External Ring Fixation versus Screw Fixation for Ankle Arthrodesis: A Biomechanical Comparison

Abstract

The use of external ring fixation for ankle arthrodesis offers an alternative to internal screw fixation when bone quality is suboptimal, when complex ankle pathology is present, and as a salvage procedure for complicated cases. Additionally, it permits earlier weightbearing and postoperative adjustment of bone alignment and joint compression. This study was designed to determine whether there are differences in initial ankle joint fixation integrity between these two techniques. Ten fresh-frozen cadaveric lower extremities underwent ankle arthrodesis with a hybrid ring fixator, and the bending and torsional stiffness of each arthrodesed joint was quantified. Stiffness was calculated from angulation measured at the tibiotalar joint using electronic clinometers attached to those bones. The external fixators were then removed and ankle arthrodesis performed using 6.5-mm cannulated screws: three across the ankle joint, one fixing the fibula to the tibia, and one fixing the fibula to the talus. Stiffness testing was then repeated. No statistically significant difference in bending stiffness, torsional stiffness, or joint rotation under torsional load was demonstrable between the two techniques. The similarity in ankle fusion site stability achieved with external ring fixation and an optimized screw fixation technique under the described testing conditions indicates that, in cases in which suboptimal bone quality or complex ankle pathology preclude the use of internal fixation, an external fixator is a viable option. Establishing that the primary stability of external ring fixation is comparable to that of screw fixation provides a basis for its use in cases in which screw fixation may be problematic.