George fractures his humerus at the surgical neck, damaging the Axillary nerve running posterior to it which innervates two muscles. What deficits might we see in George's injured limb?

Question

BlackTom AI · Accepted Answer

To tackle this question, let’s first recall what the axillary nerve supplies and what functions would be affected if it is damaged.

Option 1: Weak abduction of the upper limb.
This is the correct choice. The axillary nerve innervates the deltoid and teres minor. The deltoid is the main muscle responsible for abduction of the arm beyond the initial 15 degrees produced by the supraspinatus. When the axillary nerve is injured, deltoid (and teres minor) weakness leads to impaired abduction of the upper limb, especially noticeable after the first 15 degrees. Thus, weakness in abduction is a hallmark deficit.

Option 2: Loss of shoulder adduction.
Shoulder adduction is mainly performed by the latissimus dorsi, teres major, and pectoralis major. These muscles are innervated by nerves other than the axillary nerve (e.g., thoracodorsal, lower subscapular, and medial/lateral pectoral nerves). Therefore, axillary nerve injury does not produce a primary loss of shoulder adduction, making this option incorrect.

Option 3: Complete loss of medial rotation of arm.
Medial rotation involves several muscles, including subscapularis (upper and lower subscapular nerves) and teres major (lower subscapular nerve), as well as the anterior fibers of the deltoid to a lesser extent. While axillary nerve damage may weaken some aspects of shoulder movement, it does not cause a complete loss of medial rotation since other muscles driven by different nerves can still facilitate medial rotation. This option overstates the effect of axillary injury and is therefore incorrect.

Option 4: Loss of flexion of the forearm.
Forearm flexion is primarily carried out by the biceps brachii and brachialis, which are innervated by the musculocutaneous nerve. The axillary nerve does not innervate these muscles, so injury to the axillary nerve would not cause loss of forearm flexion. This makes the option incorrect.

In summary, among the options provided, the deficit most directly explained by axillary nerve damage to the deltoid and teres minor is weakened abduction of the upper limb, with the other choices pointing to functions supplied by other nerves.

George fractures his humerus at the surgical neck, damaging the Axillary nerve running posterior to it which innervates two muscles. What deficits might we see in George's injured limb?Single choice

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