Study Notes · Shoulder Dislocations

Why the Nerve Exam Matters Before You Ever Touch the Joint

It's tempting to treat the neurovascular exam as a quick check before the "real" intervention — the reduction. In shoulder dislocation, the exam you do before you touch the joint may be the most medicolegally important thing you do all call.

A structured, reproducible neurovascular assessment isn't a formality here — it's a clinical and medicolegal obligation that defines the standard of care for shoulder dislocation management. The reason it carries that weight is specific: the nerve most at risk is very often already injured by the dislocation itself, before anyone has attempted to fix it.

The Nerve That's Already at Risk on Arrival

The axillary nerve is the most frequently injured nerve in anterior dislocation. It wraps around the surgical neck of the humerus and is vulnerable to stretch as the humeral head translates anteriorly and inferiorly — which is to say, it's exposed to injury by the mechanism of the dislocation itself, independent of anything a clinician does afterward. By the time you're examining the patient, the nerve may already be compromised, or it may still be intact. The only way to know which is true before you act is to test it before you act.

Why the Documentation Question Comes First

If an axillary nerve deficit is discovered after a reduction attempt, there are exactly two explanations: the nerve was already injured by the dislocation, or the reduction caused it. Without a documented pre-reduction exam, there is no way to distinguish between those two explanations — and the second one is the one that gets assumed by default. A carefully documented pre-reduction sensory and motor exam is what allows a genuinely pre-existing injury to be recognized as pre-existing, rather than attributed to the treatment.

Two tests, not one: motor function is assessed via active deltoid contraction against resistance in the 0–15° arc of shoulder abduction specifically — not full range, which the dislocation itself makes impossible to test. Sensation is assessed over the "regimental badge" area, a discrete patch of skin over the lateral deltoid roughly 5 cm distal to the acromion. Hypoaesthesia or anaesthesia in that specific distribution is a sentinel finding, and it needs to be documented carefully, in that specific location, before reduction.

Why the Motor Test Has to Be Modified

A standard motor exam for shoulder abduction assumes the joint can move through a meaningful range — an assumption a dislocated shoulder violates by definition. Testing resisted abduction only through the first 0–15 degrees respects both the injury and the exam: enough movement to assess whether the deltoid is actually contracting under axillary nerve control, without asking a dislocated joint to do something it can't safely do. Skipping this adaptation and attempting a standard motor exam isn't just uncomfortable for the patient — it risks a false or unobtainable result precisely where an accurate one matters most.

The Takeaway

The pre-reduction neurovascular exam isn't paperwork attached to the real intervention. It's the only mechanism that lets you tell the difference, after the fact, between a nerve injury the dislocation caused and one the treatment caused — and in a joint where the nerve most at risk is wrapped directly around the point of injury, that distinction is one you only get to establish once.