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Cyclops Lesions of the Knee A Narrative Review of the Literature

Kambhampati, S.B., Gollamudi, S., Shanmugasundaram, S. and Josyula, V.V., 2020. Cyclops lesions of the knee: a narrative review of the literature. Orthopaedic Journal of Sports Medicine, 8(8), p.2325967120945671.

In today’s letter

• Explanation of what is a cyclops lesion

• Rapid Results =

1. A Cyclops lesion is a small lump made of fibro-vascular tissue, which can be attached or not attached to tissue.

2. It is called a "Cyclops" lesion because under an arthroscope, the blood vessels on it resemble an eye

• 3 Reads to check out to further you knowledge about the knee

• Meme of the week: Moral of the story - Just keep sitting 🪑 

Aim of the study

• This review looked at the available research on Cyclops lesions and their different forms and summarised all the information out there.

Did you know?

• A Cyclops lesion is a fibrous lump that forms in the knee after anterior cruciate ligament (ACL) surgery, first identified in 1990.

• It develops in front of the ACL graft and consists of granulation (healing) tissue.

• “Cyclops syndrome” is used when this lesion causes knee extension issues, which is sometimes accompanied by a popping sound or sensation.

• The syndrome affects 1% to 10% of ACL surgery patients, but MRI scans show that Cyclops lesions can occur in 25% to 47% of cases

 Methods

• A keyword search was performed on March 10, 2019, using the keywords (cyclops OR “anterior arthrofibrosis” OR cyclopoid) AND (knee) to identify articles on cyclops lesion.

• 47 articles from the English-language literature were used to prepare this review.

• The available literature consisted mostly of case reports and case series.

What is a Cyclops Lesion?

• A Cyclops lesion is a small lump made of fibro-vascular tissue, which can be attached or not attached to tissue.

• It is called a "Cyclops" lesion because under an arthroscope (a surgical camera), the blood vessels on it resemble an eye.

• Symptomatic Cyclops lesions are hard and contain cartilage-like tissue with bone formation at the center, as seen under a microscope.

• Asymptomatic Cyclops lesions are softer and only contain patches of cartilage-like tissue surrounded by healing tissue.

• If the lesion forms after using a ligament augmentation device, microscopic examination shows chronic inflammation with giant cells, similar to a foreign body reaction

Variants of Cyclops Lesions

Inverted Cyclops Lesion

• An inverted cyclops lesion is a fibrous lump that forms in the femoral notch (upper part of the knee joint) instead of the tibia (lower part).

• It is associated with certain injuries like T-shaped fractures in the femur and ACL reconstruction using different graft types (e.g., bone-patellar tendon-bone or hamstring grafts).

• The lesion can sometimes have a stalk that connects to the femoral tunnel or can occur without this connection.

Cyclopoid Lesions

• Cyclopoid lesions are soft, fibrous lumps without cartilage or bone, unlike classic cyclops lesions.

• These lesions are typically asymptomatic and do not cause issues with full knee extension.

• They are usually discovered incidentally through MRI scans or arthroscopic surgery, rather than through patient symptoms.

Other Causes of Cyclops-like Presentation

• Gouty tophus, which is a deposit of urate crystals from gout, can cause a cyclops-like appearance and limit knee extension.

• Histologically, gouty tophus consists of urate crystals and inflammatory cells, often found in the fat pad below the knee.

• These gouty deposits are typically multiple but rarely appear as single lumps.

• Another cyclops-like issue can happen when a partially torn ACL graft clumps up, forming a nodule similar to a cyclops lesion.

Incidence and Impact

• With approximately 250,000 ACL tears per year in the U.S., cyclops lesions after ACL reconstruction (1%-10% of cases) can place a significant burden on healthcare.

• However, theres not many large studies on cyclops, suggesting that a lot of the cyclopse lesions may be asymptomatic and undiagnosed.

• It's possible that advances in ACL reconstruction techniques are reducing the incidence of cyclops lesions.

Classification

The authors have summarised the classification of cyclops lesions based on their location, pathological process, and clinical presentation in Table 1

Causes of Cyclops Lesion

• A Cyclops lesion is a lump or overgrown graft tissue often linked to a tibial tunnel placed too far forward or disorganised scar tissue in the front of the knee.

