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A Novel Anterior Cruciate Ligament Reconstruction Technique using LARS®-Augmented Autologous/Synthetic "Hybrid" Graft -High Re-Operation Rate in a Case-Control Study Corresponding author Medical & Clinical Research

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The paper compares hamstring autograft with a "hybrid" graft of hamstrings and a small LARS ligament in ACL reconstruction patients. The paper concludes ACLR utilizing a hybrid autologous/LARS® construct facilitated accelerated rehabilitation without evidence of increased failure or early graft stretch. Additionally, there was no clinical difference in functional outcome scores between the HYBRID and CONTROL groups. Although not statistically significant, the HYBRID group had an unacceptably high re-operation rate at 2-years post ACLR, and is therefore not recommended as a surgical technique by the primary author. The refinement of ACLR to facilitate patients’ safe and early return to previous levels of function presents a topic for future research.
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A Novel Anterior Cruciate Ligament Reconstruction Technique using LARS®-Augmented
Autologous/Synthetic “Hybrid” Gra - High Re-Operation Rate in a Case-Control Study
Research Article
1
Fiona Stanley Hospital, 11 Robin Warren Drive, Murdoch 6150,
Western Australia, Australia
2
Perth Orthopaedic & Sports Medicine Centre, 31 Outram Street,
West Perth 6005, Western Australia, Australia
3
Royal Perth Hospital, 197 Wellington Street, Perth 6000Western
Australia, Australia
Levy Benjamin*1, Travis M Falconer2, Sheldon Moniz1, David Hille3 and Peter Annear2
*Corresponding author
Dr. Sheldon Moniz, Fiona Stanley Hospital, 11 Robin Warren Drive, Murdoch
6150, Western Australia, Australia
Submitted: 03 Apr 2020; Accepted: 08 May 2020; Published: 16 May 2020
Medical & Clinical Research
ISSN: 2577-8005
Introduction
Anterior cruciate ligament reconstruction (ACLR) improves knee
function and stability in patients with ACL deficiency [1, 2].
Traditional ACLR rehabilitation programs recommend that
patients avoid returning to sports early to prevent graft stretch and
failure [3-6]. Earlier return to function, however, represents a
desirable clinical outcome.
After ACLR, the graft undergoes biological integration and
revascularization. In that period, the graft is temporarily
mechanically inferior to a mature graft, rendering it prone to graft
laxity [5, 7-12]. Historically, attempts at avoiding early laxity led
surgeons to perform ACLR with synthetic ligament substitutes.
The use of first-generation synthetic ligaments had universally
poor results with high rates of re-rupture and symptomatic
synovitis resulting from graft microparticalization [13-15]. A
systematic review by Newman et al, of modern, third-generation
synthetic grafts constructed of polyethylene terephthalate showed
lower rates of failure and synovitis at intermediate-term follow-up
[16].
Hybrid grafting using a combined synthetic/autologous graft is a
technique designed to facilitate accelerated rehabilitation (return
to sports at 2-6 months), and may offer an alternative to full
synthetic reconstruction. The superior mechanical properties of
the synthetic component may prevent graft stretching during
accelerated rehabilitation. The autologous component may provide
a lasting biological graft while enhancing biological ingrowth,
longevity, and safety of the prosthetic graft.
ACLR using a hybrid technique with combination autologous/
synthetic grafts within the same construct is a safe and satisfactory
option for patients with short or undersized donor grafts [17].
Furthermore, Hamido et al, published a retrospective study
demonstrating that patients with short or undersized hamstring grafts
that received reconstructions using similar hybrid grafts showed
superior knee stability compared with patients that received
reconstructions using autologous four-strand hamstring grafts [18].
The patients with the hybrid grafts also had a significant improvement
in International Knee Documentation Committee (IKDC) scores;
however, the rehabilitation program was not reported.
To our knowledge, no study has compared the clinical and
functional outcomes of hybrid ACLR combined with accelerated
rehabilitation against those of autologous ACLR combined with
conventional rehabilitation. Thus, the aim of this study was to
determine if faster rehabilitation can be achieved safely using a
hybrid ACL construct comprised of a hamstring auto graft and a
synthetic ligament (LARS–Ligament Augmentation Reconstruction
System, Corin Pty. Ltd.). Patient function, knee laxity, incidence
of failure, and complications were compared at a minimum of 2
years post-reconstruction.
