Tibial tuberosity advancement (TTA) Procedure
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It has been widely accepted that a major factor causing the cranial cruciate ligament (CCL) to rupture is an abnormal force (shear force) which is a component of the total joint force generated through the stifle (knee) joint when the dog stands and walks. This abnormal force is due in large part to slope at the back of the tibial plateau.
The first method to dynamically eliminate the shear force was the tibial plateau leveling osteotomy (TPLO) designed by Dr. Barkley Slocum. This is accomplished by cutting the upper portion of the tibia and rotating the plateau until the slope is level to the ground surface. TPLO surgery has resulted in great success for stabilization of the stifle joint and restoration of limb function.
A new surgical procedure, the tibial tuberosity advancement (TTA) was developed at the University of Zurich by Dr. Slobodan Tepic and Professor Pierre Montavon approximately 4 years ago. They determined through biomechanical analysis, that the total joint force in the stifle joint is approximately parallel to the patellar ligament. If the angle between the patellar ligament and the tibial plateau (alpha) is 90 degrees, there is no shear force, and the cranial and caudal cruciate ligaments are not loaded. In the canine stifle, the alpha is 90 degrees at 90 degrees of flexion. This is referred to the cross-over flexion point. In full extension alpha is approximately 105 degrees, and in full flexion alpha is approximately 70 degrees. With respect to the cross-over point, in extension the load is on the cranial cruciate ligament, and the load is on the caudal cruciate ligament in flexion.
TTA is also designed to stabilize the joint by shifting the cross-over point towards full extension thereby eliminating the abnormal force (shear force). It is accomplished by advancing the tibial tuberosity cranially (forward) a predetermined distance so the patellar ligament, and therefore total joint force is at 90 degrees to the tibial plateau. The procedure causes only a slight modification in the geometry of the stifle yet renders it stable throughout the range of motion.
The advantages of the TTA are less soft tissue dissection, the bone is cut along the nonweight bearing portion of the tibia, and less implant problems. In general, the outcome of the TTA and TPLO are the same in terms of stabilizing the stifle, restoration of function, and minimizing arthritis. TTA was fully released for clinical use by the end of 2005. Currently over 200 surgeons worldwide have utilized this procedure in approximately 7000 cases.
Veterinary Specialties has used this procedure in approximately 350 cases since the spring of 2005 and we are very pleased with the outcome.