This may seem like a strange question, surely TTA is Tibial Tuberosity Advancement. I suppose we need to ask how we know when anything is anything. We could argue that we know for example that a table is a table because it looks like a table. If we follow this argument then appearance to the senses is the defining characteristic of the object.
Function is also used to define an object. From a functional perspective, a table is an object that functions to hold objects in a stable position above the level of the ground. The inclusion of function with regards to correctly identifying an object is generally more powerful than observing its appearance. A garden trampoline looks like a table, but it certainly wouldn’t function as one. This would be an example of understanding that one object is not another despite sharing similar appearances as a result of lacking the characteristics that permit it to function as the true object.
In reality an object is a table when it functions as a table. Anything else is not a table. Function is derived from the various parts of the object acting to perform a specific action or behave in a specific way and therefore many things that function in a similar way will have similar parts arranged in a similar way. It is this last fact that often leads to the classification of objects by appearance and this often leads to reaching the wrong conclusion regarding the identification of an object.
How can we apply this to the question in the title: “When is a TTA not a TTA?”. Well I suppose if we go back to our analogy we would argue that it is when it looks like a TTA and functions like a TTA. On that basis, it is not a TTA if it simply looks like one!
My Definition of TTA: The definition of a TTA is an opening osteotomy of the tibia in the craniocaudal plane such that the tibial tuberosity comes to occupy a position cranial to the proximal tibia resulting in an angle between the Straight Patellar Tendon and the Tibial Plateau of 90 degrees. The advanced tibial tuberosity is held in this position by a plate anchored to the tibial tuberosity and the tibial diaphysis and a cage of variable size. The osteosynthesis should be of sufficient strength to withstand the distractive pull of the Quadriceps mechanism to permit the osteotomy gap to fill with bone.
A TTA...or is it?
So that is all about appearance then, there is a gap, there is a plate, there are screws and there is a cage. The key part of that (overly long) sentence above though is “resulting in an angle between the Straight Patellar Tendon and the Tibial Plateau of 90 degrees”. That sentence is key because it is that aspect of the appearance that gives TTA its function. If we have a set of post op radiographs following TTA and that element is missing then:
That is not a TTA
No combination of plate, screw, fork, cage is a TTA unless it stabilises the cruciate deficient stifle. The goal of TTA; neutralisation of the cranial displacement of the tibia in a Cruciate Deficient stifle has been shown to be achievable by Kim and Pozzi. Their work is “Proof of Concept”. The goal is however only achieved when the angle of the common tangent of the femorotibial joint is perpendicular to the Straight Patellar Tendon. Surely if this is the goal, and we do not achieve it; we have failed.
Question: How many surgeons measure the relationship between the Common Tangent and the Straight Patellar Tendon Post Operatively? Be honest now. Instead, the tendency is to focus on the implant position, the osteotomy and so forth. This is the same as someone selling a Trampoline as a table! Failure to understand how something actually functions leads to the production of things that look similar but do not possess the appropriate mechanical characteristics.
Call to Arms: If you are a TTA surgeon, measure how close to the goal you got.
Did we even get close to the target? Did we hit the Bull’s eye? If you don’t check the target after you shoot, you won’t know! If you don’t check your post op radiographs for proximity to the goal, you won’t know either.
So if we write in our clinical notes: Performed TTA, but don’t follow that statement with ” and achieved a post op angle of 90 degrees” then the first statement was wrong.
This is the first in a series of articles on TTA. If you are the kind of reader that likes a conclusion, then here it is: