Introduction
Rupture of the cranial cruciate ligament (CrCL) in the stifle of the dog is probably the most common cause of hindlimb lameness seen in the general practice setting. Injury to the CrCL is thought to be due to a hyperextension injury of the knee with an internal rotation of the tibia. CrCL tears may be partial initially, complicating the diagnosis, but eventually most end up in complete tear due to the imbalance of forces that act on the joint resulting in cranial tibial thrust. This abnormal translation of the tibia relative to the femur may also result in additional injury to the medial meniscus, necessitating a partial or complete meniscectomy. Most practitioners opt for the modified retinacular imbrication technique utilizing heavy monofilament nylon as a repair method, or refer to surgeons capable of performing tibial plateau leveling osteotomy (TPLO), which is in a broad consensus, considered state of the art.

Rationale for TTA
First, the total joint force of the stifle is approximately parallel to the patellar ligament. If the patellar ligament is perpendicular to the tibial plateau, there is no shear component of the total joint force, and the cruciate ligaments are not loaded. The angle between the patellar ligament and the tibial plateau changes with flexion and extension, and in fact the two are 90 degrees to each other when the stifle is in 90 degrees of flexion, the cross-over point. So, when the CrCL is ruptured, the stifle can be stabilized by shifting the cross-over point to full extension of the joint. This can be performed this can be preformed by either TPLO, or TTA.

The Procedure
The amount of advancement required to move the tibial tuberosity is determined from a preoperative standing angle lateral radiograph of the stifle. The stifle is approached medially, and a frontal plane osteotomy is performed. The tibial tuberosity and cranial border are held in advancement by (1) a titanium cage, (2) a titanium fork, and a (3) titanium tension band plate. The cage transfers the compression component of the patellar ligament force from the tuberosity to the proximal tibia. The tension band plate transfers the axial component of the patellar ligament force from the tibial tuberosity to the proximal diaphysis of the tibia. The open-wedge osteotomy may be grafted by cancellous bone or a commercially available product.

Speaker: Jeff Mayo, DVM, CVLS, Diplomate ABVP
Dr. Jeff Mayo received his Doctorate of Veterinary Medicine from the Oregon State University College of veterinary medicine. Much of his focus during 11 years of private practice in the state of Washington was on laser surgery, orthopedics, and new, practical techniques in rigid endoscopy for small animals.

Dr. Mayo studied TPLO techniques starting in 2003, followed quickly by TTA procedure in 2004. Dr. Mayo was one of the first in the country to perform TTA and was trained by Slobodan Tepic. Dr Mayo now travels the US and Canada teaching various privately owned veterinary hospitals and has performed over 500 TPLOs and 1500 TTAs.

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