Tibiofemoral joint
This joint between the thigh and shin bones allows the knee's main bending and straightening motion, along with a small amount of rotation when the knee is bent.
The knee joint combines two articulations: the tibiofemoral joint between the thigh and shin bones, which primarily allows bending and straightening, and the patellofemoral joint between the kneecap and thigh bone, which assists the quadriceps in extending the leg.
Because the bony surfaces of the knee are relatively flat compared with a deep socket joint like the hip, stability depends heavily on four major ligaments and two C-shaped menisci that cushion and help guide movement between the bones.
Key structures
Anterior cruciate ligament (ACL)
This central ligament resists forward sliding of the shin bone and excessive rotation, and is one of the most frequently injured structures in pivoting sports.
Menisci
Two C-shaped cartilage pads between the thigh and shin bones cushion load and improve the fit between the joint surfaces, and can tear from twisting injuries or gradual degeneration.
Quadriceps femoris and patellar tendon
The quadriceps muscle group extends the knee through the patellar tendon, and this extensor mechanism is central to activities such as squatting, jumping, and climbing stairs.
Medial and lateral collateral ligaments
These ligaments on the inner and outer sides of the knee resist excessive sideways bending forces, commonly stressed during contact sports.
Patellofemoral joint
The kneecap glides within a groove on the thigh bone during bending and straightening, and its tracking pattern is a common focus in patellofemoral pain syndrome.
Planes & range
Knee flexion from full extension to a deeply bent position represents the joint's largest range of motion, essential for activities such as squatting, kneeling, and climbing stairs.
This reliance on ligaments and cartilage rather than bony shape for stability explains why the knee is prone to both acute traumatic injuries during sport and gradual, cumulative wear over decades of use.
Keep exploring
More in Lower limb
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