Knee anatomy - the bones from the front - straight knee

ANATOMY OVERVIEW anatomy intro bones from front (bent knee) bones from front (straight knee) bones from side bones from above patella capsule collateral ligaments cruciate ligaments medial plica meniscus from side meniscus from top muscles from front muscles from back

When the knee is straight, the rounded condyles are rolled over onto the flat surface of the tibial plateau, so the white cartilage (gristle) of the femur largely disappears from view.

In the straight-leg position, the patella sits above the joint line, above the trochlea of the femur (the underlying groove in which it rides). Compare the bent knee.

X-rays taken in the straight-leg position are called AP views (AP=antero-posterior). These may be taken lying on the back, but 'standing' AP x-rays are very useful as they show the bones in their normal situation, often revealing a narrowed joint space if there is meniscal destruction or arthritis on one side. In this AP view, you can see the patella as a whiter circle 2-3 cm above the joint line. The joint space between the bones appears black - the space is actually filled with the meniscus, which is not visible under x-ray.