Agility Implant

source: http://www.myanklereplacement.com/binary/org/DEPUY/images/joint/ankle/new/Agility.jpg

The Agility ankle prosthesis was designed by Dr.Frank Alvine was first inserted in a patient in 1984 and it was the first ankle replacement to receive FDA approval. It is used in the majority of ankle arthroplasties performed in the United States. It is a semi-constrained, two part prosthesis which resurfaces the medial, lateral and superior articular surfaces of the ankle joint.

It consists of a titanium tibial component with sintered titanium beads and a cobalt-chromium talar component with sintered cobalt-chromium beads. A modular polyethylene inserts locks into the tibial component. The first ankles were all constructed of titanium but since 1989 cobalt-chromium has been used due to loosening of two talar components in the first 3 years. Thicker tibial component was also used start from the first time due to two broken components in the first 21 ankles implanted.

The tibial articular surface is larger compared to the talar component as this will allow axial rotation. The problem with this was that during the axial rotation, incongruent articulation will take place on the articulating surface. On the other hand, during the dorsiflexion and plantarflexion, congruent articulation can be achieved. When Agility prosthesis is inserted, it is combined with an arthrodesis of the tibiofibular syndesmosis using one, or more, which commonly was two screws.

Ankle arthrodesis or Total ankle replacement?

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It may be that you have known it or not, ankle arthrodesis is referring to fusion of our joint. This is including the process of gluing the related joint bones together using screw or any attachment methods that are available. This process will cause our joint to lose it normal upwards and downwards movement which surely disturb our daily walking ability. This will also increase the stress applied to the joint. Due to the fixation of the joint, it will leads to arthritis at the joint near to it that can cause more complication afterwards. This is one reason why Total Ankle Replacement becomes favorite among nowadays patients.

Experience will be needed in order to put in the implant nicely to avoid complication to the amputees in the future. Surgeon that have undergo many time of surgery will be better in completing the surgery process. This is important as different people will have different conditions and that is why there will be many variable to be considered during the insertion of the implant.

After receiving this implant, patients will be able to do their simple movements back. It is better to avoid activities that can overstress the joint. Patients can cycle, walk, hike, climb and even ski after the surgery and rehabilitation. They should avoid doing activities that can cause the joint to experience repetitive pounding and great stress such as running and heavy labor.

Good candidate for receiving this implant are those who are 50 years and over of age, not too heavy and not too active. Surgeons need to observe the receiver joint’s range of motion, having diabetes or not, nerve condition and bone quality. In some cases, arthrodesis is more suitable for patients as their range of motion of the joint is very small and they will less likely to realize the effect of arthrodesis to their joint’s movements. Diabetes and nerve condition need to be considered because they will affect the condition of the implant. Poor bone quality will disturb the performance of the implant and can cause loosening of the implant or broken of the bone.

After surgery, rehabilitation is very crucial so that patients can train they “new ankle joint”. After removing the surgery stitch, cycling and swimming can help to train the joint.

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Advantages of 3 parts Ankle Prosthesis

Let us together dig the answers on why 3 parts ankle implant is better compared to previous 2 parts implant. After this discussion session, you may proceed to knowing what's best for the unexpected future.

First of all I would like to say about how this type of implant design will help in providing normal ankle joint movements to the receiver. Let the picture below help us in understanding this:



By reffering on the above picture, these 3 parts components will produce 2 sliding surfaces (also known as articulating surface). Bottom surface will allow inversion and flexion while above surface will support rotation. It is clearly seen that these 2 sliding surfaces will share the movements and in total give the ankle complex movements back to its owner. 2 parts implant with only 1 sliding surface makes it hard to suport all 3 ankle movements. This is advantage number one.

When it comes to stress distribution, 3 parts ankle implant will perform better. Back to the 2 sliding surfaces that I mentioned before, stress created by loading from patient's weight and movements will be distributed between the surfaces. Simply said that 2 surfaces will provide less stress concentration at each surfaces compared to the 1 surface ankle implant. Low stress concentration will leads to lower wear rate and longer life span. We want this implant to last as long as possible to avoid any complication to the receiver later in the future.

There maybe many more advantages but let us stop here for now as these 2 answers is ample enough to open our eyes to this desgin type. Feel free to do some extra reading about this matter if you are interested and stay tuned with me for more informations. :)

Ankle Replacement - 2nd Generation

Today I am going to discuss about some the 2nd generation of Ankle Prosthesis (Implant). As I mentioned in the previous post, the 1st generation of ankle Prosthesis was a failure. Lack of natural anatomy through the usage of the 1st generation designs was the reason of the failure. This makes people rely more on the fusion (arthrodesis) even though it cost them to lose their normal movements.

Patients want to stop themselves from continue to suffer from the pain caused by the broken articular surface in their ankle joint. As long as they didn’t suffer from the pain, it is okay for them to lose their normal movements. This situation happens because there is no other option for them.

