Semimembranosus Recess of the Knee

recessus semimembranosi genus

The semimembranosus bursa communicates with the posterior knee joint capsule via an opening between the medial head of gastrocnemius and the semimembranosus tendon in approximately 50% of adults, forming a posterior medial recess of the knee joint. Baker's cyst develops when this communication allows joint fluid to accumulate in the bursa.

Region: Knee

Clinical Relevance

Clinical Notes

The semimembranosus-gastrocnemius communicating recess is the anatomical basis for Baker's cyst (popliteal cyst) — the one-way valve mechanism allows joint fluid to enter the bursa but not return, producing progressive cyst enlargement with knee pathology. MRI demonstrates the cyst neck at the joint-bursa communication point between the medial gastrocnemius and semimembranosus. Treatment of the underlying intra-articular pathology (meniscal tear, OA) reduces Baker's cyst size.

Pathology

Common Injuries & Conditions

Baker's Cyst from Semimembranosus-Gastrocnemius Communication

Posterior knee synovial cyst from knee joint fluid accumulating in the semimembranosus bursa via the one-way valve communication, producing a popliteal fossa mass that enlarges with knee pathology and reduces with treatment of the primary intra-articular cause.