Orthopedic implant: More comfortable thanks to full weight-bearing capacity

Orthopedic implants – they are a necessity when it comes to congenital or acquired limb length discrepancies. However, full weight-bearing during the limb lengthening process is not feasible with previous implant models. For the first time, the 3D Surgery division at the Medical Center of the University of Munich has succeeded in using an implant that facilitates immediate weight-bearing.

In this MEDICA.de interview, Dr. Peter Helmut Thaller talks about the technique behind the new orthopedic implant, describes the three phases of limb lengthening and lists the features of a perfect leg implant.

On January 29, the Medical Center of the University of Munich successfully used an implant that already offers patients full weight-bearing during the limb lengthening process. It is presently the first and only approved leg implant that offers this type of function in Europe. What makes full weight-bearing possible?

Dr. Peter Helmut Thaller: Unlike earlier models, this implant features a more robust construction, which makes full weight-bearing possible. This is due to a stainless steel alloy composition and interlocking options.

Do the new prosthetic implants offer additional advantages over other implants?

Thaller: There are no further advantages. However, the certified full weight-bearing feature is an important milestone that will drive progress in this area. What’s more, the new prosthetic implant promises rapid recovery at all levels – bone regeneration, overall tropism, and basic joint mobility. Tropism refers to circulation and tissue health. Typically, patients who undergo limb lengthening surgery with an implant that doesn’t allow full weight-bearing learn to walk with the aid of crutches. This means less leg stimulation and more protection for the implant. Meanwhile, in my view, the stimulation of full weight-bearing improves bone regeneration and subsequently tropism.

For which types of impairments/diseases are the new orthopedic implants best suited for?

Thaller: The new orthopedic implants can be used to treat congenital or acquired limb length discrepancies for example. Oftentimes, limb length discrepancies are accompanied by other deformities such as bow legs or knock knees. The implant corrects these deformities. Dwarfism is another implementation for this type of implant. People with dwarfism are restricted in everyday activities due to their condition and this new orthopedic implant promises an improved quality of life. Surgeries are also increasingly performed in younger children and adolescents. That’s something we don’t approve of because the growth plates are still open or haven’t completely hardened yet. The consequences this implant prompts in adult patients is uncertain. That’s why our facility only administers this type of treatment in young children or adolescents in rare, exceptional circumstances that are well-justified.

What technology is the new orthopedic implant based on?

Thaller: The mechanism of the current, fully weight-bearing implant is based on a telescoping technique with a magnetomotive force actuator. This technique can be compared to a car antenna that’s being extended. Most intramedullary lengthening nails are based on this telescoping technique.

How does the body react to the implant after it has been inserted?

Thaller: Normally, it reacts like it is supposed to – by promoting bone growth. This gets more difficult in the case of allergies or incompatibility. We stopped using nickel-containing metal implants ten years ago. This implant has been successful in hundreds of cases, with only three patients exhibiting a nickel allergy. Nevertheless, the limb lengthening process ran smoothly under close supervision until the implants were removed, typically after 1-2 years. In a few cases, we noticed small bone cavities and always at the same spot. These were probably caused by corrosion. The intramedullary nail had to be removed in this case. We use minimally invasive procedures to do this. The largest incision to implant or remove the nail is less than two inches long. We have not used the implants since then.

What are the risks of the new orthopedic implants?

Thaller: There are risks that can occur with any type of implant. They range from dislocation and infection to poor self-healing ability. Having said that, when it comes to the new implant technique, it is essential to consider the relationship between bone regeneration and the planned position of bone fragments. Careful analysis and planning, our enhanced surgical procedures and experience in distraction and aftercare can minimize the risks outlined in medical literature.

Bone formation during limb lengthening is divided into 3 phases: the distraction, consolidation and remodeling phases. So far, limb lengthening involved the use of fully implantable intramedullary nails. On average, how long is the recovery time for patients with intramedullary nails compared to patients with the new orthopedic implants?

Thaller: The distraction phase is the critical phase because it requires the most experience. In this setting, the bone is usually lengthened 1 mm per day. That is to say, if you want to achieve 30 mm in length, the distraction phase lasts 30 days. There is no change during this phase, except that unlike patients with conventional implants, our patients are soon able to walk without the aid of crutches. The consolidation phase is next. Previously, the normal length of the consolidation phase is either as long or twice as long as the distraction phase. That is to say, limb lengthening of 30 mm takes 30 - 60 days of consolidation. A major characteristic of this phase is much faster bone regeneration and significantly improved general recovery. I am certain the faster recovery is a result of full weight-bearing. Remodeling takes several months. Patients are barely restricted during this phase. In my view, this phase is comparable to the time required by earlier implant models.

In your opinion, what are the features of a perfect orthopedic implant?

Thaller: A perfect intramedullary lengthening nail should have a safe and strong actuator, that is to say, it should not shorten when subjected to weight-bearing. The actuator should also facilitate a controlled shortening. The shortening of the intramedullary nail should not require anesthesia or need for surgery
for the patient. What’s more, the actuator should also be robust and prevent uncontrolled backtracking. Full weight-bearing is likewise an important characteristic, which is now a feature of our approved new implant. Miniaturization is equally important because not every bone is big enough to place an earlier implant model. In this case, we would appreciate intramedullary nails that are thinner and possibly shorter but still ensure the same lengthening capacity. This would allow us to use intramedullary nails in bones that were previously too small for these types of procedures. Having said that, it is important to take static, structural and material limitations into account.