What is the primary injury type associated with Erb-Duchenne palsy?

• A. Lower brachial plexus injury
• B. C5-6 traction injury of the brachial plexus
• C. C8-T1 neuropathy
• D. Upper extremity fracture

Answer: (B)

Erb-Duchenne palsy is primarily caused by a traction injury to the upper trunk of the brachial plexus, specifically affecting the C5 and C6 nerve roots. This injury often occurs during delivery when excessive lateral traction is applied to the head and neck of the infant.

The mechanics of this injury involve overstretching of the nerves, which can result in motor and sensory deficits in the affected arm, manifesting as weakness in shoulder abduction, external rotation, and elbow flexion. The arm may present with a characteristic position where it hangs by the side with the shoulder adducted and internally rotated, resembling a "waiter's tip" posture.

Understanding the anatomy and the specific nerve roots involved helps clarify why the C5-6 traction injury is the most relevant diagnosis for Erb-Duchenne palsy as opposed to other injury types or conditions. Other options listed relate to different mechanisms of nerve damage or injuries not specifically associated with this classic presentation.