A Review of Extra-Articular Prosthetic Stabilization of the Cranial Cruciate Ligament-Deficient Stifle C

Review Article © Schattauer 2011 167

A review of extra-articular prosthetic stabilization of the cranial cruciate ligament-deficient stifle C. A. Tonks; D. D. Lewis; A. Pozzi University of Florida, Comparative Orthopaedics Biomechanics Laboratory, Department of Small Animal Clinical Sciences, Gainesville, Florida, USA

Introduction (17, 18). The screw-home mechanism is a Keywords term used to describe the cranial (gliding) Cranial cruciate ligament, extra-articular, Cranial cruciate ligament (CrCL) insuffi- and external rotation (sliding) motion the lateral circumfabellar-tibial suture ciency is a common cause of hindlimb tibia undergoes relative to the femur as the

Summary lameness in dogs that can precipitate me- stifle is extended (19). This phenomenon, Extra-articular prosthetic stabilization tech- niscal injury and inevitably incites osteoar- which has been comprehensively described niques have been used as a method of stabi- thritis (OA) of the stifle (1, 2). Adult, large in the human knee, is also thought to occur lization of the cranial cruciate ligament breed dogs are most frequently affected by in the dog’s stifle (17–21). (CrCL)-deficient stifle for decades. During CrCL insufficiency with Rottweilers, New- Multiple studies have evaluated the ef- foundlands, and American Staffordshire fects of CrCL insufficiency on stifle bio- extra-articular prosthetic stabilization, the prosthesis is anchored to the femur and Terriers being over represented breeds mechanics, kinematics, and gait (21–25). (3–5). Although the risk for CrCL insuffi- Cranial cruciate ligament deficiency alters tibia, and tensioned in the attempt to resolve femorotibial instability. The position of the ciency increases with age,many large breed stifle and hindlimb kinematics resulting in anchor points of the prosthesis is crucial for dogs sustain CrCL insufficiency in young cranial tibial translation, increased internal restoring a normal range of joint motion and adulthood (3–5). Cranial cruciate ligament rotation and adduction of the tibia es- mitigating alterations in prosthesis tension insufficiency in dogs is most commonly pecially during the stance phase of the gait due to progressive, mid-substance, patho- cycle (22, 23). Gait and kinematics analysis during motion. Recently developed techniques offer several innovations with poten- logical ligamentous failure (6).Despite nu- of dogs with unilateral transection of the tial advantages such as bone-to-bone fix- merous investigations, the aetiopathogen- CrCL did not reveal any improvement in ation, prosthetic materials with better mech- esis of CrCL insufficiency in dogs remains cranial tibial translation or coronal plane unknown (7–13). Dogs with unilateral instability over a two-year study period anical properties, and improved isometry of the anchor points. Whether these inno- CrCL insufficiency have a 37% incidence of (23). The kinematic changes that occur in vations provide clinically superior results to developing CrCL insufficiency in the the CrCL-deficient stifle alter loading of the the traditional techniques such as lateral contralateral stifle within a year of the in- articular cartilage and this has been postu- circumfabellar-tibial suture techniques has itial diagnosis of the initial ligament failure lated to be an initiating factor in the devel- yet to be determined. (14). Cranial cruciate ligament insufficien- opment of OA (22–24, 26). Studies map- cy can also occur as a result of a traumatic ping articular contact pressures and dis- injury, but traumatic CrCL rupture is less tribution have shown alterations in peak

Correspondence to: common and typically unilateral (15). and mean pressures as well as in contact Dr. Antonio Pozzi, DMV, MS, Diplomate ACVS The CrCL has a complex structure and is area in cadaveric stifles following CrCL Department of Small Animal Clinical Sciences composed of fibre bundles organized into transection (27–29). In addition, abnormal College of Veterinary Medicine two distinct bands: the smaller cranio- kinematics alter surface velocity and in- University of Florida PO Box 100126 medial band which remains taut in both ex- crease the plowing friction, which has been Gainesville, Florida 32610 tension and flexion, and the larger caudo- recently proposed as another mechanism United States lateral band which is taut in extension and to explain the relationship between abnor- Phone: +1 352 392 2226 lax in flexion (6, 16, 17). The CrCL func- mal articular surface interaction and the Fax: +1 352 392 6125

E-Mail: [email protected] tions to stabilize the stifle by preventing hy- development and progression of OA (21). perextension, cranial tibial translation, and Restoration of normal stifle kinematics and Vet Comp Orthop Traumatol 2011; 24: 167–177 doi:10.3415/VCOT-10-06-0084 excessive internal tibial rotation (16). The contact mechanics should be a primary ob- Received: June 3, 2010 CrCL also guides the stifle through its glid- jective of CrCL insufficiency treatment Accepted: December 22, 2010 ing and sliding motion, which is classically (25). The multiplanar motion of the stifle Pre-published online: March 3, 2011 described as the screw-home mechanism coupled with the complex structure and

Vet Comp Orthop Traumatol 3/2011 168 C. Tonks et al.: Extra-articular prosthetic stabilization

function of the CrCL, make optimal treat- cient stifle in dogs and to offer some per- technique, but in essence, it was the first ment of CrCL insufficiency problematic spective as to the rationale behind the effi- true circumfabellar technique (42). Flo’s and challenging (16, 19, 30). cacy of these described techniques. modified retinacular imbrication tech- Dogs suffering from CrCL insufficiency nique involved placement of both medial can be managed either with or without sur- and lateral circumfabellar-tibial sutures gery. Non-surgical management involves History (42). The sutures were anchored around activity modification, body weight man- the fabellae in the gastrocnemius muscles agement, and administration of analgesic The original extra-articular prosthetic stabi- and passed through a hole drilled in the ti- and anti-inflammatory drugs (31). Non- lization procedure described by Childers bial tuberosity (42). Securing the prosthesis surgical management can result in im- was a lateral retinaculum imbrication tech- in the proximal tibia was a novel concept, as provement of lameness in some dogs (31). nique performed by placing a series of catgut all previous techniques described using the In one study evaluating the efficacy of non- sutures in a Lembert pattern in the lateral patellar tendon as the cranial suture an- surgical management of dogs with CrCL fascia of the stifle (38). Pearson modified this chorage point. The location of the hole in insufficiency, 83% of dogs weighing less technique by adding a second layer of Lem- the tibial tuberosity was described as 6 mm than 15 kg had improvement of lameness; bert sutures to the lateral fascia as well as a distal to the proximal insertion point of the whereas, lameness improved in only 13% of series of medial imbrication sutures (39). patellar tendon and 6 mm caudal to the dogs weighing greater than 15 kg (31). Pearson advocated using heat-sterilized cranial surface of the tibial tubercle (42). An array of surgical techniques intend- medium-weight, synthetic, non-absorbable The stability afforded by the circumfabellar ed to address CrCL insufficiency have been suture material (39). An experimental study sutures was augmented by a suture placed described including intra-articular stabili- comparing Pearson’s extra-articular stabili- through the lateral fabellar fascia and then zation, extra-articular stabilization, and ti- zation technique and Paatsama’s intra-ar- passed just lateral to the patella to act as an bial osteotomy techniques (32–60). Intra- ticular stabilization technique found better imbrication suture (42). articular stabilization techniques utilize clinical and post-mortem results with the Six years later, Gambardella et al. pro- autografts, allografts, xenografts, and syn- extra-articular stabilization technique (32, posed a circumfabellar technique that in- thetic materials to replace the incompetent 39, 62). In 1970, a major advancement was cluded one lateral circumfabellar suture and CrCL (32–37). Extra-articular stabilization made by DeAngelis and Lau with the publi- two sutures placed through the lateral collat- techniques are predicated on transiently re- cation of the description of extra-articular eral ligament with all three sutures passing straining abnormal stifle motion until suf- stabilization by the placement of two Da- through the patellar tendon as the cranial ficient joint adaptation occurs to provide cron sutures or stainless steel wires in the lat- anchorage points (43). In 1990, Brinker et al. functional stability and improved limb eral retinacular tissues immediately caudo- described a modification of Flo’s technique, function (44). Tibial osteotomy techniques proximal to the fabella in the lateral head of called the three-in-one technique, in which alter tibial, and therefore stifle, con- the gastrocnemius muscle (40). The sutures medial and lateral circumfabellar sutures formation to restore functional stability to were also placed through the lateral third of were placed as Flo had described with the ex- the CrCL-deficient stifle (53–59). the patellar tendon just proximal to the in- ception that medial and lateral fascial imbri- Two categories of extra-articular stabili- sertion on the tibial tuberosity to limit cran- cation was added instead of placing the third zation techniques have emerged: tech- ial drawer motion, internal rotation of the suture that was originally described by Flo niques using transposed autogenous struc- tibia, and hyperextension of the stifle. The (42, 44). The three-in-one, or a modification tures or synthetic materials. Extra-articular DeAngelis and Lau lateral retinacular imbri- that involves placement of only one or techniques using autografts include pro- cation technique was one of the last imbri- multiple lateral circumfabellar-tibial tube- cedures such as fibular head transposition, cation techniques to be described, but it rosity prostheses, are techniques still com- popliteal tendon transposition, and long paved the way for the circumfabellar suture monly performed for extra-articular stabili- digital extensor tendon transposition techniques (40). zation of CrCL-deficient stifles in dogs (44, (48–51). Extra-articular stabilization tech- Nineteen seventy-five was a sentinel 61, 63–65). niques utilizing synthetic materials can be year in the evolution of extra-articular Another development in extra-articular subcategorized to include capsular imbri- prosthetic stabilization techniques, with prosthetic stabilization techniques was the cation, circumfabellar prostheses, anchor, two new techniques described (41, 42). One use of suture anchors (45). Suture anchors and bone tunnel techniques (38–47, 52). technique, described by Hohn and New- are used to provide secure, precise fixation With numerous modifications and ad- ton, involved performing a caudolateral of the prosthesis’ origin, insertion, or both. vancements reported over the years, extra- capsulorrhaphy and imbrication of the lat- Although the use of suture anchors had articular stabilization is still a technique eral retinaculum of the stifle (41). However, been described for other applications in that is commonly used today (38–52, 61). according to a survey of veterinary sur- dogs, Edwards et al. were the first to report The purpose of this article was to review geons’ preferred techniques, this technique the use of a human suture anchora for the clinical and experimental data pub- is almost never performed now (61). In lished regarding extra-articular prosthetic 1975, Flo also described what she referred a Mitek G2 tissue anchor: Mitek Surgical products, stabilization techniques for the CrCL-defi- to as a modified retinacular imbrication Norwood, MA, USA

