You attend the delivery of an LGA infant of a diabetic mothe…

You attend the delivery of an LGA infant of a diabetic mother. The delivery was complicated by shoulder dystocia. On your exam, you find the the infant is holding the left arm adducted and internally rotated with extension at the elbow, pronation at the forearm, and flexion of the wrist. The grasp is intact, but the moro is absent on the left arm. You are concerned about: