Tag Archives: Cruciate Pathology

Tibial Tuberosity Advancement Planning Part 1: Radiographic Considerations

First let me apologise for the lack of posts recently…things have been a bit hectic in the past couple of months. We now have over 1200 users accessing the site via the iPhone App which is fantastic. The key with these things though is user interaction, so if you have any comments or queries regarding this or other posts, don’t hesitate to feedback.

Introduction

This series is drawn from a presentation I prepared and presented at last weekend’s TTA training course at Zurich Vet School and at the Kyon Symposium 2012 again in Zurich. The point of this series is to explore the variables regarding post operative TTA radiographs and using our planning to control these, thereby getting a more consistent piece of surgery with more consistent outcome for our patients and clients. TTA (when performed with Kyon implants) is a procedure which forgives the surgeon for a reasonable amount of deviation from the ideal post operative appearance in most cases. It is for precisely this reason that we as surgeons need to be more diligent in terms of our planning. This sounds like a contradiction but if we consider that the ideal outcome will be derived from the ideal modification of the geometry of the tibia, when we miss the mark, we may not give our patients all of the potential benefits that have been shown to be associated with Tibial Tuberosity Advancement (TTA) such as normalisation of intra articular pressure profile and therefore the long term benefits that may be associated with this unique attribute (progression of DJD, Incidence of Late Meniscal Injury etc). So the surgeon “gets away with it” but our patients may not!

Goals of Planning

There are four main goals in our TTA planning:

Determining Optimal Plate Size.
Determining Optimal Plate Position.
Determining Osteotomy Position and Orientation.
Determining the required amount of advancement to give a 90 degree relationship between the Straight Patellar Tendon and the Tibial Tuberosity.

This post will deal with the key to establishing these measurements/assessments which is optimal positioning for radiography.

Basis for Precise Planning

It is not possible to achieve optimal planning from suboptimal radiographs. The key variables are:

Stifle Angle.
Rotation (Femur and/or Tibia).
The presence of femorotibial subluxation.

These must be controlled prior to engaging in planning for TTA.

1. Stifle Angle

There has been a bit of confusion here. The key is to remember that TTA is designed to provide femorotibial stability in stance phase. For this reason, all of the templating should be performed with the stifle in the normal standing angle on the mediolateral projection. This will vary from breed to breed and patient to patient. Previously people suggested that the stifle should be at 135 degrees extension, this should not be used for the reasons just stated. It can be difficult to assess the normal standing angle in cruciate deficient patients as, if the condition is unilateral, the contra lateral limb is likely being held in slight hyperextension to offload the affected limb, if it is bilateral, the patient’s pathological standing angle will be altered too. For this reason we should not simply rely on the person positioning the patient but go to the patient and palpate the Straight Patellar Tendon (SPT), if this feels to have low tone, then we are in an overextended position for that patient if it is very taut then we are likely in hyper flexion, we should use our experience in this assessment. If we see the following appearance on the radiograph then we are definitely hyper extended:

Note the wavy appearance of the Straight Patellar Tendon indicating Hyper Extension.

This abnormality is easily identifiable and the stifle should be re positioned to eliminate this appearance. Measuring advancement from hyper extended radiographs will underestimate the required amount of advancement and therefore influence post operative stability and all that may result from this.

2. Rotation.

Measuring from radiographs with rotated femur and/or tibia will seriously affect our measurement in terms of plate, advancement required and osteotomy position and orientation. We should reposition the patient until we have the ideal. Whilst there are adjustments we can make in our templating in radiographs with a rotated femur, it will always be more precise if our templating is from perfect mediolateral projection with femoral condyles superimposed. We will return to the issue of femoral rotation when we look at assessment of advancement. For now we will focus on Tibial rotation.

Given that the Cranial Cruciate Ligament (CCL) limits internal tibial rotation, pathology of the CCL will result in increased internal tibial rotation and therefore this is the most common problem encountered. We first need to be able to recognise when this has happened, and this is not as easy as determining femoral rotation. The key areas to look at are:

The caudal cortices of the Tibia.
The relationship between the Tibia and the Fibula.
The definition of the distal aspect of the Tibial Crest.