Vet Comp Orthop Traumatol 3/2011 © Schattauer 2011 C. Tonks et al.: Extra-articular prosthetic stabilization 169 extra-articular suture stabilization of lactamj, and braided polyestersk, l, m were lene oxide had the least elongation and CrCL-deficient stifles in dogs in 1993 (45, other suture materials that were initially most strength preservation in comparison 66). Suture anchorsb, c, d, e have been devel- advocated due to the availability of these to the other materials tested (72). Stainless oped for veterinary use, and in vitro studies materials in large diameter sizes (up to No. steel wire has also been advocated for use as evaluating performance have been per- 7 metric for the polyesters) and thus a per- a prosthesis for extra-articular stabilization formed in dog tibiae and femora (67–69). ceived increased strength. Braided materi- of the CrCL-deficient stifle (73). A retro- Another extra-articular stabilization al, specifically coated caprolactam, has spective study evaluating dogs that under- technique was developed by Cook and been implicated in the formation of drain- went circumfabellar-tibial tuberosity termed the TightRope CCL f (47). The ing tracts (70). In one study, draining tracts extra-articular stabilization with stainless technique utilizes bone tunnels drilled in formed in as many as 21% of cases seven to steel wire found that 93% of dogs had one the femur and tibia to place a braided poly- 280 days after implantation of an extra-ar- or more breaks in the wire six month fol- ester coated polyethyleneg suture on the lat- ticular braided suture material (70). Sta- lowing surgery (76). Other materials, such eral aspect of the stifle. The suture is passed phylococcus aureus was the most commonly as an ethylene tetrafluoroethylene tie, through the tunnels and anchored to the isolated bacteria in these cases (70). Resol- nylon band, polyvinylidene fluoride, medial aspect of the femur and tibia where ution of the draining tracts occurred after braided polyester coated polyethylene su- the bone tunnels emerge using toggle but- removal of the suture in all cases; however, turesq, r, and tapeg, have been proposed for tons (47). Another similar transcondylar lameness resolved in only 65% of the dogs use in extra-articular stabilization; how- toggle systemh has also been described (52). after suture removal (70). The soaking of ever, most of these materials are not rou- Although limited clinical results for these braided suture material in chlorhexidine tinely used (47, 52, 61, 74, 77–79). new techniques are positive, long-term solution before implantation has been re- Materials such as nylon fishing line and clinical assessments and biomechanical ported to decrease the frequency of drain- monofilament nylon leader material must studies evaluating the TightRope CCL ing tracts (75). Nevertheless, the use of be sterilized prior to implantation. Several procedure and other similar techniques braided suture materials has been generally studies have been done to evaluate how dif- still need to be investigated (47, 52). supplanted by the use of monofilament ferent sterilization methods affect the materials in circumfabellar techniques mechanical properties of these materials (61). Monofilament suture materials are (71, 72, 80). Steam-sterilization, including Prosthetic material infrequently associated with the devel- one cycle and five cycles in an autoclave, as opment of draining tracts; however, No. 5 well as ethylene oxide sterilization have As the development of extra-articular pros- metric nylonn and polypropyleneo are the been the major methods evaluated. In in thetic stabilization techniques has prog- largest diameter materials readily available vitro mechanical studies, ethylene oxide ressed, numerous factors affecting the tech- (75). For this reason, larger diameter sterilization was found to conserve the ma- niques have been evaluated including the monofilament materials such as monofila- terial properties and handling character- prosthetic materials, methods of sterilizing ment nylon fishing line and monofilament istics of monofilament nylon leader ma- and securing the prosthesis, the locations nylon leader material have been used for terial better than steam sterilization (71, 72, where the prosthesis are secured, and the extra-articular stabilization (71, 72). In a 80). Steam sterilization undesirably in- position of the stifle at the time the pros- study comparing No. 5 metric polypropy- creases elongation and decreases stiffness thesis is secured (38, 42–44, 46–47, 61, lene, No. 7 metric multifilament polyester, of both fishing line and leader material 70–74, 80–86, 92–93, 103–105). A number and monofilament nylon leader material, (80). of materials have been proposed for use as the monofilament nylon leader material Securing the loop of material used as an extra-articular prostheses (38, 47, 61, was able to maintain a significantly greater extra-articular prosthesis is another vari- 70–74). Catgut was one of the earliest su- percentage of static tensile load compared able that has received considerable atten- ture materials used for extra-articular sta- to the other materials tested (71). A similar tion. Knotting the material or using a crimp bilizations (38). Polyesteri, coated capro- study comparing monofilament nylon clamp are the two methods commonly util- leader materials and monofilament nylon ized to secure extra-articular prosthesis fishing materials found that monofilament (42–44, 46, 47, 72, 80–86). Knotting the p b BoneBiter: Innovative Animal Products Inc., Ro- nylon leader material sterilized with ethy- material is the traditional method of secur- chester, MN, USA ing the extra-articular prosthesis and sev- c IMEX Veterinary Inc., Longview, TX, USA eral types of knots have been described for d Securos Inc., Charleston, MA, USA this use including square knots, clamped e FlexiTwist: Innovative Animal Products Inc., Ro- j Vetafil: S Jackson Inc, Washington, DC, USA chester, MN, USA k Polydek: Deknatel, Riverfalls, MA, USA square knots, sliding half-hitch knots, sur- f Tightrope CCL Technique: http://www.innovati l Mersilene: Ethicon, Somerville, NJ, USA veanimalproducts.com/tightrope.php m Ticron: Davis & Geck, Danbury, CT, USA g Fibertape: Arthrex Vet Systems, Naples, FL, USA n Ethilon: Ethicon, Somerville, NJ, USA h Transcondylar Toggle System: Securos Inc., o Prolene: Ethicon, Somerville, NJ, USA q OrthoFiber: Securos Veterinary Orthopedics, Fisk- Charleston, MA, USA (52) p Mason Hard Type Monofilament Nylon Leader dale, MA, USA i Ethibond: Ethicon, Somerville, NJ, USA Material: Mason Tackle Co., Otisville, MI, USA r Fiberwire: Arthrex Vet Systems, Naples, FL, USA

