Cyclops lesions associated with both bundles and selective bundle repair of the anterior cruciate ligament

Abstract

Background

The remnant of a ruptured anterior cruciate ligament (ACL) can increase the risk of impingement or a cyclops lesion, which can increase challenges to proper tunnel placement.

Purpose

To evaluate the prevalence of cyclops lesions after ACL reconstruction and to assess the difference in the incidence of cyclops lesions between single-bundle repair and selective bundle repair of the ACL.

Material and Methods

This retrospective study included 151 patients who were diagnosed with an ACL tear after knee joint magnetic resonance imaging (MRI) who underwent ACL reconstruction surgery. MRI diagnosis of cyclops lesion formation was made if a soft-tissue mass was seen anteriorly in the intercondylar notch near the tibial insertion of the reconstructed ACL, based on sagittal T2-weighted (T2W) imaging. The size of the cyclops lesions was recorded as the largest diameter on the sagittal T2W imaging.

Results

A cyclops lesion was detected in 74 (38.5%) cases. Cyclops lesions were detected more frequently in cases with single-bundle repair of the ACL, but the results were not statistically significant (P = 0.609). Compared with selective bundle repair, cyclops lesions had a significantly higher prevalence in the posterolateral (PL) bundle repair than in the anteromedial (AM) bundle repair (P = 0.027) based on MR images at 6–12 months after surgery.

Conclusion

The incidence of cyclops lesions did not differ significantly in single-bundle repair and selective bundle repair of ACL. However, selective PL bundle repair of the ACL showed a significantly increased incidence of cyclops lesions compared with selective AM bundle repair.

Keywords

Magnetic resonance imaging meniscus arthrofibrosis anterior cruciate ligament

Introduction

Anterior cruciate ligament (ACL) rupture is a common and serious knee injury and arthroscopic reconstruction of the torn ACL using a graft is the treatment of choice. A cyclops lesion is a serious complication that can occur after ACL reconstruction. These lesions were first described by Jackson and Schaefer in 1990 (1). The cyclops lesion, also known as localized anterior arthrofibrosis, is a focal nodule of fibrous tissue located in the intercondylar notch, tightly attached to the reconstructed ACL graft and mostly located anterior to the graft (2,3).

Cyclops syndrome is a clinical syndrome that is defined as a loss of knee extension associated with pain at terminal extension; it usually occurs within the first two years after surgery and is caused by graft impingement and cyclops lesions (4). The exact pathogenesis of the fibrous tissue is uncertain, and numerous etiology factors have been proposed as causes of the fibrosis of the cyclops lesion. The possible causes include the following: bone and cartilage debris from the surgical drilling and preparation of the bony tunnel; remnants of the native ACL; inflammation caused by graft impingement; and torn graft fibers that lead to a fibro-proliferative response (1 –8). Considering that the pathogenesis of cyclops lesions is associated with surgical procedures, the incidence of cyclops lesions may vary depending on the type of surgical procedure (2).

The ACL consists of two major fiber bundles, the anteromedial (AM) and posterolateral (PL) bundles, which have distinct and reciprocal relationships for knee joint stabilization (5,9,10). The application of selective bundle reconstruction is increasing with selective bundle tear cases, because of the reported improved outcomes relative to single-bundle reconstruction (5,11 –14). Variation in the remnant bundle preservation technique, including selective bundle reconstruction and preservation of the ACL tibial remnant, have also been associated with improved outcomes (5,15,16). However, the remnant of a ruptured ACL can also increase the risk of impingement or a cyclops lesion, which can increase challenges to proper tunnel placement (16).

Our hypothesis was that the incidence of cyclops lesions differed according to the surgical type of ACL reconstruction. We also wanted to determine if the incidence would be comparable to the rates reported in previous studies. Therefore, the aim of the present study was to evaluate the prevalence of cyclops lesions after ACL reconstruction and to assess the difference in the incidence of the cyclops between single-bundle repair and selective bundle repair of the ACL.

Material and Methods

Case selection

The present study was approved by the ethical Institutional Review Board of the Kangbuk Samsung Hospital and patient consent requirements were waived due to the retrospective design. We retrospectively evaluated consecutive 384 patients diagnosed with ACL tears on knee joint magnetic resonance imaging (MRI) and underwent ACL reconstruction surgery between July 2016 and August 2019. Among them, 205 cases met the following inclusion criterion: the first postoperative MRI was obtained 6–12 months after ACL reconstruction. The cases with re-tear of reconstructed ACL were excluded (n = 13). Finally, 192 cases (151 men, 41 women; mean age = 32.6 ± 10.5 years; age range = 14–57 years) were enrolled in the study.

