Complications Associated with Extracapsular Stabilization using Multifilament Material


8
Complications Associated with Extracapsular Stabilization using Multifilament Material


Matt Corse and Ian G. Holsworth


8.1 Introduction


Surgeons must understand the goals and vulnerabilities of each procedure they perform to maximize the probability of a successful outcome. Orthopedic surgery is a process that requires deliberate preoperative planning, intraoperative execution, and postoperative management to consistently produce the intended outcome. Surgeons must have a comprehensive understanding of common errors and pitfalls of a given procedure to avoid, manage, and correct complications. This chapter provides specific preoperative, intraoperative, and postoperative guides for the surgeon to help direct successful navigation through the process of performing extracapsular stabilization using synthetic multifilament material to manage canine cranial cruciate ligament (CCL) rupture in the dog.


8.1.1 Preoperative Goals of Extracapsular Stabilization



  • Predict the probability of success of the procedure in the individual patient.

8.1.2 Intraoperative Goals of Extracapsular Stabilization



  • Evaluate and manage the meniscus.
  • Produce a mechanically sound knee.
  • Minimize risk of infection.

8.1.3 Postoperative Goals of Extracapsular Stabilization



  • Maintain a mechanically sound knee.
  • Avoid infection.
  • Restore the patient to normal activity in a predictable manner.

8.2 Preoperative Planning


8.2.1 Introduction


It is a responsibility of the surgeon to determine whether a patient is appropriate for the procedure they plan to perform. Some patient characteristics may clearly identify them as inappropriate for a procedure, but more frequently patients have features with less conclusive risk profiles that the surgeon must consider carefully to help them decide whether or not to proceed. For this reason, it oversimplistic to provide a list of disqualifiers for a given procedure. Instead, the surgeon must consider how specific patient factors may impact operative and postoperative objectives and vulnerabilities of the procedure they wish to perform.


When performing extracapsular stifle stabilization procedures using multifilament material, a successful outcome requires a well‐executed surgery, bone tunnel maturation and periarticular fibrosis formation in the recovery period, and the avoidance of bacterial colonization of implants. The surgeon’s preoperative objective should be to determine whether these intraoperative and postoperative goals can be achieved with a high degree of certainty. To do so, surgeons should consider four questions during preoperative patient assessment.



  1. Can I easily perform the procedure in this patient?
  2. Does the patient have features that will stress the repair?
  3. Does the patient have predisposing risk factors for infection?
  4. Will this patient and this client be compliant postoperatively?

Failing to satisfactorily ask these questions or misjudgment in answering them during the preoperative period will result in deleterious consequences either at surgery or during the recovery period.


8.2.1.1 Can I Easily Perform the Procedure in This Patient?


Regardless of surgeon experience, the technical ease of extracapsular stifle stabilization varies with patient size, body conformation, and body condition score. Size of implants relative to the patient, ideal bone tunnel angles, and ease of dissection to identify isometric points should be considered preoperatively.



  • Very small patients: implants and bone tunnels may be too large to be accurately placed in an isometric position. Some bone anchors are too large for smaller patients. The surgeon needs to have a comprehensive knowledge of the implant options in their toolbox, and size tolerances specific to each implant.
  • Small patients with chondrodystrophoid (aka “hockey‐stick”) distal femoral morphology: in small patients with 90° caudal femoral metaphyseal deviation, it may not be possible to create a 30–45° tunnel from the femoral isometric point (Figure 8.1). Selecting a flatter trajectory of the bone tunnel or anchor socket that is more perpendicular to the joint line can result in:

    • implants or bone tunnels unintentionally being directed into the joint
    • increased implant stresses risking implant failure
    • increased abrasion on bone tunnels and socket exit sites predisposing to bone tunnel widening.

  • Dogs with dense body weight and small bone morphology: muscular dogs with relatively small bone morphology (like English Bulldogs) make identification of isometric points and optimal directing of bone tunnels challenging.
    Photo depicts 90° “hockey stick” morphology of the distal femur of a toy-breed dog. A 25 mm radiopaque calibration ball provides a size reference. The orange dot represents the optimal initiation point for the femoral bone tunnel. This distal femoral morphology combined with small patient size lead to the creation of a bone tunnel angled 30–45° away from the joint.

    Figure 8.1 90° “hockey stick” morphology of the distal femur of a toy‐breed dog. A 25 mm radiopaque calibration ball provides a size reference. The orange dot represents the optimal initiation point for the femoral bone tunnel. This distal femoral morphology combined with small patient size lead to the creation of a bone tunnel angled 30–45° away from the joint.


