External dynamic fixation in fractures of the humerus: can it still be considered treatment of second choice?

The authors report 40 patients affected with diaphyseal fracture of the humerus treated by dynamic axial fixator (FAD Orthofix). Minimum follow-up was 2 years. A clinical and radiographic retrospective study was conducted with the purpose of verifying the validity of external fixation as treatment of choice in diaphyseal fractures of the humerus. The results were evaluated considering healing time, extent and type of complications, long-term clinical, radiographic and functional findings. Results were: excellent: 35; good: 2; fair: 2; poor: 1. Complications were: nonunione: 1; reimplantation of FAD screws: 1; 4 infections of the screw holes, 3 realignments due to secondary displacement, 1 re-fracture after removal of the implant. There were no iatrogenic lesions of the radial nerve, or infections of the fracture site. The authors conclude that this semi-invasive, versatile and well-tolerated method, may be considered a valid alternative to conservative treatment, or to internal fixation even in cases of single trauma, despite limits related to the degree of collaboration of the patient, particularly with regard to debridement of the screw holes and periodical clinical and radiographic monitoring.

Biomechanical factors in designing screws for the Orthofix system.

In a monolateral external fixation system, bone grip is achieved optimally using half pins. This article reports the mathematical modeling used to design the screws and the drills of the Orthofix system. The diameter of the shank must be such that there is no risk of fracture at the screw entry point. It must also provide high strength under weight-bearing deformation stresses. The shape of the threaded part must allow the highest possible bone-gripping strength while minimizing slackening in relation to external and internal loads. The thermal effects of drilling and screw insertion must be considered to minimize necrotic damage that may stimulate reabsorption phenomena around the screw. The design of the different components of the pins must vary according to all the above factors to ensure optimal interaction between the fixator, screw, and bone.