Teaching Case

A 24-year-old female presents with pain in her right knee for over a year. She had had previous arthroscopic reconstruction of the anterior cruciate ligament (ACL) of the same knee 5 years before in the context of a LCA rupture after a ski trauma.

The arthro-magnetic resonance imaging shows postsurgical changes with well-positioned bone tunnels and anterior cruciate ligament plasty.

In the anterior intercondylar notch there’s a lesion resembling a cyclops lesion, with intermediate signal intensity on proton density and PD fat-saturated images (Figures 1-5). However, it doesn’t have the characteristics of arthofibrosis. Instead, it extends directly from the fixation tunnel, and it has a linear fibrillar morphology and signal characteristics that are compatible with an ACL. This is caused by a rupture of the ACL graft which subsequently folded anteriorly forming a folded stump which is called a pseudocyclops lesion.

A. Background
After an arthroscopic reconstruction of the anterior cruciate ligament there are some possible complications. The complication rate is around 10-25% and include for example mechanical impingement, graft failure, arthrofibrosis, cystic degeneration of the graft, complications from the fixation materials and infection. [1; 2]
In the case of arthrofibrosis a granulation tissue is formed because of synovial hyperplasia and fibrotic tissue formation due to inflammatory changes [3].
Arthrofibrosis can be diffuse or localized. When the formed mass is located anteriorly to the reconstructed ACL it is called Cyclops lesion because of its arthroscopic appearance, and it’s a complication that happens in around 1-10% of the ACL reconstructions [3]

The Pseudocyclops lesion is a rare complication of the arthroscopic reconstruction of the ACL in which a partial graft tear occurs and subsequently the torn fibres are flipped anteriorly mimicking a Cyclops lesion. It is not an actual Cyclops lesion as it is a torn ACL instead of fibrotic tissue.

B. Clinical Perspective
The Pseudocyclops lesion, which is the torn graft located anteriorly in the intercondylar notch, can cause the same symptoms as a Cyclops lesion as it can cause a mechanical impingement, with loss of knee extension.
In these cases, an MRI exam is important to exclude other complications and to diagnose the graft tear with ACL folding and differentiate it from arthrofibrosis.

C. Imaging Perspective
MRI is the preferred imaging method for imaging the postoperative knee. [4]
Even with the postoperative changes, MRI is a useful noninvasive tool to examine patients with symptoms after ACL reconstruction, namely to detect Cyclops lesion which is a possible differen-tial diagnosis [5]. MRI also allows to detect other complications such as roof impingement, abnor-mal tunnel location, and graft tears [2].
The key finding of Pseudocyclops lesion is a linear fibrillary lesion with intermediate signal intensity located in the intercondylar notch resembling a torn ACL and in continuity with the remaining graft.

D. Outcome
The therapeutic option is arthroscopic repair of the graft tear.

E. Take Home Message, Teaching Points
- One of the complications of arthroscopic ACL repair is the formation of a fibrotic mass in the anterior joint recess, being this called “Cyclops lesion”.
- Another complication is graft tear with the torn fibres folding anteriorly and getting entrapped in the intercondylar notch, which is called a Pseudocyclops lesion as it resembles the fibrotic Cyclops mass.

Written informed patient consent for publication has been obtained.