*2.1.1 Joint capsule*

It is a thick, fibrous structure mainly formed by muscle tendons and their expansions that wrap around the knee joint. It forms a thick ligamentous sheath around the knee joint. The synovial membrane lying inside the outer fibrous layer lubricates the articular surfaces, reduces friction, and nourishes the joint cartilage. It also has several fluid-filled pouches called bursae that also reduce friction within the knee joint. The folds of the synovium within the joint are called plicae [4].

The synovial fluid in the soaked cartilage (like water in a sponge) squeezes out when the knee bends or bears weight. The osteoarthritic changes in the joint lead to a decrease in synovial fluid that exacerbate joint friction. The anterior capsule has an opening for the attachment to the patella. Similarly, the posterior capsule has an opening for the passage of the popliteus tendon.

## *2.1.2 Extracapsular ligaments*

Extracapsular ligaments include the patellar, popliteal (oblique and arcuate), and collateral (medial and lateral) ligaments.

	- a. Oblique popliteal ligament (Bourgery ligament) connects the medial tibial condyle with the lateral femoral condyle. It is an expanded portion

of the semimembranosus tendon that spans the intercondylar fossa. It reinforces the posterior capsule by blending with it in the central portion.

	- a. Medial (tibial) collateral ligament (MCL) is a broad and flat ligament that lies on the medial side of the knee joint. It attaches proximally to the medial femoral epicondyle and distally to the medial tibial condyle. It prevents excessive sideways movement by restricting external and internal rotation of the extended knee.
	- b. Lateral (fibular) collateral ligament (LCL) is thin and rounder than MCL that attaches proximally to the lateral femoral epicondyle and distally to the lateral fibular head splitting the biceps femoris tendon. It lies deep to the lateral patellar retinaculum and superficial to the popliteal tendon.
