INTRAARTICULAR CALCANEUS FRACTURES - A BIOMECHANICAL COMPARISON OF 2 FIXATION METHODS

Objective: To compare the strength of fixation obtained using two unic ortical 4.0 mm diameter cancellous screws versus two bicortical 3.5 mm diameter cortical screws in the fixation of intra-articular calcaneus fractures. Design: In eight paired fresh frozen cadaver feet, the sub talar joint complex, consisting of the talus, interosseous ligaments, and calcaneus was removed as a unit. An oblique osteotomy of the calca neus was then created in the sagittal plane. The two fragments were re duced and stabilized using either two unicortical 3.0 mm diameter canc ellous screws or two biocortical 3.5 mm diameter cortical screws. A fo rce was then applied to the medial calcaneal tuberosity until failure occurred. In all specimens testing was discontinued due to ligamentous failure, without causing bony disruption. Results: In all specimens t he force applied to the calcaneus created a disruption of the inteross eous ligaments across the subtalar joint and rotation of the calcaneus on the talus. Thus in each specimen, testing was discontinued due to interosseous ligamentous failure, without causing bony disruption. The re was no statistically significant difference in force to failure bet ween the specimens fixed with 3.5 mm diameter cortical screws as compa red to those fixed with 3.0 mm diameter cancellous screws. Conclusions : The lack of a statistically significant difference in force to failu re of the intra-articular calcaneus fractures fixed using 3.5 mm diame ter cortical screws as compared to those fixed using 4.0 mm diameter c ancellous screws and, the fact that the mode of failure was a disrupti on of ligaments rather than bony disruption suggest that either method of screw fixation is biomechanically adequate.