Clinical Biomechanics 77 (2020) 105065

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Clinical Biomechanics
journal homepage: www.elsevier.com/locate/clinbiomech

Biomechanical comparison of anterior cruciate ligament repair with internal T

brace augmentation versus anterior cruciate ligament repair without
augmentation
⁎
Patrick Massey , David Parker, Kaylan McClary, James Robinson, R. Shane Barton,
Giovanni F. Solitro
Department of Orthopaedic Surgery, Louisiana State University Health Sciences Center- Shreveport, 1501 Kings Highway, Shreveport, LA 71103, USA

A R T I C LE I N FO A B S T R A C T

Keywords: Background: Newer repair techniques of anterior cruciate ligament tears, including augmentation with internal
Anterior cruciate ligament repair brace, have shown promising clinical results. Few biomechanical studies exist comparing anterior cruciate li-
Anterior cruciate ligament augmentation gament repair only versus repair with internal brace. The purpose of this study was to compare the load to failure
Ligament repair and stiffness of anterior cruciate ligament repair with internal brace augmentation versus repair-only.
Internal brace
Methods: Proximal femoral avulsion type anterior cruciate ligament injuries were created in 20 cadaver knees.
Ligament augmentation
Anterior cruciate ligament repair-only or repair with internal brace was performed using arthroscopic tools.
Load to failure and failure modes were collected, with calculations of stiffness and energy to failure performed.
Findings: The average load to failure for the internal brace group was higher than the repair-only group: 693 N
(SD 248) versus 279 N (SD 91), P = .002. The stiffness and energy to failure values were higher for the internal
brace group than the repair-only group: 83 N/mm versus 58 N/mm, P = .02 and 16.88 J (SD 12.44) versus
6.91 J (SD 2.49), P = .04, respectively. Failure modes differed between groups (P = .00097) with 80% failure in
the repair-only due to suture pull through the anterior cruciate ligament and 90% failure in the internal brace
group due to suture button pull through the femur.
Interpretation: There was higher load to failure, stiffness, and energy to failure for the internal brace group
compared to the repair-only group, and a high positive correlation between bone density and load to failure for
the internal brace group.
Clinical significance: Anterior cruciate ligament repair with internal brace augmentation demonstrates sig-
nificantly higher load to failure. It may be a useful adjunct to protect the anterior cruciate ligament repair from
failure during the early stages of healing.

1. Introduction several additional studies showed high failure rates with mid-substance
ACL repair and lower failure rates with proximal avulsion repair
Anterior cruciate ligament (ACL) repair has been reported in the (Kaplan et al., 1990; Odensten et al., 1984; Sherman et al., 1991;
literature as early as 1895 (Robson, 1903), but did not gain popularity Weaver et al., 1985).
until the 1930s and '50s (Campbell, 1939; McCulloch et al., 2007; More recently, there has been renewed interest in ACL repair. In
O'Donoghue, 1955; Palmer, 2007). These procedures were performed order to protect the ACL repair and improve outcomes, augmented re-
open, and while commonly employed in the U.S. during 1970s and '80s, pair with internal brace (IB) has been developed. MacKay et al. reported
they lacked long-term follow-up supporting their efficacy (McCulloch supplementation of primary ACL repair with heavy-braided augmented
et al., 2007). Feagin and Curl reported ACL repair data which demon- suture (2.5 mm polyethylene tape). This was made possible due to the
strated deterioration in mid- to long-term follow-up with 53% re-injury use of an alternative means of fixation using suspensory button tech-
rate at five years, in conjunction with high rates of pain, instability, and niques rather than suture anchors (MacKay et al., 2015). In their study,
stiffness (Feagin Jr. and Curl, 1976). Throughout the 1980s and '90s, only 1 of 27 patients who underwent primary repair with an internal

⁎
Corresponding author.
E-mail addresses: pmasse@lsuhsc.edu (P. Massey), kmccla@lsuhsc.edu (K. McClary), jrob38@lsuhsc.edu (J. Robinson), rsbart@lsuhsc.edu (R.S. Barton),
gsolit@lsuhsc.edu (G.F. Solitro).

