Cyclops Lesions

For Medical Students

What It Shows

A cyclops lesion is a nodule of fibrous tissue at the front of the intercondylar notch, lying ahead of the graft. 5.7.9 covers cruciate reconstruction.

It forms after a reconstruction and blocks the notch mechanically in extension. 2.7.12 covers the surgical anatomy.

It matters because loss of terminal extension after a reconstruction has several causes and this is the one with a direct mechanical answer. 4.7.8 covers the extension lag.

How It Is Acquired

Look at the sagittal images through the anterior notch, which is where the nodule sits. 5.5.1 covers the standard protocol.

Assess its signal, since a fibrous nodule is lower in signal than fluid and higher than cortical bone. 5.2.15 covers proton density imaging.

Assess the tibial tunnel position, because a forward tunnel is the association. 5.7.12 covers tunnel assessment.

Assess the graft itself, since the nodule sits in front of it rather than within it. 5.7.10 covers graft maturation.

Correlate with the extension deficit, because the finding without the deficit means little. 4.7.5 covers the end feel.

What Abnormal Looks Like

A rounded nodule of intermediate to low signal in the anterior intercondylar notch, in front of the graft.

A nodule abutting the roof of the notch, which is the contact that limits extension. 2.7.12 covers the surgical anatomy.

An anteriorly placed tibial tunnel in the same study. 5.7.12 covers tunnel assessment.

A graft that is itself continuous and normally positioned. 5.7.9 covers cruciate reconstruction.

MRCS Level

How It Is Acquired

In a viva this is the lesion to name when asked why a reconstructed knee will not straighten.

The expected points are the anterior notch on sagittal images, the signal, the tibial tunnel, the graft, and the clinical deficit.

Say that you would correlate the finding with the extension deficit. 4.7.8 covers the extension lag.

Say that a forward tibial tunnel is the association to look for. 5.7.12 covers tunnel assessment.

Say that the differential includes generalised arthrofibrosis rather than a discrete nodule. 4.7.7 covers the contractures.

What Abnormal Looks Like

The reasoning expected is that a graft or a tunnel placed forward brings tissue into contact with the notch roof in extension, and repeated contact produces fibrous proliferation at that point. 3.7.20 covers the reconstruction biomechanics.

The nodule then becomes the block itself, so the cause and the lesion reinforce each other mechanically. 2.7.12 covers the surgical anatomy.

Its fibrous composition is why it is lower in signal than the fluid around it, and that signal is the main thing separating it from a joint effusion in the notch. 5.2.14 covers T2 imaging.

The distinction from diffuse arthrofibrosis matters because a discrete nodule can be excised and a diffuse process cannot. 4.7.7 covers the contractures.

How Good It Is

Magnetic resonance imaging shows the nodule well when it is looked for and omits it when it is not.

Its best contribution is separating a discrete mechanical block from diffuse scarring, which changes the treatment. 4.7.7 covers the contractures.

It is limited by the lesion being small, by its position at the edge of the usual search, and by not everything that looks like it causing symptoms. 5.1.6 covers imaging pitfalls.

No figures appear for accuracy on this page, under decision 028, and the comparison is the claim: the lesion is seen well when sought and poorly when not, which is a comparison rather than a number.

FRCS Level

How Good It Is

At decision level the nodule matters when it explains a deficit, and the report should connect the two or say it cannot.

A discrete nodule with a firm block to terminal extension is the case for arthroscopic excision, and the imaging supports the plan. 4.7.5 covers the end feel.

The same appearance in a knee with full extension is incidental. 5.1.6 covers imaging pitfalls.

A forward tibial tunnel alongside the nodule means excision alone may not prevent recurrence, which is a planning point rather than a diagnosis. 5.7.12 covers tunnel assessment.

Diffuse capsular thickening without a nodule is a different problem with a different answer. 4.7.7 covers the contractures.

Where It Misleads

The commonest error is not looking in the anterior notch, so the lesion is absent from the report. 5.20.7 covers reporting the post-operative knee.

Fluid in the anterior notch is reported as a nodule. 5.2.14 covers T2 imaging.

The nodule is reported without the extension deficit being known, so its significance is unstated. 5.20.1 covers structured reporting.

The tibial tunnel is not assessed, so the mechanical association is missed. 5.7.12 covers tunnel assessment.

Diffuse arthrofibrosis is reported as a cyclops lesion, which proposes an operation that will not help. 4.7.7 covers the contractures.

Fellowship Level

Where It Misleads

At fellowship level the cyclops lesion is a reminder that a small finding at the edge of the field can be the only thing in the study that matters.

Its prevalence on imaging after reconstruction exceeds the prevalence of extension loss, so the appearance alone over-diagnoses the condition. 5.1.6 covers imaging pitfalls.

No size or signal criterion separates a symptomatic nodule from an incidental one, which is why no measurement appears on this page. 5.21.2 covers the cruciate imaging literature.

The name describes an arthroscopic appearance rather than an imaging one, so the imaging diagnosis is an inference about what a surgeon would see. 2.7.12 covers the surgical anatomy.

Recurrence after excision is related to the underlying tunnel geometry, and a report that names the nodule without the tunnel leaves out the part that predicts the result. 5.7.12 covers tunnel assessment.

The useful report says whether there is a discrete block, where it is, and whether the tunnel explains it, and current reports rarely answer the third. 5.20.1 covers structured reporting.