6.1 Introduction

The use of an extracapsular suture (ECS) system for the attempted stabilization of the canine cranial cruciate ligament (CCL)‐deficient stifle is the oldest, most widespread stifle stabilization technique and most commonly used canine orthopedic joint procedure in the world. First introduced in the 1950s, the procedure has endured many changes in technique and materials [1, 2]. The procedure’s aim is to replace or augment the function of the native CCL that has been damaged and no longer provides sufficient stifle stability to the affected patient. This hopefully allows a return to acceptable function. Although the synthetic material used for the suture is varied and the location of suture placement has expanded over time, the procedural aim is the same.

The primary challenge that all ECS procedures face is true restoration of native stability. There is no definitive scientific evidence that this is possible. In fact, the scientific evidence points to a perceived improvement in patient function without true resolution of stifle instability. The attainment of functional stability is therefore the challenge that surgeons face when they elect to offer and perform an ECS procedure. It is very important that when discussing the ECS option with clients prior to performing the procedure, it is made very clear what the aim of the procedure is, what the possible end‐result will be for the patient and what the potential operative, immediate post‐operative, delayed post‐operative, and long‐term complications may be. Informed consent must be sought and without a frank and open discussion with clients regarding possible outcomes and complications, surgeons may find themselves in some difficulty during the patient recovery process. The recommendation to clients to perform ECS stabilization by many veterinarians has diminished significantly over time as other stabilization techniques have been developed and more research has been undertaken into the ECS effect and patient response [3–6].

The most common and significant complications encountered in ECS patients fall into four main categories:

• persistent stifle laxity
  
• infection
  
• subsequent meniscal tear
  
• progressive osteoarthritis.

While all these complications are possible and occur not infrequently, the most common complication is persistent post‐operative laxity. The causes of persistent stifle laxity include inherent issues with the ECS technique, the structural characteristics of the material used, including the technique of securing the material to itself or to the periarticular tissues, and technical errors during implantation.

A body of scientific research has been performed to investigate ECS construct stability in vitro and in vivo and much has been learned about the shortfalls of this technique [7–13]. There is currently a discrepancy between the objective investigational findings and perception of surgical success when owners and veterinarians are asked to evaluate the post‐operative patient’s subjective clinical progress. It appears that the correlation between objective post‐operative laxity and patient’s subjective function is not linear and is nonpredictive [14–17]. The use of objective gait analysis to determine the degree of return of normal limb function in post‐operative ECS patients has mostly shown a failure to achieve normal limb function [18–23]. In the small number of studies that did demonstrate objectively normal limb function post‐operatively, experimental, not clinical patients were measured [24] and some study conclusions were debatable [25]. When radiographic analysis of progressive osteoarthritis is used to determine ECS success in slowing or stopping degenerative joint disease, the ECS patients examined showed significant visible osteoarthritis progression over time [26–28]. In light of the published scientific data currently available, it is wise that the veterinarian presenting stifle ECS to clients does not state that normal stifle stability or limb function will be restored, and that degenerative osteoarthritis of the affected joint will progress over time.

6.2 Preoperative Patient Classification and Suitability for Extracapsular Suture Procedure

Prior to the decision to proceed with ECS stabilization, it is important to evaluate and understand relevant patient characteristics that may influence the veterinarian to choose ECS as a viable option. The patient factors that may play a role are age, size, activity level, and concurrent medical issues.

As the degree of post‐operative stability that is possible with the ECS technique is subnormal and continued instability can affect the patient’s ability to exercise comfortably, care should be taken to avoid selecting young, active, and large‐breed dogs as ideal ECS patients. As load to the postsurgical joint increases with more intense exercise, more prolonged exercise, larger patient size and weight, the inherent issue of post‐operative instability may increase and patient function may be compromised. Use of the ECS technique in older, smaller, and less active patients may be more appropriate.

In patients with concurrent immune‐mediated arthropathy, care must be taken when placing an intraarticular implant. The presence of monofilament or multifilament suture material within the joint capsule or exposed to the joint fluid could exacerbate the underlying condition and potentially lead to worsening of the joint inflammation present.

6.3 Preoperative Planning Strategies to Minimize Complications both Intra‐operatively and Post‐operatively

It is important that all patients scheduled for ECS stabilization undergo a detailed whole‐body orthopedic examination with particular care to examine and categorize the salient clinical features of the affected stifle joint. The presence and severity of clinical lameness, the presence of a partial versus complete CCL tear, the degree of palpable laxity (mild, moderate, or severe), the presence and severity of preexisting degenerative joint disease (mild, moderate, or severe) and the presence of concurrent patellar instability should all be determined and recorded in the medical record for future reference.

