Cranial cruciate ligament disease (CrCLD) is a leading cause of lameness in dogs. There are many surgical and nonsurgical treatment options. Several recent studies show that properly performed tibial plateau leveling osteotomy (TPLO) provides the best patient outcomes in large and giant breed dogs.
Since the TPLO is a very technical procedure, superior patient outcomes with minimal risk of complications can only be anticipated when a highly trained team provides the pre-, intra- and postoperative care with conscientious attention to detail.
Precise patient positioning is required for the radiographs used in preoperative planning. These radiographs are often made immediately prior to the TPLO surgery because general anesthesia facilitates precise positioning. A metallic sphere of known diameter is placed at the level of the tibia so that the radiographic image can be calibrated for magnification. Prior to preoperative TPLO planning, the radiographs are reviewed first for supportive evidence of CrCLD and next to screen for evidence of comorbidities (patellar luxation, osteochondrosis, neoplasia, limb deformities, etc.) that may modify the treatment plan.
The mediolateral view is used to measure tibial plateau angle (TPA), determine the saw blade size, identify the proper osteotomy location and determine that necessary rotation can be safely performed on the patient's tibial morphology. Details of patient positioning and technique for TPA measurement have been described.1 The caudocranial view is used to determine the location of the palpable fibular head with respect to the joint space and to screen for tibial angular and torsional deformities.
The positioning of the osteotomy is a critical detail for safe and accurate tibial plateau rotation. While the mathematical ideal is to center the osteotomy upon the tibial eminence, an acceptable compromise involves a subtle shift of the osteotomy center to the intersection of the tibial long axis and the medial tibial plateau line. In practicality, this minor osteotomy eccentricity centers the osteotomy very near to a properly positioned proximal jig pin. Digital templates representing available TPLO saw blade sizes are positioned upon this point to determine the saw blade size that will protect the tibial articular surface (and menisci), allow for properly sized fixation implants and produce an appropriately sized and shaped tibial tubercle segment. In general, the osteotomy should produce a tibial tuberosity that gradually widens from proximal to distal and is of adequate size to avoid fracture in the postoperative period (rule of thumb: ≥ 10 mm in a large breed dog). Intraoperatively, it is important to accurately duplicate the planned position of the osteotomy and jig and there are several methods by which this can be done; identification of key points for blade position relative to palpable/visible intraoperative landmarks is the key to these methods. Evaluating the accuracy of actual osteotomy placement on postoperative radiographs to planned osteotomy location on preoperative radiographs is evidence of the sort of attention to detail that is required to develop expertise with this procedure.
The surgical technique, properly performed, requires great attention to detail and precision fostered by detailed knowledge of regional anatomy and development of acute 3-dimensional spatial awareness. A typical surgery resident in a US-based training program performs > 100 TPLOs under expert supervision before developing the expertise necessary to be the lead surgeon. Additionally, a trained and knowledgeable surgical assistant is invaluable for procedural precision.
Intraarticular structures (menisci, cruciate ligaments, articular cartilage, patella-femoral joint, synovium) are evaluated via arthroscopy or arthrotomy. Meniscal tears detected visually or via palpation with a blunt probe are treated as indicated; most commonly debridement or caudal horn meniscectomy. Torn CrCL remnants are debrided. There is considerable debate as to whether or not grossly intact and healthy portions of the CrCL should be preserved. A detailed description of the TPLO surgical technique has been published.1
Important details and tips will be included here:
Targeted and precise circumferential elevation of the soft tissues from the proximal tibia and packing with radiopaque marked gauze sponges protect the muscles and popliteal vasculature from injury during the osteotomy.