We hypothesized that the use of a hybrid ACLR technique would
allow accelerated rehabilitation protocols, while protecting the
graft from early stretch or failure. Furthermore, we hypothesized
that patients that received hybrid ACLR would achieve objective
and subjective knee outcome scores and complication rates
comparable to those of patients that received autologous ACLR.
Additionally, we explored differences in the patient groups’
descriptive characteristics in choosing different grafts, as well as
unexpected differences in outcomes.
Materials and Methods
Enrolled Patients
Patients were considered if they underwent primary ACLR
performed by a single surgeon between August 2008 and February
2013. A total of 59 consecutive, consenting patients underwent
combined autologous/synthetic (HYBRID) ACLR. Forty-four
patients underwent primary autologous (CONTROL) ACLR. This
study was conducted with institutional ethics approval. Patients
included were skeletally mature, normally aligned, undergoing
primary ACLR not requiring concomitant ligament repair,
operated within six months of injury, and with an unaffected
contralateral knee. Patients with compensable knee injury were
excluded. After pre-operative counseling participants were given
the choice to receive either a hybrid graft with accelerated
rehabilitation or an autologous graft with a traditional rehabilitation
protocol. The patients’ demographic data are shown in Table 1.
The patient flow through the study is shown in (Figure 1).
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Figure 1
Assessment of eligibility
111patients consent to
hybrid LARS/autologous
graft
44patients consent to
autolo
g
ous
g
raft
Lost to follow up n=20
(18.1%)
Follow up
Total reviewed at 2 years n=91
(81.2%)
Clinical review n=61
Analysis
Clinicalexam & outcome measures n=59
(2 lost to follow up)
HYBRID cohort CONTROL cohort
103patients
received
autologous ACL
59patients did
not consent to
participate
44patients followed
up at 2 years
Follow up
Analysis
Clinicalexamination n=44
Outcomemeasures n=44
Figure 1
Propensity Score Matching (PSM) was undertaken, using Age and
Gender, in order to select a subset of the CONTROL group that is
matched to the HYBRID group. Of the 44 Control patients, 25
were used for matching to the 59 Hybrid Patient. Table 1.1 shows
a comparison of matched groups after PSM. The two groups are
no longer independent, and are therefore analysed as paired
samples.
Table 1: Descriptive Data
Control Hybrid
P value
n 44 59
Sex, female/male 26/18 18/41 .004a
Age at surgery, years
Mean ± SD
Median (range)
30.95 ± 11.82
27.19 (15.20 – 58.28)
32.03 ± 10.84
32.00 (14.84 – 53.27) .636b
Time to follow-up, years
Mean ± SD
Median (range)
2.51 ± 0.46
2.39 (1.90 – 3.91)
2.69 ± 0.64
2.46 (1.97 – 4.10) .099b
Age at follow-up, years
Mean ± SD
Median (range)
33.46 ± 11.60
30.35 (18.29 –
60.45)
34.72 ± 10.85
34.66 (18.00 – 55.42) .576b
aChi-square test
bIndependent samples t test
cFisher’s exact test
Table 1.1: Descriptive Data after Matching
Matched Controls Hybrid
P value
n59 59
Sex, female/male 18/41 18/41 1.000a
Age at surgery, years
Mean ± SD
Median (range)
32.01 ± 10.85
33.24 (15.20 – 57.12)
32.03 ± 10.84
32.00 (14.84 – 53.27) .937b
Time to follow-up, years
Mean ± SD
Median (range)
2.46 ± 0.43
2.30 (1.92 – 3.91)
2.69 ± 0.64
2.46 (1.97 – 4.10) .027b
Age at follow-up, years
Mean ± SD
Median (range)
34.47 ± 10.58
35.53 (18.30 – 59.42)
34.72 ± 10.85
34.66 (18.00 – 55.42) .280b
aChi-square test
bPaired samples t test
Graft Constructs
Both the CONTROL and HYBRID groups of the study received
arthroscopic-assisted, four-tunnel anatomical double-bundle
ACLR using semitendinosis and gracilis tendons. Those who
received a HYBRID graft configuration had the anteromedial
bundle (AMB) augmented with a LARS prosthetic ligament
(Corin Group Product Code 104.133 “LARS anterior cruciate
reinforcement). The AMB was selected for augmentation because
it was considered able to withstand greater forces during early,
non-cutting, accelerated rehabilitation. Doubled gracilis tendon
was used in the posterolateral bundle (PLB) in both groups. The
prosthetic graft was added with the aim of stiffening the construct
to limit graft stretch or failure, as reported in previous studies
investigating accelerated rehabilitation programs in patients
undergoing autologous hamstring ACLR [5, 19-21]. In addition,
the combination of the synthetic graft with a native hamstring
tendon was intended to protect the knee from particulate wear by
encouraging biological ingrowth.
