Cyclops Lesion (knee)

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Clinically Relevant Anatomy
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Cyclops lesion, also called anterior arthrofibrosis, is a post-surgical complication of anterior cruciate ligament reconstruction (ACLR)[1] that leads to limited knee extension range of motion. It 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].

Mechanism of Injury / Pathological Process
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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[3]. This may be due the larger volume of the graft impinging in the knee joint[3].

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-point 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


Noailles et al found the incidence of cyclops lesion, symptomatic and asymptomatic, on MRI to be 33.0% to 46.8%[4]. The incidence of symptomatic cyclops syndrome was 1.9-10.2% following single-bundle reconstruction and 3.6-10/9% following double-bundle reconstruction[4].

Diagnostic Procedures[edit | edit source]

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

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[6]. It is not recommended to remove asymptomatic lesions[2].

Differential Diagnosis
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Gouty tophus can cause loss of knee extension and cyclops-like appearance due to build up of gouty deposits[7]. Kambhampati et al reported other causes of cyclops-like lesions include space-occupying lesions, ganglia, pigmented villonodular synovitis and are diagnosed through histological examination[2].

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 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. 3.0 3.1 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.
  4. 4.0 4.1 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.
  5. Bradley DM, Bergman AG, Dillingham MF. MR imaging of cyclops lesions. AJR Am J Roentgenol. 2000 Mar;174(3):719-26
  6. 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.
  7. 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.