geon’s knots, and self-locking knots cranial drawer motion and abnormal vent postoperative meniscal injuries which (82–84). In vitro studies have demonstrated radiographic location of the crimp clamp, may necessitate additional surgery (75, 88). that the type of knot can influence the was found to occur in eight percent of 110 structural properties of some suture ma- cranial cruciate ligament deficient stifles terial loops (80, 83). For instance, when 27 stabilized with a circumfabellar-tibial Biomechanics kg monofilament nylon leader material was monofilament nylon suture (87). Crimp knotted with a surgeon’s knot the suture’s clamp placement does require additional In addition to the mechanical evaluation of stiffness was reduced by 27% and when the equipment and is currently only commer- the extra-articular prostheses, several bio- same material was knotted with a sliding cially available for use with specific pros- mechanical aspects of extra-articular stabi- half-hitch the suture’s load-to-yield was re- thetic materials. The loop configuration of lization techniques have been investigated. duced by 20% (83). Knot type, however, did the prosthetic material may be an addi- The lateral circumfabellar-tibial suture not affect the stiffness or load-to-yield of tional factor affecting its performance technique is the most widely used extra-ar- No. 5 metric nylon or polybutester (83). A (106). In a mechanical study, the strongest ticular stabilization procedure for the square knot in which the first throw is configuration, with a significantly higher CrCL-deficient stifle (64, 89). The lateral clamped to maintain loop tension as the mean ultimate load and load at yield, was circumfabellar-tibial suture technique is rest of the knot is tied has been evaluated the interlocking loop configuration (106). frequently performed by placing a prosthe- for a number of suture materials with no The double strand group with uneven loop sis around the lateral fabella and through a detrimental effects to the structural prop- length performed very poorly, with signifi- hole drilled in the tibial tuberosity. After erties of 27 kg monofilament nylon fishing cantly lower mean stiffness and ultimate passing the prosthesis under the patellar line, No. 5 metric nylon, or No. 5 metric load than all of the single strand groups tendon, the ends of the suture are secured polybutester (80, 83). Conversely, clamping (106). with a knot or a crimp clamp on the lateral the first throw of a square knot in mono- In most cases, the tension of the pros- aspect of the joint (ǠFig. 1) (64). Vari- filament nylon leader material has been thetic suture is not conserved for longer ations of this technique include passing the shown to increase failure load by two per- than six to eight weeks post-implantation suture through two bone tunnels in the cent and stiffness by 16%, and to decrease (76). The most common mechanisms of tibia or through a small hole drilled in the elongation by 12% (80). Thus according to prosthesis failure are elongation or rup- lateral fabella (90, 91). Huber et al., clamping the first throw of a ture, but pullout from the anchorage site The lateral circumfabellar-tibial suture square knot of leader material to aid in has also been reported (76, 81). Failure of technique is intended to resolve cranial ti- maintaining loop tension is preferable to the prosthesis by loosening may occur if the bial thrust by maintaining the tension ap- securing the same material with a sliding prosthesis is not anchored properly. Cir- plied to the prosthesis at the time of implan- half-hitch to maximize the suture’s struc- cumfabellar prostheses should be placed tation. Clinical guidelines regarding how to tural properties (83). through the femorofabellar ligament to an- tighten the prosthesis and on the amount of An alternative to knotting the prosthesis chor the prostheses around the fabella. A tension necessary to stabilize the stifle are is securing the loop with a crimp clamp (72, common mistake is to anchor the prosthe- unclear. It has been suggested that to elimin- 84–86). An in vitro biomechanical study sis caudal and distal to the fabella (75). The ate cranial drawer, the tibia should also be comparing sliding half-hitch knotted type of prosthetic material and the method externally rotated while the stifle is held at a monofilament nylon leader material to the used to secure the prosthesis effects the weight-bearing angle during the appli- same material secured with a crimp clamp mechanism of failure. Knotted or crimped cation of an extra-articular prosthesis (86, demonstrated that monofilament nylon nylon leader materials are more likely to fail 92, 93). The use of pointed reduction leader material secured with a crimp clamp by elongation, while nylon leader material forcepss have been described for this pur- had significantly less elongation, greater secured by a bone anchor may predispose pose (92). Self-retaining tensioner devices failure load, and the potential to achieve the prosthesis to failure by rupture (69, 80). can be also used to tension the prosthesis higher initial tension than the knotted Prosthetic materials with a high load-to- and test for cranial drawer before tying the prosthesis in single load-to-failure and cyc- failure and an increased resistance to elon- knot or securing crimps (94). A recent cada- lic tests (85). Vianna and Roe had similar gation such as braided polyester coated veric study investigated whether the joint findings when evaluating monofilament polyethylene materialsg, q, r are more prone angle at which the prosthesis is secured ef- nylon leader material secured with either a to failure by anchor pullout rather than fects prosthetic tension through a full range crimp clamp or a clamped square knot; al- prosthesis elongation or rupture (69). It of stifle motion for circumfabellar-tibial su- though the clamped square knot resisted a has been suggested that maintaining the in- ture and anchor techniques (95). Based on greater peak load, the leader material se- itial tension of the prosthesis for two the results of this study, tightening the su- cured with a crimp clamp had less elon- months should be sufficient to allow re- ture at about 100 degrees of stifle flexion gation and more stiffness in both static and covery and improved function. However, provided sufficient joint stabilization and cyclic tests when compared to the knotted some dogs may need more prolonged stabi- leader material (84). Premature crimp lization to allow for joint adaptation, to re- s AO pointed reduction forceps: Synthes, West clamp slippage, as deemed by significant gain satisfactory limb function, and pre- Chester, PA, USA

