Ron Ben‐Amotz and Joshua S. Zuckerman Cranial cruciate ligament (CCL) rupture is the most common cause of pelvic limb lameness in dogs. Although numerous surgical techniques have been described to address this condition, the tibial plateau leveling osteotomy (TPLO) remains one of the most commonly performed among both board‐certified and non board‐certified surgeons [1–3]. TPLO was first described by Slocum in 1983 as a modification of the cranial closing wedge osteotomy (CCWO), and the theory behind the procedure has since been further evaluated in numerous cadaveric studies [4–6]. These studies tried to justify and confirm the theory that use of a radial osteotomy to level the plateau (to an angle of approximately 6.5°) neutralizes cranial tibial thrust, thus restoring stifle stability in the stance phase [7–9]. More recent studies, however, have found that about 30% of postoperative TPLOs continue to exhibit some degree of cranial tibial subluxation during the stance phase [10, 11]. Over the last four decades, many studies have reported the clinical outcome of patients following TPLO, with reported complication rates ranging from 9.7% to 39% [12–17]. Incisional complications, tibial tuberosity fractures, and implant failure were the most commonly reported complications after TPLO surgery [14, 16]. Swelling, bruising, and seroma formation may occur in the short or intermediate time period after surgery. Although these may not typically be considered major complications, they carry the potential for significant patient morbidity such as pain and lameness. Meticulous soft tissue handling and dead‐space closure (Halsted’s principles) will reduce their occurrence. Tibial diaphyseal fractures, avulsion fractures of the tibial tuberosity, patellar fracture, fibular fracture, and patella luxation are categorized as bony related complications [18–21]. Other reported complications are categorized as implant related, including intraarticular placement of a jig pin, K‐wire, or screw that can cause damage to the articular cartilage. Implants may also fail (bend, break, loosen) which can result in significant loss of limb function [12, 13]. Therefore, their immediate identification and prompt treatment are of utmost importance. Careful surgical planning, accurate execution of the surgical procedure, and increased surgeon experience will reduce the incidence of complications. The purpose of this chapter is to provide a comprehensive review of the reported complications and to provide the reader with a stepwise approach to prevention, early recognition, and treatment of these complications. The complications discussed will be divided into the timeframes in which they are most likely to occur: the preoperative, intraoperative, and both immediate (<14 days) and delayed (>14 days) postoperative periods. High‐quality, well‐positioned mediolateral and craniocaudal radiographs are necessary for thorough surgical planning [22]. These films should include the distal third of the femur, the stifle joint, and the tarsus to ensure appropriate positioning. To facilitate accurate positioning and mitigate the potential for motion artifacts, we strongly recommend that films are obtained with the patient under heavy sedation or a short general anesthetic protocol. We also strongly recommend use of a calibration marker placed adjacent to the tibia to ensure the accuracy of digital measurements [23]. To position the limb for the mediolateral (sagittal) radiograph, the tibia should be parallel to the beam/cassette, with both the stifle and tarsus flexed to 90° angles. During positioning, it is imperative to ensure that neither the femur nor tibia is rotated. In order to minimize projection artifact, the beam should be centered over the stifle joint. Provided there is no deformity present, both the tibial and femoral condyles should appear perfectly superimposed (Figure 10.1a). An appropriately positioned mediolateral radiograph allows not only for accurate measurement of the tibial plateau angle (TPA), but also for assessment of distal femoral deformities (both varus/valgus and rotational). It should also be used to determine an approximation of the appropriate radial saw blade to be used and for determining the location of the anticipated osteotomy. When digital radiography is used, additional software applications may be used to quantify the magnitude of the required tibial plateau rotation, and to determine whether this rotation will exceed the accepted “safe point” (the insertion point of the patellar tendon). Often, these software applications include templates of various TPLO plates, allowing the surgeon to preemptively determine the most appropriate implant size and the approximate location of the implant relative to the planned osteotomy (Figure 10.1b). When the limb is positioned for a radiograph in the craniocaudal (frontal) plane, the stifle joint should be extended and the tibia should again be held parallel to the beam/cassette with care taken to avoid internal or external rotation. In a well‐positioned film, the proximal aspect of the calcaneus should be observed bisecting the medial cortex of the distal tibia and the fabellae should be centered