demonstrate the detailed distribution of footprint types according to sex (boys/girls) and the laterality of the foot (right/left). No type VI footprint was found in any child in this population. No significant differences (P ⫽ .1) were found between the right and left footprints. In contrast, there was a statistically significant relationship between sex and footprint in some specific age groups. Specifi-
FIGURE 3 A graph demonstrating the footprint-type frequencies in boys among age groups.
FIGURE 4 A graph demonstrating the footprint-type frequencies in girls among age groups.
cally, the distribution of footprint-type frequencies between boys and girls differed significantly (P ⬍ .05) at the ages of 7, 9, 11, 14, and 15. Boys appeared to demonstrate significantly higher rates of low-arched feet compared with girls of the same age. In both sexes, there was a tendency to reach higher rates of normal footprint types compared with the low- and higharched types during the growth of the foot (P ⬍ .01 for boys and P ⬍ .001 for girls) (Figs 3 and 4). Discussion Footprint evaluation is an old but time-tested method to delineate foot morphology. It remains an inexpensive, fast, simple, noninvasive, and reliable method that can be used effectively for screening and follow-up studies (16, 21, 22). The basic concept behind its application is that a higher
MLA produces a narrower isthmus imprint, whereas a lower arch causes a flattening of the cavity and a wider isthmus area on the imprint (2, 7, 16). Numerous parameters have been proposed for the evaluation of the footprint, such as the footprint angle, the arch index, and the Chippaux-Smirak index (1–3, 7–13). Some studies report that there is no relationship between directly measured arch height and footprint parameters (9), or radiographs and footprint parameters (5). However, the majority of authors have stated that these parameters provide a valid basis for prediction or categorization of arch height (7, 8, 16). Gilmour and Burns also demonstrated a relationship between arch index and a clinical measurement of the vertical height of the navicular, and concluded that footprints can be as reliable as clinical measurements to delineate the shape of the foot (2). Furthermore, in a study of 38 children with flexible pes planus, Kanatli et al found a positive correlation between radiographic angles and the arch index determined from footprint analyses (22). Nevertheless, it seems that there exists a broad range of normal values and foot shapes, which has not been reported by previous studies of foot morphology based on footprint evaluation. In these past studies, the sample size may have not been sufficiently large or wide in age distribution to establish all the foot variants (3, 21, 23). The current study used a classification system (13) that attempted to include all foot types (Fig 2). This grading system could be considered an expansion of Morley’s original classification, which included children aged 1 to 11 years (23). It should be noted that the extreme types of low-arched and high-arched foot should not be misinterpreted as pes planus and cavus foot, respectively. These entities represent more complex severe deformities or pathological conditions that involve alterations in other parts of the foot not always disclosed by footprints. As was expected, no type VI was found in this series, as was the case in previous studies (13). This foot type possesses structural abnormalities, which can be traced on a footprint, and is often encountered in pathological conditions like tarsal coalition or vertical talus. The fact that these children may require operative treatment at an early (pre-school) age, and that foot pathology was the exclusion factor of this study, may explain why this type of footprint was not found in our study population. The significant difference in the frequency of footprint types between boys and girls among ages 7, 9, 11, 14, and 15 years may reflect the different growth potential between the sexes. Jaworski and Puch found that the footprint angle increases up to age 13 in girls and 15 in boys, whereas the Chippaux-Smirak index decreases up to age 11 in boys and 12 in girls (24). Both findings indicate that the physiological process of foot development from the low-arched types to normal types occurs earlier in girls compared with boys, which is consistent with our results. In the present study, the frequency of both low (type V)
