EXPERIMENTAL-STUDY OF THE STABILIZATION C APABILITY OF DIFFERENT EXTERNAL FIXATORS IN THE UPPER METAPHYSEAL TIBIAL FRACTURES

Purpose of the study The major problem in external fixation of upper m etaphyseal tibial fractures with a double-frame Hoffmann device is poo r healing. With a dynamic fixation, it would be possible, with no chan ge in technique, to compress the fracture site in a second phase, and therefore to facilitate the healing process. However, a new fixation d evice should not compromise the primary stability of the fixation. The aim of this experimental study on cadavers was to compare, in conditi ons very close to a clinical situation, the initial stabilization capa bility of five types of external fixation. Material Five types of exte rnal fixators were tested on cadavers specimens:1- a standard double-f rame Hoffmann's device; 2- a double-frame Hoffmann's device sagittaly reinforced with two additional anterior-posterior half-pins; 3- a type -1 axial dynamic fixation device using 6-mm conical pins; 4-a type-2 d ynamic axial fixation device with 5-mm cylindrical pins; and 5- a mixe d device including an llizarov-type epiphyseal fixation and a monoplan e diaphyseal fixation. Methods The metaphyseal fracture was simulated by a transversal resection of a 20-mm segment. Specimens received by i ncrements a toad of up to 310 N, with which it was possible to determi ne stiffness components in valgus/varus, flexion/extension, rotation a round the vertical axis and axial vertical displacement. The bone mine ral content of the specimens was measured by Di Energy X-Ray Absorptio metry. Results The stabilization caracteristics of type-1 axial dynami c fixation were identical to those of the standard Hoffmann's device i n flexion/extension and in rotation as well as axially, but a greater mobility in valgus/varus was observed. The sagittal reinforcement of H offmann's device increased its rigidity in flexion/extension. The mixe d Ilizarov fixation was stiffer than the standard Hoffmann's device in rotation; it was equivalent in valgus/varus and flexion/extension and less stiff in axial vertical displacement. in this study it was showe d that the individual variability of bone mineral content is a neglige able parameter. Discussion The experimental behaviour of the mixed Ili zarov device gives to assume that it may facilitate the healing proces s without endangering the primary stability of the fixation. However, this theoretical advantage should be validated in a randomized prospec tive clinical study.