Original Research
Hamstring Contracture After ACL
Reconstruction Is Associated With an
Increased Risk of Cyclops Syndrome
Francisco Guerra-Pinto,* MD, Mathieu Thaunat,† MD, Matt Daggett,‡ DO, MBA,
Charles Kajetanek,† MD, Tiago Marques,† MD, Tales Guimaraes,† MD, Bénédicte Quelard,† MD,
and Bertrand Sonnery-Cottet,†§ MD
Investigation performed at Centre Orthopédique Santy, FIFA Medical Center of Excellence,
Générale de Santé, Hôpital Privé Jean Mermoz, Lyon, France
Background: Cyclops syndrome is characterized by loss of terminal knee extension due to proliferative fibrous nodule formation in
the intercondylar notch. This complication occurs in the early postoperative period after anterior cruciate ligament reconstruction
(ACLR). The pathogenesis of Cyclops syndrome is not well understood.
Hypothesis: Persistent hamstring contracture after ACLR is associated with an increased risk of subsequent Cyclops syndrome.
Study Design: Case-control study; Level of evidence, 3.
Methods: The files of 45 patients who underwent arthroscopic debridement of a Cyclops lesion after ACLR were analyzed.
Recorded data included demographic information and technical details of surgery. Preoperative magnetic resonance images were
also analyzed, and patients with femoral bone bruising were identified. Passive and active range of motion were recorded in all
patients preoperatively and at 3 and 6 weeks after surgery to address the Cyclops lesion. Passive extension deficit was evaluated
in comparison with the contralateral limb and classified as secondary to hamstring contracture when contracture was observed
and palpated in the prone position and when the extension deficit was reversed after exercises performed to fatigue the hamstrings. A control group was selected using a random numbers table among our entire ACLR cohort. Statistical analysis was
performed to analyze differences between the 2 groups.
Results: There was no significant difference between the groups with regard to age at ACLR, sex distribution, time from injury to
surgery (P > .05), proportion of professional athletes, presence of femoral bone bruise, or technical aspects of surgery. The overall
extension deficit incidence was significantly higher in the Cyclops group at 3 weeks (Cyclops, 71%; control, 22%) (P < .001) and at
6 weeks (Cyclops, 60%; control, 7%) (P < .001). The extension deficit related to hamstring contracture was significantly higher in
the Cyclops group at 3 weeks (Cyclops, 58%; control, 22%) (P < .001) and at 6 weeks (Cyclops, 29%; control, 2%) (P < .001).
Conclusion: The Cyclops lesion is associated with a persistent hamstring contracture at 3 and 6 weeks after ACLR.
Keywords: Cyclops syndrome; hamstring contracture; knee extension deficit; rehabilitation; anterior cruciate ligament; knee
Cyclops syndrome is characterized by loss of terminal knee
extension due to proliferative fibrous nodule formation in
the intercondylar notch after anterior cruciate ligament
reconstruction (ACLR).7,23 It is 1 of the 4 described types
of arthrofibrosis.18 A critical size seems necessary to result
in observable disability.11 However, when it does occur,
the functional consequences are often severe enough to
warrant reoperation. In the first description of this type
of lesion, Jackson and Schaefer 7 stated that ‘‘Cyclops
appeared in those patients who failed to regain extension
early,’’ and more recently, a possible correlation between
Cyclops syndrome and an extension deficit due to a reflex
hamstring contracture after anterior cruciate ligament
(ACL) surgery has been hypothesized but not clearly
demonstrated.19
§
Address correspondence to Bertrand Sonnery-Cottet, MD, Centre
Orthopédique Santy, 24 Avenue Paul Santy, 69008 Lyon, France (email:
sonnerycottet@aol.com).
*Hospital José de Almeida, Cascais, Portugal.
†
Centre Orthopédique Santy, FIFA Medical Center of Excellence,
Générale de Santé, Hôpital Privé Jean Mermoz, Lyon, France.
‡
Kansas City University, Kansas City, Missouri, USA.