Thanks to the continuous study made by the people who want to improve the problems from the 1st generation ankle prosthesis, 2nd generation designs come out. This time, it is more anatomy friendly and allows patients to get their normal movements back while stopping the pain in the joint. It is same as they get new ankle to replace their old one.

The founding of this 2nd design makes arthrodesis become last choice for anyone who suffer ankle joint problems. It is not that this 2nd design doesn’t have any weaknesses. These designs were still in study process and are new compared to hip and knee prosthesis. Thus, continuous study is still under progress. As until today, there are no massive reports showing that these 2nd (can be considered as New Design) generation designs are not good. Most of the patients will choose Total Ankle Replacement as their method of recovering.

Talking about the technical stuffs of this 2nd generation design of ankle prosthesis, it uses mobile bearing concept. This is something totally different from the 1st generation concept as it only using 2 part ankle prosthesis. Mobile bearing concept is using 3 part ankle prosthesis which allow normal ankle movements. For your information, our ankle joint can do at least 3 type of movements which result in complex anatomy. If the implant does not support either one of these movements, broke down of the joint functions and implant may happen. 2 parts ankle prosthesis is hardly manage to support all these movements of ankle joint. We will see why is the mobile bearing implant can easily support of the ankle joint movements compared to the compared to the 2 parts ankle prosthesis later in the next post.

Until then, all the best to you. Knowledge is treasure, you have to search for it. This blog is one of them. Stay tuned and enjoy.. =)

Constrained vs Unconstrained Implants

Constrained implants are the one that do not provide 100% free movements to the ankle joints while unconstrained implants gave the opposite.  Each of these types of implants will have their own advantage and disadvantage.

Constrained implants will allow only the normal movements of the ankle joint.  But in case of emergency or in critical condition such as the patient fell or stumbled, the ankle joint movements will be a lot more compared to the normal movements.  This will cause the constrained implant to received unexpected stress at the constrained area which tends to make it become dislocated.  It will cause complication to the patients.

Unconstrained implant on the other hands will allow free movements of the ankle under the control of ligaments.  This condition is good for the critical condition situations where dislocated of the implant will less likely to be happen.  Disadvantage to this type of implant will be the over-stressed of ligaments which cause higher risks of ligaments to be injured.

Both of these implants have their own features which will contribute in one area but causing problem at another area.  More research should be conducted in order to find ways to improve these conditions of implants.

I will try to discuss about how to overcome these problems later. And also I will search for more literature reviews about this matter.


Regards,


Timben

The First Generation of Ankle Implants

It is Lord and Marotte the first to attempt to replace the ankle joint in 1970. They used an inverted hip stem implanted into the tibia and a cemented acetabular cup in the calcaneus. They completely removed the talus. 



The above part is the tibia bone and the bottom part is the talus bone.


They concluded that only 7 of 25 cases could be considered satisfactory and that arthrodesis was better option for the patients. From there, it is known that ankle prosthesis should not be just a simple hinge (flexion - extension) device due to the small amount of rotation required at the ankle.

For the first generation of Total Ankle Replacement implants were only two parts system which either one is made of metal and the other one is made of polyethylene. These 2 parts implant consist of the talar part and the talus part which only have 1 touching surface that will be allowing only (flexion - extension). These implants were using cemented fixation to fix the implant in the bone.


Regards,


Tim

Addition to the joints movements of Ankle..

Hi, =)

After further reading about the ankle anatomy,
I found out that our ankle is not as simple
as we thought. It consists of 2 important
joints inside our ankle joint. "What is that?"
I know you are wondering.

Ok let me continue. Inside our ankle got this
two types of joints that each one supports
different types of movements which combines to
become the 3 movements that I've mentioned before.
I also think that there is only 1 joint inside
our ankle that support all the 3 movements.
But our ankle is not just a simple hinge. It's
way more than that. :)

So this the name of the joints. Introducing the
first joint, Talocrural joints. This joint is
the meeting point of the Tibia bone and the Talus
bone. This joint supports mainly the dorsiflexion
and plantarflexion. It also support a portion of
the total ankle rotation movements. In extreme
condition, such as the patients stumble or fall,
the Talocrural joint can also support a little
inversion and eversion movement.

The next joint is the Subtalar joint. This is the
meeting point of the Talus bone and the calcaneous
bone. This joint support mainly inversion and
eversion and also a portion of ankle rotation
movement.

Combination of these two joints will produce the
complex movements of ankle. In my project I will
focus on the Talocrural joint as that joint will
be the main problem area because of the arthritis.
As we can see that this joint still supports all
three movements in extreme condition. As a
designer, we need to think of the worst scenario
that can happen so that the implant that we design
will not fail and have as long as possible life
cycles.

As for our ankle rotation movement, it is shared
by the Talocrural and the Subtalar joints. I hope
this infomation can help you to understand about our
ankle and to realize that our ankle are so special
and we need to take a very good care of it. :)

So that's all for now, I will add to this blog in
the near future. Until then, have a nice day.


Regards,


Tim