Plantar response in infancy

The objective of the study was to characterize the plantar response at various ages in infancy in Indian children. The subjects were 1281 apparently healthy children born at term and without any history suggestive of neurological disease, enrolled between the ages of 1 and 12 months. The plantar response was elicited in both feet by thumbnail drag method and graded as flexor, extensor and equivocal. The percentage of extensor, flexor and equivocal responses was compared between right and left foot and the average of these two responses was compared between the age categories [1-3 months (n=389), 3.1-6 months (n=332), 6.1-9 months (n=354) and 9.1-12 months (n=206)]. Frequency (%) of various combinations of bilateral responses was also calculated for different age categories. Results showed that the extensor plantar response was the predominant response till 6 months of age. Bilateral extensor response was seen in 79.4%, 67.8%, 32.5% and 31.1% in the four age categories respectively; bilateral flexor response in the corresponding age groups was 0.3%, 5.1%, 26.6% and 39.3% respectively. The percentage of asymmetrical responses was 20.7%, 25.3%, 40.3%, and 28.7% in different age categories. We concluded that normal plantar response is predominantly extensor in early infancy; the transition to flexor response starts occurring after 6 months of age. A fairly high number of infants continue to have an extensor response even after 6 months; and the transition may be advanced in one foot leading to asymmetrical plantar response.