Which secondary injury is most likely to occur due to improper crutch fitting?

Improper crutch fitting can result in axillary nerve damage, which is located in the shoulder area and innervates the deltoid and teres minor muscles. When crutches are not adjusted to the correct height, users may adopt an improper posture that puts excessive pressure on the shoulder region, particularly around the axillary nerve. This can lead to nerve compression or trauma, causing pain, weakness, or numbness in the arm and shoulder.

While other injuries listed can occur due to various factors or imbalances in other contexts, they are not typically associated with the direct consequences of incorrectly fitted crutches. For example, rotator cuff injuries may arise from overuse or acute trauma but are not specifically linked to crutch fitting. Ulnar nerve entrapment is related to pressure or injury at the elbow and not typically something that would be exacerbated by improper use of crutches. Similarly, patellar tendonitis is generally described in relation to knee overuse or loading, rather than issues with crutch fit.

Thus, the most plausible secondary injury from improper crutch fitting is indeed damage to the axillary nerve, highlighting the importance of correct crutch adjustments for the safety and comfort of users.