The posterior knee capsule is the fibrous posterior joint capsule, reinforced by the oblique popliteal ligament (OPL, from the semimembranosus expansion), the arcuate ligament complex (from the posterior fibula), and the posterior horn meniscal capsular attachments. The posterior capsule in full extension is taut and contributes to knee hyperextension resistance; in flexion it becomes lax. The posterior capsule houses the popliteus tendon hiatus and the posterior fat pad.
Provides the posterior joint containment of the knee, resisting hyperextension in conjunction with the PCL and posterior meniscal attachments; contains the posterior joint recesses where Baker cysts form; provides attachment for the OPL, semimembranosus, and posterior horn capsular fibres.
Posterior capsule contracture is the primary cause of knee flexion contracture after TKA and after prolonged immobilisation: posterior capsular release is performed at TKA to correct preoperative flexion contractures and restore full extension. In PCL injuries with posterolateral corner disruption, the posterior capsule is torn along with the capsular ligament complex. Posterior capsule calcification (Baker's cysts with calcified bodies, or posterior capsule ossification in severe OA) complicates TKA by limiting exposure and requiring careful release to avoid injury to popliteal neurovascular structures.
Severe knee OA with chronic flexion deformity produces posterior capsular contracture that persists if not corrected at TKA; posterior capsular release through the posteromedial and posterolateral corners allows full knee extension on the trial components and prevents residual flexion deformity that significantly impairs TKA outcome.
