Use of Biologically and Mechanically Compatible Implants in Neurosurgery: Main Principles

E.A. Davydov1, O.N. Dreval2, A.A. Ilyin3, M.Yu. Kollerov3

( 1 Polenov Research Neurosurgical Institute, Saint Petersburg;
2 Faculty of Neurosurgery, Russian Medical Academy of Postgraduate Education;
3 Russian Aviation Technological Institute-Tsiolkovsky State Technological University, Moscow)

A concept of using biologically and mechanically compatible implants (BMCI) in neurosurgery was formed at the end of the XXth century. Its further development continued in the XXIst century. This concept is a result of close cooperation of doctors and engineers.

The concept of BMCI reflects a new ideology and original principles of design, production and use of hyperelastic fixators, imitating live tissues, for surgical treatment. It has united up-to-date or, as a matter of fact, cosmic technologies of fixators production and possibilities, granted by their use in modern medicine.

Hyperelastic implants are intended for restoration or strengthening bony, cartilaginous and fibrous structures of the spine. They ensure physiologic mobility of vertebral locomotive segments, as well as joining of bones of the skull and facial skeleton. Besides, these implants can be applied in traumatology and orthopedics for fixation of bone, cartilaginous and fibrous tissue of the rest skeleton. Outside Russia some modalities, included into this concept, are called dynamic fixation.

BMCI are made of materials with thermomechanical memory of a shape. These materials are based on titanium nickelide with a heterophasic microstructure, which provides pre-set and stable characteristics of both an effect of memorizing a shape and hyperelasticity.

Thermomechanical memory of a shape means, that a fixator, deformed in a cooled state, can keep this shape as long as one wants. When heated within a preselected range of temperatures, it restores its initial shape and manifests its hyperelastic properties. If an external counteraction hampers its restoring an initial (operating) shape, there appears reactive tension and the fixator begins to act, slowly bringing together fixed segments or correcting axial deformity.

Products, made of titanium and nickel alloy, endure more than 50 000 cycles of sign-variable loads. It concerns even elongations, which are ten times bigger, that those, endured by devices, made of conventional materials.

The spine is a complex mobile structure, allowing to flex, extend and rotate in different planes. A fixator with unique properties gives surgeons a chance not only to restore a lost fragment of the spine or some other anatomic structure, but also to imitate such absent function, as, for example, movement of an intervertebral disc, extension of interspinous and supraspinous ligaments, etc.