https://doi.org/10.1016/j.clinbiomech.2020.105065
Received 21 December 2019; Accepted 26 May 2020
0268-0033/ © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/BY-NC-ND/4.0/).
P. Massey, et al. Clinical Biomechanics 77 (2020) 105065

brace construct went on to failure and was subsequently converted to 2.3. Repair with internal brace (IB) technique
formal reconstruction. The theory behind the internal brace is that it
protects the repair and increases the strength during early healing, al- The technique for the knees in the ACL repair with suture-tape
lowing early mobilization (MacKay et al., 2015). The mechanism of augmentation group was performed in a similar manner to the RO
failure of suspensory fixation has been shown to be due to button pull group. The femur and tibia were secured in 120 degrees of flexion while
through the bone as opposed to suture failure (Arthrex, 2013). With this a #2 FiberWire® (Arthrex, Naples, FL USA) was passed through the
suspensory type of fixation, it may be that bone with lower bone density proximal ACL as stated above. The same 2.4 mm guide-pin was passed
has a lower load to failure as the button pulls through the softer bone. through the ACL footprint on the femur with the same 7 mm offset
While there is increasing clinical data on the ACL repair with IB guide. In contrast to the RO technique, a 4.5 mm reamer was passed
augmentation, there is a paucity of studies evaluating the stiffness and over the guide-pin. Next, a 2 mm wide polyethylene tape
failure loads of this new technique. The purpose of this study was to (InternalBrace, Arthrex, Naples, Fl USA) was passed through the loop of
compare the load to failure and stiffness of ACL repair with IB aug- an ACL TightRope (Arthrex, Naples, Fl USA). The TightRope button was
mentation versus ACL repair without augmentation. The hypothesis passed with the FiberWire from the ACL repair through the femoral
was that ACL repair augmented with IB would have a higher load to tunnel and flipped on the lateral femur. The ACL TightRope was cin-
failure and stiffness than ACL repair alone. A secondary aim was to ched so that the loop of the tape was juxtaposed to the femoral tunnel.
evaluate the modes of failure between each group and to determine if The #2 FiberWire which had also passed through the tightrope button
there was a correlation between bone density and load to failure in both was tensioned and tied. For the tibial side of the InternalBrace ®
groups. (Arthrex, Naples, FL USA), a 2.4 mm tibia tunnel was drilled using an
ACL guide set to 55 degrees with the aiming point set on the center of
the tibial ACL footprint. The two limbs of the suture tape were then
2. Methods passed through the tibia tunnel (see Fig. 2). In order to set a standar-
dized length of the internal brace and simulate a posterior drawer, the
2.1. Specimens femur was held flat on a one-inch-thick polyethylene block with the
tibia held flat on a table. The two limbs of the polyethylene tape were
As this study was a cadaver biomechanical study, it did not require hand tensioned, then tied over a four-hole button on the tibia. After
Institutional Review Board approval under current guidelines. Twenty preparation of the repair, the tibia and femur were instrumented along
fresh frozen cadaver knees were used in this study with 10 in each the medial-lateral direction with a three-inch long 3/16″ stainless steel
group: ACL repair-only (RO) group or the ACL repair with IB group. Out rod and potted in 3.5x3x2 inch metal boxes using a polyester resin (3 M
of the 20 cadaver knees, there were 10 right knees and 10 left knees. Bondo, Maplewood, MN).
Fourteen knees were paired from the same cadavers, whereas the re-
maining 6 knees came from 6 different donors. The 6 knees represented 2.4. Testing
with 3 right and 3 left knees and were paired according to demographic
data. Within each pair of knees, the assignment of the left vs right knee During mechanical testing, the femur was constrained to the ac-