One or more of the authors has declared the following potential conflict
of interest or source of funding: B.S.C. is a paid consultant, receives
royalties, receives research support, and has made presentations for
Arthrex. M.T. is a paid consultant, receives research support, and has
made presentations for Arthrex.
Ethical approval for this study was obtained from Centre Orthopédique
Santy (approval number 2016-16).
The Orthopaedic Journal of Sports Medicine, 5(1), 2325967116684121
DOI: 10.1177/2325967116684121
ª The Author(s) 2017
This open-access article is published and distributed under the Creative Commons Attribution - NonCommercial - No Derivatives License (http://creativecommons.org/
licenses/by-nc-nd/3.0/), which permits the noncommercial use, distribution, and reproduction of the article in any medium, provided the original author and source are
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1
2
Guerra-Pinto et al
The purpose of this study was to analyze the correlation
between immediate postoperative reflex hamstring contracture and the development of a Cyclops lesion after
ACLR. Our hypothesis is that there is an association
between a persistent hamstrings contracture at the early
phase of ACLR and the Cyclops syndrome.
METHODS
The case notes of 45 patients who underwent an arthroscopic arthrolysis for Cyclops syndrome after a primary
ACLR between 2010 and 2014 were retrospectively
reviewed. Both surgeries (ACLR and Cyclops) were performed by the senior author (B.S.C.). The exclusion criteria
were a first surgery other than primary ACLR (all revisions
were excluded) and cases with a final diagnosis other than
Cyclops syndrome. To test our hypothesis, we compared our
Cyclops cohort (n ¼ 45) with a random control group taken
from our ACLR universe of 2089 patients operated on in the
same time period.
Recorded data included the age at first (ACLR) and second (Cyclops) surgery, the time period between ACL rupture and the ACLR, the type and level of sports in which the
patient was involved, as well as all surgical technical
details: type of graft, meniscal tears, and associated
extra-articular tenodesis. The data from the preoperative
magnetic resonance images were also analyzed, and
patients with femoral bone bruising were identified.9
The clinical files after the ACLR were analyzed regarding clinical examination at 3 weeks, 6 weeks, and just
before the Cyclops surgery. We registered both passive and
active range of motion, and all patients were examined in
prone and supine positions. Passive extension deficit was
evaluated in comparison with the contralateral limb. Any
extension deficit asymmetry greater than 5 was
considered.
This extension deficit was classified as related to hamstring contracture when:
observation and palpation of the hamstring muscle
belly in the prone position revealed a contracture;
extension deficit was improved after repeated flexion
against resistance in the prone position (to obtain
hamstring muscle fatigue and stunning) resulting
in restoration of passive full extension symmetrical
to the contralateral side (see Figure 1 and the Video
Supplement).
Once passive full extension was achieved, we required
the patient to turn supine to access his or her quadriceps
function through inspection and palpation, asking the
patient to fully extend the knee on the bench and comparing the quadriceps contraction between both knees by symmetric palpation.
Control Group
A control group of similar size (n ¼ 45) was selected among
our entire ACLR cohort of 2089 patients without Cyclops
syndrome. We used a random numbers table generated by
The Orthopaedic Journal of Sports Medicine
Microsoft Excel for Windows 2013, according to Monte
Carlo calculations.
Surgical Procedure
Our standard ACLR surgical technique includes high, fat
pad–sparing, arthroscopic portals; full arthroscopic examination; and ACL remnant preservation. In rare cases when
this was not possible (related to a poor ACL remnant), we
performed an ACLR using a bone–patellar tendon–bone
(BPTB) graft.4 The tibial tunnel is drilled in close to full
extension to avoid missing any preoperative Cyclops due
to the retraction of the ACL stump, particularly the classic
bell-hammer posterolateral remnant.9 A shaver is passed
through the tibial tunnel and into the remnant so that the
remnant is hollowed out for passage of the graft. At the end
of the ACLR, a full arthroscopic evaluation was made to
check for presence or absence of graft impingement. All
knees achieved full extension at the end of the procedure,
and this was again clinically confirmed by the senior surgeon (B.S.C.) before the patient left the hospital. All
patients were operated on under general anesthesia, without any nerve block, but with a hamstring donor site naropeine injection.1
Statistical Analysis
We analyzed the conditions of applicability of parametric
tests on the numeric data: age and delay from ACL injury to
ACL surgery. Normality of data was tested using the
Kolmogorov-Smirnov test, which showed that the variables
do not follow a normal distribution (Page ¼ .029 and Pdelay <
.001). For these reasons, we used the Mann-Whitney test (a
nonparametric test) to compare the 2 independent samples.