  • Morbidly obese patients: morbidly obese dogs can challenge the technical ease of identifying optimal isometric points.

8.2.1.2 Does the Patient Have Physical Features That Will Stress the Repair?


In dogs, the answer to this question is always yes, but some patients will have characteristics that may stress the repair more than others. Biomechanical factors should be considered when planning stifle surgery in the dog. As described by Slocum, the magnitude of cranial tibial thrust is enhanced by tibial plateau slope and the weight of the dog and is counteracted by passive restraint from the CCL and active restraint from the biceps femoris muscle and hamstring muscle group [1]. When extracapsular stifle stabilization is performed to manage CCL rupture, the suture implants function in part to passively restrain cranial tibial thrust. Evaluating these opposing biomechanical factors for each potential surgical candidate should influence surgeon decision making.



  • Long‐legged dogs: because stifle extension produces a less favorable lever arm for the caudal thigh muscles to resist cranial tibial thrust, tall, long‐legged dogs with a straighter stifle conformation may expose extracapsular stabilization implants to relatively higher loads as compared to shorter, squat dogs that generate more effective active muscle restraint to tibial thrust.
  • Dogs with dense body weight and small bone morphology: dogs like English Bulldogs that have heavy body weight relative to their smaller skeletal frame may require larger implants than their bone size can accommodate.
  • Morbidly obese patients: increased patient body weight enhances the magnitude of cranial tibial thrust, exposing extracapsular implants to higher loads.
  • Dogs with steep tibial plateau angles: tibial plateau angle (TPA) is not the sole determinant of load on the joint, but it is a metric that should be considered prior to every stifle surgery [2]. Taken in relation to other patient features (for example, considering the mechanics of a tall, long‐legged dog with long joint levers versus a shorter, squat dog with shorter joint levers), patients with steep TPAs may be better suited for corrective osteotomy procedures than extracapsular stabilization. Although there is no red line TPA directing whether one type of stifle surgical repair would be indicated over another, these authors recommend looking closely at all contributing patient factors, particularly when TPA exceeds 30°.

8.2.1.3 Does the Patient Have Predisposing Risk Factors for Infection?


Surgical site infections (SSIs) that are deep, implant associated and involve multifilament implant material are often major complications that can have catastrophic results. Bacterial colonization of surgical implants can occur during surgery, by local extension of superficial incisional infections postoperatively, or by hematogenous colonization in the postoperative period. Because of the devastating consequences of implant‐associated SSI, the surgeon must have comprehensive processes in the preoperative, intraoperative, and postoperative periods to minimize patient risk of implant colonization.


In the preoperative period, the surgeon is responsible for screening each patient for infection risk factors that may disqualify them from the procedure. Chapter 2 provides in‐depth information on ways to minimize SSIs. The surgeon must review patient medical records, perform a thorough physical exam (including evaluation of skin for any current pyoderma), and conduct a thorough client interview to assess their willingness and capacity for postoperative compliance. It is recommended to perform a complete blood work in order to rule out any systemic diseases that might preclude performance of the surgical procedure.



  • Patients with active or recurrent infections: pyoderma and recurrent urinary tract infection are two common forms of recurrent infection observed in dogs. Dogs with recurrent pyoderma that have had medical treatment may have an increased skin flora of antibiotic‐resistant bacteria that can increase the risk of a postoperative incisional infection. In addition, recurrent pyoderma can predispose to infection from hematogenous implant colonization at any point later in life. Similar risk for hematogenous infection can result from recurrent urinary tract infections. In patients with active pyoderma or urinary tract infection, the authors would recommend delaying extracapsular stifle stabilization until the infection is treated. Patients with recurrent pyoderma or recurrent urinary infections that are well controlled with medication or diet should remain on their treatment. In patients with recurrent skin, urinary tract, or other sources of infection, the surgeon must weigh relative risk and potential consequence of a surgical infection to determine whether to proceed with the procedure.
  • Immunocompromised patients: although studies have not documented an increased risk of postoperative infection in patients immunosuppressed from endocrine disease (Cushing disease, diabetes mellitus) or with conditions treated with immunosuppressive drugs, the authors recommend evaluating these patients cautiously when considering extracapsular stifle stabilization surgery using multifilament material.

