Articular capsule of knee joint

At a glance

English

Articular capsule of knee joint

Latin (TA2)

Capsula articularis genus

System

Joint

Region

Lower limb

Side

Paired, left and right

About the articular capsule of knee joint

The articular capsule of the knee encloses the largest joint in the body, made up of the tibiofemoral and patellofemoral articulations. It has an outer fibrous membrane and an inner synovial membrane, separated in places by pads of fat. The fibrous membrane is fixed to the femur a little beyond the articular margins of the condyles and the intercondylar fossa, and to the tibia around the condyles. In front it has no wall of its own: there it is replaced by the quadriceps tendon, the patella and the patellar ligament, and on each side by the medial and lateral patellar retinacula.

The synovial membrane is the most extensive in the body. It is attached at the margins of the articular cartilage of femur and tibia, and above the patella it balloons upwards beneath the quadriceps as the suprapatellar bursa, which communicates freely with the joint. The small articularis genus muscle pulls this pouch up during extension so it is not caught. Behind, the membrane covers the femoral condyles and then passes forward in front of the cruciate ligaments, which therefore lie inside the fibrous capsule but outside the synovial cavity. Below the patella the membrane is pushed back by the infrapatellar fat pad and forms the infrapatellar and alar folds. The menisci are attached at their outer edges to the capsule by the coronary ligaments.

Many ligaments strengthen the capsule. The tibial collateral ligament is fused with it and with the medial meniscus, whereas the fibular collateral ligament stands apart from both. At the back, the oblique popliteal ligament, an expansion of the semimembranosus tendon, and the arcuate popliteal ligament reinforce the thin posterior wall, and the popliteus tendon pierces the capsule.

Because the capsule is so large, an injured knee readily fills with fluid or blood, and the swelling first appears in the suprapatellar pouch above the kneecap. Needles for aspiration are usually passed into this pouch. Septic arthritis, synovitis and arthroscopic portals all involve this membrane.

Attachments and function

Formed by

Attached to the femur just beyond the articular margins of the condyles and the intercondylar fossa.

Joins

Attached to the tibia around the margins of the condyles; in front its place is taken by the quadriceps tendon, patella and patellar ligament.

Movements

Encloses and seals the knee joint, holds synovial fluid, and with its ligaments and retinacula stabilises the joint during flexion, extension and rotation.

Nerve supply

Genicular branches of the femoral, obturator, tibial and common fibular nerves.

Blood supply

The genicular anastomosis: superior, middle and inferior genicular branches of the popliteal artery, the anterior tibial recurrent artery and the descending genicular artery.