to each group was randomly selected to the RO vs IB group. For the tuator of a servohydraulic testing system (Model 8874, Instron, Canton,
final groups, there were 5 left knee IB versus 5 right knee RO pairs and MA) in a flexed position relative to the stationary tibia to simulate
5 right knee IB compared to 5 left knee RO pairs. The average age of the anterior drawer testing (see Fig. 3). The specimens were preconditioned
cadaver knees was 62.2 years (SD 4.0) with 7 male and 13 female with 100 Cycles at 0.5 Hz in load ranging from 50 to 200 N, and then
knees. loaded in tension at a rate of 20 mm/min until failure. The condition of
The knees were thawed at room temperature for 24 h. The soft failure was defined as reduction in load equivalent to 80% of the
tissue was carefully dissected, including removal of the collateral and maximal measured load. The mechanical performance of each specimen
posterior cruciate ligaments, so that the ACL remained the only at- was evaluated via failure load, stiffness, and toughness.
tachment remaining between the femur and the tibia. The tibia and The failure load (Fmax) was defined as the peak load measured
femur were cut 6 in. from the joint line to standardize the moment arm. during testing. The toughness was calculated as the energy spent to
The center of the proximal ACL footprint was marked on the femur, and peak load (Epeak), and up to failure (Efail). The graft stiffness was
the ACL was elevated from the femur using a scalpel (to simulate an characterized by values of stiffness measured as the slopes of the linear
ACL avulsion off the femur). Then the ACL repair or repair with IB was regressions built for intervals of 50 N surrounding the reference loads of
performed. In order to mitigate variability, all of the repairs in both 50 (S50), 150 (S150), and 300 N (S300). These three load values were
groups were performed by the primary author. used in consideration of the loads at which the ACL is reported to be
subject to during gait (Helgason et al., 2008). The stiffness referenced
was the S150 value, as most repairs survived past 150 N.
2.2. Repair-only (RO) technique During testing, it was noted that the primary mode of failure for the
IB group occurred at the bone implant interface; therefore the decision
In order to simulate arthroscopic conditions, the tibia and femur was made to evaluate the bone density of the specimens to determine if
were placed in separate vice-clamps with the knee at 120 degrees of there was a relationship between the failure and the bone density as a
flexion. A #2 FiberWire (Arthrex, Naples, FL USA) was passed in a secondary aim. The density of the distal femur has been previously
common Krackow fashion with 3 locking stitched passed down one side estimated through the values of CT attenuation coefficient expressed in
of the ACL to the mid-point of the ligament longitudinally, and then Hounsfield Units (HU) (Grassi et al., 2012; Helgason et al., 2008;
passed to the other side of the ligament and run back up proximally Taddei et al., 2006). In accordance, each isolated femur was CT scanned
with three more locking stiches. A 2.4 mm guide-pin was passed with a LightSpeed VCT (GE Healthcare, Little Chalfont, United
through the footprint of the ACL with a 7 mm offset guide placed (to Kingdom) at 120 kV/100 mA with a pixel size of 0.516 mm and a slice
simulate an anteromedial approach). The two ends of the repair sutures thickness of 0.625 mm. The reconstructed, 3D images of each femur
were passed with the guide-pin, hand tensioned, and tied over a four- were segmented in 3D slicer (Kikinis et al., 2014). The density was
hole 12 mm button (Arthrex, Naples, FL USA) on the lateral femur (see measured for each segment with a computer model in the plane per-
Fig. 1). All knots were tied with a surgeon's knot with 5 additional half- pendicular to the anatomical axis and passing through the most prox-
hitches. imal point of the trochlea considering 0 HU (Hounsfield Unit) as lower
limit for the threshold (Schreiber et al., 2011). The average HU value

