A cyclops lesion is a bunched up area of scar tissue in the notch of the femur, usually seen as a complication of anterior cruciate ligament reconstruction.

cyclops lesion after ACL reconstruction

A cyclops lesion filling the notch of the femur anterior to the reconstructed anterior cruciate ligament (ACL).

cyclops cartoon

The original cyclops of mythology was a one-eyed monster.


Extension deficit as a result of a cyclops lesion

The bunched up tissue causes problems with achieving full extension. There may be a complete inability to achieve full extension, or it may be possible with an uncomfortable clunk.


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.

An 'interpretation'of an article from 2000 describing the possible causes of loss of full extension in the knee after cruciate ligament reconstruction, how it is managed, and highlighting the importance of rehabilitation in preventing loss of full range of movement in the first place.



Case Series: Cyclops lesion - extension loss after ACL reconstruction. Dhanda S, Sanghvi D and Pardiwala D. Indian J Radiol Imaging. 2010 Aug; 20(3): 208–210.

The cyclops lesion after bicruciate-retaining total knee replacement. Klaassen MA and Aikins JL. Arthroplast Today. 2017 Dec; 3(4): 242–246.

See also -