Use of a properly positioned jig reduces the likelihood of inaccurate osteotomy angulation, fibular fracture and fixation failure. The proper position for the proximal jig pin is ~ 3–4 mm distal to the articular surface at the approximate level of the medial collateral ligament (MCL). The articular surface can be identified using a 25 g needle passed through the MCL. It is important that the jig pin not excessively damage the MCL; this can be accomplished by reflecting the MCL slightly cranially with the pin or by making a discrete vertical ~ 3 mm incision in the MCL (oriented parallel to its fibers). Once the tip of the jig pin is properly positioned, it is inserted into the tibia using a slow-speed, high-torque power drill. The proximal jig pin is oriented parallel to the joint surface (perpendicular to the patellar tendon) and perpendicular to the sagittal plane of the tibia. If the jig pin has been properly oriented, the sagittal (flexion-extension) plane of the stifle will be parallel to the sagittal plane of the proximal jig articulation. Palpation of the pin as it exits the lateral tibial cortex allows one to evaluate its exit point relative to the preoperative plan. The distal jig pin is placed through the jig, parallel to the proximal jig pin, starting in the craniocaudal center of the tibia; slow-speed power, moderate pressure and irrigation are used to avoid heat necrosis in hard diaphyseal bone. The sagittal plane of the distal jig articulation may not be parallel to the extension-flexion plane of the tarsus if the patient has a tibial torsional or frontal plane (varus-valgus) angulation.
The proximal jig pin is cut at the level of the jig so that the saw blade can be positioned according to the preoperative plan. The surgical assistant helps to isolate the patellar tendon from the saw blade while the surgeon stabilizes the blade to accurately initiate the osteotomy in the planned location. Once the kerf of the cut is established, the surgeon is careful to orient the osteotomy down the "virtual" axis of the properly position proximal jig pin. An adjustable saw guide is available for blade bracing if desired (DePuy-Synthes Vet, Paoli, PA). The cut is made ~ 50% across the tibia. A small, sharp osteotome and precision caliper is used to make the "rotation marks" on each side of the osteotomy that correspond to the rotation necessary for correction of the TPA to 5°.1 The osteotomy is completed and the protective gauze sponges are removed.
A small Steinmann pin (3.2 mm for large breed dog) is placed from proximo-cranial to slightly disto-caudal (aimed toward the popliteal notch of the tibia) in the tibial plateau segment. This "rotator" pin should reach, but not breach the caudal tibial cortex as it will be used to as a bone holding forceps to rotate the tibial plateau about the proximal jig pin until the rotation marks align. No effort is made to make the medial tibial surface "flush" as this will induce a tibial deformity.
With the proper rotational correction manually held in place, a K-wire (1.6 mm in large breed dog) is passed from the tibial tubercle, across the osteotomy, and seated into the tibial plateau segment to maintain the desired rotation during bone plate application. This K-wire should be proximal to the terminal insertional fibers of the patellar tendon to reduce the likelihood of postoperative tibial tubercle fracture.
Limb alignment assessment and corrections are made at this time by manipulating the distal jig pin.
Use of anatomically pre-contoured locking bone plates & screws is recommended for technical ease as well as improved maintenance of tibial plateau rotation and improved osteotomy healing compared to conventional screws.
Screws are applied according to standard internal fixation principles and manufacturer guidelines using care to avoid placement of screws into osteotomy or joint surfaces. Anatomically pre-shaped locking bone plates are advantageous in this regard because the manufacturer has predetermined the fixed screw angulation (TPLO plate, Depuy-Synthes Vet, Paoli, PA); however the surgeon must be aware that the plate must be properly positioned because the plate, rather than the surgeon, determines screw angulation. Also, plate contouring alters the pre-set screw angulation relative to the tibial anatomy. The tibial tuberosity K-wire is typically removed after plate application.
Thorough lavage of the surgical field and meticulous anatomic closure of the surgical approach is performed. Short-term incisional protection with an adherent barrier dressing (TegadermTM, 3M, St. Paul, MN) is applied. Radiographs are made and critically analyzed. Detailed and attentive postoperative care is critical to the success of this procedure and has been described.1
1. Kowaleski MP, Boudrieau RJ, Pozzi A. Tibial plateau leveling osteotomy. In: Tobias KM, Johnston SA, eds. Veterinary Surgery - Small Animal. St. Louis, MO: Elsevier Saunders; 2012:947–957.