The images below show Perfect unrotated, internally rotated and external rotated isolated tibias:

The Tibia is perfectly positioned. The asymmetry of the caudal tibial cortices is minimal.

The Tibia is externally rotated and the medial cortex of the tibia is in a cranial position.

The Tibia has been internally rotated and the lateral cortex is now positioned cranially.

The degree of rotation above is not exaggerated beyond that which we may commonly encounter in our radiography pre surgery. The following image shows the change in relationship between the Tibia and Fibula associated with rotation of the tibia.

Left: Normal, Middle Internal Tibial Rotation, Right External Tibial Rotation

The Image below shows the impact on the definition of the Tibial Crest of the same types of rotation (this can also be seen above). The effect of this will vary between patients but in general if it is difficult to identify the distal aspect of the crest on the radiograph, go to the patient and palpate this area. If you can feel it distinctly in the patient, you should be able to see it on the radiograph!

3. Femorotibial Subluxation

If the tibia is cranially displaced (due to CCL pathology) on our planning radiograph, this will have a variable impact on our estimation of required advancement as the Tibial Tuberosity is already advanced. We need to identify landmarks that may indicate that this is present. These are:

The relationship between the Tibial Eminence and the intercondylar region of the femur.
The relationship between the caudal aspect of the tibial condyles and the femoral condyles.
The relationship between the Origin of the Long Digital Extensor Tendon and the Sulcus for this tendon on the tibia.

The image below shows these points. If we identify subluxation, we need to correct it before proceeding to templating otherwise we will undersize the cage and fail to achieve sufficient advancement. Note also that the tibia and femur are rotated on the radiograph below as identified by a lack of superimposition of the femoral condyles, indistinct fibula, indistinct distal aspect of the crest and increased distance between the tibial cortices.

If we avoid these three potential pitfalls, we will be more likely to achieve reliable measurements in our planning that will guide our surgical execution and determine our surgical outcome. We need to make precise measurements from well positioned radiographs in order to deliver the perfect opportunity for perfect outcome.

Next… Plate Size and Position.

Diagnosing Cranial Cruciate Pathology-Part 4: Palpation

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So far in this series, we have established that there are no significant criteria in terms of radiographic appearance or synovial fluid aspirate findings that will permit a definitive diagnosis of Cranial Cruciate Ligament Rupture. All that we can say form these tests is that there is evidence of increased (non-inflammatory) synovial fluid production in a stifle displaying varying degrees of Degenerative Joint Disease.

As the key function of the Cranial Cruciate ligament is to limit cranial tibial displacement and internal tibial rotation, the presence of a palpable increase in either of these two components would (in most cases) be a definitive diagnostic finding. There are two main tests of femorotibial stability:

Anterior Drawer Test

In this test we place a thumb behind the fibular head with index finger on the tibial tuberosity with one hand and with the the other hand place a thumb behind the lateral fabella and index finger on the patella. We then push the tibial hand forward without moving the femoral hand. If the tibia slides forwards, this is indicative (in most cases) of cranial cruciate ligament degeneration. This test should be performed in both flexion and extension for the following reason:

The Cranial Cruciate comprises two main bands: The Craniomedial Band and the Caudolateral Band:

The Caudolateral band is shown in pink

The Craniomedial band is taut in both flexion and extension whilst the Caudolateral band is only taut in extension:

Both Bands are taut in extension

In Flexion, the Craniomedial Band is still taut but the Caudolateral Band is loose.

If the Anterior Drawer Test is performed only in extension, then partial ruptures (which are most common) may be missed. If the stifle is stable in extension but unstable in flexion, this indicates that partial rupture involving the Craniomedial Band is present as in flexion the Craniomedial Band should provide stability whilst the caudolateral band is loose. For this reason, this test should be performed in flexion and extension.