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P. Massey, et al. Clinical Biomechanics 77 (2020) 105065

Fig. 1. a. Illustration of a left knee ACL suture repair

only with 3 locking sutures (white) on each side of
the proximal ACL. The 2 suture ends are passed
through the femur tunnel and tied over a button. b.
Illustration of a left knee ACL suture repair with
Internal Brace augmentation. The Internal Brace su-
ture tape (blue) is passed into the femur tunnel then
two tape limbs are tied over a button on the ante-
romedial tibia in addition to the ACL Repair with 3
locking sutures (white). (For interpretation of the
references to colour in this figure legend, the reader
is referred to the web version of this article.)

Fig. 2. a. Right knee ACL repaired with #2 FiberWire repair only tied over a button. b. Left knee repaired with a #2 FiberWire and InternalBrace (Arthrex, Naples, FL
USA).

was then computed as the average HU of the voxel included in each of confidence interval was calculated for both the RO and IB groups. A
the obtained segments. The bone density values were used to evaluate regression analysis was performed to evaluate if there was any corre-
any differences between groups or correlation between load to failure lation between bone density based on HU and load to failure. A chi
and bone density. square was used to compare categorical differences between the two
groups (Rosner, 2010).
2.5. Statistics
3. Results
An a-priori power analysis was done to determine the number
needed in each group for a power equal or 1 - β equal to 0.8. Based off Twenty human cadaver knees were tested, 10 in the RO group and
of the load to failure from previous studies comparing failure load of 10 in the IB group. The average age of the cadaver knees was 62.2 years
ATFL (Anterior-talofibular ligament) repair (mean 68.2 N SD 27.8) and (SD 4.0). The average age of the RO group was 62.3 years (SD 3.3)
ATFL repair with IB augmentation (mean 250.8 N SD 122.7), it was versus 62.1 years (SD 4.8) for the IB group with no significant differ-
determined that the number needed for each group was 3 (Viens et al., ence (P = .91). There was no statistical difference in sex distribution
2014; Waldrop 3rd et al., 2012). These were the only available studies between the RO and IB groups (4 males, 6 females in RO group, 3 males
reporting failure loads of ligament repair versus ligament repair with IB and 7 females in IB group, P = .64). The average load to failure for the
augmentation. IB group was 693 N (SD 248), range 430 to 1128, which was higher
The failure loads, stiffness and bone density were evaluated and than the RO group load to failure of 279 N (SD 91), range 100 to 392,
compared using a matched student's two sample t-test with SPSS (IBM P = .002 (see Fig. 4). The IB load to failure 95% confidence interval
SPSS Statistics, Armonk, NY) to compare both groups. A 95% was 539 N to 846 N, while the RO group was 223 N to 335 N. The

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P. Massey, et al. Clinical Biomechanics 77 (2020) 105065

density based on HU between both groups, with an average for the RO

group versus IB group of 245HU (SD 65) versus 233HU (SD 54), re-
spectively, P = .68. There was a small correlation between bone mi-
neral density based on HU versus load to failure overall, r2 = 0.26.
However, only the IB group showed a strong correlation with bone
density versus load to failure, r2 = 0.82 (P = .003). The repair only
group had a weak negative correlation with bone density vs load to
failure, r2 = −0.16 (P = .61).

4. Discussion

While ACL repair techniques have demonstrated high failure rates

historically, newer arthroscopic techniques have yielded more suc-
cessful results (DiFelice et al., 2015; DiFelice and van der List, 2016;
MacKay et al., 2015). Several authors have postulated that ACL repair
may offer many clinical benefits including preservation of blood supply,
preservation of proprioception, potential for faster healing times, and
Fig. 3. Testing with Instron of the ACL repair with a right tibia potted and decreased morbidity. These authors also proposed that the reason for
clamped and knee flexed to 90 degrees with a right femur potted and clamped. lower failure rates may be attributable to newer instrumentation and
Anterior drawer is the force applied. the ability to protect the repair with suture-tape augmentation. While
early clinical outcomes for ACL repair are promising, many questions
remain. The current study demonstrated that the ACL repair with IB
had a higher load to failure, stiffness and energy to failure compared to
RO technique. Additionally, the mode of failure was different between
groups, and there was a correlation between bone density and failure
load for the IB group.
The forces placed on the ACL during daily physiologic activity vary.
Some studies report peak forces with ground level walking to be as high
as 303 N to 355 N (Escamilla et al., 2012). Activities such as seated
knee extension can have peak forces as high as 349 N and 396 N
(Escamilla et al., 2012). Our study showed the ACL repair alone had an
average load to failure of 279 N which is lower than the peak forces
placed on the ACL with walking. A recent study by van der List and
DiFelice evaluated repair only of ACL proximal stump with a suture
button versus a suture anchor. They showed the failure load was 310 N
for the suture button repair group versus 176 N in the suture anchor
group, with no difference between the two techniques (P = .144) (van
der List and DiFelice, 2016). These RO failure loads are also lower than
the physiologic loads placed on the ACL during level ground walking
Fig. 4. Average Load to Failure (N) of ACL Repair Only group versus Repair (Escamilla et al., 2012). The failure loads of the suture repair with
with Internal Brace group, P = .0001. Standard deviation is denoted with error button performed by van der List and DiFelice were comparable to the
bars. RO group in our study, which was also below the peak forces during
level ground walking. This may explain the high failure rates of ACL
RO, as the repair sutures are likely not able to sustain the peak loads of
stiffness was also higher for the IB group than the RO group (83 N/mm2
normal walking.
versus 58 N/mm2, P = .02). The energy to failure was higher in the IB
An additional study performed by Hoogeslag et al. evaluated ante-
group than the RO group (P = .04) (see Table 1).
rior tibial translation for ACL intact knees, ACL deficient knees, ACL
The modes of failure in the RO group were 8 suture cut-out of the
repair with suture-tape augmentation, and ACL repair with dynamic
ligament (see Fig. 5) and 2 ACL mid-substance ruptures below or distal
interligamentary augmentation. While no load to failure was de-
to the repair. In the IB group, the modes of failure were 8 due to pull
termined, the authors did compare an internal-brace-like construct
through of the button through the lateral femoral cortex (see Fig. 5b), 1
(static augmentation) with ACL intact and deficient knees. They showed
pull through of both the distal button through the tibia and the prox-
that ACL repair with static tape augmentation had anterior tibial
imal button through the lateral cortex of the femur, and 1 mid-sub-
translation which was statistically no different than the ACL intact
stance ACL tear. There was a statistically significant difference in the
knees and less than the ACL deficient knees (Hoogeslag et al., 2018).
modes of failure between the RO and IB group (P = .00097).
Providing a baseline for the native ACL biomechanical properties,
The average overall bone density of the femurs used was 238 HU
there are several studies on the native ACL and various suspensory
(SD 65). There was no statically significant difference in the bone
constructs. A previous study comparing the Endobutton (Smith &

Table 1
Biomechanical data of ACL repair only group versus ACL repair with Internal Brace group.
Group Load to failure (N) SD(N) Stiffness (N/mm) SD(N/mm) Energy to max load (J) SD (J)

Repair only 279 91 58 9.6 6.91 2.49

Repair with internal brace 693 248 83 22.7 16.88 12.44
P Value 0.002 0.02 0.04

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P. Massey, et al. Clinical Biomechanics 77 (2020) 105065

Fig. 5. a. Posterior view of right knee with ACL repair only. Failure occurred from pullout of locking suture through ligament. b. Lateral view of left knee with ACL
repair augmented with Internal Brace. Failure occurred from button pulling through the lateral femur bone.