Surgical techniques

Surgical reports in electronic medical records were reviewed. An orthopedic surgeon (AJH) with 37 years of experience in knee joint surgery performed all arthroscopic surgeries. The surgeon assessed the integrity of the ACL during ACL reconstruction. If both bundles were disrupted, both-bundle tear was diagnosed. If one of the PL or AM bundles had lost its continuity, but the other bundle remained intact, selective bundle tear was diagnosed. The choice of surgical technique was determined by the types of ACL tear. Single-bundle repair was performed in cases with both-bundle tear and selective bundle repair was performed in cases with selective PL or AM bundle tear. All ACL reconstruction was preformed using a four-strand hamstring tendon autograft (both single-bundle repair and selective bundle repair).

MRI parameters

We used a 3.0-T MRI scanner (Achieva; Philips, Best, The Netherlands) and an eight-channel (SENSE), phased-array, knee joint–dedicated coil. The detailed parameters for each MRI sequence are described in Table 1.

Table 1.

MRI sequences and parameters.

Imaging parameter	Coronal T1 ¹FSE	Coronal ²FS T2 FSE	Sagittal FS ³PD FSE	Sagittal T2 FSE	Axial FS T2 FSE	Oblique sagittal ACL view T2 FSE	Oblique coronal ACL view T2 FSE
TR (ms)	500–800	3500–4500	3500–4500	3500–4500	4000–5500	2500–5000	2500–5000
TE (ms)	10–20	60–90	30–40	70–90	60–90	50–80	50–80
Flip angle (°)	90	90	90	90	90	90	90
Matrix size (pixels)	350 × 350	320 × 300	320 × 250	350 × 290	310 × 250	500 × 300	500 × 300
Field of view (mm)	160 × 160	160 × 160	160 × 160	160 × 160	160	150	150
Slice thickness (mm)	3.0	3.0	3.0	3.0	3.0	3.0	3.0
Inter-slice gap (mm)	0.3	0.3	0.3	0.3	0.3	0.3	0.3
Bandwidth (kHz)	280	260	260	240	280	400	400
Echo train length	5	14	12	14	15	16	16
Signal average	1	1	1	1	1	1	1
Scan time (min:s)	2:35	2:25	2:30	2:30	2:30	2:00	1:55

Notes: FSE = fast spin-echo; FS = fat saturation; PD = proton density

FS, fat saturation; FSE, fast spin-echo; MRI, magnetic resonance imaging; PD, proton density.

Image analysis

MR image interpretation was performed in parallel by two experienced musculoskeletal radiologists (fellowship-trained musculoskeletal radiologists with 18 and 10 years of experience, respectively). MRI diagnosis of formation of cyclops lesions were made if a soft-tissue mass was identified anteriorly in the intercondylar notch near the tibial insertion of the reconstructed ACL, based on sagittal T2-weighted (T2W) images and sagittal proton density weighted images (Figs. 1–3). The size of the cyclops lesions was recorded as the largest diameter on sagittal T2W images (Fig. 1).

Statistical analysis

The chi-square test was used to analyze the association between the type of ACL bundle repair (single-bundle repair vs. selective bundle repair, AM bundle repair vs. PL bundle repair) and presence of cyclops lesions. The Student's t test was performed to evaluate the difference in the size of cyclops lesions between different types of ACL repairs (single-bundle repair vs. selective bundle repair). Statistical analysis was performed using SPSS version 22.0 (IBM Corp., Armonk, NY, USA). A P value ≤ 0.05 was considered to be statistically significant.

Results

All participants (n = 192) were scanned before and 6–12 months after surgery. Two-year follow-up MRI scans were available for 53 (27.6%) cases, and four-year follow-up MRI scans were available for 58 (30.2%) cases. Among the 192 patients that underwent ACL reconstruction surgery, single-bundle repair was completed in 151 (79%) patients (119 men, 32 women; mean age = 33 years; age range = 14–57 years) and selective bundle repair was performed in 41 (21%) patients (32 men, 9 women; mean age = 32 years; age range = 15–57 years). In the 41 selective bundle repair cases, 18 (44%) underwent an AM bundle repair and 23 (56%) underwent a PL bundle repair. There was no statistically significant difference in sex (P = 0.916) and age (P = 0.731) according to the types of ACL repair. Cyclops lesions were detected in 74 (38.5%) cases (59 men, 15 women; mean age = 33.6 years; age range = 14–57 years) on postoperative MR images at 6–12 months after surgery (n = 192), with a mean largest diameter of 9.57 ± 2.79 mm (range = 3.45–15.93 mm). There was no statistically significant difference between patients with or without cyclops lesions with regard to age (P = 0.216) and sex (P = 0.772). In addition, the size of the cyclops lesions was not correlated with age (P = 0.224) and sex (P = 0.905). At two years after surgery (n = 53), 24 (45.2%) cases (41 men, 12 women; mean age = 31.04 years; age range = 14–55 years) presented with a cyclops lesion with a mean largest diameter of 7.97 ± 2.56 mm (range = 3.71–11.94 mm). At four years (n = 58), 23 (39.6%) cases (194 men, 4 women; mean age, 35.4 years; age range = 15–54 years) presented with a cyclops lesion with a mean largest diameter of 10.50 ± 3.36 mm (range = 5.42–15.93 mm). There was no significant difference in the incidence of cyclops lesions, based on the follow-up period (P = 0.075). The size of the cyclops lesion was not correlated with age, sex, or the follow-up period (P = 0.044, P = 0.492, and P = 0.411, respectively).

