Simulation for Reduction of Transverse Acetabular Fractures in Sawbones Models

PURPOSE: The transversely oriented fracture lines are very difficult to reduce during operations, even after clear exposure of the fracture site, in acetabular fractures. The purpose of this study is to verify the quality of reduction between the different subtypes (transtectal, juxtatectal, and infratectal) of transverse fractures. This study also determined the proper type of clamps to use and the proper zone for achieving accurate reductions in Sawbones models. MATERIALS AND METHODS: Six fractures in 3 different subtypes of transverse fractures were artificially created. Ten different reduction clamps were applied for reduction of the fractures. Twelve holes around the fracture were drilled for the maintenance of the clamps. The fracture displacements were measured at the extra-articular area and the intra-articular joint portion. The pictures of the intra-articular fracture displacements were taken by a camera and these were uploaded and analyzed by the TraumaCad® computer program (Brainlab). RESULTS: The reduction quality was poor in order of transtectal, juxtatectal and infratectal. The intraarticular opening was more prominent in the transtectal subtype. The safe zone, when giving consideration of the neurovascular bundles, was a quadrilateral surface of the ilium. Drill holes are useful for maintenance of the reduction clamps. Reduction clamps with points (Weber clamp) were the best for maintenance and accurate reduction. Regarding the concerns of placement of clamps, the middle to posterior combination was the best. The upper hole among the posterior holes in the ilium was the most likely to well reduce the intra-articular opening. CONCLUSION: Transtectal was the more complicated subtype in the aspect of reduction quality. The Weber type reduction clamp was the best for reduction by centrally located holes in the quadrilateral surface and posteriorly located iliac holes in transverse acetabular fractures. The upper hole, among the posterior holes in the ilium, was the best for reduction of the fracture displacements in the intraarticular portion of acetabulum.

Biomechanical Comparison of Inter-fragmentary Compression Pressures: Lag Screw versus Herbert Screw for Anterior Odontoid Screw Fixation

OBJECTIVE: The purpose of the present study was to compare inter-fragmentary compression pressures after fixation of a simulated type II odontoid fracture with the headless compression Herbert screw and a half threaded cannulated lag screw. METHODS: We compared inter-fragmentary compression pressures between 40- and 45-mm long 4.5-mm Herbert screws (n=8 and n=9, respectively) and 40- and 45-mm long 4.0-mm cannulated lag screws (n=7 and n=10, respectively) after insertion into rigid polyurethane foam test blocks (Sawbones, Vashon, WA, USA). A washer load cell was placed between the two segments of test blocks to measure the compression force. Because the total length of each foam block was 42 mm, the 40-mm screws were embedded in the cancellous foam, while the 45-mm screws penetrated the denser cortical foam at the bottom. This enabled us to compare inter-fragmentary compression pressures as they are affected by the penetration of the apical dens tip by the screws. RESULTS: The mean compression pressures of the 40- and 45-mm long cannulated lag screws were 50.48±1.20 N and 53.88±1.02 N, respectively, which was not statistically significant (p=0.0551). The mean compression pressures of the 40-mm long Herbert screw was 52.82±2.17 N, and was not statistically significant compared with the 40-mm long cannulated lag screw (p=0.3679). However, 45-mm Herbert screw had significantly higher mean compression pressure (60.68±2.03 N) than both the 45-mm cannulated lag screw and the 40-mm Herbert screw (p=0.0049 and p=0.0246, respectively). CONCLUSION: Our results showed that inter-fragmentary compression pressures of the Herbert screw were significantly increased when the screw tip penetrated the opposite dens cortical foam. This can support the generally recommended surgical technique that, in order to facilitate maximal reduction of the fracture gap using anterior odontoid screws, it is essential to penetrate the apical dens tip with the screw.