Obstetric Brachial Plexus Injury
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Direct answer
Downward traction on the fetal head during a shoulder dystocia — or less often, unaided intrauterine forces — stretches the C5–T1 nerve roots and produces obstetric brachial plexus injury. Erb palsy (C5–C6) produces the waiter's-tip arm — adducted shoulder, extended elbow, pronated forearm with intact grasp — and accounts for the vast majority; Klumpke palsy (C8–T1) gives a claw hand with possible Horner syndrome and is far rarer. Most upper-trunk injuries recover spontaneously within months, but absence of biceps recovery by around three months is the accepted trigger for referral to brachial plexus surgery. Prevention lies in dystocia manoeuvres, never fundal pressure.
What you must remember
- Erb palsy (C5–C6, upper trunk): arm adducted and internally rotated, elbow extended, forearm pronated, wrist flexed — "waiter's tip" posture; grasp is preserved, which distinguishes it from more extensive injury.
- Klumpke palsy (C8–T1, lower trunk): claw hand from intrinsic muscle weakness; a coincident Horner syndrome (ptosis, miosis) signals avulsion near the stellate ganglion and a worse prognosis; phrenic nerve palsy with diaphragmatic paralysis can accompany upper injuries.
- Narakas classification: group 1 (C5–6) recovers well; group 2 (C5–7) moderate outcome; group 3 (C5–T1) poor spontaneous recovery; group 4 (pan-plexal with Horner) worst — flail arm and sympathectomy signs.
- Prognostic anchor: return of biceps function by 3 months (some units accept 3–6) predicts near-complete spontaneous recovery; failure by that point prompts MRI (CT myelography historically) and microsurgical consideration.
- Risk factors: birth weight above 4 kg, shoulder dystocia, prolonged second stage, instrumental (especially rotational) delivery, maternal diabetes; a minority occur without any dystocia, from intrauterine forces — important when defence counsel asks.
- Immediate management: physiotherapy with passive range-of-motion exercises from the first weeks to prevent contractures, plus developmental follow-up; "physiotherapy within the first weeks, surgery if biceps fails by 3 months" is the exam sentence.
- Prevention at the shoulder: McRoberts manoeuvre with suprapubic pressure, avoid fundal pressure and excessive lateral head traction, consider prophylactic caesarean for estimated weight above 4.5 kg in a diabetic mother (4–4.5 kg thresholds debated per unit protocol).
- Associated findings to examine for: clavicle or humerus fracture (pseudoparalysis mimics palsy — X-ray first if uncertain), facial palsy, and respiratory effort if phrenic involvement is suspected.
Reading the newborn arm correctly
A 4.4 kg baby of a diabetic mother is born after a shoulder dystocia resolved with McRoberts; the right arm hangs limp at the side, elbow straight, forearm pronated, but the baby grips the examiner's finger. That grip is the diagnostic pivot: it localises the lesion to the upper trunk (Erb pattern) and spares the hand, which predicts a good outcome. Passive shoulder and elbow movements begin under physiotherapy within the first week, and the parents are told the truth about natural history — most such arms recover substantially by 6–12 months. The arm that must raise suspicion differently shows a motionless hand and fingers with a small pupil on the same side: Klumpke-plus-Horner implies lower-trunk avulsion, and the neonatal team plans imaging and early referral. A third baby holds the arm still but moves it fully on stimulation — pseudoparalysis; the X-ray shows a fractured clavicle, and the "palsy" resolves with the fracture. Three limps, three anatomies, three prognoses — this discrimination is what the exam rewards.
How the exam frames it
The viva marches through predictable stations: name the root values, define the posture, grade it by Narakas, and state the surgical referral timing. The trap that eliminates candidates is assuming injury equals dystocia — examiners quote that a proportion of brachial plexus injuries occur without any shoulder problem, sometimes with caesarean births, and expect the candidate to know litigation around this exists. The second trap is confusing Erb and Klumpke grasps: Erb keeps the hand, Klumpke loses it. A third recurring question pairs the injury with its prevention — why fundal pressure is condemned (it impacts the shoulders against the pelvis and worsens traction) and why supra-pubic rather than fundal pressure is used. Finally, imaging logic: chest X-ray may show an elevated hemidiaphragm from phrenic palsy. Quoting the biceps-by-three-months rule earns the closing marks.
Frequently asked questions
Which root levels are injured in Erb and Klumpke palsies?
Erb palsy involves C5–C6 (upper trunk) causing the waiter's-tip posture; Klumpke involves C8–T1 (lower trunk) causing a claw hand.
What sign suggests root avulsion and a poor prognosis?
Horner syndrome alongside the palsy — it implies injury extending toward the sympathetic chain, typical of pan-plexal (Narakas group 4) lesions.
When should surgical referral be considered?
When biceps function has not recovered by around 3 months of age, despite physiotherapy from the first weeks.
Can brachial plexus injury occur without shoulder dystocia?
Yes — intrauterine maladaptation and labour forces cause a minority of cases, including some after caesarean birth, which is important in medico-legal discussion.
Why must clavicle fracture be excluded in a floppy newborn arm?
Pseudoparalysis from a painful clavicle or humeral fracture mimics palsy; the limb moves fully once pain settles, and the X-ray prevents needless referral.