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and high (type I and II) MLA feet found in the youngest age groups decreased with age, whereas the opposite was observed for the normal types III and IV. This is in accordance with earlier studies (2, 16, 25). Previous reports have also suggested that there is a significant development of the MLA of the foot, particularly in the pre-school years (14, 15). Although it is well established that the major morphological changes and adaptation of the foot occur during this period, this study demonstrates that ongoing development of foot structures also takes place during school ages. The lowarched foot observed in young children may be a manifestation of constitutional laxity of the ligaments, which improves as the foot matures (1, 15), and our study supports this over a wide range of ages. Even though some evidence exists concerning the influence of weight gain during growth, as seen with static and dynamic plantar pressures and flattening of the MLA, the foot complex appears to be able to maintain the longitudinal arch through compensatory mechanisms (26). Mann and Hagy suggested that better muscle and balance control is expected to develop as a child’s central nervous system matures, subsequently allowing for better control of the lower limb and a more normalized stance (27). Furthermore, the gradual ossification of bony structures may lead to better stabilization of the arch during weightbearing (28). Finally, considering that the ongoing external tibial rotation, from the in-toeing position after birth to the out-toeing position during growth, results in proportional decrease in the valgus configuration of the hindfoot and elevation of the MLA (29). Some limitations of this study should also be mentioned. As pathological deformities and/or pain develop over time, it is probable that a greater proportion of children could have been excluded from the older age groups compared with the younger age groups. This may create the appearance of a decrease in low- and high-arched feet over time. Moreover, during the last several decades, the high variability of this population, due to the increasing immigration of a considerable number of people into Greece from several nations, could have changed the ethnological mix of the different age groups. The exact magnitude to which these factors could have contributed to the outcome is not known. This study is not considered to be a solution to the controversy over the efficacy of footprints in delineating foot morphology and classifying the normal variants of foot shape during growth. It is a study based within a large pediatric population (and, to the best of our knowledge, is the largest such population that has ever been evaluated), where the necessity for a wider classification of footprints became evident. As genetic and extrinsic factors are expected to influence foot development during the entire growth period, it is not surprising that changes in foot morphology were depicted beyond the age of 6 through adolescence. Thereby, the surgical treatment of adolescent foot conditions should be approached with these findings in mind.
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References 1. Staheli LT, Chew DE, Corbett M. The longitudinal arch. J Bone Joint Surg (Am) 69(3):426 – 428, 1987. 2. Gilmour JC, Burns Y. The measurement of the medial longitudinal arch in children. Foot Ankle Int 22(6):493– 498, 2001. 3. Saltzman CL, Nawoczenski DA, Talbot KD. Measurement of the medial longitudinal arch. Arch Phys Med Rehab 76(1):45– 49, 1995. 4. Rose GK, Welton EA, Marshall T. The diagnosis of flat foot in the child. J Bone Joint Surg (Br) 67(1):71–78, 1985. 5. Cobey JC, Sella E. Standardizing methods of measurement of foot shape by including the effects of subtalar rotation. Foot Ankle 2(1): 30 –36, 1981. 6. Hennig EM, Cavanagh PR. Ultrasonic quantification of the arch of the weight-bearing foot. In Biomechanics, pp 211–216, edited by DA Winter, RW Norman, RP Wells, KC Hayes, AE Patla, Human Kinetics Publishers, Champaign, IL, 1985. 7. Cavanagh PR, Rodgers MM. The arch index: a useful measure from footprints. J Biomechanics 20(5):547–551, 1987. 8. Clarke HH. An objective method of measuring the height of the longitudinal arch in foot examinations. Res Q 4:99 –107, 1933. 9. Hawes MR, Nachbauer W, Sovak D, Nigg BM. Footprint parameters as a measure of arch height. Foot Ankle 13(1):22–26, 1992. 10. Schwartz L, Britten RH, Thompson LR. Studies in physical development and posture. US Public Health Bulletin No. 179, US Government printing office, Washington DC, Washington, DC, 1928. 11. Chippaux C. Elements d’anthropologie. Marseille, Le Phar, 1947. 12. Smirak J. Prispeveck k problematice ploche nohy u skolni a praijici mladeze. Slabikar Pedagogicke Nacladatelstvi, Prague, 1960. 13. Grivas TB. Survey on the lower limbs of early school age children. MD Thesis, University of Athens, Greece, 1984. 14. Mosca VS. Flexible flatfoot and skewfoot. J Bone Joint Surg (Am) 77(12):1937–1945, 1995. 15. Staheli LT. Footwear for children. Instr Course Lect 43:193–197, 1994. 16. Forriol F, Pascual J. Footprint analysis between three and seventeen years of age. Foot Ankle 11(2):101–104, 1990. 17. Volpon JB. Footprint analysis during the growth period. J Pediatr Orthop 14(1):83– 85, 1994. 18. Lin CJ, Lai KA, Kuan TS, Chou YL. Correlating factors and clinical significance of flexible flatfoot in preschool children. J Pediatr Orthop 21(3):378 –382, 2001. 19. Capello T, Song KM. Determining treatment of flatfeet in children. Curr Opin Pediatr 10(1):77– 81, 1998. 20. Wenger DR, Leach J. Foot deformities in infants and children. Pediatr Clin North Am 33(6):1411–1427, 1986. 