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Portrait of Bursa

Anatomy · Joints & cartilage

Bursa

Latin for 'purse'

Musculoskeletal · friction cushions

A bursa is a small flattened sac lined with a synovial membrane and containing a thin film of synovial fluid. It lies where tendons, muscles or skin rub over bone and acts as a friction-reducing cushion. The body has well over a hundred, and inflammation of one, bursitis, is a common cause of pain around the shoulder, elbow, hip and knee.

How to spot them

  • ▸A flat, fluid-filled sac between a tendon, muscle or skin and a bony prominence
  • ▸Lined by a synovial membrane, and sometimes communicating with a nearby joint cavity
  • ▸Named after its site: subacromial, olecranon, prepatellar, trochanteric, retrocalcaneal
  • ▸Swells and becomes hot and tender when inflamed

What to know

A tiny purse of synovial-lined tissue that lets a tendon slide over bone

Bursa — the Latin word means purse.

The one between the acromion and the rotator cuff is often involved in shoulder pain when the arm is raised

Bursa — the subacromial bursa.

Swelling in front of the patella from kneeling on a hard floor gives a Victorian job title to the condition

Bursa — prepatellar bursitis, housemaid's knee.

Swelling over the point of the ulna is nicknamed after students or miners, who lean on their elbows

Bursa — olecranon bursitis.

One can develop over a pressure point where none existed before, such as over a bunion

Bursa — an adventitious bursa.

Key ideas

  • Bursae and tendon sheaths are the body's friction reducers, sacs of synovial fluid where structures rub.

Quick-fire facts

  • •Bursae are lined by a synovial membrane and contain a thin layer of synovial fluid.
  • •The human body has more than 150 bursae, by common counts.
  • •The subacromial bursa lies between the acromion and the supraspinatus tendon.
  • •Prepatellar bursitis is 'housemaid's knee'; infrapatellar bursitis is sometimes called 'clergyman's knee'.
  • •Olecranon bursitis: 'student's elbow' or 'miner's elbow'.
  • •Retrocalcaneal bursitis affects the heel, just in front of the Achilles tendon.
  • •Septic bursitis needs antibiotics; non-infective bursitis often settles with rest, ice and analgesia (NHS).

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