• It is the second most common reason for limited knee extension, following graft impingement.

• Cyclops lesions can occur with both complete and partial tears of the ACL

• In ACL tears, the lump is thought to form from small pieces of bone being pulled away from the tibial attachment site of the ACL.

• If knee extension is still limited more than two months after aggressive rehabilitation following an ACL tear, a Cyclops lesion should be suspected

• In a study of 1,012 ACL injuries in China, 2.4% of cases had ACL remnants and 1.9% of those caused knee extension problems.

• Factors like age, time since the injury, partial weight-bearing, meniscal surgery, or other ligament injuries did not affect the incidence of Cyclops lesions.

• Men had a higher chance of knee extension loss compared to women in this study.

• Early reports showed Cyclops lesions were more common after bone-patellar tendon-bone (BPTB) ACL reconstruction, but there’s no significant difference in incidence between hamstring and BPTB grafts.

• Cyclops lesions are more common with double-bundle and quadriceps graft ACL reconstructions than with single-bundle or hamstring grafts.

• Studies have shown that women have up to 4 times higher rates of Cyclops lesions compared to men.

• Cyclops lesions have also been found more frequently after bicruciate-retaining total knee replacements, even when the ACL was not directly injured.

• The cause may be damage to the ACL during prosthesis implantation or sharp edges on the tibial bone.

• A study of 113 ACL reconstruction patients found no link between the size of a Cyclops lesion and pain or symptoms but did find that women and those with smaller notches had more Cyclops lesions.

• In a different study by von Essen & colleagues, no difference in the incidence of Cyclops lesions was found whether ACL reconstruction was done within 8 days or 6 weeks after injury.

• While Cyclops lesions are usually blamed for limiting knee extension, some research shows that hamstring tightness might contribute in extension problems in patients with Cyclops lesions

Diagnosis

• Most Cyclops lesions do not cause symptoms and are usually discovered by chance on MRI scans after surgery.

• Only 2% to 10% of all Cyclops lesions cause noticeable symptoms.

• When symptomatic, patients may experience:

1. Loss of full knee extension

2. Discomfort while walking, running, or lying on their back

3. Sometimes hear or feel a "clunk" when extending the knee fully.

• Around 1% to 9.8% of patients with limited knee extension after ACL surgery have Cyclops lesions, and this extension loss (about 20°) becomes more noticeable over 4 months after surgery.

• Symptoms include pain at the end of knee extension, cracking or popping sounds, stiffness, and difficulty fully extending the knee, as well as pain when climbing stairs.

• In 93% of cases, Cyclops lesions are diagnosed within 6 months of surgery, and 78% of patients show symptoms of extension loss within 6 weeks after surgery.

• Cyclops lesions can occur even years after surgery, with some reported as late as 10 years after ACL reconstruction and 23 years after a partial ACL tear without surgery.

• If knee irritation persists for more than 4 weeks after ACL surgery, Cyclops lesions or other types of scar tissue buildup (arthrofibrosis) should be considered.

• Cyclops lesions can affect a patient’s walking pattern by altering knee movements and may contribute to cartilage degeneration in the medial knee joint within a year after ACL surgery.

• MRI is about 85% accurate in diagnosing these lesions

Surgical Findings and Treatment

• Loss of knee extension from an ACL rupture may go away under anesthesia, but if caused by Cyclops syndrome, it will persist.

• Asymptomatic Cyclops lesions are typically left untreated, while Cyclops syndrome usually requires surgery to restore normal knee function, although no direct comparison studies exist.

• Early excision of the lesion (within 12 weeks) has shown good results, with no reported recurrences, though recurrence is common with other causes of knee extension loss.

• During surgery, the lesion’s edges are carefully defined and removed using a shaver or bur to clear the fibrous tissue.

• The knee is moved through its full range of motion during surgery to ensure there’s no impingement of the ACL graft.

• After excision, the prognosis is good, with symptoms resolving within a few weeks and patients regaining full range of motion.

3 resources to check out

To learn more about cyclops lesion

1. Cyclops lesion - A case report - LINK

2. Assessing a cyclops lesion - LINK

3. MRI & quick explanation of cyclops lesion (Video) - LINK

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