21. Welton A. The Harris and Beath footprint: interpretation and clinical value. Foot Ankle 13(8):462– 468, 1992. 22. Kanatli U, Yetkin H, Cila E. Footprint and radiographic analysis of the feet. J Pediatr Orthop 21(2):225–228, 2001. 23. Morley AJ. Knock knee in children. Br Med J 33(5051):976 –979, 1957. 24. Jaworski JM, Puch EA. Morphology of overweighted children foot. Proceedings of the 82nd Anatomy Society meeting, pp 89–94, Leipzig, 1987. 25. Echarri JJ, Forriol F. The development in footprint morphology in 1851 Congolese children from urban and rural areas and the relationship between this and wearing shoes. J Pediatr Orthop B 12(2):141–146, 2003. 26. Dowling AM, Steele JR, Baur LA. Does obesity influence foot structure and plantar pressure patterns in prepubescent children? Int J Obes Relat Metab Disord 25(6):845– 852, 2001. 27. Mann RA, Hagy JL. The function of the toes in walking, jogging and running. Clin Orthop 142:34 –39, 1979. 28. Van Boerum DH, Sangeorzan BJ. Biomechanics and pathophysiology of flat foot. Foot Ankle Clin 8(3):419 – 430, 2003. 29. Grivas TB. Flexible flatfoot, in Grivas TB (ed): Foot and Ankle, Vol. 1.Athens, Ch. Vasiliadis Publisher, 2002, pp 185-231.
The Evolution of Foot Morphology in Children Between 6 and 17 Years of Age: A Cross-Sectional Study Based on Footprints in a Mediterranean Population Panagiotis Stavlas, MD,1 Theodoros B. Grivas, MD,2 Constantinos Michas, MD,3 Elias Vasiliadis, MD,4 and Vassilios Polyzois, MD5 Footprint evaluation is a widely used method for the determination of foot morphology, but its efficacy and validity are considered controversial. Dynamic footprints were obtained from both feet of 5,866 school-aged children (6-17 years old) to detect any foot changes during growth. The interpretation of the imprint was performed using a classification scheme consisting of 6 types of footprints. In this scheme, footprint types I and II represent the typical and intermediate high-arched foot, respectively. Types III and IV represent normal foot variants, while type V corresponds to the low-arched foot and type VI to the severe flat foot, the latter often encountered in pathological conditions. There was statistically significant difference (P ⬍ .05) in footprint-type frequencies between boys and girls of ages 7, 9, 11, 14, and 15, which probably indicates the difference in growth potential of the foot between sexes. The proportion of high- and low-arched foot types decreased with increasing age in both boys and girls. Even though critical changes of the foot are believed to occur during pre-school development, this study shows that considerable changes also take place during school age and until late adolescence. ( The Journal of Foot & Ankle Surgery 44(6):424 – 428, 2005) Key words: footprint, foot morphology, foot growth, foot growth natural history, footprint classification
T he classification of foot morphology based on its medial longitudinal arch (MLA) height is still a controversial topic for foot and ankle specialists. The variety of techniques that have been used to assess the MLA indicates that a single and reliable method has not been universally adopted. Ink or digital footprints (1, 2) and photographic techniques (3) are
Address correspondence to: Panagiotis Stavlas, MD, 53, Mitropoulou St., TK 12462, Dasos Chaidari, Athens, Greece. E-mail: [email protected] 1 Orthopaedic Fellow, Department of Orthopaedics, University Hospital of Aarhus, Aarhus, Denmark. 2 Consultant Orthopaedic Surgeon, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. 3 Resident, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. 4 Resident, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. 5 Resident, Department of Orthopaedics, “Thriassio” General Hospital, Athens, Greece. Copyright © 2005 by the American College of Foot and Ankle Surgeons 1067-2516/05/4406-0002$30.00/0 doi:10.1053/j.jfas.2005.07.023
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indirect methods of measurement, whereas direct methods include somatometric measurements, clinical assessment (4), radiographic evaluation (5), or ultrasonography quantification (6). There are specific limitations associated with each of these techniques. Radiographic and other imaging methods carry potential health risks, especially for the pediatric population, and are costly and subject to different methods of interpretation. On the other hand, although clinical evaluation is the most applicable method for the assessment of foot shape, it can be subjective. One of the most widely used methods for the study of the MLA is the footprint. A typical footprint consists of the hindfoot (or calcaneus) imprint, the midfoot imprint (with the intelligible foot arch and the isthmus of the foot), and the forefoot imprint (with the metatarsal heads and the toes). Several measurement methods and footprint parameters have been proposed to classify the foot into lower, normal, and higher arch types (1–3, 7–9). These parameters quantify the shape of the foot by considering that the height of the MLA must directly correlate to the shape of the footprint (2, 7).
FIGURE 1 Footprint parameters. s, footprint angle; arch index, B/(A ⫹ B ⫹ C); Chippaux-Smirak index, g/f(%)
Schwartz et al proposed the use of the footprint angle in the evaluation of footprints (10). This angle was defined between the line connecting the most medial points of the heel and metatarsal regions, and the line connecting the most lateral point on the medial foot border to the most medial point of the metatarsal region. They assumed that as the arch becomes higher, this arch angle increases. Clarke modified Schwartz’s method slightly and provided additional objective data (8). Cavanagh and Rodgers introduced the arch index and classified footprints in 3 categories (high, normal, and flat arch) using the ratio of the area of the middle third of the toeless footprint to the total toeless footprint area (7). The ChippauxSmirak index is another parameter that has been used in footprint evaluation (11, 12). It describes the ratio of the maximal width of the metatarsal region to the minimal width of the arch region on the footprint. A large index indicates a high width in the arch area (Fig 1). In 1984, the senior author of this study (T.B.G.) proposed a wider footprint classification system (13). According to this method, the main parameters of a footprint can be identified are shown in Fig 2. Six footprint types can be differentiated, depending on the relationship between these parameters. In footprint type I, the longitudinal axis of the calcaneus (LAC) axis lies lateral to the longitudinal axis of the foot (LAF) axis, and there is no isthmus imprint (x ⫽ y). This footprint type represents the typical high-arched foot. The intermediate higharched foot is represented by footprint type II, where y ⬎ x ⱖ 3/4 y. In footprint type III, the isthmus is wider such that 3/4 y ⬎ x ⱖ 2/4 y. This is considered to be a normal footprint type, similar to type IV, where 2/4 y ⬎ x ⱖ 1/4 y. In the latter, the LAC axis lies lateral or on the LAF axis. In type V, the isthmus is very wide. The LAC axis is over or lies medial to the LAF axis and 1/4 y ⬎ x ⱖ 0. This footprint type represents the
FIGURE 2 A typical footprint and the 6 footprint types are shown. The longitudinal axis of the foot (LAF) is the line from the center of hindfoot (or calcaneus) imprint to the second toe. The longitudinal axis of calcaneus imprint (LAC) is the line that dissects the imprint of the hindfoot (the so-called calcaneal oval or calcaneal egg). In every footprint, a line (M) is drawn along the medial border of the foot. A perpendicular line (y) is then drawn, from line (M) to the lateral outline of the isthmus, corresponding to the width of midfoot. An additional line (x), which is parallel to (y), is drawn in the midfoot, corresponding to the width of the arch. As it is clearly seen, the result of y-x is the width of the isthmus of the footprint. According to the relationship between these axes (LAF and LAC) and lines (x and y), 6 footprint types are described (see text for details).
