Prof. Bruno Magnan
Institute of Clinical Orthopaedics and Traumatology, University of Verona
Endorthesis screws are indicated for calcaneo-stop surgery that is proposed as a conceptually ideal solution for the treatment of calcaneal valgism in children,
What is the retrograde endorthesis screw?
The retrograde endorthesis screw is an implantable device that makes it possible to perform calcaneo stop operations in a modern and safe fashion.
What is a calcaneo stop operation?
It is a surgical procedure to easily perform a subtalar arthrodesis, that is limiting joint excursion of the subtalar joint of the foot-that is, the joint between the talus and the underlying calcar-used in pathological cases in which the joint excursion is excessive.
What are the indications?Precisely those syndrome, those situations that today are defined as syndromes of excessive pronation of the subtalus.
Basically, they are those once known as "flat feet" or "flat-footedness" and which today have as a common aetiopathogenetic factor this excessive excursion toward the pronator, that is, outward, the "valgus" we can say of the subtalar joint.
The calcaneo stop alteration followed by implantation of the retrograde endorthesis screw is indicated electively at a developing age, and by this we mean when indications for surgery exist, that is, between nine and thirteen years. All of this to say that not all flat feet in children or adolescents must be operated upon, but only those feet that today we define functionally and not solely morphologically flat, and therefore not only with a flat appearance as was often believed in the past.
They are those feet that throughout the entire execution of a step, during the active phase of muscular contraction, remain flat; they never contract and therefore maintain unchanged this position of the subtalar joint. It is on this element that a calcaneo stop operation followed by implantation of the endorthesis screw can most certainly have an important effect.
How is the device applied?
These devices in general, many of them exist, are placed at the level of the external opening of the tarsal sinus, which is a virtual space that exists between the talus and the exterior calcar, which does not involve the cartilaginous joint surfaces between the two.
The peculiarity of this retrograde device is precisely the direction of application which is called for in a retrograde direction, that is distoproximally from the plantar surfaces of the calcar: toward the talus it perforates and penetrates into the tarsal sinus until it abuts at the correct length on the lateral process of the talus.
This is also common to other devices, but with the retrograde screw it makes it possible to avoid surgical assault, to not open the tarsal sinus, and this makes it possible to avoid damaging its content, which are many proprioceptive receptors and many neuroreceptors that are important and one of the mechanisms of the action of the endorthesis.
Are their contraindications?Contraindications do exist, and are those flat feet in which the screw cannot function; that is secondary flat-footedness, as for example in neurological diseases.
These neurotransmitters, these neuroreceptors do not function, there is a deficit in the neurological mechanism and therefore the screw does not transmit the impulses required for active correction of the deformity, even in cases of flat-footedness from pathological capsuloligamentous laxity.
To give an example, the so-called Marfan's syndrome: laxity due to pathological accumulations, for example of a polysaccharide type or in Down's syndrome in which the neurological mechanisms or those of ligamental laxity pathology are combined. In this situation it has been seen that endorthesis is insufficient precisely because of the lack of one of the mechanisms that completes the correction.
How does the endorthesis screw work?
The retrograde endorthesis screw of the calcaneo stop acts with a dual mechanism, a passive mechanism and an active mechanism. The passive mechanism is rather intuitive: it creates a stop for excessive excursion of the joint, and therefore of penetration, the deepening of the lateral process of the talus on the surface above the calcar.
The presence of this metallic screw holds back the talus and therefore creates a stop avoiding excess pronation.
Certainly this is a mechanism that will not be sufficient, because in the long run this method of synthesis would cause damage to the talus, it would penetrate inside the bone structure, principally in the case of children, and this has in fact been seen in situations of secondary neurological flat-footedness.
The active mechanism on the other hand, is a stimulus that has as a different point all of the receptors in which the tarsal sinus is so rich, both proprioceptive and sensitive, and which integrate at the medullary and spinal level a contracting reflex of the supinators that during a step provide corrective action precisely during that phase in which it is lacking in all flat-footedness that today we call functional.
Are further surgical steps required?Yes, in certain cases it is necessary to associate other surgical steps.
We have looked at the review of a very extensive number of case studies, that this can occur in approximately 40-50% of cases-that is, for 50-60% just the endorthesis is sufficient to achieve full correction.
In some cases for example, in the presence of pathological shortness of the Achilles tendon, it is necessary to lengthen this tendon, which we do today with an invasive method, making small percutaneous incisions in order to lengthen this tendon, which is considered one of the causes that institutes sustained flat-footedness.
Another situation that requires a further surgical procedure is when the pronatory syndrome, this flat-footedness, involves in a serious fashion the other parts of the foot such as the midfoot or forefoot.
These are the so-called "flat-oval" feet, which are serious and require the correction to be completed on these structures as well, and therefore calls for a surgical procedure that will be performed medially at the level of the midfoot. There are various techniques that can be associated equally successfully with the calcaneo stop.
Is the implant permanent or temporary?
We can say that many of the devices conceived for the calcaneo stop in the past, relying on simple osteosynthesis screws, were considered temporary; that is, they had to be necessarily removed after a period ranging from 18 to 36 months, that is, at the end of their function. Retrograde endorthesis however was conceived and designed to be permanent.
This is because of a special shape that allows it to be as if involved and incorporated into the bone structure of the calcar during growth at the end of its function. In fact, we were able to examine multicentric case studies of feet operated with this retrograde screw technique in approximately 500 cases, and we were able to observe that the screw had been removed in approximately 9% of cases, and of these in 6% due to the effective presence of a complaint or pain that required removal when correction was terminated.
What are the results?I'd say that they're very good and encouraging over time.
By now the calcaneo stop has a 20-year history; the retrograde endorthesis screw came to light in 1983.
Today if we can define the ideal operation for correcting flat feet, which is a delicate elective operation in children, we can say that the operation must be easy, safe, brief, not very traumatic, and effective.
Even if, as always happens, the perfect operation does not exist, I would say that the calcaneo stop using retrograde endorthesis meets these requirements.
In the over 500 case studies that I referred to earlier, we found that the correction desired was obtained in approximately 92-93% of cases.
Compared with a higher incidence of complications, and by that I mean infections, breakage of the device, or damage to the joint surfaces, less than 1%, therefore fully confirming the approach of this operation.