Bones of the Knee

For Young Learners

Structure and Location

Four bones are involved. The femur is the thigh bone, the longest bone in your body. It ends in two rounded knuckles called condyles.

The tibia is the shin bone. Its top is broad and almost flat, like a table top, and the rounded end of the femur sits on it.

The patella is the kneecap. It is a small bone that sits inside the big tendon at the front, and it slides in a groove on the femur as you bend and straighten.

The fibula is the thin bone on the outside of your shin. It does not take much weight. It gives things somewhere to attach.

Function

A round thing on a flat thing is not a stable arrangement, and that is exactly what the femur on the tibia is. The bones alone would slide apart. Everything else in the knee exists to stop that happening.

The kneecap has a cleverer job. By sitting in front of the joint it holds the thigh tendon further away from the centre of the knee, which makes the muscle more effective. It works like moving your hand further down a spanner.

For Patients

Structure and Location

The femur is the thigh bone. Its lower end widens into two rounded prominences, the medial and lateral condyles, separated at the back by a notch and joined at the front by a groove called the trochlea.

The tibia is the shin bone and takes nearly all the weight passing through the leg. Its upper surface, the tibial plateau, is broad and only gently dished.

The patella is the kneecap, the largest sesamoid bone in the body, meaning a bone formed within a tendon. Its back surface is covered in thick cartilage and glides in the trochlear groove.

The fibula lies on the outer side of the shin. It carries little weight but anchors ligaments and tendons on that side.

Function

The bones set the geometry and little else. Because the femoral condyles are rounded and the tibial plateau is nearly flat, the surfaces do not lock together, which is what allows the wide range of movement.

The patella increases the mechanical advantage of the thigh muscle. Without it, straightening the knee against resistance would take considerably more force.

Clinical Relevance

The shape of these bones explains several everyday findings. A shallow trochlear groove allows the kneecap to track poorly or slip out of place. Differences in condyle shape and in the slope of the tibial plateau affect how the joint is loaded and how it behaves after injury.

The ends of these bones are also where pain is often felt and where swelling collects, which is why clinicians press along specific bony landmarks during an examination.

Fractures of these bones are covered in the conditions section rather than here.

For Medical Students

Structure and Location

The distal femur expands into medial and lateral condyles, separated behind by the intercondylar notch and continuous in front with the trochlear groove. The proximal tibia presents medial and lateral plateaus, broad and only gently dished. The patella is triangular, with the thickest articular cartilage in the body on its posterior surface, divided into medial and lateral facets. The fibula sits laterally and transmits little axial load.

The detailed morphology of each bone, and the attachments it carries, belong to the Anatomy Academy.

Function

Articular incongruity between convex femoral condyles and a relatively flat tibial plateau permits rolling, gliding and rotation, at the cost of bony stability. The intercondylar notch houses the cruciate ligaments.

The patella acts as an anatomical pulley, displacing the extensor tendon forwards and increasing its moment arm about the flexion axis, with the gain greatest in terminal extension.

Clinical Relevance

Trochlear shape governs patellar tracking, and a shallow groove predisposes to maltracking and instability. The backward slope of the tibial plateau influences how the tibia translates under load and is of interest in cruciate injury.

Palpable landmarks structure the clinical examination: the joint line, the femoral epicondyles, the tibial tubercle and the fibular head.

Fracture patterns and their management belong to the conditions and surgery sections.