What condition results from the severing of the upper trunk nerves at C5-6?

The condition that results from the severing of the upper trunk nerves at C5-6 is known as Erb's Palsy. This condition occurs when there is an injury to the brachial plexus, specifically affecting the upper trunk, which is formed by the fifth and sixth cervical nerves.

In the case of Erb's Palsy, the injury often leads to weakness or paralysis of the muscles that are innervated by these nerve roots, which primarily include those that control shoulder abduction, elbow flexion, and forearm supination. Typical signs include the inability to raise the arm, a characteristic “waiter's tip” posture with the arm adducted and internally rotated, and weakness in the wrist and hand.

Understanding Erb's Palsy is important in the context of obstetric brachial plexus injuries that can occur during childbirth, but it can also result from trauma or other causes. The specific involvement of the C5-6 nerve roots in this scenario clearly identifies it as distinct from other conditions listed, as these involve different nerve roots and anatomical structures.