Lower limb
Popliteal and semimembranosus bursae (Baker's cyst)
Bursae popliteae, semimembranosi et gastrocnemii
- Origin
- Complex group of posterior knee bursae, predominantly the gastrocnemio-semimembranosus bursa between medial gastrocnemius head and semimembranosus tendon
- Insertion
- Located in the medial popliteal fossa; communicates with the knee joint cavity via a valve-like slit in >50% of adults
- Function
- Minimizes friction between posterior knee flexor tendons and the posterior capsule
- Innervation
- Sensory branches of the tibial nerve
- Movement & chain
- Compressed in deep flexion; one-way valve forces synovial fluid into the bursa during joint movement
- Palpation
- Palpable as a tense fullness in the medial popliteal fossa with the knee fully extended (Foucher's sign)
- Clinical
- Baker's cyst (popliteal cyst arising secondary to meniscal tears or osteoarthritis); rupture produces sudden severe calf pain, erythema, and swelling mimicking acute DVT (pseudothrombophlebitis)
- Segmental innervation
- L4–S2 spinal segments
- In clinical practice
- Foucher's sign; ultrasound evaluation ruling out DVT vs ruptured cyst; treatment targets the underlying intra-articular derangement
- Region in the model
- Lower limb