Radiographic examination of the affected stifle and contralateral stifle prior to surgery is also essential (See Chapter 1 for more information on the radiographic examination). The presence of primary bone or joint pathology (infection, neoplasia, immune‐mediated arthropathy) must be ruled out, the presence of bony abnormalities that may affect the surgical plan must be quantified, and the measurement of tibial plateau angle to avoid ECS performance in patients with excessive tibial plateau angle (eTPA) is paramount. Unfortunately, the TPA angle’s effect on ECS success has not been investigated closely enough to determine at what tibial plateau angle the ECS becomes an inappropriate choice for the patient. Below a measured TPA of 35° there were no significant correlations with objective or subjective outcome measures when ECS was compared to tibial plateau leveling osteotomy (TPLO) [29]. In the author’s opinion, a TPA above 35° is a criterion to move to a plateau leveling osteotomy procedure and above 30°, clients should be advised that concern exists about the ability of the ECS technique to control laxity sufficiently.

6.4 Operative Features of Extracapsular Suture

As the published techniques for ECS surgery have evolved over the past 50 years from the lateral retinacular imbrication technique to the knotless, interference anchor fixation [30–35], a corresponding evolution of surgical site preparation has occurred. As surgical site infection (SSI) has become more widely examined and the presence of antibiotic‐resistant bacterial strains with their concomitant biofilm has increased in the community, it has become increasingly important that patients and their surgical fields are prepared carefully and completely to minimize preoperative and intraoperative surgery site contamination. More detailed information on patient preparation to minimize SSI can be found in Chapter 2; the following is pertinent to the ECS procedure.

The choice of skin disinfectant [36–38], the type and arrangement of surgical draping [39], and the routine use of an antimicrobial‐impregnated incision drape [40–44] can all affect the inadvertent bacterial contamination of the surgical site during the ECS procedure. These protocol choices should be closely scrutinized and controlled by the primary surgeon. Evidence‐based guidelines continue to evolve in the veterinary patient, the surgical team, and for surgical site preparation. Because of this, definitive recommendations are not possible at this stage for many of these areas for the ECS procedure. Surgical teams must review current guidelines, adapt current protocols as new information in these areas becomes available, and continue to evolve surgical preparation protocols to limit surgical site contamination.

Skin sterilization agents have evolved from the universal use of aqueous povidone‐iodine‐based scrubs and solutions to the adoption by some surgical teams of chlorhexidine‐based products. Although experimental findings vary in the human surgical field, chlorhexidine‐based products appear somewhat superior in the prevention of post‐operative SSI [38].

The other significant change in skin antisepsis protocols has been the introduction of combination products. Applicators with a combination of povidone‐iodine or chlorhexidine and 70% plus isopropyl alcohol (Duraprep^TM, 3M, Chloraprep^TM_, BD) are now readily available. The development of a film‐forming iodine acrylate copolymer, povacrylex (Duraprep™) has enhanced water resistance to iodine removal and improved adhesive drape adherence. The combined use of both product types also more effectively reduced the contamination of human surgical wounds [45].

Once the patient’s leg skin has been effectively cleaned and prepared for surgery, the draping procedure is initiated. For more information on step‐by‐step draping for CCL surgery, please refer to Chapter 2. Briefly, placement of four corner drapes to isolate the patient leg and effective, water‐resistant, sterile foot covering is recommended for the ECS procedure. A larger fenestrated patient drape can then be placed over the foot to cover the four corner drapes and the rest of the patient’s body. Some human and veterinary surgeons use a single fenestrated drape or “key sheet.” This drape has a central elastic insert section that is fenestrated and forms a tight, sealed cuff around the thigh. Although this drape type is convenient, its use must not compromise an effective barrier between the patient’s aseptic and contaminated skin areas. Migration of the central cuff during surgery can lead to surgical site contamination.

Although an absolute consensus on the value of adhesive drapes in reducing surgical wound contamination and subsequent SSI rates is not possible in either the human or veterinary surgical arenas, it is thought that maintaining an occlusive barrier between the skin surrounding the surgical incision and the surgeon may allow less contamination of the surgical team’s gloves during procedural limb manipulation. As part of an asepsis protocol in canine stifle surgery, there is a documented decrease in SSI rates [46] although the many variables involved make it impossible to definitively state that impregnated adhesive drapes should be used for all canine stifle surgery.