Surgical Technique
Arthroscopic-assisted, double-tunnel ACLR was performed as
previously described by Falconer et al [22, 23]. The patients in the
CONTROL group had the knee cycled 15 times with the graft
under maximal manual tension. The PLB was fixed at 20° flexion
using a Milagro Advance screw (DePuySynthes Pty. Ltd.). The
AMB was fixed at 45° flexion using an Intrafix screw
(DePuySynthes Pty. Ltd.). The patients in the HYBRID group had
the knee cycled ten times with the graft under maximum manual
tension. Both the AMB and the PLB were fixed in hyperextension
with maximal manual tension placed in the autograft components.
The LARS component was secured under minimal tension to
avoid over-constraining the knee.
Post-operative Rehabilitation
The CONTROL group patients underwent a conventional
rehabilitation protocol. The patients were permitted to bear weight
as tolerated in a resting splint for the first 2 weeks. Initial
rehabilitation focused on swelling reduction, knee range of motion,
and patella mobility. The brace was discontinued once the patients’
knee effusion had resolved. Pivoting activities and return to sport
commenced at 9–12 months post-operation.
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The HYBRID patients underwent an accelerated rehabilitation
protocol at a single rehabilitation center. The rehabilitation
protocol had a set timeline, although progression through the
program was individualized according to patients’ range of motion,
swelling, function, and pain. The program aimed to have the
patients performing pivoting/cutting movements at 16 weeks and
returning to sports at 6 months post-operation. Details of the
rehabilitation protocols are outlined in (Figure 2).
Figure 2 – Rehabilitation protocol
0-3 weeks
Resting extension splint
Crutch weight bearing
Inpatient exercises focused on regaining knee range of motion, patella
mobility, and swelling reduction
Cease use of brace once knee effusion resolved
CONTROL HYBRID
6 weeks
Closed chain exercises
Hydrotherapy
Stationary cycling
4 months
Jogging
Progressing to change of
direction exercises and sport specific
exercises by 6 months
9 months
Commence full sport and
pivoting activities
8 weeks
Jogging
Open Chain Exercises
4 months
Change of direction exercises
6 months
Commence full sport
Time Postoperatively
3-6 weeks as above 3-8 weeks
closed chain strengthening
swimming
Figure 2: Rehabilitation protocol
Clinical Assessment
All patients were followed up for a minimum of 2 years by a single
experienced physiotherapist. Subjective assessment included
Tegner Activity Score, Lysholm Knee Scale, IKDC Subjective
score, Cincinnati Knee Rating System, and ACL Quality of Life
Questionnaire (ACL QOL). Objective assessments included IKDC
objective scores, knee range of motion (ROM), presence of
effusion, and graft laxity KT-1000 instrumented arthrometry
(MEDmetric, San Diego, CA). Graft failure and the requirement
and cause for re-operation were also recorded.
Statistical Analysis
Results were analyzed using R statistical computing software and
IBM SPSS Statistics. Propensity Score Matching (PSM) was used
to select a subset of patients from the control group, with
replacement, that matched closest to the hybrid group. Paired
samples t-tests were used to compare means between continuous
variables. For some outcomes, the data failed to meet the
assumptions of the t test. In those cases, Wilcoxon Signed Rank
tests were used. Odds ratios, Chi-square tests, and Fisher’s exact
tests were used for categorical variables. Statistical significance
was considered when P<0.05.