Vet Comp Orthop Traumatol 3/2011 © Schattauer 2011 C. Tonks et al.: Extra-articular prosthetic stabilization 171 uniform prosthetic tension throughout the full range-of-motion (95). These guidelines should be considered cautiously as cadaveric studies cannot replicate the complex in vivo motion of the joint. Guidelines regarding suture tension are also unclear, probably because other variables such as fixation points (soft tissue versus bone) and Fig. 1 mechanical properties of the prosthesis Craniocaudal and would affect long-term tension of the pros- lateral illustrations of thesis. Although complete elimination of a stifle with a lateral cranial drawer motion might be deemed de- circumfabellar-tibial suture technique. sirable because it is an abnormal motion re- Note that a small sulting from the CrCL insufficiency,excess- portion of the ‘extra- ive suture tension may be more detrimental articular’ suture is than minor joint instability (23). In a retro- within the joint. spective clinical study, dogs which had satisfactory functional outcomes had increased cranial drawer motion and greater stifle range-of-motion at a mean follow-up time of 34 months compared to dogs which had unsatisfactory outcomes (96). Excessive suture tension may predispose to early failure of the suture, decrease range-of-motion and abnormal intra-articular pressure. An ex vivo biomechanical study which investigated the effects of extra-articular stabilization upon the contact mechanics of the lateral compartment of the stifle found that excessive extra-articular prosthesis tension Fig. 2 caused increased lateral compartmental Craniocaudal and pressures (94). The effect of an over- lateral illustrations of tightened extra-articular prosthetic suture a stifle with an may be more relevant in smaller dogs and in anchor technique. non-weight-bearing conditions as it was shown that axial compression redistributed the abnormal pressure distribution to both cranial and caudal to the extensor groove). Despite positive clinical results, extra- compartments (94). The tibial crest position resulted in the least articular stabilization techniques do not Joint stability following extra-articular displacement supporting its use when achieve the optimal treatment goal of res- stabilization techniques has been investi- combined with the circumfabellar place- toration of normal stifle kinematics to the gated in cadaveric models (46, 97). Harper ment. The lateral graft technique evaluated CrCL-insufficient stifle (81, 98–101). A et al. evaluated cranial-caudal femoral dis- by Harper et al. and Snow et al. incorpor- radiographic study showed that CrCL-defi- placement following three variations of the ates the fascia lata into an autograft used as cient stifles stabilized with the De Angelis lateral circumfabellar-tibial suture tech- an extracapsular graft (46, 97). Snow et al. and Lau lateral retinacular stabilization nique and a lateral autograft technique modified the technique by using a referenc- technique had an abnormal instant centre using a material testing machine to apply ing instrument to find the relative isome- of motion (18, 40). Furthermore, ex vivo loads to the femur ranging from -65 N tric location for the fascia lata translocation evaluation of the three-dimensional kine- (caudal drawer) to 80 N (cranial drawer) technique (97). Both studies evaluated the matics of the CrCL-deficient stifle after sta- (46). The authors did not find any signifi- static stability immediately after implan- bilization with the modified retinacular cant differences in displacements between tation (46, 97). Future studies should inves- imbrication technique found that there was stifles stabilized with the circumfabellar-ti- tigate the stability of the extracapsular sta- a 30 degree decrease in stifle flexion and in- bial suture technique and intact stifles (46). bilization technique after cyclic fatigue. creased external rotation and abduction of Femoral displacement was also evaluated More importantly, further studies are war- the tibia (42, 102). Complete elimination of with the circumfabellar suture attached to ranted to determine if these techniques re- tibial rotation by the extra-articular pros- three separate tibial points (tibial crest, store normal joint kinematics. thesis is undesirable since a small degree of