low-arched foot. In type VI, x is greater than y, and the LAC axis lies medial to the LAF axis. This type is found in pathological conditions with severe flat foot (that is, vertical talus, tarsal coalition). It is thought that the development of the MLA of the foot occurs mainly in the pre-school years of life (14, 15). The aim of our study was to analyze the evolution of foot morphology in a large population of school-aged children. These findings can then be correlated to previous studies that have reported MLA development to continue after pre-school age and gradually increase during growth (16 –18). The establishment of reliable criteria to identify specific foot types (that is, flatfoot) that may require management continues to evolve. It is hoped that the results of this survey could contribute to this ongoing discussion (4, 19, 20). Materials and Methods Footprints were analyzed from both feet of 5,866 children (2,935 boys and 2,931 girls) aged between 6 and 17 years. The survey was carried out in 31 elementary and high schools in the area of Western Attica in Greece. Informed consent was obtained from the parents of all children after both a verbal and a written explanation of the study. Children who demonstrated a history of neuromuscular disease or lower-limb injury, abnormal gait and discomfort in walking, or any kind of foot deformity were excluded from the
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TABLE 1 Age group
6 7 8 9 10 11 12 13 14 15 16 17 Total
TABLE 2 Age group
6 7 8 9 10 11 12 13 14 15 16 17 Total
Footprint type values of right feet among boys and girls, with respective percentages in parentheses n
110 312 326 430 466 466 626 626 626 626 626 626 5866
Boys
Girls
I
II
III
IV
V
I
II
III
IV
V
1 (1.8) 6 (3.8) 8 (4.8) 9 (4.1) 11 (4.7) 11 (4.7) 15 (4.8) 9 (2.8) 1 (0.3) 1 (0.3) 3 (0.9) 5 (1.6)
12 (21.8) 24 (15.3) 31 (18.7) 31 (14.4) 43 (18.4) 46 (19.7) 36 (11.5) 47 (15) 25 (8) 22 (7) 27 (8.6) 24 (7.6)
29 (52.7) 94 (60.2) 96 (58.1) 137 (63.7) 150 (64.3) 130 (55.8) 221 (70.6) 203 (64.8) 233 (74.4) 258 (82.4) 255 (81.4) 264 (84.3) 2935
8 (14.5) 14 (8.9) 19 (11.5) 29 (13.4) 21 (9) 28 (12) 25 (8) 27 (8.6) 36 (11.5) 19 (6) 22 (7) 18 (5.7)
5 (9) 18 (11.5) 11 (6.6) 9 (4.1) 8 (3.4) 18 (7.7) 16 (5.1) 27 (8.6) 18 (5.7) 13 (4.1) 6 (1.9) 2 (0.6)
2 (3.6) 9 (5.7) 6 (3.7) 15 (6.9) 11 (4.7) 13 (5.5) 13 (4.1) 6 (1.9) 1 (0.3) 4 (1.2) 4 (1.2) 3 (0.9)
12 (21.8) 29 (18.5) 28 (17.3) 46 (21.4) 40 (17.1) 42 (18) 41 (13) 28 (8.9) 40 (12.7) 34 (10.8) 24 (7.6) 27 (8.6)
30 (54.5) 97 (62.1) 108 (67) 132 (61.4) 161 (69) 157 (67.3) 231 (73.8) 236 (75.4) 251 (80.1) 256 (81.7) 265 (84.6) 264 (84.3) 2931
7 (12.7) 17 (10.8) 10 (6.2) 10 (4.6) 10 (4.3) 17 (7.3) 17 (5.4) 26 (8.3) 14 (4.4) 14 (4.4) 18 (5.7) 14 (4.4)
4 (7.2) 4 (2.5) 9 (5.6) 12 (5.5) 11 (4.7) 4 (1.7) 11 (3.5) 17 (5.4) 7 (2.2) 5 (1.6) 2 (0.6) 5 (1.6)
Footprint type values of left feet among boys and girls, with respective percentages in parentheses n
110 312 326 430 466 466 626 626 626 626 626 626 5866
Boys
Girls
I
II
III
IV
V
I
II
III
IV
V
1 (1.8) 1 (0.6) 10 (6) 6 (2.8) 14 (6) 10 (4.3) 13 (4.1) 9 (2.8) 3 (0.9) 2 (0.6) 2 (0.6) 3 (0.9)