The test is best performed in anaesthetised patients as the pressure applied by the digits can cause pain and muscle tension can make it difficult to elicit a positive response even in a very unstable stifle. Care in interpreting the findings should be exercised in very young patients and in patients with effusions for other reasons. These patients may show a degree of Drawer, but there will be an abrupt stop to the Drawer motion in these patients which feels different from that felt in the Cruciate deficient stifle.

Tibial Compression Test

This test is often easier to perform in conscious patients but needs some practice to become confident that a negative response is a true finding rather than being due to error in technique. In patients that will bear weight on the affected limb it can often be tested by simply lifting the contralateral limb with a finger placed on the Tibial Tuberosity when the affected limb is loaded. In many patients you will easily appreciate the cranial tibial thrust as the limb is loaded. If the patient is non weight bearing, the procedure is to fix the stifle with one hand whilst upward pressure is applied to the paw of the same limb with the hock on a neutral standing position. This will elicit anterior displacement of the Tibia in most Cruciate Deficient stifles.

The problem with both of these tests is that they may give false negative results. As mentioned above, many patients will present in the partial rupture phase and it may be partial in the craniomedial band with intact caudolateral band. In these patients both of the above tests may prove negative. In Boxers in particular, there tends to be a marked fibrotic response from the joint capsule in the Cruciate Deficient stifle and this fibrosis may result in a degree of palpable stability that mimics the normal stifle. These are the “problem cases” and the clinician may fall back on history, breed, age and lack of contradictory findings to establish a strongly tentative diagnosis in these cases. If further certainty is needed, then arthroscopy or MRI may be used to visualise the cranial cruciate ligament pathology before proceeding to manage the patient with the appropriate surgical technique. In most cases however this is unnecessary as long as all of the tests indicated in this series have been followed and their results interpreted correctly.

Diagnosing CCL Rupture Part 3: Synovial Fluid Aspiration

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In this third part of diagnosing cranial Cruciate Ligament Rupture, we will look at Synovial Fluid aspiration and analysis. In general this is an under performed procedure and in my view should be part of the work up for any lameness that is suspected to be due to joint pathology. Synovial fluid reflects the current and (in some cases) historic environment of the joint. The chief role of synovial fluid aspiration and evaluation in respect to suspected Cranial Cruciate Ligament pathology is in confirming the absence of contradictory findings. As with any presenting patient, their history, clinical signs, physical findings and so forth form the basis for a differential diagnosis list. As most readers will know, this is a list of possible explanations for the clinical picture presented. This list is generally ordered in the clinician’s mind with some possible explanations being more likely than others. As we saw in the radiography post, the findings there simply reflect increased joint fluid production (effusion) with the possible addition (depending on duration of pathology) of findings consistent with Degenerative Joint Disease (DJD). These findings are not specific to CCL pathology. We still need to explain the presence of effusion. As mentioned in the previous post, effusion represents “active” joint pathology, the question remains: “What has activated the pathology?”.

Most pathologies can be categorised using the DAMNIT mnemonic:

Differential Diagnosis using DAMNIT mnemonic

With regards to stifle effusion we would generally consider that there are conditions within each of these groups that may explain the clinical and radiographic findings. Only synovial fluid aspiration and analysis will permit us to narrow this list. The expected characteristics of Synovial fluid aspirated from the Cruciate deficient stifle would be an increased volume of cytologically normal synovial fluid. We would not expect to see evidence of increased White cell populations or the presence of neoplastic cells. An example of some of the different appearances of synovial fluid can be seen in the next image:

Some of the pathological processes that may be seen in Synovial Fluid

The gross physical and cytological characteristics of synovial fluid aspirated from joints with different pathologies can be seen in the table below:

Table showing the gross and cytological aspects of Synovial Fluid associated with different pathologies.

In terms of Diagnosing CCL pathology we want to exclude the presence of significant inflammatory disease or neoplastic processes. We may therefore see fluid that is consistent with DJD and we may see evidence of erythrophagocytosis indicative of recurrent historic bleeds into the joint.