corroborated in a retrospective clinical study (81). Although an isometric point has been described for the tibia, suture anchors are used infrequently to secure extra- articular prostheses to the tibia (81, 103). The prosthesis is generally secured through a hole drilled in the tibia positioned within or just caudal to the proximal aspect of the Fig. 3 groove of the long digital extensor tendon Medial, cranio- (103). caudal, and lateral The term isometry should be used cau- illustrations of a tiously when referring to anchorage points stifle with a modified of prostheses for CrCL reconstruction and anchor technique. stabilization. The origin and insertion of the CrCL are not isometric, explaining why some of the fibres become lax at certain angles of stifle flexion and extension (6, 16, 17). Thus, extra-articular suture anchor points cannot be isometric as the stifle is not a pure hinged joint (17–19). The anchorage points used for extra-articular stabilization may be better defined as ‘quasi- isometric’ because these points aim to be as close as possible to isometric. Cognizant of Fig. 4 this limitation, the goal of the stabilization Medial, craniocaudal, and lateral technique shifts to a ‘physiological illustrations of a isometry’ rather than a geometrical stifle with the Tight- isometry. Physiological isometry allows for rope CCL technique. some minor elongation, as long as the devi- ation throughout the range-of-motion re- produces that of the native CrCL. Physi- axial rotation is a normal part of stifle mo- tal plane isometric extra-articular suture ologic isometry should approximate nor- tion (16, 20). These studies highlight the placement points for the femur and tibia mal joint kinematics and may vary between limitations of the extra-articular stabiliza- (103). Hyman et al. and Hulse et al. found dogs. In considering physiological tion techniques in restoring normal kine- similar isometric points by measuring the isometry, the material properties of the matics and contact mechanics of the CCL- change in strain of a suture attached to dif- prosthesis cannot be ignored. Anchor deficient stifle (18, 102). ferent femoral and tibial anchorage sites points of stiffer prostheses such as FiberTa- Another variant of extra-articular stabi- (104, 105). Both methods for determining peg, FiberWirer, and OrthoFiberq should lization technique utilizes bone anchors the isometric points had limitations which more closely approximate isometry than and tunnels to fix the prosthetic suture were discussed in a recent study by Fischer less stiff prosthetic materials because the across the stifle. Following a standard ap- et al (95). In this study, the authors found stiffer prosthesis will generate much higher proach as for the circumfabellar suture that neither the circumfabellar suture nor forces if isometry is poor. Re-establishing technique, a bone anchor is placed in the the anchor techniques provided a constant normal joint kinematics remains the ulti- caudal aspect of the femoral condyle distal suture tension while moving the stabilized mate goal of any CrCL stabilization tech- to the lateral fabella. The suture is passed stifle through a full range-of-motion (95). nique; however, the ‘quasi-isometry’ of the through one or two tunnels in the tibia and The significant increase in tension ( >100 extra-articular prosthetic anchor points tied laterally (ǠFig. 2). Variations of this N) measured with the joint in flexion could may achieve a physiologic isometry that technique include using multiple anchors, predispose to over-constraint of the joint, can result in a good functional outcome a single or double tibial tunnel, or a toggle premature failure of the prosthesis, or fail- (47, 81). button placed on the medial aspect of the ure of the bone anchor (67–69, 81, 95, 103). Creep, stress-relaxation, ultimate load- tibia (ǠFig. 3) (79). One of the proposed Cadaveric studies have demonstrated that to-failure and other material properties of advantages of this technique is to allow higher acute load-to-failure of the anchor the prosthesis used for extra-articular sta- more isometric suture placement than occurs when the anchor is placed in the bilization, and the properties of the tissues other extra-articular techniques. In a caudolateral aspect of the lateral femoral to which the prosthesis is anchored (bone radiographic study, Roe et al. defined sagit- condyle (68, 69). These results have been or soft tissue) are additional variables that

Vet Comp Orthop Traumatol 3/2011 © Schattauer 2011 C. Tonks et al.: Extra-articular prosthetic stabilization 173

Table 1 The table summarizes some of the most important clinical studies on extra-articular stabilization techniques that have been published in veterinary literature.

Reference & Technique Study type & Subjects Force plate Owner Physical Radiographic level of evidence follow-up evaluated evaluation assessment examination examination Jevens DJ et al. (99) Modified retinacular Experimental 6 dogs Yes No No No Level 3 imbrication technique Randomized (MRIT) 20 weeks Budsberg SC et al. (98) MRIT using hard type Prospective 9 dogs Yes No No No Level 3 monofilament nylon Non-randomized leader material 7-10 months Conzemius MG et al. (100) Lateral circumfabellar Prospective 47 dogs Yes No No No Level 3 tibial suture Non-randomized technique (LS) 6 months Moore KW et al. (97) LS Retrospective 58 dogs No Yes Yes No Level 4 mean: 20.6 ± 15.1 months Guenego L et al. (80) Suture anchor Retrospective 42 dogs No Yes Yes Yes Level 4 technique mean: 18 months Elkins AD et al. (2) LS Retrospective 58 dogs No Yes Yes Yes Level 4 mean: 23 months (range: 6 - 132) Au KK et al. (107) LS Prospective 35 dogs Yes No No Yes Level 3 Non-randomized 24 months Cook JL et al. (47) Tightrope CCL Prospective 24 dogs No Yes Yes Yes Level 2 technique 6 months

