The surgical procedure is explained step by step
Positioning of the patient. Dorsal recumbency with abducted legs. The leg to be operated on should be maneuvered so that the axial alignment can be evaluated by flexing and extending the stifle. The surgical access is centered on the medial side of tibial crest.
The skin incision is performed about at one third of the tibial width, and extends from a couple of cm proximal to the insertion of the patellar tendon to one cm distal to the tibial crest.
The crural fascia is incised and retracted. This usually causes a minimal bleeding. The incision is deepened caudally to the patellar ligament insertion, allowing to enter the joint capsule.
The Gerdi tubercle is palpated on the lateral side of the joint. Then, a 1.5-mm K wire is inserted in the joint opening, and pushed until it can be palpated closed to the Gerdi tubercle. Use this K wire as a landmark for the most caudal point of the tibial osteotomy, which lies on the same frontal plane of the Gerdi tubercle.
A 1-mm K wire is inserted into the proximal tibia, close to the joint, in the same cranio-caudal position as the intraarticular wire. The limb is positioned vertically, so that its sagittal plane can be evaluated. The K wire inserted in the tibia should move in the horizontal plane. If not, it can be bent manually until it lies on the horizontal plane. This will assure that the osteotomy will be performed on the frontal plane of the tibia.
Insert a second 1-mm K wire in the calculated position in the distal part of the tibial crest, holding it parallel to the first one. If the surgeon prefers to perform a Maquet’s hole in the distal tibial crest, the drill bit can be inserted instead of the K wire, but with the same criteria.
Insert the two K wires through the slot of the TTA guide. They can slide in the slot in order to find the position where the guide best fits with the tibial surface. If a drill bit is used instead of the distal K wire, it should be placed through one of the larger holes in the guide. Put the distractor underneath the patellar tendon, in order to protect it during the osteotomy procedure.
Usually, the guide is used just to perform the first cortical cut, and then removed to better visualize the osteotomy direction. The saw blade should be held on the same plane of the wires or drill bit. Once the osteotomy path is defined, the wires or drill bit are removed and the osteotomy completed. It is mandatory to flush with saline throughout the process to avoid bone thermal necrosis.
Once checked that the osteotomy is complete, the advancement of the tibial tuberosity should be performed very progressively, taking advantage of the visco-elastic properties of the bone, in order to prevent the potential fracture of the distal crest. The distractor should be positioned at the very proximal extremity of the osteotomy, to avoid any interference with the positioning of the wedge.
An advancement one mm larger than the scheduled wedge should be achieved. The distractor maintains the opening while the wedge is introduced. The advancement required is calculated preoperatively. The depth of the osteotomy is measured with a depth gauge and represent the width of the wedge.
Despite the fact that the calculated wedge is inserted in the osteotomy gap, an intraoperative tibial compression test should be performed, to check for any residual joint instability.
When the surgeon experiences problems in introducing the wedge, instead of keep going distracting the osteotomy, which can increase the risk of fracturing the tibial crest, an impactor can
be used to facilitate its introduction. Usually a firm stroke it is enough to seat the wedge inside the osteotomy gap.
The tibial crest is stabilized by means of the appropriate plate. The cortical tibial screw should be placed more distal than the end of the osteotomy, and the plate's arm over the tibial crest should encompass its length, with the most proximal screw positioned just distally to the area of patellar tendon insertion.
The standard technique uses locking screws, but for the tibial screw, which is always cortical. The use of guide sleeve for the positioning of locking screws on the tibial crest is mandatory.
The wedge must be in contact with both the medial and lateral cortices. The proximal end of the wedge is placed below the level of the proximal tibial tuberosity, without trapping any soft tissue. Its positioning a more distal than the standard level allows for intermediate advancements compared to those of standard wedges. Never place the proximal end of the wedge more distal than the distal insertion of the patellar tendon, because this will increase dramatically the risk of crest fracture.
The stabilization of the plate on the tibia by means of a single cortical screw has a significant impact on the transmission of loads. In this way, the plate allows the cyclic loading of the osteotomized tuberosity, thus stimulating osteo-induction. Using NOT LOCKING PLATES, the tibial screw should be positioned first, and it should not be tightened completely. Then the most proximal screw on the crest is inserted, while manually pushing slightly on the crest. After all the screws are inserted in the crest it's possible to tighten the one on the tibia.
If a LOCKED PLATE is used, it should be cautiously bent in the way explained during the course. The tibial screw is inserted first and it's tightened. The plate should lay flat on the bone surface. If not, it's preferable to untighten the screw and contour the plate adequately, to avoid any leverage on the tibial crest. When the plate arm laying on the crest is flat on the bone surface, the screws are inserted in the crest, so that the plate will stay stable in the previously determined position.
The surgical wound is sutured in a routine way.
No bandage is usually applied, just an adhesive protection on the wound area.