Results
There were no significant demographic differences between the
matched CONTROL group and the HYBRID group.
Subjective Comparisons: The IKDC Subjective was significantly
higher in the matched CONTROLS groups compared with the
HYBRID group (p = 0.013) There were no significant differences
found between the two matched groups across the other four
subjective knee scores (Table 2). Objective Comparisons: There
were no significant differences found between the two matched
groups for objective measures (Table 3). The KT-1000 side-to-side
difference mean for match CONTROLs was 0.94 mm and for
HYBRIDS was 0.46 mm.
Table 2.1: Subjective Clinical Comparisons
Outcome Matched Controls Hybrid P Value
Tegner 6.32 ± 2.10 6.41 ± 2.03 .723a
Cincinnati 371.61 ± 63.50 371.55 ± 41.41 .302b
Lysholm95 84.50 ± 14.72 85.72 ± 8.98 .555b
IKDC Sub. 88.46 ± 15.14 84.91 ± 11.60 .013b
ACL QOL 81.84 ± 18.12 79.96 ± 19.42 .434a
aPaired samples t test
bWilcoxon Signed Ranks test
KDC - International Knee Documentation Committee
ACL QOL – Anterior Cruciate Ligament Quality of Life Questionnaire
Table 3.1: Objective Knee Measures
Matched
Controls
Hybrid P Value
IKDC Objective, n (%)
A
B
C
D
41 (69%)
18 (31%)
0 (0%)
0 (0%)
36 (62%)
21 (36%)
1 (2%)
0 (0%)
.494a
Difference in ROM, Mean ± SD -3.25 ± 3.32 -2.10 ± 2.93 .056b
KT-1000 SSD (mm), Mean ± SD 0.94 ± 0.84 0.46 ± 1.66 .075c
SSD (<=3 mm) 98.3% 93.2% .364a
aFisher’s exact test
bWilcoxon Signed Ranks test
cPaired samples t test
SSD – Side-to-side difference
Complications/Return to Theatre
A summary of complications across both groups is detailed in
(Table 4).
Table 4: Complications
Matched
Controls
Hybrid Odds Ratio (95% CI)
Graft rupture 0 1 -
Graft laxity SSD > 3 mm 1 4 4.22 (0.46, 38.92)
Re-operations
Re-rupture
Arthrofibrosis
Meniscal/chondral
Deep infection
1
0
1
0
0
10
1
4
4
1
11.84 (1.46, 95.75)
SSD – Side-to-side difference
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Graft failure and synovitis: In the matched CONTROL group,
there were no graft ruptures during the follow-up period. In the
HYBRID group one patient (1.8%) required surgical revision for
graft rupture at 34 months post ACLR. No patients in either group
had knee synovitis.
Re-operations: The odds ratio comparing reoperations between the
matched CONTROL group and the HYBRID group 11.84 (95% CI:
1.46, 95.75). Subdividing causes, the HYBRID group had a higher
rate of secondary meniscal surgery and arthrofibrosis surgery. The
subset of patients receiving re-operations was not large enough to
compute meaningful odds ratios. Among the matched CONTROLS,
there was one re-operations for symptomatic graft impingement
requiring arthroscopic notchplasty at four months post ACLR. In the
HYBRID group, there were ten re-operations (16.9%). One patient
(1.7%) was known to be immunocompromised and acquired a deep
infection. Four patients (6.8%) received surgical intervention for
menisco-chondral symptoms. A further four patients (6.8%) required
surgery for arthrofibrosis resulting in anterior knee pain and loss of
extension. Surgical intervention for arthrofibrosis consisted of notch
debridement with lateral retinacular release and was performed
within the first 12 months post ACLR. The odds ratio comparing
graft laxity between the matched CONTROL group and the
HYBRID group was not statistically significant. The outcomes of
the patients that returned to theatre are summarized in (Table 5).
Table 5: Clinical Features of Patients that Required Return to Theatre
Age (years) Sex Tegner IKDC
(Subj.)
IKDC
(Obj.)
