Which sign is exhibited when an infant's hamstring muscles spasms upon leg extension?

The sign exhibited when an infant's hamstring muscles spasms upon leg extension is known as the Kernig sign. This sign is typically tested in a clinical setting to assess for meningeal irritation or central nervous system pathology. When the leg is extended at the knee while the hip remains flexed, a positive response indicates irritation of the meninges, as the hamstring muscles contract spasmodically due to this irritation.

This response is particularly relevant in infants, as their neurological systems are still developing, and they may show different signs in comparison to older children or adults. Kernig's sign helps healthcare providers assess potential issues such as meningitis, where inflammation of the protective membranes covering the brain and spinal cord occurs.

In contrast, the other signs mentioned have different clinical significances. The Babinski reflex is a normal response in infants where the toes fan out when the sole of the foot is stroked. The Romberg sign tests balance and proprioceptive function and does not involve leg extension or muscle spasms. The Clonus response indicates a repetitive muscle spasm and is typically assessed in scenarios involving neurological conditions but is not specifically related to the hamstrings or leg extension in the same way as Kernig's sign.