can influence the effectiveness of circum- Fiberq, and 36 kg test monofilament nylon evaluating extra-articular stabilization fabellar-tibial or more isometric suture an- leader linep (107). FiberTapeg was deter- techniques, with the exception of a few chor or bone tunnel techniques. One of the mined to have the greatest stiffness, greatest non-randomized prospective studies, are potential advantages of the TightRope ultimate load at failure, and least elon- retrospective in nature with subjective data CCL (ǠFig. 4) is the utilization of a stiffer gation of the materials tested (104). The su- assessments (2, 81, 98–101). Despite this prosthesis. In a recent study, the materials perior mechanical properties of FiberTapeg deficiency in the literature, extra-articular properties of FiberTapeg were compared to may have advantages with respect to stifle stabilization techniques have generally four different commercially available stability in techniques that rely on soft tis- positive reported clinical results (81, extra-articular prostheses: No. 5 metric Fi- sue fixation. However, the relatively stiff Fi- 98–101). Moore and Read reported the berWirer, 36 kg test monofilament nylon berTapeg puts the joint at higher risk if the retrospective evaluation of 40 dogs ap- leader line, OrthoFiberq, and braided poly- prosthesis is over-tightened or if the proximately 20 months after using No. 5 ethylene fibret (47). The authors found that isometry of the fixation points is poor (94). metric polypropylene or 37 kg test mono- FiberTapeg had significantly less cyclic dis- Instances of poor application of the stiff filament nylon leader material in a circum- placement than the other materials tested prosthesis may detrimentally increase joint fabellar-tibial tuberosity technique to (47). FiberTapeg was significantly stiffer forces or cause premature failure of the achieve extra-articular stabilization of and had significantly greater yield loads extra-articular stabilization (94). CrCL-deficient stifles (98). Ninety percent and ultimate load-at-failure than the other of the owners were satisfied with the treat- prostheses (47). These results are sup- ment result based on telephone question- ported by an in vitro biomechanical study Clinical results naire (98). On follow-up examination of 11 by Burgess et al. which compared Fiber- of the 40 dogs, there was a 12 degree loss of Tape g, No. 2 metric FiberWirer, Ortho- There has been a scarcity of evidence-based flexion in the stabilized stifle; however, the literature thus preventing direct compari- majority of the dogs’ lameness improved sons of the multitude of extra-articular sta- following surgery (98). Improvement was t Braided polyethylene fiber used in LigaFiba Iso Toggle System: Jorgensen Laboratories, Loveland, bilization techniques that have been devel- also noted in a prospective clinical study CO, USA oped (30) (ǠTable 1). Most clinical studies performed in 12 dogs with unilateral CrCL

injuries (99). Force plate data was used as of surgical technique on limb function per- in dogs after TPLO or lateral circumfabel- an objective measure of limb function. formed in Labrador retrievers with unilat- lar-tibial suture (101, 110). A criticism of Prior to surgery, peak vertical force, associ- eral CrCL insufficiency and medial menis- that study was the use of early postoper- ated impulses, and weight distribution cal injuries, the force plate parameters of ative physical rehabilitation for dogs were significantly less in the affected hind- dogs which had extra-articular stabiliza- treated by lateral circumfabellar-tibial su- limb than in the contralateral limb without tion using monofilament nylon leader ma- ture compared with dogs undergoing stifle pathology (99). Dogs were examined terial were not significantly different to TPLO that had exercise restriction for six to again seven to 10 months following extra- those of dogs that had tibial plateau level- eight weeks after surgery (101). Despite articular stabilization using monofilament ling osteotomies at two and six months fol- elimination of this confounding factor by nylon leader material and excision of dam- lowing surgery (101). All dogs in this study using identical rehabilitation protocol for aged menisci (99). At the time of follow-up had medial meniscal injuries and the dam- both groups, no difference was found be- evaluation, peak vertical force, vertical im- aged meniscus was either partially or com- tween dogs treated with TPLO and lateral pulse and weight distribution had in- pletely excised, but only dogs that had circumfabellar-tibial suture (110). This re- creased significantly in the operated limb in extra-articular stabilization underwent ag- sult should be interpreted carefully as dogs all dogs (99). Despite the fact that three of gressive postoperative physical therapy. in the lateral circumfabellar-tibial suture the dogs had palpable drawer movement in Peak vertical force was 93% and vertical group were significantly lighter than dogs the stabilized stifle, there were not any sig- impulse was 96% of normal values in the in the TPLO group (110). It is possible that nificant differences detected in the ground limbs of dogs that had extra-articular stabi- dogs of larger size treated with lateral cir- reaction forces measured between the lization at six months following surgery. cumfabellar-tibial suture would have had limbs that had undergone extra-articular Peak vertical force and vertical impulse worse outcome. stabilization and the contralateral, normal were both 96% of normal in the limbs of Guenego et al. reported the retrospec- hindlimbs (99). Additionally, an experi- dogs that had tibial plateau levelling osteot- tive clinical and radiographic results of 42 mental study by Jevens et al. demonstrated omies at six months following surgery. Al- large or giant breed dogs with CrCL insuffi- that normal dogs which had a unilateral though only 40% of dogs that underwent ciency treated with a lateral extra-articular transection of the CrCL followed by a extra-articular stabilizations were con- braided polyester suture and bone anchors modified retinacular imbrication tech- sidered to have normal limb function based (81). The suture was secured using a suture nique using monofilament nylon leader on the author’s definition, an even smaller anchorj placed in the lateral femoral con- material did not have any significant differ- percentage (34%) of the dogs that had a ti- dyle and passed through two bone tunnels ence in peak vertical force and vertical im- bial plateau levelling osteotomy (TPLO), in the proximal tibia located just cranial to pulses at 20 weeks after extra-articular sta- were considered to have normal limb func- the groove of the long digital extensor ten- bilization as compared to preoperative tion six months following surgery. Thus in don. Twenty-one percent of the suture an- values in the same limb (100). In this study, this study the clinical results obtained fol- chors had pulled out of the femoral condyle the preoperative CrCL-intact stifle was lowing extra-articular stabilization were at the end of the 18 month study period; used to define normal limb function rather not found to be significantly different to re- however, lameness was only reported in than using the contralateral hindlimb due sults obtained in dogs which underwent a two of these dogs (81). Anchor pullout was to a significant increase in peak vertical TPLO (101). frequently associated with imprecise an- force in the contralateral hindlimb at all A recent study compared the short- and chor placement in the femoral condyle, oc- times points measured after CrCL transec- long-term functional and radiographic curring most often in cases of chronic tion (100). The redistribution of vertical outcome of CrCL-deficient dogs treated CrCL rupture. Anchor pullout was less forces in dogs with chronic unilateral hind- with identical physical rehabilitation often a problem if the anchor was placed in limb lameness may indicate that the use of regimens and either TPLO or lateral cir- the caudolateral aspect of the lateral femo- data from the preoperative limb more ac- cumfabellar-tibial suture (110). Peak verti- ral condyle, just cranial to the fabella (81). curately characterizes normal limb func- cal force and vertical impulse measured Two dogs required a revision surgery after tion in comparison to data from the with force plate analysis at three, five and the suture broke adjacent to the femoral contralateral hindlimb after unilateral seven weeks, and at six and 24 months post- anchor (81). No draining tracts were re- CrCL transection and stabilization (100). operatively were used to compare the func- ported despite the use of braided suture Careful consideration of how individual tional outcome. Radiographic evaluation material (81). The progression of radio- studies define ‘normal’ is of particular im- of osteoarthritis progression was done at 24 graphic signs of osteoarthritis was noted in portance when interpreting and compar- months postoperatively. In both treatment all cases irrespective of the isometry of the ing results between studies. Additionally, groups, peak vertical force increased from suture anchorage points (81, 103). A retro- the inclusion or exclusion of postoperative preoperative to 24 months, but the differ- spective radiographic study by Elkins et al. rehabilitation is another variable that af- ences between the groups were not signifi- evaluated 58 dogs after extra-articular sta- fects clinical outcome as documented by cant at any time point (110). This study bilization using a monofilament nylon su- Marsolais et al. and others (108, 109). In a confirmed the results of Conzemius et al. turen, p placed around the lateral fabella and prospective clinical evaluation of the effect where similar limb function was observed through a single hole made in the cranial

