During quiet wakefulness, hypotonic neonates have a characteristic posture. Their arms are either flexed at the elbow with the backs of the hands resting against the bed (Figure 88.1 [A]) or extended with the palms facing up or down. Their legs are fully abducted and flexed at the knees so that the lateral aspect of the thighs rest on the bed. In contrast, normal neonates have their arms raised from the bed and flexed at the elbows during quiet wakefulness, and their hips and knees are flexed so that only the gluteal region and the soles of the feet rest on the bed (Figure 88.1 [B]).
Figure 88.1.— [A] Posture of a hypotonic neonate (click on picture). [B] Posture of a normal neonate.
ARM TRACTION RESPONSE
The arm traction response is obtained by slowly pulling the neonate by the hands to achieve a sitting position. A hypotonic neonate shows head lag, no arm pull is felt by the examiner, the arms remain extended as the body is pulled up, and the legs remain in contact with the bed (Figure 88.2 [A]). A normal neonate shows minimal head lag, a backward pull is felt by the examiner as the neonate’s arms are pulled, and there is flexion of the elbows, knees, and ankles (Figure 88.2 [B]).
Figure 88.2.— [A] Hypotonic arm traction response. [B] Normal arm traction response.