Erb palsy is due to paralysis of which part of the nervous system?

Erb palsy, also known as Erb-Duchenne palsy, is primarily the result of injury to the upper trunk of the brachial plexus. This condition often occurs during childbirth, particularly in cases where the infant's shoulder becomes impacted in the birth canal, leading to excessive stretching of the nerves that arise from the cervical spine segments C5 and C6.

Injuries to this area of the brachial plexus can result in weakness or paralysis of the muscles that control the shoulder, arm, and hand on the affected side. Patients may present with characteristic symptoms such as an arm that hangs by the side and is rotated internally, often referred to as the "waiter's tip" position. This focuses on the functional aspects of the upper arm and the shoulder, while the lower brachial plexus and other options listed would not typically result in the same clinical picture associated with Erb palsy.

Understanding the anatomy and physiology of the brachial plexus is critical for the diagnosis and management of conditions like Erb palsy, emphasizing the significance of the upper brachial plexus injuries in this context.