SwiveLock Bone Anchor Stabilization of the Cranial Cruciate Ligament Deficient Stifle in Dogs: Clinical Outcome

doi:10.4236/ojvm.2013.37048

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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

Email: [email protected]

Received September 19, 2103; revised October 27, 2013; accepted November 6, 2013

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.

Open Access OJVM

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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