Notch impingement is when a cruciate ligament graft is wrongly placed or too bulky, and the fibres impinge on the roof of the bony notch of the femur.

normal femoral notch
cyclops lesion obstructing notch
cyclops lesion obstructing extension


Notch impingement and the Cyclops Lesion

Impingement may prevent the knee from straightening fully, and sometimes the impinging bit bunches up into a lump called a 'cyclops lesion' which can also add a 'clunk' as the person forces the knee into extension (ie straight). Eventually it may become impossible to fully extend the knee.


A discussion about problems with regaining extension after ACL reconstruction because of a Cyclops Lesion.

ACL graft failure due to graft impingement

ACL reconstruction failure and revisions - Part 5b - by Dr Frank Noyes.

The editor's interpretation of a 2004 article highlighting the important anatomy associated with arthrofibrosis of the knee.


Cyclops Lesions are Associated with Altered Gait Patterns and Medial Knee Joint Cartilage Degeneration at One Year after ACL-Reconstruction. Samaan MA, Facchett L, Pedoia V, Tanaka MS, Link TM, Souza RB, Ma B and Li X. J Orthop Res. 2017 Oct; 35(10): 2275–2281.

See also -

Here is a very nice video embedded courtesy of Dr Pablo de la Cuadra, showing how the bunched-up cyclops tissue appears on MRI (from various angles) and then during arthroscopic surgery.