over the lateral and medial femoral condyles. Radiographs in this plane allow for identification and quantification of any angular or rotational deformities that may be present, as well as for identification of the location of the fibular head relative to the proximal tibia, which may be used as an intraoperative reference point to aid in screw placement and avoidance of articular penetration (Figure 10.1c). Overall, many of the reported intraoperative complications are the result of technical error. The authors believe that with surgeon experience, careful preoperative planning, and careful attention to procedural execution, many of these complications can be mitigated. As is the case with any surgical procedure, the potential for soft tissue complications (bruising, hematoma, seroma formation) may be minimized by careful attention to Halsted’s principles, with particular attention given to gentle tissue handling. During the initial approach, the saphenous neuromuscular bundle should be identified and preserved (Figure 10.2). This is especially important when TPLO is performed in small patients, in which case this structure may be found in a more superficial position and closer to the intended incision than anticipated. As the approach to the tibia continues, one must be meticulous in elevation of the aponeurosis attachments of the caudal part of the sartorius, semitendinosus, and gracilis muscles (Figure 10.2b,c) which will allow for robust soft tissue closure and therefore implant coverage, ultimately aiding in the reduction of soft tissue complications in the immediate postoperative period. During elevation of the muscle, it is imperative to identify the medial collateral ligament that lies deep to it at the caudomedial aspect of the proximal tibia. In some dogs, this structure may be obscured by a thin layer of fascia/fat that can be carefully removed with a gauze sponge in a gentle rubbing motion (Figure 10.2d). Figure 10.1(a) Appropriate limb positioning for a radiograph in the mediolateral (sagittal) plane. The stifle joint and the tarsocrural joint are flexed to a 90° angle and the tibia is positioned parallel to the cassette. Both the tibial and femoral condyles (medial and lateral) are superimposed. In dogs with femoral or tibial angular or torsional deformities, this usually cannot be accomplished. In this image, a ball marker has been used for calibration purposes. (b) The mediolateral projection is used for accurate measuring of the tibial plateau angle (TPA), determination of the appropriate saw blade size, plate size, and for the determination of the D1/D2 reference lines. Source: vPOP‐pro, VetSOS Education Ltd, veterinary preoperative orthopedic planning software. (c) Limb positioning for a radiograph in the craniocaudal (frontal) plane. The proximal and medial aspects of the calcaneus should be observed bisecting the distal tibial cortices and the fabellae should be centered over the lateral and medial femoral condyles. Next, the popliteus muscle should be partially elevated from the caudal aspect of the proximal tibia using a large periosteal elevator. In order to minimize muscle trauma and bleeding, the author (RBA) recommends elevating the muscle along with its associated fascia (Figure 10.2e). Care must be taken to ensure the periosteal elevator maintains contact with the caudal cortex of the tibia during elevation, as deviation into the caudal or lateral soft tissue may result in significant hemorrhage (discussed later). Calibrated preoperative radiographs are necessary to accurately determine the required plate size and for determining the appropriate location of the osteotomy [24]. Templated radiographs allow the surgeon to define D1, D2, and the size of the blade required to achieve the planned osteotomy based on these measurements [25–27]. Due to the somewhat variable morphology of the proximal tibia in dogs, it is important to confirm the accuracy of the preplanned measurements intraoperatively before performing the cut, ensuring the planned osteotomy line will not only intersect D1 and D2 but will also result in a cut that exits the caudal cortex of the tibia at a 90° angle. Figure 10.2(a) The saphenous neurovascular bundle (black arrow). (b) Identification of the aponeurosis of the semitendinosus, gracilis, and caudal part of the sartorius muscles. The black arrows indicate the location of the aponeurosis incision. The incision should commence distal to the aponeurosis attachment directly over the tibial diaphysis and continue proximally while remaining as close to the bone as possible to prevent muscle laceration. (c) Elevation of the muscular aponeurosis attachment to the proximal medial tibia. The black arrows indicate caudal reflection of the aponeurosis. Yellow arrows: medial collateral ligament. (d) Note the location of the medial collateral ligament (outlined in yellow) and the popliteus muscle (black arrow, cranial to the forceps). (e) Popliteus muscle elevation using a periosteal elevator. Note that the fascia is elevated along with the muscle. The medial collateral ligament is bordered by yellow lines. In order to identify the point of origin of D1, the insertion point of the patellar tendon