CorpusHuman Anatomy
SkeletalMembrane

Bursa

Bursa synovialis

Also known as: bursae, synovial bursa, tendon sheath

A flattened, closed sac lined by synovial membrane and containing a capillary film of synovial fluid, located where tendons, muscles or skin glide over bone or other structures.

Synovial Joint — Structure

Overview

Bursae reduce friction between moving structures. Some are subcutaneous (prepatellar, olecranon), some subtendinous or submuscular (subacromial/subdeltoid between the rotator cuff and the acromion and deltoid; trochanteric under gluteus maximus; infrapatellar), and some communicate with a joint cavity (suprapatellar bursa with the knee; subscapular bursa with the shoulder). Adventitious bursae form in response to abnormal pressure or friction, e.g. over a bunion. Synovial tendon sheaths are elongated bursae wrapped around tendons where they pass through osseofibrous tunnels (e.g. the digital flexor sheaths, carpal tunnel bursae).

Knee bursae: suprapatellar (communicates), prepatellar (housemaid's knee), superficial infrapatellar (clergyman's knee), deep infrapatellar, pes anserinus and semimembranosus bursae — the last may enlarge as a popliteal (Baker) cyst.

Location

Around joints, between tendons/muscles/skin and bony prominences.

Parts & subdivisions

  1. Subacromial (subdeltoid) bursa
    Between rotator cuff and acromion/deltoid; inflamed in impingement.
  2. Olecranon bursa
    Subcutaneous over the olecranon ("student’s elbow").
  3. Prepatellar and infrapatellar bursae
    Housemaid’s and clergyman’s knee.
  4. Suprapatellar bursa
    Extension of the knee joint cavity above the patella.
  5. Trochanteric bursa
    Over the greater trochanter beneath gluteus maximus.

Function

  • Reduce friction where structures glide over one another
  • Facilitate tendon movement and protect bony prominences

Clinical significance

Bursitis

Inflammation from repetitive friction, trauma, crystal deposition, infection (especially subcutaneous bursae — prepatellar, olecranon — often S. aureus) or inflammatory arthritis: localised swelling and tenderness.

Baker (popliteal) cyst

Distension of the semimembranosus–gastrocnemius bursa communicating with the knee, secondary to effusions (OA, meniscal tear); rupture mimics DVT.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.