8.2.1.4 Will This Patient and Client Be Compliant Postoperatively?



  • Noncompliant clients unwilling to prevent licking: patient self‐trauma to their incision (i.e., licking) is an avoidable but common cause of poor postoperative incisional healing in dogs. Clients must commit to strict use of an Elizabethan collar or other lick‐preventing device in the postoperative period while their pet’s incision is healing. The surgeon must clearly and persuasively educate about the significant and often costly consequences that can occur from a patient licking their incision. The surgeon must also assess a client’s willingness for compliance, as patients owned by clients unwilling to commit to this responsibility may be disqualified from the procedure.
  • Noncompliant clients unwilling to activity restrict their pet: long‐term mechanical integrity of the stifle repaired with extracapsular stabilization techniques depends on both bone tunnel maturation and periarticular fibrosis formation in the postoperative period. The bone tunnel maturation process requires 6–8 weeks of deliberate activity restriction to avoid damage to the wall of the bone tunnels during the vulnerable postoperative period. Periarticular fibrosis formation requires a similar time frame to sufficiently protect the synthetic suture implants from both cyclical fatigue and acute compromise from premature overactivity. Because of the importance of these processes, the surgeon must communicate about the postoperative plan with the client with persuasive and uncompromising clarity before proceeding with surgery. Surgeon failure to preoperatively identify and exclude clients who are unwilling to adhere to postoperative activity restriction may result in a deleterious outcome.
  • Noncompliant patients that cannot be activity restricted: extremely rambunctious dogs and dogs with severe separation anxiety are at higher risk of premature limb overuse. Sedation should be used liberally in these patients to help them through the recovery process. For these patients, it is highly advisable to perform a preoperative trial of the sedation and activity confinement protocol. This will help determine whether the protocol will be sufficient to control the patient postoperatively and assist in deeming them an acceptable candidate for the procedure.

8.2.2 Preoperative Planning Summary


Ultimately, every patient requires careful assessment in the preoperative period to help the surgeon decide if the patient is an appropriate candidate for an extracapsular stifle stabilization using multifilament material [2]. Only by weighing the technical requirements of the surgery, the spectrum of patient features that influence surgery and recovery, the factors that could compromise repair, and the client commitment to the process can the surgeon reasonably predict the likelihood of a successful outcome.


8.3 Intraoperative Procedure


8.3.1 Intraoperative Objectives of Extracapsular Stifle Stabilization with Multifilament Material



  1. Evaluate and manage meniscus.
  2. Identify optimal isometric points.
  3. Create appropriate bone tunnels and/or anchor sites.
  4. Apply appropriate tension to implants.
  5. Evaluate and manage implant and tissue creep.
  6. Maintain meticulous aseptic technique throughout the procedure.

As with all surgical techniques to manage CCL rupture, careful meniscal evaluation and treatment is a critical component of any extracapsular stabilization surgery. Failure to recognize meniscal tears and treat them when present may result in poor recovery and ultimately failed outcome. Surgeons who are insufficiently trained in meniscal evaluation and treatment should not perform stifle surgery. More information on meniscal treatment decisions can be found in Chapter 18.


Additional intraoperative focus must be aimed at identifying optimal isometric points, creating appropriate bone tunnels and/or anchor sites, applying appropriate tension to implants, and maintaining meticulous aseptic technique throughout the procedure. Failure to execute any of these goals will lead to a predictable detrimental outcome.


8.3.2 Intraoperative Mechanical Objectives


The goal of extracapsular stifle stabilization is to restore mechanics as closely as possible to normal [3–6].



  • Tarsal range of motion should be unimpeded throughout flexion and extension without restriction or conflict.
  • Stifle range of motion should be unimpeded throughout flexion and extension without palpable areas of restriction or conflict.
  • Cranial drawer and cranial tibial thrust should be 3 mm or less.
  • The tibia should not be fixed in external rotation, and the surgeon should be able to internally rotate the stifle 10–20° after tensioning suture implants.

Failure to achieve these goals can indicate a technical error in isometry, an error in implant/bone anchor placement, or errant implant tensioning. Intraoperative assessment of limb mechanics must be performed by the surgeon during each procedure to validate that mechanical goals have been achieved, and if problems are identified the surgeon must determine the correction required.


8.3.2.1 Identifying and Correcting Intraoperative Mechanical Errors


8.3.2.1.1 Impaired Tarsal Range of Motion:

Following extracapsular stifle stabilization with multifilament implants, stifle and tarsal range of motion should be unimpeded. Restricted tarsal range of motion following implant placement requires close inspection of the tibial bone tunnel and tibial implant path, as this typically indicates entrapment of the long digital extensor tendon (LDE) (Figure 8.2). Whether the origin of the tibial bone tunnel is at Gerdy’s sister (i.e., the tibial bony prominence demarcating the caudal border of the extensor groove) or within the proximal aspect of the extensor groove, the LDE should be reflected cranially to avoid entrapment. If Gerdy’s sister is used for the origin of the tibial bone tunnel, it is possible to improperly direct the tunnel cranially in a manner that breaks directly into the extensor groove which could allow the implant to cross over the LDE, entrapping it. LDE entrapment necessitates replacement of the implant with the LDE properly retracted cranially or redrilling a more caudally directed tibial bone tunnel.