6.5 Placement of Implant: Femoral and Tibial Insertion Sites and Options

Extracapsular suture implantation technique and materials have been examined extensively over the past decade and different combinations of the anatomical site, implant type, and means of securing the implant to the patient have been investigated [3447–55]. The major technical decisions made by the surgeon include the choice of attachment sites, synthetic material used, the preimplantation material protocol, how the implant is tensioned prior to securement (Figure 6.1), the method of securing the implant to itself and the patient, and the protocol to minimize intraoperative implant contamination.

The choice of femoral and tibial attachment sites is surgeon dependent but should be guided by the underlying research. There are no true isometric extraarticular anatomical locations that effectively replicate the intraarticular origin and insertion of the native CCL. The described sites on the lateral aspect of the stifle differ between different studies and are better termed quasiisometric as they approximate rather than accurately mimic the native sites in biomechanical testing. The femoral attachment site is either a soft tissue anchor site at the lateral femorofabellar ligament, with the ECS being looped around the fabella during implantation to capture the ligament (circumfabellar placement), or the identification of a site on the lateral femoral condyle distal to the fabellar articulation and caudal to the lateral collateral ligament where a bone anchor or femoral tunnel can be placed (femoral condyle tunnel). Tibial bone tunnels are utilized distally in all techniques.

The two methods of femoral attachment, circumfabellar or femoral condyle bone tunnel (FCBT), are inherently different and should be considered independently when assessing technique, efficacy, and complications. The circumfabellar lateral fabellotibial suture (LFTS) has a soft tissue‐based attachment proximally. Please refer to Chapter 7 for more information on the circumfabellar technique for ECS using nylon leader line. The femoral condyle bone tunnel technique (FCBT) includes both tunnel and the techniques that utilize bone anchors placed at the femoral tunnel origin site. The most well‐recognized form of the FCBT in the surgical literature is the Tightrope^® CCL. Detailed information regarding complications associated with using multifilament material can be found in Chapter 8.

The tibial insertion sites for bone tunnels have been investigated and vary between surgeons. The long digital extensor tendon groove is abutted cranially by Gerdy’s tubercle. Placement of the tibial fixation site 2 mm below the tibial joint line and either cranial, within or caudal to the extensor groove are all options that have been evaluated. There is no definitive evidence for the superiority of any of these sites and different ECS techniques utilize different points. The surgeon must become familiar with the proximal lateral tibial anatomy, be able to consistently localize the chosen landmark for tunnel initiation, and be able to consistently create an accurate, well‐formed tunnel for ECS material introduction.

6.6 Choice of Synthetic Material (Monofilament, Multifilament)

The major delineation between implant materials used is the choice of monofilament versus multifilament. Monofilament nylon has been investigated extensively in terms of its mechanical characteristics [56–58]. Multifilament polyblend polyethylene sutures are stronger and stiffer, and elongate less than nylon leader in direct mechanical comparisons [59, 60]. Choice of material between multi‐ and monofilament affects the method that can be used to secure the material. Monofilament material does not interact with bone anchors as the suture is prone to breakage where it is passed through an anchor eyelet and has too much volume to be pushed into a tunnel alongside a bone interference anchor. Nylon monofilaments are not used routinely in the FCBT technique. For more information on the ECS procedure using nylon monofilament, please refer to Chapter 7.

Biomechanical comparison of traditional round core suture multifilament with a circular cross‐section to an ovoid cross‐section suture tape showed suture tape had greater knot security, ultimate load to failure, and tensile stiffness [61]. Direct comparison of the two material types in a short‐term LFTS outcome study found a higher failure rate with knotted polyethylene multifilament LFTS versus knotted monofilament nylon LFTS; importantly, all multifilament failures were due to suture pull‐through of the fabellofemoral ligament, not failure of the suture material itself [62]. Replacing the circular cross‐section multifilament suture with an ovoid cross‐section tape suture may decrease the propensity for the multifilament material to saw through soft tissue attachments under tension. In human tendon repair, polyblend tape performs more favorably than circular polyblend round suture, with a greater mean load before suture pull‐through [63]. Immature bone tunnel damage from multifilament sutures within the FCBT tunnel is recorded and care must be taken to allow bone tunnel maturation prior to excessive stifle motion to allow the tunnel maturation to occur post surgery.

