Open Journal of Veterinary Medicine, 2013, 3, 297-301
Published Online November 2013 (http://www.scirp.org/journal/ojvm)
http://dx.doi.org/10.4236/ojvm.2013.37048
Open Access OJVM
SwiveLock Bone Anchor Stabilization of the Cranial
Cruciate Ligament Deficient Stifle in Dogs:
Clinical Outcome
Matthew Raske1, Don Hulse2
1Capital Area Veterinary Specialists, Austin, USA
2Department of Veterinary Small Animal Clinical Sciences, College of Veterinary Medicine,
Texas A&M University, College Station, USA
Received September 19, 2103; revised October 27, 2013; accepted November 6, 2013
Copyright © 2013 Matthew Raske, Don Hulse. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
A number of surgical procedures have been reported for the cranial cruciate ligament (CCL) deficient stifle in dogs. The
objectives of this study were to report long-term outcomes in dogs with CCL deficient stifles stabilized with a knotless
SwiveLock bone anchor preloaded with FiberTape and to report associated complications. Medical records were re-
viewed to identify dogs with unilateral CCL deficient stifles treated with the SwiveLock system (n = 41) between June
2008 and January 2012. Dogs were divided into three groups according to body weight to assess differences between
owner assessed functional outcomes. Complications were recorded and a validated owner questionnaire was used to
evaluate long-term outcomes at least 6 months postoperatively. Owner assessment prior to and after treatment with the
SwiveLock system was statistically significant for each of the categories of the validated owner questionnaire. There
was no significant difference among the weight groups for any of the preoperative and postoperative treatment owner
questions. Complications requiring surgical revision occurred in three (7.3%) dogs. Two had surgical site infections and
one had a subsequent meniscal tear. The authors concluded that the SwiveLock system placed at near isometric sites is
an effective surgical option for the treatment of dogs with CCL deficient stifles.
Keywords: Canine; Cranial Cruciate Ligament; FiberTape; Isometric Stabilization; SwiveLock
1. Introduction
Cranial cruciate ligament (CCL) injury is a primary cause
of lameness in the canine, which leads to stifle instability
and predisposes to degenerative changes [1]. There are
numerous surgical options for treating the CCL deficient
stifle, but one technique has not been proven to be supe-
rior. Popular methods for treating the CCL deficient stifle
include extracapsular stabilization (ES) and tibial os-
teotomies that alter joint mechanics [2,3]. Extracapsular
stabilization (ES) has been used for over the past half
century to treat CCL injuries and has yielded good to
excellent results [3,4]. Advantages of ES compared to
other procedures include a better safety profile and a
procedure that is less technically demanding [2].
The knotless SwiveLock anchor system1 is a stifle sta-
bilization technique that utilizes a bone anchor and 2 mm
multifilament FiberTape2. This stabilizing suture is placed
at near isometric points F2-T3 (the location is at the dis-
tal pole of the fabella just cranial to the margin of the
articular cartilage on the lateral femoral condyle and at
the bony prominence just caudal to the long digital ex-
tensor groove of the proximal tibia) allowing for minimal
changes of suture tension through flexion/extension,
while allowing for a more natural stifle movement [5].
Ultimately, the near isometric points reduce incidence of
implant failure and may result in improved clinical out-
comes [6].
The purpose of this manuscript is to report the
long-term outcomes of dogs with CCL deficient stifles
stabilized with a knotless SwiveLock bone anchor pre-
loaded with 2 mm FiberTape placed at near isometric
1SwiveLock Knotless Anchor System; Arthrex Vet Systems, Naples,
Florida, USA. 2FiberTape; Arthrex Vet Systems, Naples, Florida, USA.

M. RASKE, D. HULSE 298
sites.
2. Materials and Methods
Medical records of dogs with CCL injury treated with a
knotless SwiveLock bone anchor preloaded with 2 mm
FiberTape from June 2008-January 2012 were reviewed.
Dogs that were at least 6 months post operative after sta-
bilization were considered for inclusion. Dogs were ex-
cluded when additional orthopedic and/or neurological
disorders were diagnosed before or after surgery, if the
patient was deceased, or if owners could not be reached
for follow up.
Data obtained from the medical records included sig-
nalment (breed, age, weight, and gender), affected limb,
extent of CCL injury, meniscal damage, presence of cra-
nial drawer at final clinical exam (7 - 8 week recheck),
complications, and time to telephone or e-mail follow up.
