TempoLife › Features › Muscle and body-part reference › knee-joint

Knee joint

The largest joint in the body, a hinge with a twist, held together almost entirely by ligaments and muscle.

Latin name: Articulatio genus. In plain English, the hinge between thigh and shin. It is filed here under joints, tendons and fascia.

Reference information, not a diagnosis. Where a symptom is described below, it is there so you can describe your own more precisely to a clinician — not so you can name what you have.

Where it is

The knee is two rounded femoral condyles resting on a nearly flat tibial plateau — an inherently unstable arrangement made workable by soft tissue. Two C-shaped wedges of fibrocartilage, the menisci, deepen the surface and spread load across it. The cruciate ligaments cross inside the joint, the anterior one resisting the tibia sliding forward and the posterior one resisting it sliding back; the collateral ligaments resist sideways angulation.

The patellofemoral compartment is a joint in its own right. The kneecap glides in a groove on the front of the femur, and the forces across that surface rise steeply with knee flexion, which is why stairs, squatting and prolonged sitting are the classic aggravators of kneecap pain.

What it does

It bends and straightens, and it rotates slightly when bent, which is what allows the foot to be positioned without moving the whole leg. Near full extension the joint locks into its most stable position through a small rotation, sometimes called the screw-home mechanism, and it has to be unlocked by popliteus before flexion can begin.

Its injuries follow its design. Anterior cruciate ligament ruptures happen typically in non-contact deceleration and pivoting, often with a pop, immediate swelling and a knee that feels unreliable. Meniscal tears happen with twisting on a loaded bent knee in younger people and degeneratively in older ones. Osteoarthritis is the common long-term issue, and exercise therapy is the first-line treatment across essentially every clinical guideline.

Movements that load it

The knee responds well to load applied gradually. Squats, lunges and step-ups build the quadriceps and hip muscles that control it; cycling loads it with low impact through a controlled range, which is why it is a mainstay of early knee rehabilitation. Running does not wear knees out in healthy people — recreational runners have not been shown to have more knee osteoarthritis than non-runners.

Keeping its range

Restoring full extension matters more than any stretch: a knee that cannot straighten fully changes how you walk and how the quadriceps work. Prone hangs, heel props and gentle bending range work are the usual approaches after injury or surgery. Beyond that, keeping the hips and calves mobile does more for the knee than stretching the knee itself.

When it goes wrong

A knee that swells within an hour of an injury, locks so it cannot be straightened, gives way, or cannot bear weight needs an in-person examination. A hot, red, very painful knee with fever is a medical emergency.

Nothing on this page is a treatment plan. If a problem is limiting what you do, is not improving, or is getting worse, the right next step is an assessment by a doctor or a physiotherapist who can examine you.

Sources: descriptive anatomy from Gray's Anatomy of the Human Body, 20th US edition (1918), which is in the public domain; Latin names follow Terminologia Anatomica, published by the Federative International Programme for Anatomical Terminology. Nerve root levels are the conventional ranges taught from those sources and vary between individuals and between textbooks. Exercise cross-links use the TempoLife exercise library. Checked 2026-09-06.

Frequently asked questions

Nearby in this reference

All 34 body parts · Exercise library · Body map