Among 151 cases that underwent single-bundle repair of the ACL, 56 (37.1%) showed cyclops lesions on MRI at 6–12 months after surgery. Among 41 cases that underwent selective bundle repair of the ACL, cyclops lesions were detected in 17 (41.5%) on MRI at 6–12 months after surgery. Cyclops lesions were more frequently detected in cases with single-bundle repair of the ACL, but this result was not statistically significant (P = 0.609) (Table 2). Compared with selective bundle repair, cyclops lesions were identified with a significantly higher prevalence in PL bundle repair than in AM bundle repair (P = 0.027) (Table 3) on MRI at 6–12 months after surgery. There were no statistically significant differences in the size of the cyclops lesions according to the types of ACL repair (P = 0.863, P = 0.569) (Table 4).

Table 2.

Cyclops lesion prevalence according to type of anterior cruciate ligament reconstruction.

Type of reconstruction	Cyclops lesion	n (%)
Single-bundle repair	−	94/151 (62.3)
Single-bundle repair	+	57/151 (37.7)
Selective bundle repair	−	24/41 (58.5)
Selective bundle repair	+	17/41 (41.5)
P value		0.665

Table 3.

Cyclops lesion prevalence according to type of anterior cruciate ligament reconstruction in selective bundle tear.

Type of reconstruction	Cyclops lesion	n (%)
Anteromedial bundle repair	−	14/18 (77.8)
Anteromedial bundle repair	+	4/18 (22.2)
Posterolateral bundle repair	−	10/23 (43.5)
Posterolateral bundle repair	+	13/23 (56.5)
P value		0.027

Table 4.

Size of cyclops lesion according to type of anterior cruciate ligament reconstruction.

Type of reconstruction	n	Mean size (mm)	Standard deviation (mm)	Standard error mean (mm)
Single-bundle tear	57	9.60	2.73	0.36
Selective bundle tear	17	9.46	3.07	0.74
P value	0.863
Anteromedial bundle repair	4	10.26	3.12	1.56
Posterolateral bundle repair	13	9.22	3.14	0.87
P value	0.569

Second-look arthroscopy was performed in 47 of 192 cases, and 22 cases of them were diagnosed as cyclops lesions on arthroscopy. All 22 cases were diagnosed cyclops lesion on MRI.

Discussion

In the present study, cyclops lesions were detected in cases with all types of ACL reconstruction with a prevalence of 38% at 6–12 months after surgery. This result is similar to recent studies that have reported an incidence in the range of 25%–47% based on MRI (2,6,17). “MRI cyclops” is used to denote all cyclops lesions on MRI whether they are symptomatic or asymptomatic (6,17), and using MRI to diagnose cases has demonstrated a higher confirmed incidence than that detected on second-look arthroscopy, which has identified case prevalence in the range of 1%–21.5% (1 –3,17,18). Additionally, the onset in the majority of “MRI cyclops” cases is 6–12 months (6).

A single-bundle reconstruction is performed by producing one single femoral tunnel and one single tibial tunnel, with a focus on reproducing the AM bundle. Selective single-bundle augmentation reconstruction is focused on AM or PL bundle repair with preservation of the remaining intact bundle, while double-bundle reconstruction uses two separate grafts to replace the positioning of both the AM and PL bundles (19). The etiology of cyclops lesions includes bone and cartilage residue after tibial drilling, and remnants of the native ACL. Postoperatively, a large graft can result in a loss of full extension and pain due to excess tissue in the intercondylar notch (20). In some cases, a higher volume of the graft can impinge the posterior cruciate ligament (PCL) synovium posteriorly as well as the lesion that arises from the synovium of the PCL rather than the graft (17,21). Therefore, surgical technique is an important predisposing factor for cyclops lesions.

