Final answer:
The answer is Popliteal angle, which is used to assess the flexion and extension of the infant's knee joint.
Step-by-step explanation:
The measurement described in the question refers to the Popliteal angle, which is an assessment used in pediatric examinations to evaluate the flexion and extension of the knee joint. It is performed by holding the infant's thigh against the abdomen and gently lifting upward at the heel to measure the angle formed by the knee joint. The Popliteal angle can provide information about neuromuscular development, with tighter angles suggesting possible increased muscle tone or contractures.