A 32-year-old man presents with wrist drop and inability to extend the thumb after a fracture of the mid-shaft of the humerus. Which is the most common site of radial nerve injury in such fractures?
A. Distal third of the arm near the elbow
B. Radial groove (spiral groove) of the humerus
C. Axilla
D. Forearm at the level of the supinator muscle
Explanation
Most Common Site of Radial Nerve Injury in Humeral Fractures
Anatomical Basis
Key Point
The radial nerve runs in the radial groove (spiral groove) on the posterior surface of the mid-shaft of the humerus, making this the most vulnerable site during mid-shaft humeral fractures.
The radial nerve follows a predictable course:
1.
Exits the axilla posteriorly
2.
Enters the radial groove at the junction of proximal and middle thirds
3.
Travels in the groove between the medial and lateral heads of triceps
4.
Pierces the lateral intermuscular septum in the distal third
5.
Emerges anterior to the lateral epicondyle
Incidence of Radial Nerve Injury by Fracture Location
Table
Fracture Site
Incidence of RN Injury
Mechanism
Mid-shaft (radial groove)
10–18%
Direct trauma, angulation, traction
Proximal third
2–3%
Rare, nerve already exited groove
Distal third
<5%
Nerve already anteriorly displaced
Supracondylar
Uncommon
Nerve protected by anterior displacement
Clinical Presentation of Radial Nerve Palsy
High-YieldNEET PG
The classic triad of radial nerve injury:
1.
Wrist drop — loss of extensor carpi radialis longus and brevis
2.
Thumb extension loss — extensor pollicis longus paralysis
3.
Finger extension loss — extensor digitorum paralysis
Clinical Pearl
Sensation loss over the dorsal first web space (between thumb and index finger) is a key sensory finding.
The nerve is tethered within the groove with limited mobility
Fracture fragments can directly lacerate or compress the nerve
Angulation and displacement cause traction injury
The nerve's intimate relationship with bone makes it susceptible to ischemia from vascular injury
Prognosis
Key Point
Most radial nerve injuries from humeral fractures are neurapraxia or axonotmesis (not complete transection), with 90% recovering spontaneously within 3–4 months with conservative management.
Standring Anatomy 42e Ch 48
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