2.1. Pre- and Postoperative Care
All dogs were premedicated with intramuscular (IM) ace-
promazine3 (0.025 mg/kg), hydromorphone4 (0.1 mg/kg),
and glycopyrrolate5 (0.01 mg/kg). General anesthesia was
induced intravenously (IV) with propofol6 (5 mg/kg) and
maintained with isoflurane in oxygen. After induction,
epidural analgesia was administered using preservative-
free morphine7 (0.1 mg/kg). Cefazolin8 (22 mg/kg) was
given IV as a perioperative antibiotic at the start of sur-
gery and every 90 minutes as needed. An intra-articular
morphine9 (0.5 mg/kg) block and bupivacaine10 (2.5 - 5.0
mg) local incisional block were administered postopera-
tively, as well as carprofen11 (4.4 mg/kg) subcutaneously.
Morphine9 (0.5 mg/kg) was administered IV every 4
hours for the following 24 hours as needed. Tramadol12
(3 - 5 mg/kg, per os [PO]) was administered 12 hours
postoperatively and then 4 times daily for 3 days. Car-
profen11 (2.2 mg/kg, PO) was administered 24 hours pos-
toperatively and then twice daily for 14 days and once
daily for 7 days thereafter. Dogs were administered cep-
halexin13 (22 mg/kg PO) twice daily for 7 days.
The limb affected with the CCL injury was treated by
arthroscopic assisted isometric stabilization with the
knotless SwiveLock bone anchor preloaded with 2 mm
FiberTape as previously described by Hulse et al. [6].
The size of the SwiveLock used was subjectively deter-
mined by the body weight and activity level of the pa-
tient. Craniocaudal and mediolateral radiographs were
performed postoperatively to assess isometric position by
documenting anchor and tunnel position. All dogs were
discharged with identical postoperative rehabilitation
instructions that included short restricted activity on
leash until the 7 - 8 week recheck. Physical therapy was
recommended beginning 2 weeks after surgery and con-
sisted of specific treatments including use of the under-
water treadmill, balance board, and physioroll, as well as
exercises prescribed for home. Dogs returned for final
evaluation at 7 - 8 weeks and the presence of cranial
drawer (abnormal craniocaudal translation evaluated
without sedation) and complications were recorded.
Function of the affected stifle was evaluated at least 6
months post operatively using a validated owner question-
naire [7]. Owners were contacted via telephone or e-mail
(when available) to respond to the questionnaire, which
included seven questions pertaining to their pet’s func-
tion after CCL injury, but prior to stabilization surgery
and the same seven questions pertaining to function after
surgical repair and rehabilitation. A scale of 1 - 6 was
used for all questions, with 1 being the worst and 6 being
the best.
2.2. Statistical Analysis
Dogs were grouped according to body weight to assess
differences between owner assessed functional outcome.
Dogs in group one were less than 15 kg, dogs in group
two were 15 - 30 kg, and dogs in group three were great-
er than 30 kg. Analyses for differences between owners’
responses to the pre and post stabilization questionnaire
were performed using the Wilcoxon signed- rank test. A
Kruskal Wallis test was used to examine dif- ferences
among the three weight groups. Significance was set at P
< 0.05.
3. Results
Forty-one out of forty-nine dogs treated with a knotless
Swivelock bone anchor preloaded with 2 mm FiberTape
met the inclusion criteria. One dog was excluded as it
had additional orthopedic disorders at the time the owner
was contacted to answer the validated questionnaire, two
dogs were deceased at time of follow up, and five dogs
were lost to follow up as their owners were unable to be
contacted.
3Acepromazine; Boehringer Ingelheim Vetmedica Inc., St. Joseph,
Missouri, USA.
4Hydromorphone Hydrochloride, Baxter Healthcare, Deerfield, Illinois,
USA.
5Glycopyrrolate, Baxter Healthcare, Deerfield, Illinois, USA.
6Propofol, Hospira Inc., Lake Forest, Illinois, USA.
7Duramorph, Baxter Healthcare, Deerfield, Illinois, USA.
8Cefazolin, West-Ward Injectables Inc., Eatontown, New Jersey, USA.
9Morphine Sulfate, Baxter Healthcare, Deerfield, Illinois, USA.
10Bupivacaine Hydrochloride 0.25%, Hospira Inc., Lake Forest, Illinois
USA.
11Rimadyl, Pfizer Animal Health, New York, New York, USA.