8.3.2.1.2 Stifle Conflict Palpable During Range of Motion:

Following implant placement, restriction or conflict palpable at any point through stifle range of motion requires close inspection of isometric points. When femoral and tibial anchor points are isometric, the distance between these points and the resulting suture tension should remain constant throughout full stifle range of motion [7–15]. This creates smooth unrestricted stifle motion. Suture tension in nonisometrically placed suture implants will tighten or loosen through different zones of the range of motion, creating stifle conflict. Poor isometry can result in bone tunnel widening, implant failure, stifle joint mechanical compromise, and ultimately a poor functional outcome for the patient. When stifle conflict is identified, the surgeon must determine the cause of the isometric error and make the necessary correction.

Schematic illustration of lateral stifle anatomy relevant to localization of implantation sites of femoral and tibial bone tunnels/socket.

Figure 8.2 Lateral stifle anatomy relevant to localization of implantation sites of femoral and tibial bone tunnels/socket.


Evaluating Isometric Error

For the femur, the most common isometric error is starting the femoral bone tunnel/anchor point too far cranially. This creates an insufficient caudoproximal to craniodistal suture implant trajectory across the stifle joint, resulting in a poor mechanical and isometric outcome. Sufficient lateral femoral condyle exposure to allow accurate assessment of the femoral bone tunnel/bone anchor site relative to the distal femorofabellar joint space must be performed at every surgery. Sufficient lateral femoral exposure requires visualization of the transition of the nonarticular and articular cartilage of the femoral condyle just distal to the femorofabellar joint.


To achieve this exposure, the biceps fascia is incised and retracted caudally. Grasping the lateral fabella with thumb forceps, the distal aspect of the femorofabellar joint is tented and sharply incised with a stab incision with a #15 blade to expose the joint space. Once the femorofabellar joint space is identified, distal joint capsule dissection is extended by remaining just caudal and parallel to the lateral collateral ligament. The femoral bone tunnel should be made in the lateral condyle just distal to the femorofabellar joint at the transition between nonarticular and articular portions. Because there is a tendency to create the femoral tunnel too far cranial, the authors recommend trending the tunnel placement more towards the articular portion of the transition. The femoral tunnel should be angled towards the medial femur at the level of the proximal aspect of the trochlear groove.


For the tibia, the most common errors are starting the tibial bone tunnel either too far caudal or too far distal. This also results in insufficient caudoproximal to craniodistal suture implant trajectory across the stifle joint and a detrimental isometric consequence. Sufficient identification of the LDE tendon, lateral meniscus, and Gerdy’s sister must be performed at every surgery to guarantee an appropriate isometric tibial bone tunnel site (Figure 8.2).


Evaluation of Isometry Using the Suture Tensioner

When performing extracapsular stifle stabilization with multifilament material like the TightRope® (Figure 8.3) or Knotted SwiveLock® (Figure 8.4), using a suture tensioner with tensiometer (Figure 8.5) can provide the surgeon with an objective tool to assess for suture tension changes throughout stifle range of motion. The stifle should be maintained in slight extension when tensioning the suture [10]. Once the desired suture tension is applied to the suture implants using the suture tensioner, the knee can be flexed and extended with the suture tensioner still in place. With optimal isometric suture placement, the tensiometer reading should remain static throughout stifle range of motion, without fluctuating up or down. If the tensiometer reading deviates greater than 3–4 lb/ft, isometric points should be critically reassessed and corrected before proceeding.

Schematic illustration of tightRope implant placed on the lateral aspect of the stifle in correct TightRope ECS technique with two strands of 2 mm FiberTape tensioned appropriately and secured by multi-throw square knot over a four-hole tie-button on the medial tibia.

Figure 8.3 TightRope implant placed on the lateral aspect of the stifle in correct TightRope® ECS technique with two strands of 2 mm FiberTape® tensioned appropriately and secured by multi‐throw square knot over a four‐hole tie‐button on the medial femur.


