Light and scan electron microscopic analysis of cyclops syndrome: etiopathogenic hypothesis and technical solutions

Abstract

The loss of range of motion after anterior cruciate ligament (ACL) reconstruction is one of the most common and most challenging complications of this kind of surgery. Recently, an intercondylar notch fibrous proliferation, called cyclops syndrome because of its arthroscopic appearance, has been identified as one of the specific causes of loss of extension. The incidence of cyclops syndrome is 2%-4% [17, 18], but there is still no understanding of its etiology. We speculate on the etiology and suggest some technical solutions to reduce this complication. In 180 patients submitted to arthroscopic ACL reconstruction with patellar tendon, we observed in 4 cases a fibrous nodule adherent to the neoligament that caused a loss of extension between 12 degrees and 17 degrees. In all cases, arthroscopic removal of this nodule solved completely the loss of articular motion. The nodules were subjected to light and scanning electron microscope evaluation. We observed numerous, newly formed vessels in all 4 nodules. These vessels were made up of hyperplastic and hypertrophic cells and were surrounded by bundles of disorganized fibrous tissue. No inflammatory cells or bone or cartilaginous tissue was observed. We hypothesize a microtraumatic genesis for cyclops syndrome. Repeated microtraumas expose the graft collagen fibers, which can lead to productive inflammatory process and thence to the formation of the cyclops nodule. We suggest some technical solutions to avoid graft impingement with the notch and with the tibial bone tunnel.

Cyclops lesions detected by MRI are frequent findings after ACL surgical reconstruction but do not impact clinical outcome over 2 years

“…One possible explanation may be that “harder” variants of lesions could represent a mechanical obstacle at the end of the knee extension, whereas “softer” variants, such as cyclopoid scars, do not affect the range of motion, as shown by Muellner et al [15]. However, other studies did not find any cartilage or bone tissue in cyclops lesions causing limited knee extension [10, 14]. Therefore, when evaluating a patient with clinical symptoms and decreased range of motion, the radiologist should be aware that the presence of a cyclops lesion could be both, a main finding or a finding without further clinical relevance.…”

“…Although the origin of the fibrous tissue is uncertain, it has been suggested that the formation of the cyclops lesion is stimulated by debris from the drilling and preparation of the tibial tunnel [8, 11]. Even though this lesion was previously defined as localized arthrofibrosis [6, 12, 13], histologically the cyclops lesion is composed of disorganized fibrous connective tissue with a central region of granulation tissue and newly formed vessels [8, 10, 14, 15]. Repeated microtrauma may expose the graft collagen fibres, which can lead to productive inflammatory processes and to the formation of a cyclops nodule [14].…”

“…Even though this lesion was previously defined as localized arthrofibrosis [6, 12, 13], histologically the cyclops lesion is composed of disorganized fibrous connective tissue with a central region of granulation tissue and newly formed vessels [8, 10, 14, 15]. Repeated microtrauma may expose the graft collagen fibres, which can lead to productive inflammatory processes and to the formation of a cyclops nodule [14]. Arthroscopic studies have estimated the prevalence of symptomatic cyclops lesions after ACL surgery ranging between 1% and 9.8% [16, 17].…”

Anterior Cruciate Ligament Reconstruction Using an Endoscopic Technique With Patellar Tendon Autograft

“…On the tibial side, the ACL stump should be sufficiently removed to avoid development of a Cyclops lesion. 12,13,17,22 Residual ACL tissue removal may be expedited with the use of arthroscopic scissors, an osteotome, or arthroscopic electrocautery along with the shaver. The amount of bone that is removed from the notch is variable.…”

The arthroscopic treatment of cyclops syndrome

“…Further study has indicated that the cause may be more multifactorial involving the location of the tibial tunnel, ACL stump remnants and potential microtrauma-induced neovascularization incurred during physical therapy. 6,7 Since that description, there have been few series describing this phenomenon. 7--11 Classically, cyclops syndrome occurs in the immediate postoperative course after ACL reconstruction.…”