Medial patellofemoral ligament (MPFL)

What it is

The MPFL runs from the inner edge of the kneecap to a small point on the inner femur, between two bony landmarks. It is most important in the first part of bending, roughly from straight to a third bent, before the kneecap settles deep into the trochlear groove, which then holds it in place.

Why it matters for patients

When the kneecap dislocates, usually sideways to the outer side of the knee, the MPFL almost always tears or stretches. This often happens with a twisting movement in sport or dance, particularly in teenagers and young adults. Once torn, it often heals in a lengthened position, so the kneecap can feel unstable and may dislocate again.

A first dislocation without bone or cartilage damage is usually treated with physiotherapy. For repeated dislocations, MPFL reconstruction, using a tendon graft to create a new ligament, is a common and well-established operation. A surgeon also considers groove shape, kneecap height and leg alignment, which may need treatment at the same time.

How it is examined

A surgeon checks for tenderness on the inner knee and gently pushes the kneecap outwards to see whether it feels apprehensive or loose. MRI shows the MPFL tear and any cartilage injury from the dislocation.