13 (23.6) 23 (14.7) 29 (17.5) 44 (20.4) 48 (20.6) 45 (19.3) 38 (12.1) 54 (17.2) 31 (9.9) 28 (8.9) 33 (10.5) 31 (9.9)
29 (52.7) 103 (66) 96 (58.1) 127 (59) 148 (63.5) 135 (57.9) 223 (71.2) 196 (62.6) 235 (75) 249 (79.5) 242 (77.3) 257 (82.1) 2935
6 (10.9) 14 (8.9) 20 (12.1) 27 (12.5) 15 (6.4) 31 (13.3) 21 (6.7) 29 (9.2) 25 (8) 22 (7) 26 (8.3) 17 (5.4)
6 (10.9) 15 (9.6) 10 (6) 11 (5.1) 8 (3.4) 12 (5.1) 18 (5.7) 25 (8) 19 (6) 12 (3.8) 10 (3.2) 5 (1.6)
2 (3.6) 7 (4.4) 5 (3.1) 12 (5.5) 15 (6.4) 12 (5.1) 12 (3.8) 6 (1.9) 1 (0.3) 3 (0.9) 3 (0.9) 2 (0.6)
12 (21.8) 35 (22.4) 26 (16.1) 54 (25.1) 44 (18.8) 49 (21) 43 (13.7) 35 (11.1) 43 (13.7) 40 (12.7) 31 (9.9) 34 (10.8)
31 (56.3) 93 (59.6) 111 (69) 127 (59) 155 (66.5) 151 (64.8) 227 (72.5) 234 (74.7) 243 (77.6) 250 (79.8) 257 (82.1) 257 (82.1) 2931
7 (12.7) 17 (10.9) 10 (6.2) 11 (5.1) 7 (3) 15 (6.4) 17 (5.4) 16 (5.1) 16 (5.1) 14 (4.4) 17 (5.4) 14 (4.4)
3 (5.4) 4 (2.5) 9 (5.6) 11 (5.1) 12 (5.1) 6 (2.5) 14 (4.4) 22 (7) 10 (3.2) 6 (1.9) 5 (1.6) 6 (1.9)
study. The sample was divided into 12 different age groups at 1-year intervals, and every age group was subdivided into male and female subgroups. The Harris and Beath footprinting mat (Apex Foot Health Industries, South Hackensack, NJ) was used to obtain dynamic (walking) bilateral footprints in every child (21). Prior to use, the mat was lightly and evenly inked on its ridged side with oil-soluble print ink with a printer’s roller. A sheet of slightly absorbent paper was carefully placed over the inked mat, and the child was instructed to walk over the mat using the length of the walkway. The ink footprint was then retrieved, and the border of the acquired image was immediately outlined with a pencil to ensure that any future distortion or spread of the ink could be easily recognized. The interpretation of the footprints was done by the first 2 authors of this study (P.S. and T.B.G.) with Grivas’ classification method (13). Statistical analysis of a total of 11,732 footprints was done using the Wilcoxon signed-rank test for matched pairs to determine if there was any differ426
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ence in morphology between right and left foot among groups. The Mann-Whitney 2-sample rank-sum test was performed to identify any difference in the frequency of footprint types between boys and girls in each age group. Finally, the chi-square for trend test was used to determine if there was any tendency for change of the frequency of the observed footprint types during growth. P values of less than .05 were considered to be significant.
Results Tables 1 and 2 demonstrate the detailed distribution of footprint types according to sex (boys/girls) and the laterality of the foot (right/left). No type VI footprint was found in any child in this population. No significant differences (P ⫽ .1) were found between the right and left footprints. In contrast, there was a statistically significant relationship between sex and footprint in some specific age groups. Specifi-
FIGURE 3 A graph demonstrating the footprint-type frequencies in boys among age groups.
FIGURE 4 A graph demonstrating the footprint-type frequencies in girls among age groups.
