Which muscle of the rotator cuff is in closest approximation to the subacromial bursa?

The muscle of the rotator cuff that is in closest approximation to the subacromial bursa is the Supraspinatus muscle.

Here are the steps to understand why:

1. The rotator cuff is a group of muscles and tendons that surround the shoulder joint, keeping the head of your upper arm bone firmly within the shallow socket of the shoulder. The rotator cuff includes four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis.

2. The subacromial bursa is a fluid-filled sac that is located in the subacromial space, under the acromion and over the rotator cuff. It helps to reduce friction between the bones and the muscles in this area.

3. Of the four muscles in the rotator cuff, the supraspinatus muscle is the one that is located closest to the subacromial bursa. This muscle runs from the scapula, or shoulder blade, to the humerus, or upper arm bone. It is located on the top of the shoulder, directly under the acromion. Therefore, it is in closest approximation to the subacromial bursa.