Cyclops (arthrofibrosis)

Some causes and factors, which come into play in a cyclops:

• Female due to less space in the knee joint
• Increased volume of graft relative to notch
• Bony avulsion of anterior cruciate ligament (VKB)
• Anterior placement of tibial tunnel
• Double-bundle VKB reconstruction due to larger volume of graft
• Bicruciate -preserving arthroplasty due to VKB injury or acute tibial bone island
• Hamstring contracture

Certain factors may increase the risk of one. Women are at higher risk here, probably due to a combination of anatomical differences (such as a narrower intercondylar notch), hormonal influences on connective tissue repair and greater sensitivity to quadriceps inhibition in pain.

Similarly, patients who have suffered during their anterior cruciate ligament surgery undergo another out-of-joint reconstruction, such as an ALL reconstruction or ITB tenodesis, are more likely to develop cyclopses. This additional procedure often causes more pain and difficult activation of the quadriceps, making it more difficult to mobilise the knee which promotes the formation of scar tissue in the front of the knee.

We know from other sources that factors such as a relatively large graft in a narrow notch, small bone particles after avulsion, a tibial tunnel placed too far forward or a double-bundle technique can also increase the risk.

While these factors may increase the risk of cyclops, it does not mean that this complication is inevitable. At Physio Fitaal, we therefore place extra emphasis on early knee extension, pain education and direct quadriceps activation, keeping the risk as low as possible. By recognising early signs and acting immediately, we can prevent a cyclops from becoming a permanent impairment in most cases.

• Pain at the front of the knee
• Problems walking and picking up speed (running)
• An audible click while stretching the knee
• Less mobility
• A hard end feeling when stretching the knee
• Impaired function of the quadriceps (upper leg muscle)
• Swelling present in the knee(hydrops)

* This is after the acute phase. For the first 3 months, these symptoms are due to the surgery and not due to possible cyclops in the knee.

A cyclops need not always cause symptoms. Small cyclops formations are frequently seen on MRI and often turn out to be asymptomatic. Multiple studies show that the size of the cyclops is the most important factor in the development of symptoms.

Especially when the tissue becomes larger than about 1 cm², the likelihood of mechanical blockage in the extension of the knee increases markedly. Larger scar tissue fills more space in the intercondylar notch and can therefore literally get in the way of full extension of the knee. This causes the familiar symptoms such as stretch limitation, pain or a “clunk” sensation during movement.

A cyclops with a smaller size can therefore present without problems, while larger formations (>1 cm²) are much more likely to cause functional limitations.