For the remaining variables (all nominal), the chi-square
test was used to analyze the association between the 2
groups. The Wilcoxon test was used to analyze the difference between the 2 clinical observations (at 3 and 6 weeks).
All statistical tests were performed using the software
SPSS Statistics Version 22 (IBM Corp).
RESULTS
Both groups were similar (P > .05) regarding age at ACLR,
sex distribution, and delay from ACL injury to ACLR surgery (Table 1). There was also a similar proportion between
the 2 groups of professional athletes, presence of femoral
bone bruise, type of graft (hamstring tendon [HT] or BPTB),
extra-articular tenodesis, and meniscus suture. All
patients had full extension before the ACLR except for 2
patients in the control group and 1 patient in the Cyclops
group, all due to a bucket-handle meniscal tear.
There were 3 professional athletes in the control group
(2 rugby players and 1 basketball player) and 5 in the Cyclops
group (3 rugby players, 1 hockey player, and 1 gymnast).
We found a significant difference between the 2 groups in
the incidence of extension deficit at both 3 and 6 weeks
(P < .001) (Table 2). Extension deficit at 3 weeks occurred
at an incidence of 71% in the Cyclops group and 22% in the
The Orthopaedic Journal of Sports Medicine
Hamstring Contracture and Cyclops Syndrome
3
Figure 1. Typical extension deficit related to hamstring contracture. (A) The extension deficit can be observed in the prone position.
(B) This extension deficit is reversed after resistance exercises to obtain hamstring fatigue. Arrows indicate extension deficit as
visualized by the distance between the exam table and the anterior aspect of the ankle.
TABLE 1
Characteristics of Control and Cyclops Groupsa
Variables
Age at ACL reconstruction (min-max), y
Sex
Delay from ACL injury to surgery (min-max), mo
Professional athletes, n
Femoral bone bruise, n
Type of graft
HT
BPTB
Extra-articular tenodesis
Meniscus suture
Control Group (n ¼ 45)
Cyclops Group (n ¼ 45)
31 (14-55)
34 male, 11 female
3.64 (0.1-23.7)
3
5
27 (13-48)
33 male, 12 female
3.7 (0.5-22)
5
9
33
12
10
20
36
9
14
20
Statistic
z ¼ 1.311;
w2 ¼ 0.058;
z ¼ 1.178;
w2 ¼ 0.549;
w2 ¼ 1.353;
P¼
P¼
P¼
P¼
P¼
.190
.809
.239
.459
.245
(ns)
(ns)
(ns)
(ns)
(ns)
w2 ¼ 0.559; P ¼ .455 (ns)
w2 ¼ 0.909; P ¼ .340 (ns)
w2 ¼ 0.000; P > .999 (ns)
a
ACL, anterior cruciate ligament; BPTB, bone–patellar tendon–bone; HT, hamstring tendon; min-max, minimum-maximum; ns, nonsignificant.
TABLE 2
Incidence of Extension Deficit and Hamstrings Contracture in Control and Cyclops Groups
Extension Deficit
Extension
Extension
Extension
Extension
deficit
deficit
deficit
deficit
Control Group (n ¼ 45) Cyclops Group (n ¼ 45)
at 3 wk
related to hamstrings contracture at 3 wk
at 6 wk
related to hamstrings contracture at 6 wk
10
10
3
1
in 45
in 45
in 45
in 45
(22%)
(22%)
(7%)
(2%)
32 in
26 in
27 in
13 in
45 (71%)
45 (58%)
45 (60%)
45 (29%)
Statistic
w2 ¼
w2 ¼
w2 ¼
w2 ¼
21.6;
11.8;
28.8;
12.2;
P
P
P
P
¼ 3.3 106a
¼ .0006a
¼ 8.02 108a
¼ .0005a
a
Statistically significant.
control group. At 6 weeks, this difference was also significant: 60% had an extension deficit in the Cyclops group
compared with 7% in the control group (P < .001).