6.7 Prefatigue and Tensioning of Material

Prior to placement of ECS implants, many surgeons prefatigue the ECS suture implants and remove early elastic deformability present. Prefatiguing is particularly relevant for monofilament nylon sutures. The idea of prestretching ECS implants is followed by many surgeons using nylon leader line as monofilament nylon has high memory and it is proposed that early elongation of suture length occurs. How effective pretensioning is at minimizing early post‐operative suture loosening has not been examined scientifically. The tensioning of lateral ECS sutures has also been investigated [64, 65] along with its effect on lateral stifle compartment pressure and contact area [66]. Large variability exists between different methods of tensioning and securing LFTS. The use of a mechanical tensioning device increases LFTS construct tension. However, this creates high tension within the lateral compartment which alters contact pressures within the joint in cadaver models [66]. A tensioning device is routinely recommended for the FCBT Tightrope^® CCL technique (Figure 6.1) with recommended tension limits adjusted dependent on patient size.

Ideal ECS suture tension provides maximum stability without significant increases in joint contact pressures and without limitation to stifle range of motion. Appropriate tension is assessed clinically by testing drawer, thrust, and stifle flexion/extension after securing the suture. If the suture allows cranio‐caudal instability, the tension is too low. If the suture restricts flexion/extension, the tension is too high or anchor locations are suboptimal.

6.8 Method of Securing the Material

There is conflicting published peer‐reviewed literature utilizing cadaver limb testing regarding whether the strength, resistance to cyclical loading, and overall stability of a knotted multifilament, polyblend polyethylene implant with bone tunnel fixation (FCBT Tightrope^® CCL) are superior to a knotted or crimped monofilament nylon or polyethylene multifilament LFTS construct [10, 14, 34]. As experimental load increases and cyclic loading is performed, both construct types failed to control cranial translation (caudal femoral subluxation/cranial tibial subluxation) completely, although the Tightrope^® CCL (TR) construct resisted cyclic loading for more cycles in one experimental design [34]. The native CCL was five times stronger than either construct type [10]. Internal rotation is better controlled than cranial translation with all constructs although it does not reliably restore normal rotational stability [12–14].

There is considerable discussion about the type of knot employed (for example, square vs slip knot) to secure sutures with wide variation between knot types and individual surgeon’s results in achieving optimal knot security [66–68]. The use of suture crimp clamps to secure nylon LFTS sutures is common and demonstrates an appreciable biomechanical advantage over knotted LFTS sutures [57,69–73]. Additionally, the use of bone anchors has expanded over the past decade with biocompatible interference anchors placed into FCBT bone sockets to decrease complications with traditional eyed anchor suture interface damage and allow knotless fixation of FCBT constructs to the patient bone [74–76]. Cadaver biomechanical testing of the knotless interference anchor construct showed a trend toward increased resistance to cranio‐caudal instability with dynamic cyclical testing when compared to a crimped nylon FTS construct [34].

6.9 Intraoperative Contamination and Avoidance Strategies

Of significant ongoing concern with ECS using multifilament material, and a real focus for surgeons, is the issue of intraoperative bacterial contamination of surgical sites and implants. There is considerable investigation of intraoperative interventions in human surgery with mixed evidence of efficacy [43]. It is well established that up to 80% of SSIs involve the presence of a bacteria‐produced biofilm. This biofilm‐mediated resistance to treatment of SSIs associated with biomedical implants is termed antimicrobial recalcitrance and allows persistent bacterial organisms to survive on the surface of implants in the face of patient immune‐mediated defenses and the administration of antibiotics [77]. If biofilm is present, it is frequently necessary to remove colonized implants to allow infection resolution; in the context of ECS, early removal of the implants negates any stabilizing effects of the surgery, highlighting the importance of prevention of infection.

Evidence‐based strategies for prevention of microbial biofilm development include weight‐based antibiotic prophylaxis, skin antisepsis at the surgery site, maintenance of normothermia, glycemic control, antimicrobial sutures, and the use of surgical site irrigation. The use of intraoperative irrigation solutions is strongly recommended [78] but both bactericidal and patient cytotoxic responses have to be considered [79, 80]. The simplest fluid to irrigate with is an isotonic solution such as normal saline, but of growing interest is the use of aqueous dilute 0.05% chlorhexidine gluconate as an antiseptic irrigation agent in human surgery, with reported favorable responses in both human and animal studies [78,81–83]. Surgeons should carefully examine the scientific evidence and the pros and cons of implementing antiseptic solution lavage before implementing a change to their surgical protocol. Antiseptic lavage solutions must be prepared immediately prior to surgical use, maintained in sterile form, and used judiciously with thought to what tissue is exposed to them and their potential cytotoxic effects on those patient tissues.

