Which of the following structures is commonly affected in subacromial impingement?

Subacromial impingement syndrome primarily involves the space beneath the acromion, where several structures, including tendons, can become compressed during arm movements. The most commonly affected structure in this condition is the supraspinatus tendon. This tendon is particularly vulnerable to impingement because it is situated in the subacromial space and is responsible for initiating abduction of the arm.

When the arm is raised, the supraspinatus tendon can be compressed against the acromion, leading to inflammation, pain, and dysfunction. This condition typically arises due to repetitive overhead activities or anatomical variations that reduce the size of the subacromial space, contributing to the risk of tendon irritation.

While the other tendons mentioned can also be involved in shoulder pathologies, the supraspinatus tendon remains the primary structure of concern specifically related to subacromial impingement, which is why it is recognized as the correct answer. Understanding this relationship is crucial for diagnosing and managing shoulder conditions effectively.