Anesthesiology APPLIED Exam › Neuroanesthesia and neuromuscular

Peripheral nerve injury and positioning

Neuroanesthesia and neuromuscular·~5 min read· Physician-reviewed✓ Sourced · 4

Stem

A 63-year-old man, 112 kg, BMI 37, with type 2 diabetes, had a five-hour robotic prostatectomy in steep Trendelenburg with both arms tucked. On the morning after surgery he reports numbness of the fourth and fifth fingers of his left hand and cannot spread those fingers apart. The rest of his recovery is uneventful.

Question

How do you evaluate and manage this complaint, and what could have been done to prevent it?

Ideal answer

HeadlineMost likely an ulnar neuropathy, the most commonly injured nerve.¹ I go and examine him myself, document, tell him, and arrange neurology.

Map it: ulnar sensory loss, interossei, median and radial territories, so I separate an ulnar lesion from a C8 radiculopathy or a plexus lesion.
Document my positioning record next to my findings, so the review can match the deficit against what was done.
Tell him directly and refer: sensory symptoms usually recover over weeks to months, most purely sensory ulnar deficits within 6 months; a motor deficit is more likely to persist.¹
Prevention: I position the patient myself. Arms tucked, or on boards below 90 degrees abduction, supinated or neutral, elbow padded; head neutral; no shoulder braces in Trendelenburg.
Recheck every pressure point after draping and every table change; injuries still happen despite correct positioning, and I say so honestly.

Breaking down the answer

Why it is scored — ulnar and brachial plexus injuries make up two-thirds of nerve injury claims, mostly with no identifiable error, and nerve injury is second only to death in ASA Closed Claims.¹ It doubles as an OSCE disclosure station.
The mechanism — abduction beyond 90 stretches the plexus between the clavicle and first rib; pronation presses the ulnar nerve in the cubital tunnel. The 2018 ASA advisory limits supine abduction to 90° when possible: on an armboard, supinated or neutral; tucked, neutral.²
Patient factors — in Closed Claims most ulnar injuries had no identifiable mechanism and care usually met the standard; men are about four times more affected, and symptoms can appear days later.³
Lithotomy and lateral — stirrups compress the common peroneal nerve at the fibular head, so I pad it. Hip flexion beyond 90 degrees and abduction stretch femoral and obturator nerves, so I move both legs together.
Lateral and prone checks — chest roll shifts weight off the dependent axilla;² I check the dependent ear, eye and radial pulse. Prone: eyes free and checked every 30 minutes, arms tucked or below 90 degrees with elbows flexed, abdomen free, neck neutral.
Steep Trendelenburg — shoulder braces compress the plexus against the first rib, so I refuse them;² non-slip mattress, limited time and degree, watching for sliding and for cerebral and ocular edema.
Preexisting neuropathy and blocks — diabetes or chemotherapy carries a double-crush risk; I still offer a block, but I document the baseline exam and use ultrasound and low pressure.

Follow-up question

He asks whether you did this to him and whether his hand will recover. His surgeon wants nerve studies done today. What do you say and do?

Follow-up answer

HeadlineHe needs honesty and a plan, not reassurance: an ulnar nerve injury, which occurs even with careful positioning.

Sensory symptoms usually recover and motor weakness is more likely to persist, and I will follow him with neurology.¹ I do not blame anyone or speculate about mechanism. With the surgeon: an early study to localize the lesion and detect a preexisting one, and a repeat nerve conduction study and EMG at 3–4 weeks if the deficit persists, because denervation changes take that long.¹ I document the exam, the conversation and the positioning record, report through the institution's process, and reassess his strength before discharge.

Pitfalls that cost points

Describing padding as a guarantee; injuries occur despite correct positioning, and padding applied too tightly can itself cause injury.⁴
Sending the patient to neurology without localizing the lesion yourself.
Forgetting to disclose, document and report; professionalism is scored as much as anatomy.
Treating lithotomy as a lower-limb problem only; the hand beside the body is crushed when the foot of the table is raised.

Rapid-fire

Q: Why are men more prone to ulnar neuropathy? A: A larger coronoid tubercle, a thicker flexor retinaculum and less fat over the cubital tunnel compress the nerve more easily.¹

Q: Why does the axillary roll go under the chest? A: It lifts the chest wall off the dependent shoulder so the plexus and axillary vessels are not compressed; in the axilla it causes the injury it is meant to prevent.

Q: When do you obtain an EMG? A: Early, within the first week, to localize the lesion and detect a preexisting one, and again at 3–4 weeks, when denervation changes appear and severity can be graded.¹

Q: When is a leg in lithotomy at risk of compartment syndrome? A: After about 4 hours, especially with hypotension and leg elevation reducing perfusion pressure; I ask for the legs to be lowered periodically and limit time.

Numbers to know

Item	Value
Most common injury	Ulnar nerve, then brachial plexus¹
Arm abduction limit	90 degrees or less supine; armboard supinated or neutral, tucked neutral²
Hip flexion in lithotomy	Below 90 degrees, legs moved together
Onset of ulnar symptoms	Often delayed, days after surgery
Lithotomy compartment risk	Beyond ~4 hours
EMG timing	Baseline early; localizing study at 3–4 weeks

Sources

1.Peripheral nerve injuries from positioning · OpenAnesthesia (IARS) · openanesthesia.org
2.Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies 2018 (Guideline Central summary) · ASA (Anesthesiology 2018;128:11-26), via Guideline Central, 2018 · guidelinecentral.comThe journal page was unavailable (maintenance); summary quotes the advisory: limit supine arm abduction to 90 degrees when possible; tucked forearm neutral; padded armboards and chest rolls in the lateral position may be used; avoid shoulder braces in a steep head-down position; avoid BP cuffs below the antecubital fossa; simple postoperative nerve assessment; document positioning actions.
3.Ulnar Nerve Pressure: Influence of Arm Position and Relationship to Somatosensory Evoked Potentials · Anesthesiology (Prielipp et al.), 1999 · asa2.silverchair.comBackground cites Closed Claims data: ulnar neuropathy one third of nerve injury claims; men about 4 times more likely.
4.Patient Safety Tip of the Week: Preventing Perioperative Nerve Injuries (on the ASA 2018 advisory) · Patient Safety Solutions, 2018 · patientsafetysolutions.comQuotes the 2018 advisory: avoid the inappropriate use of padding (e.g., padding too tight) to decrease the risk of perioperative neuropathy.

Facts on this page were checked against these sources on Nov 2, 2026. Guidelines change; confirm doses against current institutional protocols.