KT-1000
SSD (mm)
Cincinnati Lysholm95 ACL QOL Diff ROM
Arthrofibrosis surgery for loss of extension
CONT. Pt 23 21.6 F 6 81 B 2.7 350 78 82 0
HYBRID Pt 11 19.6 M 7 70 B -3.3 370 83 69 -7
HYBRID Pt 23 20.9 F 2 68 B -3.3 280 73 34 0
HYBRID Pt 40 27.1 M 5 59 A 1.7 360 87 75 0
HYBRID Pt 36 34.9 F 4 77 B 0.3 350 85 68 0
Arthroscopy for meniscal or chondral pathology
HYBRID Pt 20 21.9 F 6 72 B -1.7 350 73 46 0
HYBRID Pt 31 37.5 M 5 62 C 3.0 260 64 28 0
HYBRID Pt 32 33.5 M 5 67 B -1.0 280 76 40 -3
HYBRID Pt 50 50.2 F 5 85 A -2.0 290 93 66 -5
Discussion
The CONTROL and HYBRID groups had similar subjective and
objective knee scores. HYBRID patients, however, had higher
rates of re-operation for arthrofibrosis and meniscal/chondral
complications, although the differences did not reach statistical
significance. There may be an indication for ACLR using hybrid
graft constructs in patients wishing to expedite their return to
sporting activities. The increased risk of re-operation, however,
must be taken into consideration.
Appropriate rehabilitation after ACLR is essential for achieving
optimal outcomes. Traditional ACL rehabilitation protocols avoid
loading the maturing graft for the first 3 months after surgery in an
attempt to prevent graft stretch and early rupture [5, 6, 24, 25].
Studies allowing running before 2 months report increased laxity
and graft failure [21, 24]. A synthetic graft in conjunction with an
autologous ACL may protect the graft, allowing for safe,
accelerated rehabilitation.
Synthetic grafts have been employed in ACLR since the 1980s in
an attempt to achieve immediate tensile strength, reduce surgical
time, reduce donor-site morbidity, and allow earlier return to
previous function. Formerly used synthetic grafts included Dacron
Ligament Prosthesis, Leeds-Keio, Kennedy Ligament
Augmentation Device (LAD), and GORE- TEX. The outcomes of
those grafts were universally poor with high reported rates of graft
failure and synovitis [13, 26, 27].
The LARS® artificial ligament is manufactured from terephthalic
polyethylene polyester. Its porosity is proposed to create favorable
conditions for biological ingrowth, in turn decreasing the incidence of
reactive synovitis [28]. Trieb et al, demonstrated the capacity of the
LARS® ligament to encourage complete fibroblastic/osteoblastic
ingrowth within in vivo and in vitro settings at six months post-
implantation [29]. Important surgical techniques described when
using the LARS include remnant sparing, tensioning in extension, and
avoidance of impingement [22, 30, 31]. Stiffness characteristics may
be important for the autograft for limiting stress shielding and allowing
satisfactory ligamentization, thereby enhancing long-term function.
A combined LARS/hamstring hybrid graft coupled with
accelerated rehabilitation has not been previously compared with
hamstring grafts. Hamido et al compared a similar hybrid graft
with a hamstring graft cohort [18]. Their study differed, as both
grafts were single bundle, the hybrid was indicated only for
patients with small hamstrings, and recovery times were not
assessed. That study showed that hybrid patients had improved
KT-1000 stability (1.1 ± 0.3 mm vs 2.5 ± 0.5 mm; p<0.05) and
higher rates of objective IKDC A and B scores (96% vs 71%;
p<0.05) at 5 years follow-up. This is in contradiction to our study,
as we found no difference in objective knee scores. We chose a
double-bundle graft for each cohort as our preferred technique,
which may explain more stable knee scores in the hamstring group
(KT-1000 - 0.9 mm: combined IKDC A and B - 95%).
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Brunet et al studied the outcomes of acute posterior cruciate
ligament (PCL) tears reconstructed using a hybrid construct
similar to that used in our study [32]. They described the LARS®
ligament as functioning as “a tutor” for healing the PCL, similar to
our proposal for the ACL.
