A 6-week-old baby boy presents to the clinic for evaluation. The mother is concerned that her baby is having difficulty moving his left arm. The prenatal course was unremarkable. The baby was born via vaginal delivery at full-term and weight 8 pounds 9 ounces at birth. The mother mentions that the baby's head became stuck and that they required forceps to pull the baby out. Physical examination reveals a healthy baby whose weight is 10 pounds 6 ounces with an appropriate length and head circumference. There is absent deltoid and biceps function in the left arm. Function in the left hand seems to be normal.
C) C5-C6
This patient is suffering from Erb palsy, which most likely occurred secondary to a traction-related injury during the complicated delivery. Patients with Erb palsy have damage to the upper trunk (C5-C6) of the brachial plexus. Patients with Erb palsy have weakness of abduction from deltoid paralysis (C5), weakness of external rotation from infraspinatus paralysis (C5), and loss of flexion from biceps paralysis (C6). The internal muscles of the hand are unaffected. The result is an arm that hangs limply by the side in extension and internal rotation. Injury is usually caused by shoulder dystocia, resulting in traction on the shoulder, which damages the upper brachial plexus roots.
Answer choice A: C3-C4, is incorrect. C3-C4 is not part of the brachial plexus, so injury to these nerve roots would not result in the findings seen in this patient.
Answer choice B: C4-C5, is incorrect. C4 is not part of the brachial plexus, so injury to this nerve root would not result in Erb palsy.
Answer choice D: C5-C7, is incorrect. Damage to C7 is not part of Erb palsy. Injury to nerve roots C5-C7 can result in injury of the musculocutaneous nerve, causing an inability to flex or supinate the arm.
Answer choice E: C8-T1, is incorrect. Injury to the lower roots of the brachial plexus at C8-T1 causes total clawing of the hand because of paralysis of the lumbricals and finger extensors. This is known as Klumpke palsy.
Key Learning Point
Erb palsy results from damage to nerve roots C5-C6 and results in weakness of abduction from deltoid paralysis (C5), weakness of external rotation from infraspinatus paralysis (C5), and loss of flexion from biceps paralysis (C6).
