Upper-Middle Trunk Syndrome
Upper-middle trunk syndrome is characterized by a posture similar to the upper trunk syndrome but, in addition, there is weakness of extensors of the elbow, wrist, and fingers. Neonates with upper-middle trunk lesions do not have the typical flexion of the wrist that occurs with Duchenne-Erb palsy. Upper-middle trunk syndrome indicates involvement of the fibers of the C5-C7 spinal segment. The damage may occur at the roots (Figure 219.1; VR), spinal nerves (Figure 219.1; SN), ventral ramus (Figure 219.1; VRa), or trunks (Figure 219.1; ST and MT).

Figure 219.1.— Schematic representation of the brachial plexus. C5-8: cervical spinal segments. T1: first thoracic spinal segment. DR: dorsal root; VR: ventral root; DG: dorsal ganglia; SN: spinal nerve; DRa: dorsal ramus; and VRa: ventral ramus. The structures that constitute the brachial plexus include trunks (T), divisions (D), cords (C), branches (B) and nerves (N). SC: spinal cord; SF: sympathetic fibers to the eye; ST: superior trunk; MT: middle trunk; LT: lower trunk; A: anterior; P: posterior; LC: lateral cord; MC: middle cord; PC: posterior cord; LB: lateral branch; MB: medial branch; IB: internal branch; AB: anterior branch; PB: posterior branch; MC: musculocutaneous nerve; M: median nerve; U: ulnar nerve; Ax: axillary nerve; R: radial nerve.