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Cyclops Lesion Of The ACL

A Cyclops lesion is a complication following an ACL injury which occurs in about 5% of cases. It is named accordingly due to its appearance, as during surgical removal of the lesion it looks like the eye of a cyclops.

A cyclops lesion is a piece of scar tissue which develops on the anterior portion of an ACL. The lesion consists of hard fibrous tissue and sometimes bone, which after development can cause pain and limit the ability of the person to extend their leg fully.

The lesion occurs after an injury to the ACL and has been found in patients who have had a surgical repair and those who haven’t.

How does it occur?

Why a cyclops lesions develops after an ACL injury is a highly debated area of study. It isn’t fully understood why these lesions develop, however there are a few emerging theories.

The first theory is due to the orthopaedic techniques used with ACL reconstruction; some studies have suggested that the size, position and technique used for reconstruction can lead to the development of a lesion.

Other studies have suggested that having a delayed period of time between surgery and achieving full extension of the knee can lead to the develop of a cyclops lesion. Having a delayed recovery can lead to tightness in the muscles around the knee along with pain inhibition of the muscles around the knee which makes it harder for the knee to extend and can give the lesion time to grow.

What are the symptoms?

The symptoms of a cyclops lesion will usually be present within the first 12 weeks after the injury but have been reported in the literature as late as 10 years post injury.

The most common symptoms include:

  • Inability to achieve full knee extension.
  • Pain in the anterior part of the knee
  • Painful cracking and grinding noises
  • Stiffness
  • Tenderness along the sides of the knee where the joints meet
  • Locking

What is the treatment?

The treatment for a cyclops lesion is removal via surgery. Most people have great outcomes post-surgery with 85% of people reporting full range of movement and reduced pain immediately after surgery.

If you are not making gains with your rehabilitation post surgery or need advice on what to do post ACL injury, get in touch and see one of our experienced physios here in the Sydney CBD!


Kambhampati, S., Gollamudi, S., Shanmugasundaram, S., & Josyula, V. (2020). Cyclops Lesions of the Knee: A Narrative Review of the Literature. Orthopaedic journal of sports medicine8(8), 2325967120945671.

Emillie Kinkella

Emillie joined the Bend + Mend team after a move east to Sydney from Bunbury, Western Australia. Emillie graduated from Curtin University with a Bachelor of Science (Physiotherapy) in 2017 and since graduation has had experience in both the public and private settings working in musculoskeletal physiotherapy. She has undergone post graduate training in dry needling, tendinopathy management, lower back pain disorders and Clinical Pilates. Emillie grew up in a soccer orientated family and enjoys treating soccer related injuries sustained both on and off the field, along with lower back pain disorders and tendinopathies. Outside of work Emillie enjoys cooking up a storm and exploring the sights of beautiful Sydney.

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