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A 35-year-old woman, gravida 2, para 1, at 40 weeks gestation, comes to the hospital in labor. Her past medical history is significant for diabetes, which she has controlled with insulin during this pregnancy. Her pregnancy has been otherwise unremarkable. A baby boy is born via a spontaneous vaginal delivery. Physical examination shows he weighs 4.5-kg (9-lb), pulse is 140/min, respirations are 40/min, and he has good oxygen saturation on room air. His left arm is pronated and medially rotated. He is unable to move it away from his body. The infant’s right arm functions normally and he is able to move his wrists and all 10 digits. Which of the following nerve roots were most likely damaged during delivery?
Content Reviewers:Yifan Xiao, MD
In this disorder, there’s paralysis to the muscles of the shoulder and the upper arm, and it happens when the nerves that innervate these muscles are damaged.
People with this disorder have their arm stuck in a position that looks like a waiter discreetly trying to get a tip, so it’s also called waiter’s tip deformity.
Okay, so the nervous system has two parts: the central nervous system, which consists of the brain, brainstem, and spinal cord, and the peripheral nervous system, which includes all of the nerves that fan out from the central nervous system.
Broadly speaking, the nervous system is split into an afferent and an efferent division.
The afferent division brings sensory information from sensory receptors in the peripheral nervous system to the central nervous system, and the efferent division sends motor information from the central nervous system to organs like skeletal muscles, which causes them to contract.
Now, part of the peripheral nervous system are spinal nerves, which branch off the spinal cord.
There are 31 pairs of spinal nerves, which are grouped into eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves.
The brachial plexus is a network of spinal nerves that innervate the shoulder, arm, and hand, by supplying afferent or sensory nerve fibers from the skin, as well as efferent or motor nerve fibers to the muscles.
In terms of anatomy, the brachial plexus is divided into five roots, which come from the last four cervical nerves; C5, C6, C7, and C8, as well as the first thoracic nerve or T1.
The five roots will then combine to form three trunks: C5 and C6 merge to form the superior or upper trunk, C7 remains as the middle trunk, and C8 and T1 merge to form the inferior or lower trunk.
These trunks then form six divisions, which will regroup with each other to form three cords.
These cords give multiple branches.
The main three are the musculocutaneous nerve, which is made up of contributions from C5, C6, and C7, the axillary nerve – which is made up of contributions from C5 and C6, and the subscapular nerve, which is made up of contributions from C5 and C6.
Erb-Duchenne palsy happens when there’s an injury to the C5 or C6 roots, or to the upper trunk that contains nerve fibers from these roots.
This injury commonly occurs to the infant during labor, in a condition called shoulder dystocia, which is when the baby gets stuck in the birth canal when one or both shoulders become trapped against the bones of the maternal pelvis.
When the baby is pulled out, the force could cause damage to the shoulder and the nerves in the brachial plexus.
Although most common in infants, Erb-Duchenne palsy could affect people at any age when there’s shoulder trauma.
Okay, let’s look at what happens when someone gets this condition.