A significant difference was also found in the incidence of
extension deficit related to hamstring contracture at 3 and
6 weeks (P < .001). Hamstring contracture was reported in
58% of the Cyclops group and in 24% of the control group
(P < .001). At 6 weeks, a hamstring contracture was
observed in 29% of the Cyclops group and 2% of the control
group (P < .001) (Figure 2).
The secondary Cyclops surgeries were performed at a
mean of 11 months (range, 5-31 months) after the primary
ACLR. Thirteen patients (20%) also underwent additional
procedures besides the Cyclops lesion resection. Ten patients
underwent a notchplasty, 1 had a trochlear osteochondral
lesion debridement, and 2 other patients had a screw
removal. There was a good clinical result in 93% (42 of 45)
of patients. All of these 42 patients became asymptomatic
and had full range of motion. Three other patients were not
satisfied: 1 had septic arthritis after the Cyclops surgery and
2 others reported persistent anterior knee pain.
DISCUSSION
The most important finding of this study is that, in the
early phase of ACLR, the majority of extension deficits are
related to hamstring contracture and that these deficits are
4
Guerra-Pinto et al
The Orthopaedic Journal of Sports Medicine
Figure 2. Evolution of extension deficit and hamstrings contracture at 3 and 6 weeks in the control and Cyclops group.
associated with an increased incidence of Cyclops syndrome. Our data demonstrate that, at both 3 and 6 weeks,
the Cyclops group had a significantly higher incidence of
extension deficit and hamstrings contracture than the control group. In the control group, extension deficit related to
hamstrings contracture was reported in 24% of patients at
3 weeks, but this number dropped to 2% at 6 weeks. This
suggests that the persistence of hamstrings contracture
between 3 and 6 weeks after ACLR is an early predictive
factor for Cyclops syndrome.
It was previously reported that femoral bone bruising is a
risk factors for motion impairement.15 In the current study,
femoral bone bruising was slightly more prevalent in the
Cyclops group than in the control group, but this difference
was not significant. Femoral bone bruising was present in 5
patients in the control group. Two of these patients had
reported hamstrings contracture at 3 weeks but none at 6
weeks. Femoral bone bruising was also present in 9
patients in the Cyclops group. Three of these patients had
reported hamstrings contracture at 3 weeks. All of these
patients still had this deficit at 6 weeks. These findings
suggest that the persistence, between 3 and 6 weeks, of a
hamstrings contracture might be more relevant than femoral bone bruising. Contrary to a previous study,19 we
found no relation to the graft choice (HT vs BPTB) or
extra-articular tenodesis.
Our overall incidence (2.1%) of Cyclops syndrome is in
line with the current literature. Wang and Ao23 observed 48
(15%) cases of Cyclops lesions in 311 second-look arthroscopies for internal fixation device removal, whereas only
1.93% had extension loss. Delincé et al 2 described 23
patients (35%) with hypertrophic tissue in the anterior part
of the knee in 65 consecutive second-look arthroscopies for
hardware removal. The authors found different shapes and
locations of scar tissue under the notch roof and reported
‘‘smaller nodules generally situated far more anteriorly in
the knee can be discovered in asymptomatic patients.’’
Other second-look arthroscopy series, like that of Muellner
et al,12 report a 17.6% incidence, but only half of Cyclops
lesions were symptomatic.
Postoperative extension deficit after ACLR results from
preoperative, intraoperative, and postoperative factors.
Intraoperative factors, such as inadequate tibial tunnel
placement, can cause impingement of the graft and loss of
extension. With better understanding of the ACL function
and anatomy, we acknowledge that the vast majority of
patients with extension deficits have no recognizable technical flaw. Since all knees in our cohort achieved full extension at the end of surgery, failure to regain full extension
might be due to an acquired condition after surgery, and
that leads our attention to postoperative factors.
