Biomechanics and biology of fracture repair under external fixation.

The major factors determining the mechanical milieu of a healing fracture under external fixation, and thereby the mechanism of union, are the rigidity of the selected fixation device, the fracture configuration, the accuracy of fracture reduction, and the amount of physiologic stresses dictated by functional activity and loading. Bone healing problems encountered in fractures stabilized externally merely reflect the severity of the local soft-tissue and periosteal injury and should not be attributed to the inherent features of the fixation modality. Although some surgeons have had reservations concerning the use of external fixation for fracture treatment, based mainly on concerns of pin-tract infection and fracture nonunion, much of the clinical experience and basic science research results have proven the reverse. Many of the potential benefits of external fixation, such as the change of fixation stiffness, are not yet fully appreciated. Additional research and well-organized clinical trials must be performed. Pin-tract problems can be controlled, but the surgeon using such a device must be familiar with the techniques and follow the established regimens during postoperative care. One common mistake is to assume that external fixators, especially those of the simpler unilateral configuration, are easy to use and do not require learning or mastering the surgical techniques until the time of application. Periodic examination and radiographic evaluations are also essential to adjust conditions of the fracture site. The importance of balancing the biomechanical properties and the biologic consequences of different external fixation modalities has been demonstrated. Understanding this knowledge and the techniques of application associated with external fixation is the prerequisite to successful treatment. Some of the basic biomechanical information related to external fixation and bone fracture union is still unknown. This lack should provide the impetus for surgeons, bioengineers, and medical scientists to continue collaborative basic and applied research. Furthermore, by recognizing the proper cell mediators and the physical means to stimulate these cellular elements, the bone fracture healing process may be modulated, regardless of the fixation technique. The result of such effort should provide new modalities to improve fracture management.