Installing the Pre-contoured TPLO Plate
All VID pre-contoured locking TPLO plates accept 2.7mm, 3.5mm and 4.0mm locking screws. Additionally, all plates accept 3.5mm AO cortical and 3.5mm or 4.0mm cancellous screws.
Your First Screw
Place the plate over the rotated osteotomy site. Consider a straight up and down positioning. The top of the plate can be aligned with the most prominent part of the medial edge of the proximal tibia. The stem part of the plate should be parallel with the caudal cortex. In case of using a TPLO jig. The jig may needed to be elevated away from the bone to accommodate plate placement close to the proximal jig pin as needed.
The first screw is typically installed into the 3rd position counting the holes from the bottom of the plate (most distal position) up. This is the most proximal screw hole on the stem and can be referred to as the first 'anchor screw' since it acts as the initial stabilizing screw.
Engaging/tightening the first locking screw can apply a clockwise torque on the plate which could cause a shift in its position relative to the drill hole.
If the plate changes position after drilling your first hole and before inserting your first screw, there is risk of exceeding 15 degrees for a polyaxial locking screw insertion. If this occurs the locking mechanism may not fully engage thus increasing the risk of pull-through failure. If significant shifting of the plate occurs, we recommend using an alternative non-locking AO screw instead. There are 3 techniques to avoid unwanted shifting of the plate when inserting the first screw.
All Locking Screws with K-Wire
This method works best when using all 6 locking screws and is most common. Before the first screw installation use 2 x 0.062” K-wires to affix the plate to the desired location through the provided pin holes. This will provide an excellent view of the final plate placement and facilitate easy screw insertion without the risk of shifting the plate. Remember to cut the pins long enough so that they're are easy to remove, but short enough so they don't interfere with the use of screw drivers or drills. A single 0.062” K-wire works well when cut in half to utilize both pinholes. Because the K-wires do not remain in the patient, it is possible to reuse them.
The most proximal k-wire, once inserted, may obstruct the polyaxial or funnel-shaped end of the drill guide from being inserted into the head of the short pre-contoured TPLO plate.
This can be avoided by utilizing monoaxial insertion before polyaxial insertion on the head of the plate. The monoaxial portion of the drill guide has a smaller radius than the polyaxial portion of the drill guide thus allowing the surgeon to easily avoid the top k-wire. This will anchor the head of the plate and allow removal of the k-wire so that polyaxial insertion can be performed unhindered in order to avoid the joint and IM pin while utilizing maximum bone for superior stability. Note that this interference does not affect the standard sized pre-contoured 3.5mm plate, but can still be employed to create maximum available space.
Drill guide interference will be little to no concern on the stem of the plate since monoaxial insertion is most common and uses the straight portion of the drill guide; However, interference can be present with the use of a TPLO jig. In this case the method would be identical. The first screw installed in the head of the plate should be any of the 3 that does not interfere with the jig. Then the jig can be removed and the other 2 screws can be installed.
The screw holes on the head of the plate are designed to maintain perpendicular screw alignment with the stem so each of the 6 screws are parallel to each other and perpendicular to the medial cortex of the distal segment of the osteotomy with monoaxial insertion. Polyaxial insertion allows angulation of up to 15 degrees in any direction.
Screw Insertion Technique
The VID locking self-tapping screw is designed to be able to insert driven by hand or by power. The hand insertion is a slow speed rotation while the power insertion is a variable speed insertion. (Since we can slow down the equipment but can't speed up our hands the design favors the slow speed insertion) It’s recommended to use slow speed on power screwdrivers to get the best and quickest grab of the bone. High-speed screw drivers will make the initiation of the insertion more difficult.
Additionally, if you experience unusually hard bone or your insertion technique gets the 3.5 locking screw having difficulty driven in a hole created with a 2.5 mm drill bit - the 3.5 mm locking screw can be inserted into a 2.7mm drill hole with no loss of thread contact with the bone. This is typically not necessary if the screw is rotated with a slow speed at the beginning of the insertion. The 3.5 mm screw is designed for the 2.7 drill bit, but with the mild additional bone compression with the use of the 2.5 mm drill bit, there is an equally good holding power present.
All Locking Screws without K-Wire
Drill and insert the first screw in the most proximal (#3) position on the stem, but do not tighten more than before the screw head threads would engage the plate. Drill and place the second screw into the most distal position (#1) and tighten the screw in the #3 and #1 position together. Method 2 uses no pins and achieves similar results. In this case it is important to keep the plate position in check till the first 2 screws are tightened.