Nephew, London, UK) to the ACL TightRope showed ultimate loads (N) femur. A previous bovine femur study showed similar failure mechan-
of 656 N versus 749 N respectively (Arthrex, 2013). An additional isms for suspensory fixation where 6/6 of the cortical buttons pulled
porcine study showed an average failure load for the TightRope and through the bone with a suture-button and 3/6 of the cortical buttons
ZipLoop (Zimmer Biomet, Warsaw, IN) of 849 N and 645 N, respec- pulled through the bone with tight rope (Arthrex, 2013). In addition,
tively (Arthrex, 2010). The construct failed because the button pulled this mode of failure is comparable to the ATFL IB studies. One previous
through the cortex in all cases. The authors suggested that the failure study showed IB screw pullout from the talus in 4/6 specimens and
loads are lower for human bone as the porcine model is typically from the fibula in 2/6 (Schuh et al., 2016). Another ATFL IB study
stronger (Arthrex, 2010). An additional study by Noyes and Grood showed 5/6 constructs failed from screw pullout of bone from the fibula
showed that older human cadavers (48 to 86 years) had an ACL failure and 1/6 failed from screw pullout from the talus (Viens et al., 2014). In
load of 622 N and energy failure of 4.89 Nm (Noyes and Grood, 1976). all these studies utilizing tape augmentation, the main mode of failure
Previous studies show failure loads of native ACL and suspensory de- is at the screw or button interface with bone which is the main mode of
vices range from 622 N to 849 N, which is comparable to the failure failure of our IB group.
load of the IB group in the current study. The mode of failure of the An additional goal of the current study was to evaluate if there was
suspensory device study is also similar to our study where the button correlation between bone density and failure load of ACL repair. The
pulled through the cortex (Arthrex, 2010). Previous cadaver studies average bone density in our study was 238 HU. A previous study de-
have shown the native ACL stiffness ranges from 57.2 N/mm to 129 N/ monstrated that normal bone density T-score of −1.0 or greater cor-
mm (Noyes and Grood, 1976; Paschos et al., 2010). The current study related to a CT measured density of 133 HU.(Schreiber et al., 2011) In
showed stiffness values of the ACL repair with IB to be 83 N which are the same study, osteoporotic bone (T-score ≤ −2.5) had a density of
comparable to these values for the native ACL. Higher stiffness is not 78.5 HU.(Schreiber et al., 2011) Compared to this previous study, our
necessarily better; but the ACL repair with IB may have a stiffness more specimens were not osteoporotic. There was, however, a correlation
similar to the native ACL than ACL repair alone. between lower bone density (HU) and lower load to failure with the IB
While IB ACL biomechanical data is limited, IB has been more ex- group. The IB fails at higher loads than the RO, thus, mainly fails via
tensively tested on anterior talo-fibular (ATFL) repair techniques. button pull through the bone. This may explain why the IB group
Biomechanical evaluation of failure load and torque for IB has been showed a correlation between load to failure and bone density. Due to
evaluated by Viens et al., on different ATFL repair techniques. In their the fact that the failure load of the IB was much higher, it failed via the
study, no significant difference was found in load to failure or stiffness button pulled through the bone instead of suture rupture.
between suture-tape augmented Brostom repair and the native ATFL Additionally, a recent biomechanical study for the medial collateral
(Viens et al., 2014). They determined the ultimate load of the repair ligament (MCL) compared the native intact MCL, MCL repair, MCL
with IB was 250.8 N compared to another study which determined the repair with IB and allograft reconstruction. The MCL repair with IB had
ultimate load of ATFL repair only to the fibula as 79.2 N (Viens et al., 29.4% higher moment to failure than the repair alone: 95 Nm (SD 31.9)
2014; Waldrop 3rd et al., 2012). Stiffness of ATFL repair only was and 73.4 Nm (SD 27.6) respectively, p = .05) (Gilmer et al., 2016). Of
calculated to be 6.8 N/mm, while another study showed ATFL repair note, the problem of over-tightening and stress-shielding the ATFL su-
with IB stiffness was 21.1 N/mm. An additional study by Schuh et al. ture-tape augment was addressed by using a hemostat deep to the
demonstrated ATFL repair with IB had a higher torque at failure than construct while securing the anchors. This process is not easily per-
ATFL repair alone (11.2 Nm versus 8.0 Nm respectively, P = .04) formed arthroscopically for ACL repair, and presents a technical chal-
(Schuh et al., 2016). These results are comparable to the current study, lenge when performing IB. The ideal length or tension for the internal
where both the load to failure and stiffness were higher with IB than brace has not been described. For the current study, the internal brace
RO. was secured using a standard protocol in order to set a consistent
In the current study, the predominant mode of failure in the repair length. Proper tensioning maneuvers for suture-tape augmented ACL
only group was pull-through of the suture through the ACL ligament. repair warrants further evaluation to determine the effects on healing,
This is consistent with previous studies on ATFL repair, where all RO and over-tensioning. The early clinical data from recent reports have
constructs failed at the ligament-suture interface (Schuh et al., 2016). In shown successful early outcomes. A retrospective study of 56 patients
the current study, the main failure mode of IB was pull of the button showed a 14.3% rate of failure with repair alone versus 7.1% with re-
through the bone of the femur and, in one case, both the tibia and pair and suture augmentation (Jonkergouw et al., 2018). An additional

