This current meeting in Vienna is one of the seasonal events which I care about more. Everything revolves around TM-Ankle, currently the most innovative ankle prosthesis in the entire world.


– Dr. Lew Schon and Dr. Maccario –

Lew Schon, the American surgeon who designed TM-ankle, and me – a surgeon with the best experience in this kind of prosthesis in Europe – have met, shared our experiences during a pre-meeting only for the two of us at first, and then with some other surgeons, picked for their experience in terms of ankle arthrosis all over Europe.

The debate is not only about some technical presentation, but it is also completed by “Bioskills” session that is a “cadaver lab”. It is a learning method which is essential for those approaching a new prosthesis, but also important for those performing a lot of surgeries of the same kind, just like me. This is the right moment when I, during my tutoring activity for other colleagues, can find the confirmation of my assumptions and test the efficacy of new solutions.

But practically speaking, what are the changes in this prosthesis, so important that they can open us to new scenarios?

THE DESIGN: a fixed-bearing one, which is a “resurfacing” one.


– Curved cuts and implants: an actual new ankle – 

Historically, prostheses are divided into: mobile and fixbearing prostheses.

The first type, the mobile ones, are made up of 3 parts: one to replace the tibia, one to replace the talus bone, and a polyethylene mobile “bearing” to repair and compensate for the stress the ankle is subject to.

The latter, the fixbearing ones, are prosthesis made up of 2 parts: tibia and talus bone. The polyethylene is always there, for a tribological reason, but it is already place inside the tibia without not a really independent movement.

The benefit of the first type of design is clearly limiting the periarticular stress; the benefit of the second one is an often wider movement.

Regardless of the key concept behind them, prostheses are implanted by performing some cuts inside the bone, in order to allow their placement. It consists of a linear, flat cut made through the tibia and of a sequence of cuts through the talus bone (roughly, we distinguish between a 2-cut or a 3-cut design).

The first, great innovation of this prosthesis is therefore the curved cut for both surfaces: the tibial and the talus one.

Even an amateur can easily understand how Nature, by designing our ankles, wanted to give us some curved surfaces, rather than straight and pointy ones.

The curved cuts made to allow the implantation of this new prosthesis represent a Copernican revolution!

In fact, we are talking about a fix-bearing design (therefore, with an exceptional range of movement), which limits the stress the prosthesis is usually subject to. The term resurfacing indicates exactly the following: not an invasive joint replacement, more like a “renewal” of joint surfaces, where the bone cuts are minimised.

PROSTHESES MATERIAL: the trabecular-metal.


– Trabecular Metal: a hive, at the disposal of osseointegration. –

This prosthesis owes its name indeed to this material (Trabecular Metal: TM-Ankle). It is the result of the research and development activities made by Tantalio.

It is porotic, just like the bone tissue. In addition, it has its same density and the same elastic response to mechanical stimuli. In a nutshell, it is so much similar to the bone that even osteoblasts and osteocytes (the cells of our bone tissue) recognise it as such and inhabit it.

Therefore, the fixation of prostheses to the bone takes place via direct osseointegration, without the need of cement or any exaggerated press-fit.

This can be compared to an empty hive being populated with bones over the years, and it’s a very quick process!

CROSS-LINKED Polyethylene

Polyethylene is a fundamental element for any kind of prosthesis: hip, knee and, of course, ankle.

As a matter of fact, if two moving surfaces are sliding one on the other, friction and consumption problems need to be minimised.

The combination of metal and polyethylene is a solid and trustworthy solution, demonstrated through years.

For instance, talking about the hip, we moved from ceramic (still successfully used today) to metal-polyethylene and metal-metal structures (that is, structures with both metallic sides). The latter did not give the expected outcome, by causing some metallosis issues in a lot of patients, exactly linked to the friction of one metallic surface against the other.

The cross-linked polyethylene is, instead, an important evolution, which permits it to be used together with the metallic part, with an exceptional guarantee of duration and without any problem of deposit due to the combination of two metallic surfaces.



Historically, the most common access used to implant an ankle prosthesis is the anterior one, thanks to a safety interval between two tendons: tibialis anterior muscle, and extensor hallucis longus muscle. Us surgeons, we define “safety interval” as an area we can “pass through” without the risk of damaging noble structures, such as vessels and nerves.

However, the limit of such anterior access is linked to the ankle and the presence, inside of it, of tendons right under the cutaneous and subcutaneous tissue.

This is a characteristic completely different from other joint such as hip and knee, where muscles and tendons are “protected” by large areas of fat tissue. This peculiarity increases the risk of poor recovery for the injury, in comparison with other joints. Apart from this limit, the anterior approach represents a restricted risk in the possibility to foresee and treat posterior adherences. In a banal way: the anterior one is very clear and accessible, the posterior one is not.

On the contrary, the lateral approach consists in a 7-cm incision at fibula level.

It is clearly the best cosmetic effect: the scar left is not right in front of the eyes constantly, as it happens instead with the anterior approach. However, this is not the real reason to prefer it.

A lateral approach allows indeed to be equidistant from anterior and posterior noble structures, by making the treatment of adherences easier, at both levels.

Also, if lateral approach is being used, fibula offers the implant a natural protection. In fact, in case of a delay in the injury recovery, the prosthesis is literally protected by the fibula (the bone located laterally, inside our ankles), and its potential delay can be managed with extreme calm.


This implant consists of a sort of “castle” where to place the limb during the performing of the surgery.

For the surgeon, this represents a big innovation and a great help.

In fact, ankle arthrosis is often associated with deformities. The surgeon always needs to correct them, if he wants to achieve the goal of implanting a stable prosthesis over time. Sometimes, this procedure is the most difficult part of the entire operation.

This “frame” makes the difference because it permits to stabilise the accomplished correction, by allowing the surgeon to concentrate every effort and attention towards the prosthesis implant, without the fear of losing the previously-achieved corrections.



Materials, design, surgical technique: all together, they contribute to an early load and recovery for the patient.

Historically, the patient having an ankle prosthesis surgery used to undergo long periods of unburdened legs, up to 6-8 weeks.

This implant, and the velocity it is subjected to osseointegration, make a load on the operated limb which is already possible 30 days after the surgery.

Therefore, the patient who is considering surgery has to face 4 weeks only with a cast or support, but without putting his body weight on the operated limb.

He will go back, in fact, to a complete load, from the thirtieth day onwards.

However, daily activities such as driving will only be allowed after 3-4 months.

Lastly, the time needed for the patient to be truly satisfied and return to his sports activities (better if low-impact ones) swings between 6 and 9 months after the surgery.