The Knee Joint

Key points

• • It is a synovial hinge joint formed by the femoral condyles, the tibial condyles and the patella; the fibula takes no part in it.
• • The two cruciate ligaments give anteroposterior stability: the anterior cruciate stops the tibia sliding forward on the femur, and the posterior cruciate stops it sliding backward.
• • The two collateral ligaments give side-to-side stability; the medial (tibial) collateral is attached to the medial meniscus, so a blow to the outer knee can injure both together.
• • The two menisci are fibrocartilage pads that deepen the tibial surface and share load; the medial meniscus is less mobile and is torn more often.
• • Locking in full extension comes from medial rotation of the femur on the fixed tibia, and the popliteus muscle unlocks the joint to begin flexion.
• • Blood comes from an anastomosis of genicular branches of the popliteal artery, and by Hilton's law the nerve supply is from the femoral, tibial and common fibular nerves.