Review Question - QID 217496

The patient has sustained a distal 1/3rd humeral shaft fracture. While performing a posterior approach, the radial nerve can reliably be found approximately 4 centimeters (or two finger-breadths) proximal to the triceps aponeurosis. Injury to the radial nerve would cause an inability to extend the index finger (Answer 2).

The posterior approach to the distal humerus is the workhorse approach for many osteosynthetic procedures about the distal arm and elbow. Careful attention must be paid, however, to the location of the radial nerve during approach and dissection. The radial nerve, which originates from the posterior cord of the brachial plexus, courses along the medial arm, and traverses the arm laterally along the spiral groove. Injury to the radial nerve at the level of the distal humerus will cause both motor and sensory loss, including an inability to extend the hand and digits and a loss of sensation in the posterior forearm, the radial half of the dorsum of the hand, and the dorsal aspect of the radial 3.5 digits.

Gerwin et al. performed an anatomical study of the course of the radial nerve as it relates to the posterior approach to the arm. They note that the nerve begins to traverse the spiral groove at an average distance of 20.7 cm proximal to the medial epicondyle and exits the spiral groove 14.2 cm proximal to the lateral epicondyle. They go on to state that whilst performing a posterior approach, one may encounter radial nerve branches to the lateral head of the triceps, but none to the medial head.

Seigerman et al. performed a cadaveric study to elucidate a more straightforward means by which to locate the radial nerve. The authors utilized 15 matched pairs of cadaver upper extremities. They note that the radial nerve can reliably be located at a distance of 3.9 cm (two finger-breadths) proximal to the confluence of the long and lateral head of the triceps and the triceps aponeurosis.

Figure A demonstrates a distal-third humeral shaft fracture. Illustration A is an anatomic illustration of the principle proposed by Seigerman, demonstrating the radial nerve 3.9 cm proximal to the triceps aponeurosis.

Incorrect Answers:
Answer 1: the adductor pollicis is innervated by the ulnar nerve. The ulnar nerve is not found two finger-breadths proximal to the triceps aponeurosis.
Answer 3: the flexor digitorum profundus to the small finger is innervated by the ulnar nerve.
Answer 4: the flexor pollicis longus is innervated by the median nerve, which is not typically encountered during the posterior approach to the humerus.
Answer 5: forearm pronation occurs through the activation of pronator teres and pronator quadratus, both of which are innervated by the median nerve.