MPFL

For Medical Students

Structure and Location

The medial patellofemoral ligament runs from the medial side of the femur to the upper medial border of the patella.

Its femoral attachment is in a small area between the medial epicondyle and the adductor tubercle. Conventional teaching places it about 10 mm distal and 1 mm anterior to the adductor tubercle.

Its patellar attachment is broad, covering the upper third to half of the medial border. Conventional teaching gives the patellar footprint a width of about 20 mm.

It is thin. Conventional teaching gives a thickness of about 1 mm, so it is a sheet rather than a cord despite being called a ligament.

It lies in layer two of the medial knee, between the fascia above and the capsule below, which 2.9.1 covers.

Relations

Above it: vastus medialis obliquus, which overlies and partly attaches to it.

Below it: the capsule and the joint.

Behind its femoral attachment: the adductor tubercle, with adductor magnus attaching there, and the superficial medial collateral ligament just in front and below.

In front: the medial retinaculum, which it blends with. 2.12.4 covers it.

Function

It is the primary restraint to lateral movement of the patella in early flexion. Conventional teaching gives it about 50 to 60 per cent of the restraining force at 20 degrees.

Its contribution falls as the knee flexes and the patella enters the groove, because the bone takes over.

It does not move the patella. It stops the patella going too far, which is why it is a check rather than a stabiliser in the muscular sense.

Clinical Relevance

It is the structure torn in a first patellar dislocation, and 6.53 covers that.

Because it works in early flexion, instability from its loss is felt walking, turning and going down stairs rather than in deep flexion.

Its femoral attachment is close to the medial collateral ligament's, so the two are distinguished by landmark rather than by eye.

MRCS Level

Structure and Location

Describe the shape honestly: broad at the patella, narrow at the femur, fan shaped in between. Conventional teaching gives a length of about 55 mm.

The femoral attachment is the critical point and it is small. Conventional teaching places it in a saddle between the adductor tubercle above and the medial epicondyle below, and a few millimetres of error there changes the ligament's length behaviour through flexion.

Part of the patellar attachment is to the undersurface of vastus medialis obliquus rather than to bone, which is why some descriptions call the proximal part a quadriceps attachment. 2.12.3 covers that structure.

It is thin enough that it is often not seen as a discrete structure at arthroscopy, and it is found from outside rather than from inside the joint.

Relations

Layer one is the fascia, layer two carries this ligament and the other patellofemoral ligaments, layer three is the capsule. The scheme is the same one 2.9.1 uses for the medial side.

The superficial medial collateral ligament attaches about 10 mm below and in front of this ligament's femoral point, which is close enough to matter and far enough to distinguish.

The saphenous nerve's infrapatellar branch crosses the field of a medial approach, as 2.9.7 covers.

The medial patellotibial and patellomeniscal ligaments lie below it and restrain the patella distally. 2.12.4 covers them.

Blood Supply and Innervation

Supply is from the descending genicular artery and the superior and inferior medial genicular arteries, through the surrounding soft tissue.

Vascularity is adequate but the ligament usually heals lengthened rather than to length, which is the anatomical reason instability can persist after a first dislocation.

Nerve supply is from the medial articular branches and from branches of the saphenous nerve.

Function

Conventional teaching gives it about 50 to 60 per cent of the restraint to lateral translation between 0 and 30 degrees, with the figure falling beyond that.

It is close to isometric when its femoral attachment is correct, and it lengthens or shortens through flexion when it is not. That sensitivity is the point of the landmark work in 2.12.6.

Its length behaviour matters more than its strength, because it is a check that should not be loaded in normal movement at all. 3.12.5 carries the mechanics.

Clinical Relevance

Examine lateral translation at 20 to 30 degrees, because that is where this ligament carries most of the restraint.

Expect the ligament to heal in a first dislocation and expect it to heal long. Continuity and competence are different questions, as on the posterior cruciate.

Identify the femoral point from the adductor tubercle and the epicondyle together, because the ligament itself may not be identifiable.

Leave dislocation and its management to 6.53 and 7.51. This page is where the ligament is.

FRCS Level

Relations

The femoral point is the whole problem. It sits within a few millimetres of the collateral ligament's point and of the adductor tubercle, and the three are distinguished by measurement rather than by appearance.

The patellar attachment's breadth means a graft fixed at a point reproduces a line attachment with a point one, which changes how load is distributed across the medial patella.

Its blend with the retinaculum and with vastus medialis obliquus means the ligament has no clean borders, so a reconstruction creates a cleaner structure than the one it replaces.

Function

Treat it as a checkrein rather than a restraint under constant load. A normally tracking patella does not load this ligament, so a graft tensioned to be taut is tensioned wrongly.

Length change through flexion is set by the femoral point. A point too proximal tightens in flexion; a point too distal slackens. Both produce a construct that fails, and the two fail differently.

It cannot overcome bony malalignment. A ligament about 1 mm thick is not the structure to correct a trochlea or a tubercle position, and 3.12.8 carries that argument.

Clinical Relevance

Confirm the femoral point radiographically rather than by feel, and 2.12.6 covers the landmarks.

Tension the construct so the patella can still be translated laterally by a defined amount, rather than so it cannot move. Over-tensioning loads the medial facet.

Assess trochlear geometry and tubercle position before reconstructing this ligament, because a thin check cannot correct bone.

Expect a lengthened but continuous ligament in a recurrent dislocator, and read continuity on imaging accordingly.