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P. Massey, et al. Clinical Biomechanics 77 (2020) 105065

case series on 68 patients who received ACL repair with IB showed figures and edited the manuscript.
successful outcomes at one year with only one failure. While early Kaylan McClary, MD: Wrote the abstract, contributed to the dis-
clinical data is promising, ACL repair with IB augmentation should be cussion, edited the manuscript.
done selectively. Van der list and DiFelice recommend reserving repair James Robinson: Created the reference section, applied referencing
for proximal avulsions in the acute setting, when good ACL tissue is throughout the paper, and edited the manuscript.
present. Additionally, when performed, the surgeon should be ready to R Shane Barton, MD: Contributed to the discussion and editing of
perform a reconstruction if tissue quality or location prohibits direct the manuscript.
repair. While protecting the repair with the IB may prevent the repair Giovanni Solitro, PhD: Contributed to the methods and results sec-
from failing during physiologic loads, this does not necessarily translate tion of the manuscript.
into better healing. There are still concerns that, clinically, the internal All authors have read and approved the final submitted manuscript.
brace may overconstrain the knee. While our study showed stiffness
values for the internal brace similar to previous reported values on the Declaration of Competing Interest
native ACL, further studies should be done to evaluate the effect of
overtightening the internal brace. Future analysis should evaluate how This study was funded by a grant from Arthrex for cadaver speci-
to properly tension the IB to recreate the normal function of the knee. mens, supplies, and testing costs. Patrick Massey, David Parker, Kaylan
Additionally, future studies should be done to evaluate the effects of IB McClary, James Robinson, R. Shane Barton, and Giovanni Solitro de-
on the healing of ACL tissue. clare that they have no conflict of interest other than the grant de-
scribed above.
4.1. Limitations This article does not contain any studies with human participants
performed by any of the authors.
The following limitations regarding this study are described. First,
this study was not performed arthroscopically. It was necessary, during Acknowledgements
the preparation of a proximal femur ACL avulsion to open the knee and
carefully resect it from the footprint. Although arthroscopic instruments We would like to acknowledge that this study was funded by a grant
and positioning of the specimens provided simulated arthroscopic from Arthrex for cadaver specimens, supplies, and testing costs.
conditions, it remains unclear how arthroscopy would affect these re-
pairs biomechanically. Secondly, the average age of our sample was References
62 years and consisted of a 13:7 female-to-male ratio. The concern with
using an older female model for ACL repair testing is the potential Arthrex, I., 2010. Arthrex ACL TightRope and Biomet ZipLoop with ToggleLoc:
impact of osteopenia on the testing data. We were able to address this Mechanical Testing.
with bone mineral density correlation to failure for the IB group. Arthrex, I., 2013. ACL TightRope and EndoButton® Biomechanical Testing.
Campbell, W.C., 1939. Reconstruction of the ligaments of the knee. Am. J. Surg. 43,
However, this does not truly reflect the younger population that ACL 473–480. https://doi.org/10.1016/S0002-9610(39)90866-4.
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data due to the bone interface with the IB group may also be further cruciate ligament tears. Arthrosc. Tech. 5, e1057–e1061. https://doi.org/10.1016/j.
eats.2016.05.009.
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the extra-articular cortex. The result is an ovoid tunnel opening upon ligament repair. Arthroscopy 31, 2162–2171. https://doi.org/10.1016/j.arthro.2015.
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Feagin Jr., J.A., Curl, W.W., 1976. Isolated tear of the anterior cruciate ligament: 5-year
button. This was done in order to re-create previously described tech- follow-up study. Am. J. Sports Med. 4, 95–100. https://doi.org/10.1177/
niques (Jonkergouw et al., 2018; MacKay et al., 2015; Weaver et al., 036354657600400301.
1985). Nevertheless, despite these limitations in button placement and Gilmer, B.B., Crall, T., DeLong, J., et al., 2016. Biomechanical analysis of internal bracing
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