Notch impingement

This illustration shows a simple test to demonstrate an extension lag - in this case caused by an obstruction within the notch of the femur from a cyclops lesion.

Illustration of patient lying on stomach with legs unsupported - if the notch is obstructed there may be an 'extension lag'.

What is the notch of the femur?

In the knee joint, the femur bone articulates with the tibia bone at two contact points (the rounded condyles). In this illustration the knee is bent, so it is easy to see the notch. When the knee is straightened, the condyles roll forwards and the notch disappears to the back of the knee.

The notch is the gap between the two condyles and it allows plenty of space for the two large cruciate ligaments.

Illustration to show the normal notch between the rounded condyles at the lower end of the femur.

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A naturally narrow notch may contribute to anterior cruciate ligament rupture, and also an 'over-bulky' graft reconstruction may impinge on the edges of the notch if the gap is not wide enough to accommodate the new graft construct. This may cause some shredding of the graft material, creating a 'cyclops lesion' - this illustration shows a cyclops lesion related to the cruciate ligaments filling the upper part of the notch.

Impingement may prevent the knee from straightening fully, and sometimes which can lead to a 'clunk' as the person forces the knee into extension (ie straight). Eventually it may become impossible to fully extend the knee.

Illustration to show a cyclops lesion obstructing the notch.

"....important anatomic risk factors in ACL tears are the morphometric parameters of the intercondylar notch....[and] the relative angular position of the tibia with respect to the femur"

Tomás Fernández-Jaén et al

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