Bursa (anatomy)

A bursa is a small sac lined by synovial membrane and containing fluid that reduces friction between tissues, especially where tendons or muscles move over bones.

Synovial membrane: A connective-tissue membrane that lines joint cavities and produces synovial fluid. Bursal linings resemble this membrane and help maintain the fluid that eases tissue movement.
Subacromial bursa: A shoulder bursa between the rotator cuff and the acromion and deltoid. It reduces friction as the rotator cuff moves beneath the roof of the shoulder.
Bursa (medicine): A pouch-like organ in some animals, including the avian bursa of Fabricius. The shared word names an unrelated organ in anatomy beyond the musculoskeletal system.
Muscle: Contractile tissue that generates force and produces movement. Muscles move across nearby tissues, creating sites where bursae can reduce friction.
Shoulder impingement syndrome: Shoulder pain associated with compression or irritation of structures beneath the acromion during arm movement. The subacromial bursa may be involved, though symptoms do not identify one structure by themselves.
Synovial fluid: A viscous fluid that lubricates synovial joints and nourishes articular cartilage. Fluid within a bursa helps its opposing surfaces glide with less friction.
Prepatellar bursa: A bursa between the kneecap and the overlying skin. Its inflammation can produce visible swelling at the front of the knee.
Joint capsule: A fibrous enclosure surrounding a synovial joint, with an inner synovial lining. Unlike a bursa, a joint capsule encloses the joint cavity itself.
Bone: Rigid connective tissue that forms the skeleton and provides structural support. Bursae often cushion soft tissues where they pass over prominent bones.
Rotator cuff disease: A range of disorders affecting the tendons and muscles that stabilize and move the shoulder. Rotator cuff abnormalities often coexist with bursal changes, complicating attribution of shoulder pain.

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