Anterolateral Approach to Humerus: Comprehensive Surgical Anatomy & Neurovascular Risks
Key Takeaway
The anterolateral approach to the humerus treats shaft fractures, using internervous planes, primarily between biceps and brachialis. Key structures at risk include the axillary nerve proximally, and the musculocutaneous and radial nerves during mid-shaft and distal dissection. Meticulous anatomical awareness is crucial for patient safety.
A 35-year-old male presents with a mid-shaft humeral fracture following a high-energy trauma. You are planning an anterolateral approach for ORIF. Describe the internervous plane for this approach and explain how you would manage the brachialis muscle during deep dissection.
Candidate: The internervous plane is between the biceps brachii, which is supplied by the musculocutaneous nerve, and the brachialis, which is dual-innervated by the musculocutaneous and radial nerves. I would retract the biceps medially and then split the brachialis muscle longitudinally to reach the humerus.
Failure to specify the "dual innervation" of the brachialis as the justification for the safe split. Also, missing the critical step of identifying the musculocutaneous nerve in the interval between the two muscles, which places it at risk if the dissection is too medial or aggressive.
The approach utilizes the interval between the biceps brachii (musculocutaneous nerve) and the brachialis muscle. The brachialis is then split longitudinally. This is a safe maneuver because the brachialis receives dual innervation from both the musculocutaneous nerve (laterally) and the radial nerve (medially), allowing for a split without denervating a significant portion of the muscle belly. One must remain vigilant for the musculocutaneous nerve in the proximal part of the interval and the radial nerve as the approach extends distally toward the lateral intermuscular septum.
During the fixation of the humeral shaft fracture, you are preparing to place bicortical screws. How do you mitigate the risk of iatrogenic radial nerve injury?
Candidate: I would ensure I do not drill too deep and carefully measure my screw length. I'll also try to avoid placing screws in the middle of the shaft where the nerve is in the spiral groove.
Vague references to "measuring" without mentioning technical safety steps. Failing to acknowledge that the radial nerve is at risk not only in the spiral groove but also as it pierces the lateral intermuscular septum distally. Missing the importance of plate positioning relative to the nerve.
Risk mitigation is three-fold: 1. Anatomical knowledge: Recognize that the nerve traverses the spiral groove posterior to the humerus and pierces the lateral intermuscular septum roughly 10-14cm proximal to the lateral epicondyle. 2. Technical precision: Use meticulous drilling techniques; use a depth gauge to ensure screw length is accurate; use a soft-tissue protector (drill sleeve) to prevent the drill bit from 'plunging' into the posterior compartment. 3. Plate orientation: Position the plate on the anterolateral aspect. In the distal third, prioritize identification and protective retraction of the radial nerve before any drilling, as it lies between the brachialis and brachioradialis.