(x5) Locking Screws (x1) AO Cortical Screw
Use an AO non-locking screw in the center hole of the stem. Tighten the screw to stabilize the plate before drilling and inserting locking screws in the #3 and #1 position.Method 3 uses one less locking screw by utilizing an initial AO cortical screw to prevent plate shift.
(x4) Locking Screws and (x2) AO Cortical Screws
Use the center hole in the stem to insert an AO cortical screw first. Then insert the other two screws (#1 and #2) in any order you choose. There is no relevance of the order at this time. On the head of the plate you may use an AO cortical screw to shift the proximal bone segment closer to the plate. This may be useful in some cases to improve tibial crest positioning. In this case use the 1 x AO cortical screw in the most cranial position and tighten to the level desired to case a shift. Then insert locking screws in the remaining two screw holes. A VID universal locking system is very stable with just two locking screws per bone segment as long they are inserted properly and they are in good quality bone.
Because locking plates do not depend on bone to plate contact compression like non-locking plates, the following is true:
It’s important to have sufficient cranial caudal compression between the tibial crest and the proximal segment before plate installation(provided by bone clamp or digital compression) when installing the derotational pin. If there is a gap between bone segments, there is potentially increased risk of crest fracture complication. Non-locking implants with proper placement can often provide adequate forward compression but are generally less resistant to 'rock-back'.
Since all 3 screws in the head of the plate have identical function there is no reasonable preference in the order which these screws are inserted. A preferred order only exist if the structure has to be changed to accommodate sufficient room for a drill, drill guide, screw and/or screwdriver.
Shifting the proximal bone segment closer to the medial aspect can be achieved by using an AO/ASIF cortical screw in 1 of the 3 screw holes in both the head and stem segments of the plate. Pulling the bone to the stem of the plate can be done by insterting a non-locking screw first into the middle(2nd up from bottom) position on the stem. The most cranial screw hole on the head of the plate will typically be used first to pull the proximal bone segment to the head of the plate.
Using 1 AO/ASIF cortical screw and 2 locking screws in each segment provides sufficient stability in the structure to avoid 'rock-back' or shifting of the plate.
Once a locking screw is installed into a bone segment, that segment will no longer shift relative to the plate, even if AO cortical screws are installed. If non-locking screws are installed they should be done so first.
The plate can be used with all non-locking screws. In this case there is no benefit of a locking plate selection.
Since screw loosening is extremely rare in the distal segment - using all AO non-locking screws in the distal segment is an acceptable alternative.
Each hole needs to be drilled with the VID drill guide for all locking and non-locking screws to maintain the structural integrity of the plate.
In comparison to other locking TPLO plate systems the VID system has the added benefit of quick-connect drill guides - instead of the alternative threaded design.
Utilize polyaxial screw insertion as needed to avoid interference with the joint or previously placed implants.
Only VID locking screws are compatible with the universal locking system; however, the system is compatible with all AO/ASIF cortical screws.
VID locking screws are self-tapping. We also recommend using AO self-tapping cortical screws whenever locking is not used. Non self-tapping AO screws will require the use of an appropriate sized bone tap for installation and must be used with the appropriate size drill guide.
The standard and short 3.5mm pre-contoured TPLO plate accommodates TPLO saw blade sizes 18mm and up(18-27 is common).
Pre-contoured plates fit most of the bone configurations but some contouring still may be necessary. VID locking screw holes are highly resistant to deformation if plate bending affects the shape of a screw hole. It's still recommended to use the plate area between screw holes for most of the plastic deformation.
Any screw is compatible with any plate. Substitute a smaller screw for a larger screw to accommodate larger body weight or rescue stripped bone. A smaller screw can be substituted for a larger screw if drilling is close to the edge of the osteotomy or the edge of the cortex.
Same sized drill bits can be used between locking and AO screws translating to less instrumentation to buy and clean. See the compatibility chart for specifications.
Same hex screw driver can be used for locking and AO screws eliminating the need to switch back and forth between the star guide and hex.
A single screw box accommodates all screws, plates and instruments needed. This simplifies sterilization and improves flow in surgery.
The implicit practicality of system design shortens the learning curve and allows for maximum efficiency during surgery.