Several studies have reported the incidence of cyclops lesions in cases with remnant-preserving ACL reconstruction. Georgoulis et al. (22) reported that remnant preservation may increase the rate of cyclops lesions after ACL reconstruction. Ahn et al. (16) reported that single-bundle repair and selective bundle repair did not result in significant differences in the number of cyclops lesions that were detected by postoperative MRI. Gohil et al. (23) reported that incomplete debridement of the notch and the remnant of the ACL stump did not lead to an increased incidence of cyclops lesions. Tanabe et al. (24) reported that there was no difference in the incidence of cyclops lesions between remnant-preserving ACL reconstruction and remnant-resecting ACL reconstruction. Cha et al. (25) reported that the prevalence of a cyclops lesion was similar in both groups that underwent a single-bundle and remnant bundle preservation technique. Kondo et al. (26) reported that there was no significant difference in the rate of cyclops lesions between the remnant-preserving and resecting procedure in anatomic double-bundle reconstruction. In the current study, the prevalence of cyclops lesions was 37.1% in cases with single-bundle repair and in cases with selective bundle tear of the ACL it was 41.5% in cases with selective bundle repair. There was no significant difference in the prevalence of cyclops lesions between single-bundle repair and selective bundle repair. Additionally, there were no statistically significant differences in the size of cyclops lesions according to the types of ACL repair.

One study reported that no cyclops lesions were noted in 44 patients who underwent PL bundle reconstruction with AM bundle preservation (27). However, to date, a comprehensive study of the difference in cyclops lesions between AM and PL bundle repair has not yet been conducted. In the current study, cyclops lesions were detected more frequently in cases with PL bundle reconstruction (43.5%) than AM bundle reconstruction (22.2%). This could be attributable to remnant AM bundles from the procedure that could be the source of cyclops lesions (18). Tonin et al. (4) suggested that the main triggering factors for cyclops lesions is injury to the ligament and the reparative process that occurs as a reaction of the vital tissues. Even though the remnant AM bundle shows intact continuity, it can be a triggering factor for cyclops lesions after selective PL bundle reconstruction. The conflicting results from previous studies on the prevalence of cyclops lesion after remnant-preserving ACL reconstruction may be due to the lack of subdivision of the site of injury and remnant-preserving surgery (16, 22 –26). Therefore, cyclops lesions should be observed more carefully, particularly for cases with selective PL bundle ACL reconstruction.

The present study has some limitations. First, this was a single-center retrospective study. Second, the number of selective ACL bundle tears was small compared with both-bundle tears. Third, all cyclops lesions detected on MRI were not confirmed on arthroscopy. However, MRI has been widely used for assessing the knee with ACL tear and is known to have good sensitivity, specificity, and accuracy in revealing cyclops lesion (2,18,25). Lastly, clinical follow-up, mechanical symptoms, or pain could not be evaluated compared to MRI findings.

In conclusion, the incidence of cyclops lesions did not differ significantly between single-bundle repair and selective bundle repair of the ACL. However, selective PL bundle repair of the ACL showed a significant increased incidence of cyclops lesions compared with selective AM bundle repair. Therefore, clinicians and radiologists should carefully consider cyclops lesions, particularly for patients who undergo selective PL bundle repair of the ACL.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Hee Jin Park

Myung Sub Kim

References

Jackson

Schaefer

. Cyclops syndrome: loss of extension following intra-articular anterior cruciate ligament reconstruction. Arthroscopy 1990;6:171‐178.

Facchetti

Schwaiger

Gersing

, et al. Cyclops lesions detected by MRI are frequent findings after ACL surgical reconstruction but do not impact clinical outcome over 2 years. Eur Radiol 2017;27:3499‐3508.

Wang

. Analysis of different kinds of cyclops lesions with or without extension loss. Arthroscopy 2009;25:626‐631.

Tonin

Saciri

Veselko

, et al. Progressive loss of knee extension after injury. Cyclops syndrome due to a lesion of the anterior cruciate ligament. Am J Sports Med 2001;29:545‐549.

Lee

Park

Lee

, et al. Evaluation of selective bundle injury to the anterior cruciate ligament: t2-weighted fast spin-echo 3-T MRI with reformatted 3D oblique isotropic (VISTA) versus 2D technique. AJR Am J Roentgenol 2017;209:W308‐W316.

Gohil

Falconer

Breidahl

, et al. Serial MRI and clinical assessment of cyclops lesions. Knee Surg Sports Traumatol Arthrosc 2014;22:1090‐1096.

