From Prosthesis to Prosthesis
From Arthrodesis to Prosthesis
Ankle arthroplasty is the solution to pain and the functional limitations of ankle arthritis
What is Ankle Arthroplasty?
Ankle arthroplasty is the replacement of a joint with an implant that reproduces the same movement and that is as close as possible to its physiology.
The treatment for arthritis and some types of ankle deformities may require the use of this technique.
An ankle is composed of tibial and peroneal articular surfaces that meet, in the foot, with those of the talus, ensuring movement and distribution of the weight while walking.
When this delicate balance is compromised, for example due to the occurrence of post-traumatic arthritis, it may be necessary to intervene surgically to replace the degenerate articular surfaces with the implantation of an ankle prosthesis.
The Prosthetic Design
Each prosthetic design must find a point of union between two antithetical concepts:
- articular congruency, which is necessary to replicate the original anatomy as much as possible;
- constraint (the limitation of the movement of the components) to be managed carefully to avoid instability and consumption.
The first reliable union between these two concepts arises, historically, with the mobile-bearing prostheses: implants with a tibial component, an talus component, and a polyethylene mobile part placed between these two.
This implantation philosophy has allowed the dissipation on two interfaces (first, the mobile polyethylene and, second, the talus component) of the mechanical stress that the prosthesis must tackle.
Diminished stress has translated into a reduction of the necessary pieces: with mobile-bearing the historical and inconvenient bulk of the first and second generation prostheses has been reduced.
The most immediate result for patients is the longer duration of the implant.
On the contrary, the limit is the reduction of the joint range. In fact, the mobile bearing rarely offers the patient a “broad” movement, which happens in a physiological ankle.
The lesson learned from mobile-bearing is the need to keep the implants the least voluminous possible to promote bone-stock savings for the tibia and talus.
Mobile-bearing is still current today; in fact, from its heritage of acquisitions were born modern designs, with greater functional potential and reduced invasiveness for the patient.
The priority objective today is to increasingly replicate the anatomy of the original ankle: the modern prostheses associate the idea of saving the bone-stock with the goal of better functionality.
Ankle Resurfacing Prosthesis
It is possible to explain the evolution and the success of the fix-bearing resurfacing design, a prosthetic design that provides a single movement interface between the tibia and talus, without a movable part between the two, and which associates improved joint movement to important bone saving.
Resurfacing allows the reproduction of the original ankle anatomy starting from two simple, but fundamental, premises.
First of all, the articular surfaces of tibia and talus are curved.
With resurfacing, bone resection (surgical removal of a more or less extended portion of a bone) can be minimized by performing curved cuts, i.e. respecting the natural curvature of the tibia and talus.
In order to carry out these types of cuts it is necessary to have a lateral approach. Here is the first innovation of the resurfacing: curved cuts to reproduce the original anatomy of the ankle, performed on the side (through an osteotomy of the fibula that allows exposure of the joint) offering a direct view of the center of rotation of the neo-articulation.
To reproduce the anatomy of the ankle it is necessary to think of a prosthesis composed of two pieces: the tibial and the talus’ articular surface, thus excluding the compensation of the mobile part, which is a central element in the mobile-bearing prosthesis.
In order for this to be possible, it is essential to use innovative, technologically advanced materials. This is the second big innovation of resurfacing: the use of Trabecular Metal ™.
It is a material derived from the processing of Tantalum, able to faithfully reproduce the porosity and all the other biomechanical characteristics of bone tissue.
Trabecular Metal ™ allows bone reconstruction so reliable that it is recognized and hosted by the body itself as real bone tissue. This feature guarantees an unprecedented osseointegration, both in terms of stability and of healing time.
It is the Trabecular Metal ™ and the curved cuts that allow the resurfacing to give us a prosthetic implant with an intrinsic stability well above average.
These two characteristics always make it possible to renounce the third mobile element (polyethylene part): we are therefore talking about a fix-bearing arthroplasty (with 2 components), which means greater movement for neo-articulation, but also generally faster recovery times.
I immediately embraced and developed these concepts in my practice and, today, on this particular prosthetic design, my team has the greatest case study in Europe.
It is a choice that is as revolutionary as is reliable and offers great advantages.
A prosthesis that approaches a healthy ankle in form and function.
A Prosthesis that Approaches a Healthy Ankle in Form and Function: Our Scientific Research
The big difference between the ankle and other large joints of the lower limb (hip and knee) is that the ankle rarely ages.
Very often, even in very old patients, the ankles are healthy.
Pain and arthritis are outcomes of trauma (fractures) and deformity.
Therefore, it is not uncommon to see patients who have one ankle with arthritis with the other one perfectly healthy.
It is much rarer for this to happen in the knee or in the hip because the patient shows signs of arthritis bilaterally as he gets older.
This feature has given us the opportunity to compare two different prosthetic designs with the healthy ankle (the contralateral to the operated one).
It was truly an innovative study: “Tibial slope in total ankle arthroplasty: Anterior or lateral approach” that allowed us to see, with the resurfacing prosthesis, a restoration of the axes and the articular angles very similar to that of the healthy ankle.
It means that the prosthetic resurfacing design is closer to the goal of replicating the original ankle in form and function.
Of course, it is important to remind the patient that an ankle prosthesis, even the resurfacing, will never behave like the healthy ankle of a twenty-year-old patient, but the closer it is to the healthy ankle shape, the more it will replicate its performance.
My Team and Research: What we have brought to the table
When this prosthetic design was created it was obviously associated with a new surgical technique.
The limits that this new design could have had were the longer surgeries compared to other prosthetic designs. This is explained with the accuracy and precision of the tools.
Our experience in treating patients with osteoarthritis and the custom of prosthetic surgery of our group has allowed me to develop an original surgical technique, which combines the great precision of this system with reduced surgery length, with considerable advantages for the post-operative patient course.
Today two publications in international journals talk about our technique, which is proposed and taught to the many Italian and European visitors who attend our operating theaters daily with the aim of learning or improving in prosthetic surgery: “Treatment of Ankle Osteoarthritis with Total Ankle Replacement Through a Lateral Transfibular Approach “and” Total ankle replacement through a lateral approach: surgical tips “.
The key to prosthetic surgery is the attention to every detail:
- patient preparation;
- post-operative pain control;
- the precision and promptness of every gesture in the operating room, not only mine, but the team in general.
This justifies the importance of numbers in prosthetic surgery and the role that reference centers and dedicated teams should have in the treatment of ankle arthritis and in the training of surgeons who wish to learn to treat this condition.
These are subjects that we have studied and study with great interest. The summary of our thoughts is contained in two of our publications on the subject in international journals: “Identifying the learning curve for total ankle replacement using a mobile bearing prosthesis” (published in the European journal of Ankle and Foot Surgery: Foot and Ankle Surgery) and “Pearls and Pitfalls for a Surgeon New to Ankle Replacements” published in Foot and Ankle Clinics.
Today, for a standard ankle replacement surgery, without any additional times, we expect an average surgical procedure of less than 70 minutes, with patient dismissal criteria reached within 48 hours of surgery in 80% of cases.
Of course, the achievement of complete patient satisfaction follows a longer path.
In fact, our patient is discharged with an ankle cast ending under the knee, which is kept in place for a period that can vary, depending on clinical parameters, between 15 and 30 days.
The next step is that of an articulated brace that allows complete weight load. This full load support, however, is normally granted after 15 days.
The free weight load, without boot help, is usually granted for 45 days. However, even at this point, difficulty can be normal.
Patient satisfaction is reached in a period that varies between 4 and 10 months after surgery.