As indicated, we will not find evidence of CCL pathology, we are simply ruling out other conditions that may present with a similar history and have broadly similar radiographic changes. In my view this is a mandatory component of the investigation of the suspected CCL deficient stifle. Failure to perform this simple test may lead to inappropriate treatment or raise the risk of post operative sepsis if a low grade septic arthritis has been overlooked by failing to perform this simple test.

Synovial Fluid aspiration should be performed with Aseptic Technique and should be practiced in order to reduce iatrogenic injury to the structures of the joint. In general I recommend using a spinal needle as this reduces the risk of taking a skin core into the joint and the rounded end is less traumatic. I routinely use a 5 ml syringe for collection of fluid. The needle can be introduced lateral to the Straight Patellar Tendon and directed into the femorotibial joint or angled (in the slightly flexed stifle) upwards to a point below the patella. If the fluid appears turbid or if there is cytological evidence of inflammation, a small amount of the fluid should be injected into a “Bloodgrow” bottle to improve the likelihood of a positive bacterial culture in cases where Septic Arthritis is suspected. In this way Bacteriology and Sensitivity can be determined and the antibiotic regime directed by these findings which is best practice for managing any infection and reduces the risk of encouraging bacterial resistance.

When is a TTA not a TTA?

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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:

Cranial Cruciate Rupture and TTA (part 1)

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The Cranial Cruciate Ligament (CCL) maintains the stability of the Tibia relative to the Femur when the foot is in contact with the ground. It stops the Tibia from sliding forward when weight is put on the limb. When the CCL is weak or completely ruptured, it is unable to maintain this stable relationship. As a result the knee gives way under the patient when they transfer weight onto the affected limb. This is an unusual experience and causes pain by stretching the joint capsule. The patient responds by reducing load through the leg and this results in the appearance of the lameness. In man this is usually caused by an injury, whilst in most dogs this happens because the ligament weakens prematurely. This process can begin as early as seven months of age. Unfortunately in many breeds such as Labradors, Rottweilers, Retrievers, Boxers and Springer Spaniels; this will occur in both stifles simultaneously. This can result in severe poverty of action in the hindquarters, making it difficult for them to stand up and they may need help to get up from rest. This can also be seen in Hip Dysplasia which has a similar breed predisposition and is often present in dogs with CCLR. This can result is some confusion from time to time regarding the diagnosis. Cranial Cruciate Ligament Rupture requires surgical management for a successful outcome.

Tibial Tuberosity Advancement

There are many techniques to stabilise the Cranial Cruciate Deficient stifle. Tibial Tuberosity Advancement (TTA) is our favoured method management for the reasons discussed below. TTA was devised by Slobodan Tepic (Kyon) and Pierre Montavon (University of Zurich) and is used worldwide to restore stability instantaneously to the Cruciate Deficient Stifle.

Torrington Orthopaedics and Tibial Tuberosity Advancement

Why TTA?

TTA is a procedure that has a repeatedly excellent outcome in our hands. Patients are using the limb within a few days of surgery and require very little Rehab input to achieve excellent outcomes. The implant quality and design from Kyon is second to none and this makes us comfortable to use this technique in the entire spectrum of sizes of and lifestyles of our patients. Recent work by Kim and Pozzi has shown that TTA is the only technique that normalises the stresses in the stifle post surgery. TPLO has many of the benefits in terms of early limb use and so forth, but research from the same group shows that TPLO increases the stresses in the medial (inner) compartment of the stifle. We do not want to provide a stable stifle that will result in increased wear of the medial compartment over time.

Many practices do TTA why should we choose Torrington Orthopaedics

We have performed over 650 TTAs.
All of our surgeons have been trained directly by Kyon at one of their approved courses and two of the surgeons here (Andy Torrington and Turlough O’Neill) are instructors for the Kyon course.
Torrington Orthopaedics is the only UK venue for Kyon TTA training courses.
Our close association with the originating company means that we are at the forefront of developing and enhancing the technique.
We only use Kyon implants and not the cheaper and often poorly manufactured “Me too” products on the market.
Our implant failure rate was zero in this set of 650 patients.
Our complication rate was less than 1%.