Canine cruciate ligament injury
Rupture of the canine cranial cruciate ligament (CCL) is the most common orthopaedic problem seen in veterinary practice. The CCL in dogs is a band of tough fibrous tissue that attaches the femur to the tibia, thereby preventing the knee joint from over-extending or rotating. Trauma to this ligament in dogs is usually caused by the slow degeneration over time, which can trigger a cascade of events resulting in knee pain and lameness. At the earliest stage, osteoarthritis is already present. When the CCL loses its normal mechanical function the femur will roll down the natural slope of the tibia every time weight is taken on the leg causing pain and affecting the natural gait of the dog.
Tibial tuberosity advancement
One routine surgical procedure for CCL repair is tibial tuberosity advancement (TTA), involving a cut being created in the tibia to allow a change in geometry in such a way that the CCL is no longer necessary to maintain stability. The basic principle is that an altered direction of traction from the quadriceps muscle group (created by the insertion of a wedge into prepared bone of the tibial tuberosity) produces a force across the knee joint that neutralises the tendency for the femur to roll down the slope of the tibial plateau.
The cutting guide is secured using a 3.5mm drill bit which advances through both tibial cortices. The proximal pin (long) should be seated just caudal to the patellar ligament and flush to the proximal tibial surface. The position of this drill should be just caudal to the cranial cortex of the tibia. The drill should be perpendicular to the medial tibial surface. The chuck is loosened/removed leaving the drill bit in place to ensure the cutting guide remains secured.
The osteotomy is made using a saw blade of 0.4 – 0.6mm thickness and at least 40mm in length. The correlation between the cutting guide and the length of the Fusion TTA Wedge is consistent with the size of the osteotomy. The guide should then be removed and the osteotomy carefully completed into the distal drill hole.
Starting with the smallest size, the spacers are sequentially introduced into the osteotomy and rotated into position to gradually advance the tuberosity. This is repeated until the desired advancement is reached. Small pointed forceps are also useful to facilitate this process.
When suitable advancement has been achieved, the wedge can be carefully inserted using the insertion tool. This tool is used to correctly position the wedge.
The drill guide is attached to the insertion tool. The drill guide has two dierent length arms that determine the distance between the guide and the tuberosity. This distance should be as small as possible. A 1.5mm drill bit is used to pass through the tuberosity guide through the wedge. It is not necessary to drill the caudal cortex of the tibia.
A 1.6mm Ellis pin is driven through the drill hole including the caudal cortex of the tibia. The dynamic tension plate (DTP) is contoured to the cranial surface of the tibia. The DTP drilling guide is attached to the plate and a 2mm hole drilled through both cortices. The depth is measured and an appropriate length screw inserted.
The Ellis pin is cut to approximately 8-10mm and bent, using the pin bender part of the insertion tool, to ensure it lies flush to the tuberosity.