Cyclops Lesion (Knee)

Original Editor - User:Patti Cavaleri
Top Contributors - Patti Cavaleri, Niha Mulla and Kim Jackson

Definition[edit | edit source]

Cyclops lesion, is known as anterior arthrofibrosis and is a post surgical complication of anterior cruciate ligament reconstruction (ACLR)[1]that leads to limited knee extension range of motion.

Introduction[edit | edit source]

A cyclops lesion with loss of knee extension with or without an audible or palpable cluck at terminal knee extension constitutes the cyclops syndrome. Clinically it is reported to have prevalence of 1% to 10 % but magnetic resonance imaging (MRI) studies have shown the physiological changes occurring in about 25% to 47% of cyclops lesions. In some cases the studies have shown that, chances of its prevalence increases as time passes post anterior cruciate ligament reconstruction (ACLR) with the incidence being reported 25% up to first 6 month of ACLR to 33% at 1 year after ACLR, and further to 46.8% after a year of ACLR. Among all theses patients only 10% are known to be symptomatic. [2][3]

Clinically Relevant Anatomy[edit | edit source]

Cyclops lesion is commonly found to be on the anterolateral aspect of the tibial insertion site of the anterior cruciate ligament (ACL) graft and made up of fibrovascular tissue[1]. Jackson and Schaefer describe the lesion as having peripheral fibrous tissue around centrally located granulation tissue. It may have bone or cartilaginous tissue as well[1][2].

Mechanism of Injury / Pathological Process
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The cyclops lesion is a nodule of fibrovascular tissue with the arthroscopic appearance of a cyclops with peripheral fibrous tissue. Cyclops lesions have been reported after complete and partial ACL tears[2]. Microtrauma following injury leads to the formation of the nodule and has been found following different types of ACL grafts and reconstruction types[2]. Sonnery-Cottet et al. found cyclops lesions to be more common in double-bundle and quadriceps grafts compared to single-bundle and hamstring grafts[4]. This may be due the larger volume of the graft impinging in the knee joint[4].

Risk Factors[edit | edit source]

Khambhampati et al report 8 risk factors for cyclops lesions:[2]

  1. Female sex due to narrow intercondylar notch
  2. Increased volume of graft in relation to the notch size
  3. Bony avulsion of ACL from tibia
  4. Bony avulsion of ACL from femur
  5. Anterior placement of tibial tunnel
  6. Double-bundle ACL reconstruction due to higher volume of graft
  7. Bicruciate-retaining arthroplasty because of ACL injury or sharp tibial bone island
  8. Hamstring contracture

Clinical Presentation[edit | edit source]

Patients with symptomatic cyclops lesions (known as cyclops syndrome) often demonstrate loss of terminal knee extension, report discomfort with walking/running/lying supine, and have an audible or palpable clunk during terminal knee extension[1]. The loss of extension with symptoms becomes progressively worse over time after surgery, especially after 4 months[2].

Khambhampati et al report clinical symptoms include[2]:

  • Pain at terminal knee extension
  • Crepitus
  • Painful cracking
  • Rubbery end-feel to extension with a palpable pop
  • Stiffness
  • Residual laxity
  • Grinding with attempted extension beyond patient's limit
  • Joint line pain and tenderness
  • Locking of the knee
  • Discomfort with climbing stairs

Diagnostic Procedures[edit | edit source]

MRI diagnostics of cyclops lesions has 85.0% sensitivity, 84.6% specificity, and 84.8% accuracy[5].

Differential Diagnosis[edit | edit source]

  • Gouty tophus can cause loss of knee extension and cyclops-like appearance due to build up of gouty deposits[6].
  • Nodular synovitis[7]
  • Localized intraarticular giant cell tumor of the tendon sheath[7]

Management / Interventions
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For symptomatic cyclops lesions, arthroscopic surgical debridement of the lesion can restore normal biomechanics of the knee[2]. Patients typically have good prognosis of recovering function and full knee range of motion following excision surgery[8]. It is not recommended to remove asymptomatic lesions[2].

Physical therapy can only be targeted towards symptomatic relief and no matter how much a physiotherapist tries, full knee extension cannot be achieved until a second arthroscopy is carried out to remove the nodule/ scar tissue. [9]

It is extremely important to regain knee extension after a anterior cruciate ligament reconstruction (ACLR) and it can be achieved by three main knee extension exercises as mentioned below:[9]

  1. Supine Prolonged Low-Load Stretch. [9]
  2. Calf & Hamstring Stretch with Pressure. [9]
  3. Standing Banded Knee Extension.[9]

References[edit | edit source]

  1. 1.0 1.1 1.2 1.3 Jackson DW, Schaefer RK. Cyclops syndrome: loss of extension following intra-articular anterior cruciate ligament reconstruction. Arthroscopy. 1990;6(3):171-8.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Kambhampati SBS, Gollamudi S, Shanmugasundaram S, Josyula VVS. Cyclops Lesions of the Knee: A Narrative Review of the Literature. Orthop J Sports Med. 2020 Aug 28;8(8):2325967120945671.
  3. Noailles T, Chalopin A, Boissard M, Lopes R, Bouguennec N, Hardy A. Incidence and risk factors for cyclops syndrome after anterior cruciate ligament reconstruction: A systematic literature review. Orthop Traumatol Surg Res. 2019 Nov;105(7):1401-1405.
  4. 4.0 4.1 Sonnery-Cottet B, Lavoie F, Ogassawara R, Kasmaoui H, Scussiato RG, Kidder JF, Chambat P. Clinical and operative characteristics of cyclops syndrome after double-bundle anterior cruciate ligament reconstruction. Arthroscopy. 2010 Nov;26(11):1483-8.
  5. Bradley DM, Bergman AG, Dillingham MF. MR imaging of cyclops lesions. AJR Am J Roentgenol. 2000 Mar;174(3):719-26
  6. Doany M, Lopez N, Rokito A. Knee Extension Loss Secondary to a "Cyclops-Like" Gouty Tophus A Case Report and Literature Review. Bull Hosp Jt Dis (2013). 2017 May;75(3):213-216.
  7. 7.0 7.1 Gaillard F. Cyclops lesion (knee): Radiology reference article. Radiopaedia Blog RSS.; 2021. Available from:
  8. van Dijck RA, Saris DB, Willems JW, Fievez AW. Additional surgery after anterior cruciate ligament reconstruction: can we improve technical aspects of the initial procedure? Arthroscopy. 2008 Jan;24(1):88-95.
  9. 9.0 9.1 9.2 9.3 9.4 Gardiner J. ACL surgery: Cyclops lesions. POGO Physio Gold Coast. POGO Physio Gold Coast; 2020. Available from:'t%20able,to%20regain%20extension%20(2).