The higher number of re-operations in the HYBRID group was not
expected. Although it was not statistically significant, the relatively
high incidence of re-operation in the HYBRID group is of concern.
Ten patients (16.9%) in the HYBRID group required re-operation
within 2 years following ACLR. Four patients required surgery for
menisco-chondral pathology and four required arthroscopic
intervention for loss of extension/anterior knee pain. Those
patients had lower IKDC subjective scores and slower recovery
times compared with the averages across the study. The reason for
the high rate of re-operations has not been definitively established.
The augmentation of the autologous graft with a relatively inelastic
synthetic graft and a fixed working length may have contributed to
a loss of extension. Additionally, the four-tunnel ACLR and
remnant-sparing technique used in our study may have contributed
to excessive graft constraint [33, 34]. Retention of the remnant
tissue may also cause graft/notch impingement by increasing the
remnant volume. It may be that the use of synthetic grafts and
aspects of the surgical technique noted above resulted in excessive
graft constraint with associated loss of extension. Finally, we
adopted a surgically aggressive approach to patients struggling to
achieve full extension, which may reflect our high re-operation
rates.
The development of arthrofibrosis following ACLR can have
debilitating effects on knee function. Studies have shown its
potential to disrupt normal knee kinematics and lead to early
progression of degenerative joint disease [35-37]. Mayr et al,
found radiological evidence of degenerative joint disease in 88.2%
of patients with arthrofibrosis after ACLR [38]. It is currently
unknown if there is a link between over-constraint of the knee and
arthrofibrosis. We have changed our practice to performing single
bundle HYBRID ACLR due to concerns of re-operation rates,
arthrofibrosis, and knee over-constraint.
There were no adverse effects of stress shielding on the autologous
component of the hybrid graft in our study. Yoshiya et al, found
that the presence of a synthetic graft within a hybrid construct
adversely affected the ability of the construct to re-vascularize
over time. Yoshiya et al, went on to find that excessive synthetic
graft stress shielding resulted in weaker, looser grafts in canine
subjects. Similarly, McCarthy et al demonstrated that stress
shielding results in prolonged graft remodeling and a decreased
load to failure. Our graft stability and low failure rates at 2 years
may suggest stress shielding is unlikely; however, long-term
studies are required to definitively assess this [39-41].
Limitations
Selection bias may have influenced the outcomes of our study.
More motivated patients may have a tendency to opt for graft
types that facilitate an expedient return to sports. They may be
more diligent in rehabilitation and/or may take more risks to
achieve the perceived benefit of earlier return to sports. In the
current study, participants were recruited in a private-practice
setting and chose their preferred graft type with its associated
rehabilitation program. This prevented us from being able to
randomize patients into groups. A randomized controlled trial
would more clearly illustrate the impact of augmented graft
constructs coupled with accelerated rehabilitation programs,
however, this may be problematic from an ethical standpoint. We
attempted to address this using propensity score matching.
Unfortunately, given the number of controls available for matching
and the subset subsequently matched, the analysis is likely to be
underpowered [21].
The comparison of both different rehabilitation protocols and a
different surgical techniques between groups may have introduced
bias and hindered our ability to draw accurate conclusions
regarding outcomes. However, our study hypothesis aimed to
investigate a “graft plus rehabilitation” comparison as the graft /
rehabilitation combination was intended to complement one
another. In the study design phase, it was deemed unacceptable to
accelerate the rehabilitation of the CONTROL group due to the
risk of early graft damage.
The short-term follow-up limits analysis of the effects of stress
shielding and knee over-constraint in the HYBRID group. Longer
follow-up is required to evaluate this fully. Additionally, exclusion
of patients who received ACLR more than six months from injury
may have contributed to bias.
Conclusions
ACLR utilizing a hybrid autologous/LARS® construct facilitated
accelerated rehabilitation without evidence of increased failure or
early graft stretch. Additionally, there was no clinical difference in
functional outcome scores between the HYBRID and CONTROL
groups. Although not statistically significant, the HYBRID group
had an unacceptably high re-operation rate at 2-years post ACLR,
and is therefore not recommended as a surgical technique by the
primary author. The refinement of ACLR to facilitate patients’ safe
and early return to previous levels of function presents a topic for
future research.
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