Cyclops lesion (knee)

The cyclops lesion, also known as localised anterior arthrofibrosis, is a painful anterior knee mass that arise as a complication of anterior cruciate ligament (ACL) reconstruction.

Cyclops lesions occur with an estimated frequency of ~5% (range 1-9.8%) of patients following ACL reconstruction. They are rarely encountered in patients who have not had ACL reconstruction, but have nonetheless sustained ACL injuries 3

Patient's present with pain during extension of the affected knee, with an eventual audible and palpable “clunk”, occurring typically 8 to 32 weeks (16 weeks on average) after ACL repair 3

The exact aetiology is uncertain, and may be related to gradual fraying and bunching up of remnant ACL or graft fibres, excessive fibrosis, or alternatively due to uplifting of fibrocartilaginous tissue during drilling of the tibia for anterior cruciate ligament reconstruction serves as a nidus for fibrous tissue deposition.

The end result, regardless of cause, is a rounded fibrous mass sitting in the anterior intercondylar notch. Pathologically, the lesion consists of central granulation tissue surrounded by dense fibrous tissue.

MRI

As with other internal derangements of the knee, MRI is the modality of choice for assessing the post operative knee. 

At MR imaging, a soft-tissue mass is seen anteriorly or anterolaterally in the intercondylar notch near the tibial insertion of the reconstructed anterior cruciate ligament.

Because of its fibrous content, a cyclops lesion typically has intermediate to low signal intensity with all pulse sequences.

Treatment is arthroscopic excision.

The lesion was so named because of its bulbous appearance and characteristic focal areas of reddish-blue discoloration (from venous channels) that resemble an eye at arthroscopy.


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Article Information

rID: 1187
Sections: Signs, Pathology
Tag: knee
Synonyms or Alternate Spellings:
  • Localised anterior arthrofibrosis
  • Cyclops lesions

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    Figure 1: Polyphemus the Cyclops
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