Full knee extension after ACL rupture or reconstruction
depends on passive and active factors. A passive knee block
to extension might occur with a meniscal tear, loose body,
important hemarthrosis, or bell-hammer ACL tear. We had
no such findings among our Cyclops patients. It is possible
that those patients who cannot overcome a hamstrings contracture between 3 and 6 weeks are more likely to develop
Cyclops syndrome.
Many extension deficits are related to an active mechanism. Most surgeons postpone ACLR until there is full
range of motion. This might be a simplistic perspective that
does not recognize the importance of full muscle control in
ACLR. Quadriceps, hamstring, and soleus muscles are
involved in active knee extension. These are antagonist
muscles and an involuntary hamstrings contracture
(triggered by pain or effusion) may go together with a selective quadricipital ‘‘shutdown.’’16 Central activation deficits
have been recognized to be responsible for quadriceps
muscle weakness after knee injures affecting the injured
as well as the noninjured leg.5,7,22,23 Rice et al16,17 have
done extensive research on this topic and call it ‘‘arthrogenic muscle inhibition.’’ Even 20 mL of effusion can cause
quadriceps inhibition in the vastus medialis and the vastus
lateralis in otherwise healthy individuals during jogging.21
This arthrogenic muscle response, also seen in the soleus
musculature after joint effusion, was found to be regulated
by both pre- and postsynaptic control mechanisms.14
Muscular co-contraction is operationally defined as activation of both the agonist and antagonist muscle groups
crossing the same joint. An antagonistic co-contraction of
hamstring musculature seems to be a component of all
functional movements, possibly to maintain dynamic knee
stability and protect against excessive joint loads. 3,19
Despite its potential stabilizing role, it has an increased
metabolic cost and can impair performance.8,25 There are
reports on an inverse relation between quadriceps weakness and hamstrings recruitment in total knee arthroplasty
but there is no evidence on the effect of hamstrings contraction on the incidence of Cyclops syndrome after ACLR.25
The Orthopaedic Journal of Sports Medicine
The knee extension deficit at 4 weeks has been shown to be
related to extension loss at 12 weeks after ACLR, supporting
that, whatever the reason, there is a ‘‘therapeutic time window’’ in which we must obtain nearly normal knee extension. 13,15 Our physiopathology hypothesis is that a
hamstrings contracture will cause a flexion posture after
ACLR. This extension deficit, dynamic and reducible in the
first weeks, will prevent closure of the intercondylar notch
(which was shown to be narrower in patients with ACL rupture19) and allow local organization of postoperative hemarthrosis. This process might evolve as reported in contained
hematomas, from immature to mature connective tissue, the
latter with collagenous fibers.20,23 Since 2015, the senior
author (B.S.C.) has changed the early postoperative protocol
after ACL reconstruction. Patients presenting with an extension deficit related to hamstring contracture are educated
and strongly encouraged not only to perform exercises to
reverse the extension deficit but also to actively contract their
quadriceps in order to regain enduring full active extension
(Video Supplement). Our Cyclops rate has decreased dramatically (0.1% in 2015), but we cannot draw any conclusion
based on these data, and specific studies are required to demonstrate the effectiveness of this early postoperative care.
The limitations of this study include the fact that there is
no measurement tool to objectively evaluate hamstring contracture. In addition, a causal relation between hamstring
contracture and Cyclops lesions cannot be stated because,
theoretically, a causal model needs to fulfill all BradfordHill criteria,6 which is impossible in a retrospective study.
Nevertheless, a strong correlation is demonstrated. The
results of this study demonstrate a positive relation between
the published evidence on quadriceps function, hamstrings
contracture, and the reported problems on ACLR when there
is no full resolution of the extension deficit.3,10,12,16,24
CONCLUSION
Cyclops syndrome is correlated with an extension deficit at
3 and 6 weeks after ACL reconstruction. A persistent hamstring contracture in an early phase seems predictive for
Cyclops syndrome.
A Video Supplement for this article is available at
http://journals.sagepub.com/doi/suppl/10.1177/
2325967116684121.
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