Session VI - Basic Science
Sat, 10/9/04 Basic Science, Paper #34, 9:40 am
Biomechanical Evaluation of Bicortical Compression Plating versus Unicortical Locked Plating in the Fixation Forearm Fractures
Purpose: We compared the biomechanical fixation behavior of unicortical locked fixation to bicortical non-locked fixation in a forearm model.
Methods: Six matched pairs of fresh-frozen cadaveric ulnas were divided to receive locked unicortical or non-locked bicortical plate fixation. Non-destructive four-point bending tests were performed on intact specimens. Specimens were then osteotomized and fixed with use of 3.5-mm LCDC plates (Synthes), or 3.5-mm locking plates in a unicortical mode (Synthes). Non-destructive four-point bending tests were repeated. Finally, specimens were loaded to failure. Matched pairs of radii were prepared in identical fashion and torsional loading performed with the same protocol. The Student's t-test was used for statistical comparison (P <0.05). Bone densitometry (DEXA) scanning was performed on all specimens.
Results: Intact specimens with unicortical holes were stiffer in bending (47%, P <0.03) and torsion (9%, P <0.34) than those with bicortical holes. Unicortical, locked plating of osteotomized specimens showed increased stiffness during four-point bending (22%, P <0.19) and decreased stiffness during torsional loading (48%, P <0.02) compared with osteotomized specimens with bicortical fixation. Locked and non-locked fixation of the osteotomized specimens had equal failure moments during four-point bending (32.2 Nm versus 32.1 Nm), but unicortical locked plating of osteotomized specimens had reduced torque to failure (58%, P <0.01) compared with bicortical non-locked plating. Bone densitometry testing as measured by DEXA scanning showed no significant side-to-side differences within each matched pair. Comparison of bone density between specimens showed no significant relationship with behavior of fixation in various constructs.
Conclusion: In this cadaveric forearm model, intact specimens with unicortical screw holes were stiffer during the application of bending and torsional loads than those with bicortical screw holes. Unicortical locked plating of the osteotomized specimens showed increased stiffness during four-point bending and decreased stiffness during torsional loading when compared with bicortical LCDC plate fixation of the osteotomized specimens. Although locked unicortical and non-locked bicortical plate fixation of the osteotomized specimens had equal failure moments during four-point bending, unicortical locked plating of the osteotomized specimens had a much smaller torque to failure when compared with bicortical non-locked plating of the osteotomized specimens.
Clinical Significance: Forearms plated with unicortical locked fixation have less risk of re-fracture after hardware removal. Although unicortical locked plating is stronger in four-point bending, it is more likely to fail during torsional loads. Postoperative rehabilitation protocols may need to be modified to avoid torsional loading when unicortical locked-plate fixation is used in the treatment of forearm fractures.