12Tramadol Hydrochloride Tablets, Apotex Inc., Toronto, Ontario,
Canada.
13Cephalexin Capsules, Novopharm, Scarborough, Ontario, Canada.
There were 25 spayed (61.0%) and two intact females
(4.8%) and 14 neutered males (34.1%). A variety of
breeds were represented in the study: 12 mixed breeds
(29.3%), six American Staffordshire Terriers (14.6%),
Open Access OJVM

M. RASKE, D. HULSE 299
five Old English Bulldogs (12.2%), three each of Rott-
weilers and Golden Retrievers (7.3%), two each of Box-
ers and Labradors (4.8%) and one each of the following:
Bichon Frise, Catahoula, Chihuahua, Greater Swiss Moun-
tain Dog, Scottish Terrier, Shar Pei, Shetland Sheepdog,
and Shih Tzu (2.4%). The mean age was 7.0 +/− 3.7
years (range 1 - 15.9 yr). There were five dogs in group
one (less than 15 kg), 24 dogs in group two (15 - 30 kg),
and 12 dogs in group three (greater than 30 kg). Dogs in
group one had a mean body weight of 9.3 +/− 3.2 kg
(range 5.5 - 12.7 kg), dogs in group two had a mean body
weight of 24.6 +/− 2.9 kg (range 19.5 - 29.1 kg), and
dogs in group three had a mean body weight of 38.2 +/−
8.1 kg (range 30.0 - 52.4 kg). There was no significant
difference found among the different weight groups for
any of the preoperative and postoperative treatment ow-
ner questions (P > 0.05).
Of the 41 stifles, 21 were left (51.2%) and 20 were
right (48.8%). All of the affected stifle joints were evalu-
ated and treated by arthroscopy. Thirty-nine dogs (95.1%)
had a complete CCL tear, and two dogs (4.9%) had a
partial CCL injury. The medial meniscus was normal in
29 (70.7%) of the stifles, of these 15 (51.7%) had a me-
niscal release performed. A bucket handle tear was evi-
dent in 11 of the stifles and all subsequently had a partial
meniscectomy performed. One of the stifles was found to
have a previously released medial meniscus. The lateral
meniscus was normal in 40 of the stifles and one had a
radial tear. A 3.5 mm SwiveLock was used in the five
dogs (12.2%) in group one, a 4.75 mm SwiveLock was
used in 28 dogs (68.3%), 24 that were in group two and
four that were in group three, and a 5.5 mm SwiveLock
was used in eight dogs (19.5%), one that was in group
two and seven that were in group three. In two stifles, a
second FiberTape was placed at the F1-T3 isometric site.
(5) The size of suture utilized and the decision to place a
second FiberTape was subjectively determined based on
the weight and activity level of the patient.
Three (7.3%) out of the 41 cases experienced major
complications. Two of the cases involved infections that
required surgical removal of the implants and one was a
subsequent meniscal tear. No minor complications were
noted at the 4 week or 7 - 8 week recheck.
Presence of cranial drawer in millimeters was subjec-
tively assessed by the same observer (DH) on physical
examination without sedation and recorded at the final
exam (7 - 8 weeks post operative period) Thirty-six
(87.8%) of the affected stifles presented with 0 - 3 mm of
cranial drawer at 7 - 8 weeks. The remaining five (12.2%)
were subjectively assessed to have 4 - 6 mm.
Mean time from surgery to owners answering the val-
idated questionnaire was 16.5 months (range 7 to 47
months). The mean owner responses to questions per-
taining to pet’s clinical function after injury, but prior to
stabilization and mean responses to questions pertaining
to pet’s clinical function after stabilization with the knot-
less SwiveLock system are reported in Figure 1. The
surgical intervention with the SwiveLock system did
elicit statistically significant changes for all seven of the
preoperative and postoperative stabilization treatment
owner questions (P < 0.001).
4. Discussion
The knotless SwiveLock system successfully maintained
stability of the CCL deficient stifle through 7 - 8 weeks
following surgery and achieved good short to long-term
clinical function as assessed by a subjective owner ques-
tionnaire using a categorical scale. Owners reported good
to excellent clinical function based on the questionnaire.
Scores in all three of the weight groups were improved
following surgery as compared to pre stabilization values.
This clinical assessment supports in vitro studies that
demonstrate the SwiveLock system to have the least
elongation failure and least peak to peak elongation when
compared to other ES procedures [8].
