Intraarticular calcaneus fractures: a biomechanical comparison or two fixation methods.

OBJECTIVE: To compare the strength of fixation obtained using two unicortical 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 subtalar joint complex, consisting of the talus, interosseous ligaments, and calcaneus was removed as a unit. An oblique osteotomy of the calcaneus was then created in the sagittal plane. The two fragments were reduced and stabilized using either two unicortical 4.0 mm diameter cancellous screws or two bicortical 3.5 mm diameter cortical screws. A force 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 the forced applied to the calcaneus created a disruption of the interosseous 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. There was no statistically significant difference in force to failure between the specimens fixed with 3.5 mm diameter cortical screws as compared to those fixed with 4.0 mm diameter cancellous screws.

CONCLUSIONS: The lack of a statistically significant difference in force to failure of the intra-articular calcaneus fractures fixed using 3.5 mm diameter cortical screws as compared to those fixed using 4.0 mm diameter cancellous screws and, the fact that the mode of failure was a disruption of ligaments rather than bony disruption suggest that either method of screw fixation is biomechanically adequate.