on the proximal tibia (Sharpey’s fibers) must be carefully identified. In order to identify D2, an incision is made caudal to the medial edge of the patellar tendon just proximal to its attachment on the tibia, exposing the infrapatellar bursa (this also allows further cranial retraction of the patellar tendon, therefore decreasing the risk of iatrogenic trauma as the osteotomy is performed. The D2 point is then marked (Figure 10.3a). The blade may then be positioned so that it intersects both D1 and D2, allowing the surgeon to visualize the planned osteotomy. The blade should exit the caudal cortex at 90° (Figure 10.3b). Figure 10.3 (a) To mark D1, the caliper is placed with one arm at the insertion point of the patellar tendon (Sharpey’s fibers) and opened to the premeasured D1 value on the preoperative radiographs. For D2, the infrapatellar bursa (blue arrow) is opened, taking care to protect the patellar tendon (red arrow) by cranial retraction with a Senn–Miller retractor. The caliper arm is then extended to mark D2. The medial collateral ligament and the popliteus muscle are marked with yellow lines and a black arrow respectively. (b) Once D1 and D2 are marked, the appropriate size TPLO blade is selected. Care is taken to identify its exit point at a 90° angle to the caudomedial tibial cortex. In this image, a gauze sponge has been carefully packed between the elevated popliteus muscle and the caudal tibial cortex in order to decrease the risk of iatrogenic trauma to the cranial tibial artery (the distal continuation of the popliteal artery) during the osteotomy. Thermal necrosis may result in delayed healing and bone necrosis, and increases the risk of infection [27]. It is imperative to use copious lavage during any portion of the procedure in which significant heat may be generated at the bone–metal interface, including the osteotomy procedure, application of both the rotational and antirotational pins, and as screw holes are drilled. Hemorrhage resulting from iatrogenic trauma to the cranial tibial artery has been reported (Figure 10.4) [28–30]. Despite some disagreement among surgeons, the risk of arterial laceration is likely decreased by placing a radiopaque gauze sponge between the tibia and the elevated cranial tibial muscle laterally and the elevated popliteus muscle caudally [31, 32]. After the osteotomy has been completed, the sponges must be removed and the sites copiously lavaged with sterile saline to reduce retention of microscopic cotton particulate debris in the surgical site [12]. Figure 10.4 In this cadaveric image, one can identify the popliteal artery located at the caudolateral border of the tibia (red arrow) at the level of the stifle joint. The cranial tibial artery is located at the caudolateral border of the tibia distal to the joint. Yellow lines mark the medial collateral ligament. If mild hemorrhage is identified once the sponge has been removed, packing the site with an epinephrine‐impregnated sponge or use of another hemostatic agent such as Gelfoam® should result in cessation of the bleeding. More significant hemorrhage may require the use of hemoclips or suture. Identification of the lacerated artery may require further elevation and/or caudal retraction of the popliteus muscle combined with distraction of the osteotomy site. If this is ineffective, a lateral approach to the proximal tibia may be necessary to facilitate identification and control of hemorrhage at its source. In order to minimize this catastrophic complication, the author (RBA) uses blade and implant templates on preoperative radiographs (Figure 10.1b) to ensure the appropriate blade size is selected. If specialized templating software is not available, one can draw a circle (found in the menu of most commonly used digital radiography programs) at the site of the planned osteotomy on the mediolateral radiograph. The radius of the circle should correspond with available blade sizes, and the circle should be centered on the intercondylar eminences of the proximal tibia. Once placed, the proximal “exit point” of the circle should be identified and used to confirm it does not intersect with the patellar tendon (Figure 10.1b). In surgery, the proximal exit point of the osteotomy (D2) is identified following elevation of the infrapatellar bursa (Figure 10.3a). It is imperative to use a Senn retractor to retract the tendon cranially (away from the blade) as the cut is performed (Figure 10.3a). The surgical assistant should immediately make the surgeon aware of any “metal on metal” sounds or vibration of the Senn as this may indicate that the blade is at risk of coming into contact with the patellar tendon. A 3.2 mm (1/8 inch) pin (or smaller for small‐breed dogs) should be placed just caudal and proximal to the osteotomy in the proximal tibial segment. To further identify the appropriate placement site, a small depression in the bone just proximal to the osteotomy is palpated. The orientation of pin placement is from proximal and cranial to distal and caudal at an approximately 30–40° oblique angle (Figure 10.5a). A 1.6 mm (0.062 inch) Kirshner wire (or smaller for small‐breed dogs) is placed adjacent to the patellar tendon attachment line (Sharpey’s fibers) in the midpoint of the tibial crest in the frontal plane (Figure 10.5b). This will reduce the incidence of postoperative fracture of the tibial tuberosity [18]. All soft tissues are protected with a drill guide while the pin is advanced. The pin should be directed toward the caudal cortex proximal to the osteotomy line and distal to the joint surface. Placement of a 25 G needle into the distal aspect of the stifle joint is an effective and minimally invasive method for outlining the border of the joint (Figure 10.5c). Care should be taken to avoid completely advancing the needle into the joint in order to minimize the risk for iatrogenic meniscal damage. Once the plate is placed (with at least four cortices engaged in each bone segment), the K‐wire can be removed. It is important to evaluate the integrity of the pin once removed in order to assess for any implant breakage. If this occurs, further caudal retraction of the popliteus muscle will allow inspection to determine if the remnant of the pin is present exiting the caudal tibia. If present, it may be removed with a large needle driver and manual traction. If the tip cannot be found, it is likely that it is completely embedded within the bone and its retrieval is not critical. It is imperative to use copious lavage during placement of both the rotational and antirotational pins. Careful angulation of drill bits is necessary to avoid interference with other screws and the antirotational pin. This can be mitigated when locking plates are used, as the screw plate angle is predetermined. If a broken bit or pin is present within the bone, it is generally possible to bypass it with slight redirection of the drill or screw. In most cases, broken drill bits that are well seated within the bone will not result in patient morbidity, and therefore their retrieval is not necessary. However, a broken bit or pin that extends out of the bone carries the risk for soft tissue irritation that may result in morbidity, pain, and even further implant migration. Therefore, in these cases, we recommend that the offending implant be removed. Figure 10.5 (a) Identification of the insertion point for rotational pin placement. The rotational pin is placed at a 30–40° angle in the proximal tibial segment directed from cranio‐proximal to caudo‐distal. The pin should slightly penetrate the caudal cortex of the proximal tibial segment. The exit point may be identified with an index finger, taking care to avoid laceration of the glove during pin placement. For joint identification, a 25 G needle is “walked” proximally along the cranial border of the medial collateral until it is felt “dropping” into the joint. Care is taken to avoid introducing the entire needle into the joint as this can result in iatrogenic meniscal laceration. The green box represents the location of the entry point of the proximal jig pin. The jig pin is placed 5 mm distal to the articular surface (using the needle as a reference point) and caudal to the medial collateral ligament. The hatched yellow area represents a trapezoidal tibial crest. The light blue box represents the site for antirotational suture placement in case of identification of pivot shift. The medial collateral ligament is bordered by purple lines. (b) Identification of Sharpey’s fibers (black dotted line). This should be identified as a transverse tissue line that delineates the transition from the patellar tendon (bordered in green lines) to bone at the insertion point. (c) The osteotomy line (green arrow, black line), needle placement for joint identification (blue arrow), Sharpey’s fibers, and location of the holding pin (black arrow). Note the trapezoidal shape of the tibia below the osteotomy line (yellow color), bordered by the osteotomy, patellar tendon insertion, and the tibial crest. The black box indicates the antirotational suture placement site. The small yellow circle indicates a previously placed antirotational pin. Further elevation of the cranial tibial muscle on the lateral tibial surface can assist in identification of the exposed drill bit. A hand chuck can then be used to firmly secure and remove the broken tip. Inappropriate implant placement carries inherent risks. Common examples of inappropriate plate and screw application during TPLO include the following. Nonlocking screws that fail to penetrate the far (trans) cortex will result in less robust fixation both below and above the osteotomy line [33–35]. In order to achieve bicortical purchase, it is advised to add 2 mm of screw length to the measured depth of the drill hole when selecting the screw for placement. Fissure or fracture of the trans cortex as screws engage the bone can result in delayed healing and, in rare cases, even implant failure (Figure 10.6). In one paper, the incidence of transcortical fractures was higher when self‐tapping screws were used compared to non self‐tapping screws placed after the drill hole was tapped manually. It was speculated that the flute of the tap used for non self‐tapping screws is longer than the flute of a self‐tapping screw [32]. When a self‐tapping screw is used, before engaging the far (trans) cortex, it is advised to