Additional strategies that may be used for prevention of surgical site contamination include double gloving, use of thicker orthopedic surgical gloves, glove changes, and use of paper impervious gowns instead of reusable gowns [84–86]. Outer glove exchange or placement of an overglove immediately before handling implants is recommended to minimize intraoperative contamination (Figure 6.2).

Another strategy to reduce the rate of implant contamination is to keep all implants in a sterile condition until immediately before implantation. By avoiding implants being exposed to surgical operating room airflow and premature handling by operative staff, the rate of preimplantation contamination can also be reduced. Informing operating room staff of implant exposure and handling protocols is vital in implementing surgical protocol success and achieving a decreased rate of implant contamination and subsequent SSI. The primary surgeon is responsible for initiating and maintaining intraoperative protocols and should direct implant handling in a clear and thorough fashion to minimize confusion and error amongst all personnel.

6.10 Soft Tissue Plane(s) Closure and Material Used

Following ECS implantation, closure of the surgical site should be performed in an efficient and timely fashion. With multiple layer closure necessary for all major procedures, the selection of suture material and closure pattern should reflect the tissue type, its rate of healing, and the tissue plane closure strength required. The use of antibacterial sutures (triclosan‐coated) has been investigated in human surgery and a significant reduction in SSI rate has been found when triclosan‐coated sutures are employed [87–91]. Published veterinary surgical research is limited in this area but no significant benefit was demonstrated when triclosan‐impregnated suture was used for closure of tibial plateau leveling stifle stabilization [92]. The choice of skin suture, intradermal suture, or skin staple placement in terms of inflammation or infection development at the surgery site is unclear, with no clear scientific agreement on the relative merits of any of these strategies [92–94].

6.11 Identification of Intraoperative Complications

The development of intraoperative complications is not uncommon in stifle surgery and is influenced by the inherent difficulty of the surgical technique employed, the surgeon’s knowledge and experience in performing the chosen technique, and the individual challenges inherent in the broad range of patient size and differences in anatomy. In small, overweight, and heavily muscled breeds, the dissection of the lateral aspect of the stifle can be challenging. Meticulous attention to anatomical detail and surgical landmarks is essential in avoiding excessive tissue dissection trauma. Difficulties are encountered with dissection medial to the biceps femoris fascia and the fascia at the caudo‐distal aspect of the stifle adjacent to, and distal to, the lateral fabella. In this site inadvertent damage to local blood vessels with resultant hemorrhage can obscure important fabellar and femoral anchor site anatomy and result in incorrect ECS placement. The common peroneal nerve is also found running over the gastrocnemius muscle head in this location and entrapment of the nerve course during ECS placement is possible when a circumfabellar LFTS suture is used.

The intraoperative techniques used to ensure ECS implants acutely eliminate or significantly reduce cranio‐caudal stifle instability and excessive internal tibial rotation vary according to personal preference, the ECS procedure variant used, the ECS material employed, and the use of a suture tensioner with or without a tensiometer. There is no universally accepted technique at the current time and there are no scientific data that support one technique as being the most successful. Individual surgeons who hand‐tighten ECS use their judgment and experience to determine the tension prior to either knotting or placing suture crimps. Use of a tensiometer to set overall suture tension to a predetermined measurable level increases objectivity when assessing operative suture tension. When used in two‐strand suture constructs, the tensioner with tensiometer allows tension on the overall construct to be set and maintained with one suture strand while the nontensioned suture strand is secured to itself by knot or crimp. There is no evidence that the suture tension chosen at surgery is maintained post surgery once joint motion resumes and a post‐operative loss of suture tension, and therefore joint stability, is possible [95].

It is important when attempting to restore the normal anatomical relationship between the femur and the tibia that prior to final securing of the implant, any inherent creep (increase in length) in the suture material and loss of established suture tension due to soft tissue compression be minimized by preplacement loading and tensioning of suture material, by flexing and extending the stifle multiple times after initial suture placement and retensioning of the ECS construct after this process. The stifle joint angle at final tensioning and securement should be in slight extension and not flexion [50].

6.12 Evaluation and Identification of Immediate Post‐operative Complications

In the first 2 weeks after ECS surgery, the development of complications is termed immediate. The most common issues during this stage include excessive patient pain, failure of the patient to commence limb use, and the development of a SSI.

6.12.1 Excessive Patient Discomfort

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