Measurements of Normal Feet- A Guide to Prosthetic Selection
JOHN MacPHAIL WILTON BUNCH
At a recent meeting of the Amputee Clinic Chiefs it became apparent that foot-size standards for bilateral lower-limb amputees are not available. As a result, the size selected is usually based entirely on intuition. The study reported here was undertaken to provide data to aid in the selection of correctly sized prosthetic feet.
Methods and Materials
The measurements of one hundred and sixty children ranging in age from 5-11 years were studied. These children attended an elementary school in a predominantly white, middle-class neighborhood into which 20 percent black and 10 percent lower-economic-level white children are bussed. Thus the data pertain to a reasonably heterogenous population.
Four measurements were taken: height, arm span, palm length (tip of long finger to proximal palmar crease), and foot length. These values were plotted as a function of age, and the ratio of foot length to each of the other three measures was calculated.
Results and Discussion
All four measurements are a linear function of age ( Table 1 ). Within this population sex differences were not significant and therefore the sexes are grouped. The ratio of height to arm span for the entire population was 1.01 ± .03. Table 2 shows that this value is remarkably constant throughout the age group under study.
The ratio of specific interest in the study, foot length to arm span, and foot length to palm span, were also surprisingly constant ( Table 3-A and Table 3-B ). The mean ratio of foot length to arm span was .159 ± .006. The mean ratio of foot length to palm length was 1.43 ± .06. As shown in the tables, these ratios do not change significantly between the ages of 5 and 11 years.
It would seem, therefore, that the choice of proper foot size and prosthetic length in lower limbs is quite simple. The length of the prosthetic foot in a child should be 16 percent of the arm span or about 1.5 times the palm length. The height of the child should be equal to his arm span.
In growing children of elementary school age, there are constant relationships between the length of the foot, height, arm span and palm length. The child amputee clinic team and the prosthetist should find the calculated ratios an aid in determining prosthetic foot size and height in bilateral lower-limb prostheses.