Delincé

Krallis

Descamps

, et al. Different aspects of the cyclops lesion following anterior cruciate ligament reconstruction: a multifactorial etiopathogenesis. Arthroscopy 1998;14:869‐876.

Mariani

Ferretti

Conteduca

, et al. Arthroscopic treatment of flexion deformity after ACL reconstruction. Arthroscopy 1992;8:517‐521.

Zantop

Herbort

Raschke

, et al. The role of the anteromedial and posterolateral bundles of the anterior cruciate ligament in anterior tibial translation and internal rotation. Am J Sports Med 2007;25:223‐227.

10.

Gabriel

Wong

Woo

, et al. Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads. J Orthop Res 2004;22:85‐89.

11.

Yamamoto

Hsu

Woo

, et al. Knee stability and graft function after anterior cruciate ligament reconstruction: a comparison of a lateral and an anatomical femoral tunnel placement. Am J Sports Med 2004;32:1825‐1832.

12.

Freedman

D’Amato

Nedeff

, et al. Arthroscopic anterior cruciate ligament reconstruction: a metaanalysis comparing patellar tendon and hamstring tendon autografts. Am J Sports Med 2003;31:2‐11.

13.

Yagi

Wong

Kanamori

, et al. Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction. Am J Sports Med 2002;30:660‐666.

14.

Yunes

Richmond

Engels

, et al. Patellar versus hamstring tendons in anterior cruciate ligament reconstruction: a meta-analysis. Arthroscopy 2001;17:248‐257.

15.

Starman

Vanbeek

Armfield

, et al. Assessment of normal ACL double bundle anatomy in standard viewing planes by magnetic resonance imaging. Knee Surg Sports Traumatol Arthrosc 2007;15:493‐499.

16.

Ahn

Lee

Choi

, et al. Magnetic resonance imaging evaluation of anterior cruciate ligament reconstruction using quadrupled hamstring tendon autografts: comparison of remnant bundle preservation and standard technique. Am J Sports Med 2010;38:1768‐1777.

17.

Kambhampati

SBS

Gollamudi

Shanmugasundaram

, et al. Cyclops lesions of the knee: a narrative review of the literature. Orthop J Sports Med 2020;8:2325967120945671.

18.

Bradley

Bergman

Dillingham

. MR imaging of cyclops lesions. AJR Am J Roentgenol 2000;174:719‐726.

19.

Deie

Iwaki

, et al. Balance ability and proprioception after single-bundle, single-bundle augmentation, and double-bundle ACL reconstruction. ScientificWorldJournal 2014;2014:342012.

20.

Sonnery-Cottet

Panisset

Colombet

, et al. Partial ACL reconstruction with preservation of the posterolateral bundle. Orthop Traumatol Surg Res 2012;98:S165‐S170.

21.

Sonnery-Cottet

Lavoie

Ogassawara

, et al. Clinical and operative characteristics of cyclops syndrome after double-bundle anterior cruciate ligament reconstruction. Arthroscopy 2010;26:1483‐1488.

22.

Georgoulis

Pappa

Moebius

, et al. The presence of proprioceptive mechanoreceptors in the remnants of the ruptured ACL as a possible source of re-innervation of the ACL autograft. Knee Surg Sports Traumatol Arthrosc 2001;9:364‐368.

23.

Gohil

Annear

Breidahl

. Anterior cruciate ligament reconstruction using autologous double hamstrings: a comparison of standard versus minimal debridement techniques using MRI to assess revascularisation. A randomised prospective study with a one-year follow-up. J Bone Joint Surg Br 2007;89:1165‐1171.

24.

Tanabe

Yasuda

Kondo

, et al. Clinical results of anterior cruciate ligament reconstruction with ligament remnant tissue preservation: a systematic review. Asia Pac J Sports Med Arthrosc Rehabil Technol 2016;4:1‐8.

25.

Cha

Choi

Kwon

, et al. Analysis of cyclops lesions after different anterior cruciate ligament reconstructions: a comparison of the single-bundle and remnant bundle preservation techniques. Skeletal Radiol 2012;41:997‐1002.

26.

Kondo

Yasuda

Onodera

, et al. Effects of remnant tissue preservation on clinical and arthroscopic results after anatomic double-bundle anterior cruciate ligament reconstruction. Am J Sports Med 2015;43:1882‐1892.

27.

Sonnery

Zayni

Conteduca

, et al. Posterolateral bundle reconstruction with anteromedial bundle remnant preservation in ACL tears: clinical and MRI evaluation of 39 patients with 24-month follow-up. Orthop J Sports Med 2013;1:2325967113501624.