Synopsis
Use compartments, neurovascular routes, surface landmarks and bone relations to predict deficits and structures at risk in common upper- and lower-limb surgical corridors.
- The radial nerve lies against the posterior humeral shaft in the radial groove before piercing the lateral intermuscular septum; shaft injury can therefore combine wrist/finger-extension weakness with a variable sensory deficit.
- The axillary nerve winds around the surgical neck of humerus with posterior circumflex humeral vessels, while the ulnar nerve becomes superficial behind the medial epicondyle.
- In the femoral triangle, structures run lateral to medial as femoral nerve, artery, vein and lymphatic/femoral canal; the nerve lies outside the femoral sheath.
Reasoning priorities
Localise a supplied deficit to a peripheral nerve segment.
Choose movements that isolate branches above and below the suspected site, then add an autonomous sensory zone; one weak effort is insufficient.
Worked reasoning
A supplied trauma diagram shows a mid-shaft humeral fracture at the radial groove; examination inputs are weak wrist and finger extension, reduced dorsal first-web-space sensation and preserved shoulder abduction.
- Anchor the lesion to the posterior humeral shaft and trace the radial nerve with profunda brachii through the groove.
- Group weak wrist/finger extension and first-web-space sensory loss as radial motor and sensory territory distal to the supplied level.
- Use preserved shoulder abduction to avoid an axillary-nerve localisation and check triceps because proximal radial branches may have arisen before the groove.
- Conclude a radial-nerve lesion at the humeral shaft is the coherent anatomical localisation, without inferring transection or prognosis.
- Verify with branch-by-branch motor testing, an autonomous sensory site and serial neurovascular documentation around the injury.