Three cases (7.3%) with major complications were
identified. All three were considered major complications,
as they required additional surgical intervention. We did
not include the five cases that were subjectively assessed
to have 4 - 6 mm of cranial drawer as complications, as
they did not present with clinical dysfunction and did not
require further surgical intervention.
Surgical site infections (SSIs) accounted for two of
three complications (4.9%). This reported incidence of
SSIs falls within the expected infection rate of 2.5% to
5.8% that has been reported for most clean veterinary
medicine surgical procedures and is also compatible with
incidence of SSIs following ES stabilization reported in
previous studies [9-11]. Although SSIs cannot be elimi-
nated completely, preventative measures reduce their
incidence. An antimicrobial incise drape14 was used to
decrease skin flora contact and contamination of the Fi-
berTape, although this practice is of questionable benefit
in reducing contamination in canine surgical wounds [12].
FiberTape is an integral part of this procedure in that it is
stronger, elongates less than other materials, has greater
yield loads, and greater load to failure [13]. When placed
at near isometric points less stress is reported in the su-
ture tension [6]. We feel these advantages outweigh the
negative association of multifilament suture material
with increased SSI incidence [14]. Bacterial culture and
antimicrobial sensitivity testing were used to confirm the
presence of a bacterial infection and to determine antim-
icrobial sensitivity. One of the two dogs developed an
infection 4 weeks post op. The culture revealed the pres-
nce of a Methicillin-resistant Staphylococcus pseudo- e
14Ioban, 3M, Flemington, New Jersey, USA.
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M. RASKE, D. HULSE
Open Access OJVM
300
Figure 1. Validated questions posed to owners regarding pet’s condition after injury, but prior to stabilization with a knotless
SwiveLock system (blue) and after stabilization (red).
intermedius (MRSP). The dog was treated based on an-
timicrobial sensitivity results and the SwiveLock bone
anchor with FiberTape was subsequently removed. The
second dog developed a polymicrobial infection 6 weeks
following surgery. Cultures revealed Staphylococcus
aureus and Klebsiella spp. and the dog was treated for 4
weeks based on sensitivity results. Following treatment,
the SwiveLock anchor and FiberTape were removed. In
both cases, owner responses were good to excellent for
all questions answered at 8 and 41 months, respectively.
The third complication was a late onset meniscal tear.
The dog had progressed well and achieved a level of ex-
cellent clinical function until 6 months postoperative
when the patient became suddenly lame in the operated
limb. Arthroscopic 2nd look examination revealed a me-
dial meniscal tear, which was treated with partial menis-
cectomy. At the time of initial stabilization, the dog had a
normal medial meniscus and a release was not performed.
Following the 2nd surgery, the dog made a full recovery
and was clinically sound at recheck one month after the
partial meniscectomy.
Our complication rate of 7.3% is consistent with other
studies reporting complication rates after treatment with
extracapsular stabilization. Cook et al. [15] reported a
12.5% major complication rate for TightRope15 proce-
dure. Casale and McCarthy [16] found a 17.4% compli-
cation rate associated with lateral fabellotibial suture pro-
cedures. There was no incidence of bone anchor pull out
which is, in contrast to a 21% of anchor failure after a la-
teral suture anchor procedure in a separate study [17].
The authors recognize several limitations to this study.
We did not track the progression of osteoarthritis on ra-
diographs or 2nd look arthroscopy when appropriate and
the presence of cranial drawer was not assessed while the
dog was sedated. Other limitations include the small
population size and the retrospective nature of the study.
Another limitation of this study is the potential for a
caregiver placebo effect. In a study evaluating patient
response to osteoarthritis, treatment it concluded that
caregiver placebo effect should be considered when de-
termining patient response to treatment based on owner
and veterinarian subjective assessment. [18] Functional
15TightRope; Arthrex Vet Systems, Naples, Florida, USA.

M. RASKE, D. HULSE 301
outcome was based on a subjective, client answered ques-
tionnaire. The questionnaire has been found to be repea-
table and valid for assessing lameness in dogs. [6]
5. Conclusion
The knotless SwiveLock bone anchor preloaded with 2
mm FiberTape provides good to excellent long-term cli-
nical function outcomes and a low complication rate in
dogs treated for CCL deficient stifles.
6. Acknowledgements
We would like to thank Dr. Abigail D. Mariano for as-
sistance with statistical analysis.
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