Vet Comp Orthop Traumatol 3/2011 © Schattauer 2011 C. Tonks et al.: Extra-articular prosthetic stabilization 175 edge of the tibial tuberosity at the level of cal improvement (40, 42, 45, 64, 65, 101). To 7. Wilke VL, Conzemius MG, Kinghorn BP, et al. In- heritance of rupture of the cranial cruciate ligament the insertion of the patellar tendon (2). date, no specific technique has been shown in Newfoundlands. J Am Vet Med Assoc 2006; 228: Radiographic follow-up ranged from six to to yield superior results for treatment of the 61–64. 132 months with a mean of 23 months (2). CrCL-deficient stifle (30). Future studies 8. de Bruin T, de Rooster H, van Bree H, et al. Evalu- Although dogs weighing less than 15 kg had should be directed toward outlining the vir- ation of anticollagen type I antibiody titers in syn- ovial fluid of both stifle joints and the left cranial a lesser degree of osteophyte formation and tues and inadequacies of the current tech- cruciate disease. Am J Vet Res 2007; 68: 283–289. returned to weight-bearing faster than niques to establish a foundation for a better 9. Muir P, Hayashi K, Manley PA, et al. Evaluation of dogs weighing greater than 15 kg, extra-ar- understanding of how each technique effects tartrate-resistant acid phosphatase and cathepsin K ticular stabilization did not mitigate pro- stifle and limb function. In vivo kinematic in ruptured cranial cruciate ligaments in dogs. Am J Vet Res 2002; 63: 1279–1284. gression of the radiographic signs of OA in analysis has been performed in human pa- 10. Muir P, Schamberger GM, Manley PA, et al. Localiz- either group (2). Once more this outcome tients with anterior cruciate ligament rup- ation of cathepsin K and tartrate-resistant acid implies that although potentially beneficial ture and anterior cruciate ligament defi- phosphatase in synovium and cranial cruciate liga- clinically, extra-articular stabilization is not cient-knees treated with different tech- ment in dogs with cruciate disease. Vet Surg 2005; 34: 239–246. a panacea for CrCL-insufficiency. niques to gain a better understanding of the 11. Hayashi K, Frank JD, Dubinsky C, et al. Histologic The clinical outcome of TightRope effects on knee stability, function, and the changes in ruptured canine cranial cruciate liga- CCL has been recently reported in a pros- development of OA (25, 112–116). Similar ment. Vet Surg 2003; 32: 269–277. pective study comparing TightRope CCL in vivo three-dimensional kinematic studies 12. Wilke VL, Conzemius MG, Rothschild MF. SNP de- tection and association analysis of candidate genes to TPLO (47). The authors evaluated these might be useful if performed in dogs with for rupture of the cranial cruciate ligament in the techniques by comparing subjective CrCL-deficient stifles stabilized with differ- dog. Anim Genet 2005; 36: 511–542. measurement of cranial drawer and cranial ent treatment techniques. There are also vast 13. Hayashi K, Frank JD, Hao Z, et al. Evaluation of liga- tibial thrust at eight weeks and six months individual variations and other facets to ment fibroblast viability in ruptured cranial cruciate ligament of dogs. Am J Vet Res 2003; 64: after surgery, and limb function using a consider such as differences in activity level, 1010–1016. validated client questionnaire (47). Subjec- degree of periarticular fibrosis, presence of 14. Doverspike M, Vasseur PB, Harb MF, et al. Contra- tive assessment of radiographic progres- meniscal pathology and meniscal treatment lateral cranial cruciate ligament rupture: incidence in 114 dogs. 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