advance the screw in small movements (alternating a quarter turn counterclockwise with a half turn clockwise) until the screw is seated in the far cortex. This technique will help minimize an abrupt “push” of the screw into the far cortex, therefore decreasing the risk of cortical fissuring or even fracturing. Figure 10.6 (a) Postoperative TPLO using a six‐hole Synthes locking plate. The black arrow indicates a large medial and caudal cortical fragment noted once the screw was engaged into the trans cortex. The green arrow marks the loss of reduction at the osteotomy. (b) An 0.062 K‐wire was placed adjacent to Sharpey’s fibers and into the proximal tibial segment before the plate was removed to aid in reduction (black arrow). The plate was removed. The fragment was stabilized using point‐to‐point reduction forceps. A 3.5 broad locking Synthes plate was then applied. Notice that the first screw distal to the osteotomy was placed in lag fashion (yellow arrow), thus reducing the fragment into place. The second screw distal to the osteotomy is directed in a craniodistal direction to avoid the previously drilled screw hole (red arrow). The antirotational pin was left in place. The osteotomy gap has been reduced (green arrow). Source: All images courtesy of Dr. Brian Beale. If an audible crack is heard as the screw is engaged, the screw should be removed and a lateral approach to the tibia should be performed to aid in the identification of any potential fissures that have resulted. If a fissure is present, the plate should be removed and a cerclage wire applied (using standard cerclage wire application technique and principles). If the screw placement has resulted in a fracture and the fragment is of a large size, it is advised to repair the fragment with a screw placed in lag fashion (either through the plate (Figure 10.6b) or independent from the plate). Any other screws placed through the plate should then be directed away from the fracture site to avoid further displacement. If In most cases, if the fragment is small, simply redirecting the screw away from the fragment is sufficient. The effects of placement of a screw through a fracture have been reported. These include an increased risk of delayed and nonunion of the fracture site [36]. When there is any suspicion that a screw has been placed through the osteotomy line, the surgeon should remove the screw and redirect it. In cases where this is identified during postoperative radiographic evaluation, it is advised that the patient be returned to surgery and the offending screw redirected. In Figure 10.7a, double plating was used after a TPLO was performed (>70 kg dog). In the postoperative radiographs, one screw was identified in the osteotomy line; therefore, it was removed as there were a sufficient number of screws to achieve biomechanical stability (Figure 10.7b). Figure 10.7(a) Postoperative craniocaudal radiographs in which a screw is noted penetrating the osteotomy line (white arrow). (b) In order to minimize potential osteotomy healing complications, the screw was removed via a small incision directly over the screw head (white arrow). Precontoured locking TPLO plates are designed with a slight angulation at the neck of the plate to account for the natural contour of the proximomedial tibia, theoretically allowing the surgeon to place the plate directly on the bone without requiring additional bending. [31]. These plates are designed to be placed proximally, just distal to the articular surface. The proximal head screw is angled away from the articular surface (Figure 10.8a). In some cases (for example, if a large medial buttress is present), the surgeon may elect to further contour the plate to improve contact at the distal bone–plate interface. This can result in redirection of the proximal screw hole (Figure 10.8b) such that the screw may penetrate the articular surface [33] (Figure 10.9a,b). In order to decrease the risk of this potential error, we recommend taking the following precautions even for plates that have not undergone additional contouring. Figure 10.8(a) Precontoured plate. Note the direction on the proximal three screws. (b) The same plate following additional contouring. Note the direction change of the proximal three screws.
10
Complications Associated with Tibial Plateau Leveling Osteotomy
10.1 Introduction
10.2 Literature Review of Complications
10.3 Complications Specific to Tibial Plateau Leveling Osteotomy: Tips to Minimize Complications
10.3.1 Preoperative: Radiographic Positioning
10.3.2 Intraoperative
10.3.2.1 Surgical Approach (Recognition and Avoidance of Important Anatomical Structures)
10.3.2.2 Osteotomy Planning
10.3.2.3 Thermal Necrosis
10.3.2.4 Hemorrhage (Laceration of the Cranial Tibial Artery)
10.3.2.5 Patellar Tendon Laceration
10.3.2.6 Rotational and Antirotational Pin Placement
10.3.2.7 Broken Drill Bits
10.3.2.8 Complications of Implant Positioning
10.3.2.8.1 Inadequate Number of Cortices Engaged/Fissuring of the Trans Cortex During Screw Placement
10.3.2.8.2 Screws That Penetrate the Osteotomy Line Might Interfere with Osteotomy Healing
10.3.2.8.3 Screws That Penetrate the Joint
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