8.3.2.1.3 Excessive Cranial Drawer or Cranial Tibial Thrust:

Following extracapsular implant placement and tensioning, the knee should be stable with less than 3 mm of cranial drawer present. An excess of 3 mm of cranial drawer indicates:



  • a problem in isometry
  • insufficient stifle tensioning
  • tensioning the implants while the stifle was positioned in excessive cranial drawer
  • failing to address implant or tissue creep
  • the presence of soft tissue between toggle/suture buttons and the bone.

Isometric Error

If excessive cranial drawer is present after implant placement, the surgeon should start with careful inspection of tibial and femur isometric points as previously described (see Chapter 6 for more information on isometric points). If an errant isometric point or tunnel is identified, a new site should be drilled and implants replaced if possible. If proper isometric points and bone tunnels are confirmed and cranial drawer persists, the surgeon must evaluate whether they insufficiently tensioned the implants, tensioned implants while the stifle was positioned in cranial drawer, failed to sufficiently address implant or tissue creep prior to securing the implants, or interposed soft tissue between suture toggles/buttons and bone.

Schematic illustration of swiveLock implant placed on the lateral aspect of the stifle in correct Knotted SwiveLock ECS technique with two strands of 2 mm FiberTape anchored at the femoral socket and tensioned appropriately and secured by multi-throw square knot over a four-hole tie-button on the medial tibia.

Figure 8.4 SwiveLock® implant placed on the lateral aspect of the stifle in correct Knotted SwiveLock® ECS technique with two strands of 2 mm FiberTape anchored at the femoral socket and tensioned appropriately and secured by multi‐throw square knot over a four‐hole tie‐button on the medial tibia.

Photo depicts tensioner with tensiometer suture tensioning device.

Figure 8.5 Tensioner with tensiometer suture tensioning device (Arthrex® AR‐1529).


Insufficient Tensioning

Use of a tensioner with tensiometer allows incremental tension application, assessment of knee mechanics achieved, and adjustment. In addition, when using the suture tensioner, the surgeon may cycle the knee once tension is applied to assess and manage implant or soft tissue creep (see section on creep, below).


Tensioning with the Stifle in Excessive Drawer

For dogs with an extremely unstable stifle and a large amount of cranial drawer, it is possible to tension implants with the tibia unintentionally positioned in a cranially subluxated position (i.e., tensioned while in cranial drawer). In this circumstance, after suture implants are tensioned, the tibia can easily displace caudally into a reduced position, functionally alleviating all tension on the implants. If excessive cranial drawer is present after tensioning implants, the surgeon should start by making sure that the stifle was reduced when sutures were tensioned. If it is determined that the tibia was in cranial drawer when implants were tensioned, an assistant should hold the tibia in a reduced position while implants are tensioned.


Implant and Tissue Creep

Soft tissue and/or implant creep can lead to excessive cranial drawer after implant placement [16–22]. Once implants are placed, tightened, and secured, the surgeon should be able to cycle the stifle 20–30 times through the range of motion (flexion/extension, internal/external rotation, cranial/caudal displacement) without alteration in stifle stability. If cycling the stifle leads to the development of cranial drawer, creep should be suspected.


Managing Creep Using the Suture Tensioner

Using a suture tensioner with tensiometer gives the surgeon a tool to assess and manage creep. Once the desired suture tension is applied to the suture implants using the suture tensioner, the stifle can be cycled 20–30 times through the range of motion with the suture tensioner still in place. If creep has been eliminated, the tensiometer reading should not drop after cycling and there should be less than 3 mm of cranial drawer present on stifle palpation. If cycling results in a loss of suture tension and excessive cranial drawer, the implants should be retensioned to the desired level, the stifle should be re‐cycled, and stifle stability should be reassessed. This process should be repeated until creep is eliminated and the stifle remains stable after cycling. If this process does not eliminate cranial drawer, the surgeon should evaluate for other causes of excessive cranial drawer including poor isometry, tensioning the implants with the stifle positioned in cranial drawer, or the presence of soft tissue between toggle/suture buttons and the bone.


Rescuing a Knotless SwiveLock Stabilization

A limitation of the Knotless SwiveLock® (Figure 8.6) is that creep is difficult to adjust for prior to securing the implants. If excessive drawer is identified intraoperatively following a Knotless SwiveLock® stabilization (due to either insufficient tensioning or insufficient elimination of creep), the Knotless SwiveLock® can be converted to a Knotted SwiveLock® implant without use of additional implants (Figure 8.4).

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Nov 6, 2022 | Posted by in SMALL ANIMAL | Comments Off on Complications Associated with Extracapsular Stabilization using Multifilament Material

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