Erb-Duchenne palsy

**Anatomy/Pathophysiology:** Injury to the upper trunk of the brachial plexus (C5-C6 roots, sometimes C7), usually from excessive lateral traction/stretch that widens the head-shoulder angle. Common causes: shoulder dystocia in vaginal delivery (macrosomia, maternal diabetes, instrumental delivery, breech), and in adults, motorcycle accidents or falls onto the shoulder. Injury ranges from neurapraxia (most common, recovers) to axonal rupture, to root avulsion (poorest prognosis).

**Muscles/nerves affected:** - Deltoid and teres minor (axillary n.): loss of shoulder abduction - Supraspinatus (suprascapular n.): loss of initial abduction (0-15°) - Infraspinatus (suprascapular n.): loss of lateral rotation, so the arm is medially rotated - Biceps brachii, brachialis, brachioradialis (musculocutaneous n./radial n.): loss of elbow flexion and supination, so the elbow is extended and the forearm pronated - Rhomboids, levator scapulae (dorsal scapular n.), serratus anterior (C5-C7) may be involved - Sensory loss over the lateral arm and forearm (C5-C6 dermatomes)

**Clinical presentation:** "Waiter's tip" (porter's tip) posture: arm adducted and medially rotated, elbow extended, forearm pronated, wrist flexed. Asymmetric (absent) Moro reflex on the affected side. The grasp reflex is preserved because C8-T1 are intact (hand function is spared). Diaphragm paralysis (C3-C5, phrenic nerve) or Horner syndrome suggests more extensive injury.

**Associated findings:** Clavicle fracture and humeral fracture are common with birth trauma. Rule out these and cervical spine injury.

**Differential:** - Klumpke palsy: lower trunk (C8-T1), claw hand, Horner syndrome (T1 sympathetic involvement), intrinsic hand muscle weakness, often from upward traction (e.g., grabbing a branch while falling) or Pancoast tumor involvement - Clavicle fracture (pseudoparalysis) - Humeral fracture - Cerebral palsy

**Management/Prognosis:** Most cases (about 80-90%) resolve spontaneously within months with conservative care: gentle range-of-motion exercises, physical therapy, and avoiding aggressive early manipulation. Lack of biceps recovery by about 3-6 months is a surgical indication (nerve grafting/transfer, e.g., via microsurgery). Prognosis is worse with root avulsion, Horner syndrome, and complete plexus involvement.

**High-yield boards pearls:** - Erb = "Erb's point" (C5-C6 convergence), "Waiter's tip" - Upper trunk = C5-C6 - Klumpke = lower trunk, C8-T1, "claw hand" - Risk factors: macrosomia, shoulder dystocia, gestational diabetes - Hand grasp is intact in Erb palsy