The fluid-filled sac under a tendon is called which of the following?

• A. Bicipital bursa
• B. Subtendinous bursa
• C. Subtendinous tendon sheath
• D. Peritendinous sac

Answer: (B)

Bursae are small sacs filled with synovial fluid that cushion where structures such as tendons glide past bones or other tissues. When a bursa sits beneath a tendon, its name reflects that position: subtendinous bursa. This term specifically indicates a fluid-filled sac located under a tendon, reducing friction as the tendon moves.

A bicipital bursa is a specific bursa associated with the biceps tendon, not the general under-tendon location. A subtendinous tendon sheath is a tubular sleeve around a tendon, a different structure that encases the tendon rather than being a separate sac beneath it. Peritendinous sac isn’t the standard term used for this anatomy. So the subtendinous bursa best fits the description of a fluid-filled sac under a tendon.