cally, the distribution of footprint-type frequencies between boys and girls differed significantly (P ⬍ .05) at the ages of 7, 9, 11, 14, and 15. Boys appeared to demonstrate significantly higher rates of low-arched feet compared with girls of the same age. In both sexes, there was a tendency to reach higher rates of normal footprint types compared with the low- and higharched types during the growth of the foot (P ⬍ .01 for boys and P ⬍ .001 for girls) (Figs 3 and 4). Discussion Footprint evaluation is an old but time-tested method to delineate foot morphology. It remains an inexpensive, fast, simple, noninvasive, and reliable method that can be used effectively for screening and follow-up studies (16, 21, 22). The basic concept behind its application is that a higher
MLA produces a narrower isthmus imprint, whereas a lower arch causes a flattening of the cavity and a wider isthmus area on the imprint (2, 7, 16). Numerous parameters have been proposed for the evaluation of the footprint, such as the footprint angle, the arch index, and the Chippaux-Smirak index (1–3, 7–13). Some studies report that there is no relationship between directly measured arch height and footprint parameters (9), or radiographs and footprint parameters (5). However, the majority of authors have stated that these parameters provide a valid basis for prediction or categorization of arch height (7, 8, 16). Gilmour and Burns also demonstrated a relationship between arch index and a clinical measurement of the vertical height of the navicular, and concluded that footprints can be as reliable as clinical measurements to delineate the shape of the foot (2). Furthermore, in a study of 38 children with flexible pes planus, Kanatli et al found a positive correlation between radiographic angles and the arch index determined from footprint analyses (22). Nevertheless, it seems that there exists a broad range of normal values and foot shapes, which has not been reported by previous studies of foot morphology based on footprint evaluation. In these past studies, the sample size may have not been sufficiently large or wide in age distribution to establish all the foot variants (3, 21, 23). The current study used a classification system (13) that attempted to include all foot types (Fig 2). This grading system could be considered an expansion of Morley’s original classification, which included children aged 1 to 11 years (23). It should be noted that the extreme types of low-arched and high-arched foot should not be misinterpreted as pes planus and cavus foot, respectively. These entities represent more complex severe deformities or pathological conditions that involve alterations in other parts of the foot not always disclosed by footprints. As was expected, no type VI was found in this series, as was the case in previous studies (13). This foot type possesses structural abnormalities, which can be traced on a footprint, and is often encountered in pathological conditions like tarsal coalition or vertical talus. The fact that these children may require operative treatment at an early (pre-school) age, and that foot pathology was the exclusion factor of this study, may explain why this type of footprint was not found in our study population. The significant difference in the frequency of footprint types between boys and girls among ages 7, 9, 11, 14, and 15 years may reflect the different growth potential between the sexes. Jaworski and Puch found that the footprint angle increases up to age 13 in girls and 15 in boys, whereas the Chippaux-Smirak index decreases up to age 11 in boys and 12 in girls (24). Both findings indicate that the physiological process of foot development from the low-arched types to normal types occurs earlier in girls compared with boys, which is consistent with our results. In the present study, the frequency of both low (type V)
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and high (type I and II) MLA feet found in the youngest age groups decreased with age, whereas the opposite was observed for the normal types III and IV. This is in accordance with earlier studies (2, 16, 25). Previous reports have also suggested that there is a significant development of the MLA of the foot, particularly in the pre-school years (14, 15). Although it is well established that the major morphological changes and adaptation of the foot occur during this period, this study demonstrates that ongoing development of foot structures also takes place during school ages. The lowarched foot observed in young children may be a manifestation of constitutional laxity of the ligaments, which improves as the foot matures (1, 15), and our study supports this over a wide range of ages. Even though some evidence exists concerning the influence of weight gain during growth, as seen with static and dynamic plantar pressures and flattening of the MLA, the foot complex appears to be able to maintain the longitudinal arch through compensatory mechanisms (26). Mann and Hagy suggested that better muscle and balance control is expected to develop as a child’s central nervous system matures, subsequently allowing for better control of the lower limb and a more normalized stance (27). Furthermore, the gradual ossification of bony structures may lead to better stabilization of the arch during weightbearing (28). Finally, considering that the ongoing external tibial rotation, from the in-toeing position after birth to the out-toeing position during growth, results in proportional decrease in the valgus configuration of the hindfoot and elevation of the MLA (29). Some limitations of this study should also be mentioned. As pathological deformities and/or pain develop over time, it is probable that a greater proportion of children could have been excluded from the older age groups compared with the younger age groups. This may create the appearance of a decrease in low- and high-arched feet over time. Moreover, during the last several decades, the high variability of this population, due to the increasing immigration of a considerable number of people into Greece from several nations, could have changed the ethnological mix of the different age groups. The exact magnitude to which these factors could have contributed to the outcome is not known. This study is not considered to be a solution to the controversy over the efficacy of footprints in delineating foot morphology and classifying the normal variants of foot shape during growth. It is a study based within a large pediatric population (and, to the best of our knowledge, is the largest such population that has ever been evaluated), where the necessity for a wider classification of footprints became evident. As genetic and extrinsic factors are expected to influence foot development during the entire growth period, it is not surprising that changes in foot morphology were depicted beyond the age of 6 through adolescence. Thereby, the surgical treatment of adolescent foot conditions should be approached with these findings in mind.
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