Purpose of the study: The major problem in external fixation of upper metaphyseal tibial fractures with a double-frame Hoffmann device is poor healing. With a dynamic fixation, it would be possible, with no change in technique, to compress the fracture site in a second phase, and therefore to facilitate the healing process. However, a new fixation device should not compromise the primary stability of the fixation. The aim of this experimental study on cadavers was to compare, in conditions very close to a clinical situation, the initial stabilization capability of five types of external fixation.
Material: Five types of external fixators were tested on cadavers specimens: 1. a standard double-frame Hoffmann 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 dynamic axial fixation device with 5-mm cylindrical pins; and 5. a mixed device including an lizarov-type epiphyseal fixation and a monoplane diaphyseal fixation.
Methods: The metaphyseal fracture was simulated by a transversal resection of a 20-mm segment. Specimens received by increments a load of up to 310 N, with which it was possible to determine stiffness components in valgus/varus, flexion/extension, rotation around the vertical axis and axial vertical displacement. The bone mineral content of the specimens was measured by Di Energy X-ray Absorptiometry.
Results: The stabilization characteristics of type-1 axial dynamic fixation were identical to those of the standard Hofmann's device in flexion/extension and in rotation as well as axially, but a greater mobility in valgus/varus was observed. The sagittal reinforcement of Hoffmann's device increased its rigidity in flexion/extension. The mixed lizarov 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 showed that the individual variability of bone mineral content is a negligible parameter.
Discussion: The experimental behaviour of the mixed Ilizarov device gives to assume that it may facilitate the healing process without endangering the primary stability of the fixation. However, this theoretical advantage should be validated in a randomized prospective clinical study.