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.
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.
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.
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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.