The effects of screw placement on plate strain in 3.5 mm dynamic compression plates and limited-contact dynamic compression plates

Abstract

The objective of this study was to evaluate the effect of screw omission on plate strain during axial load to failure and cycling using a Delrin rod gap model. In addition, the differences between the 3.5 mm limited-contact dynamic compression plate (LC-DCP) and the 3.5 mm dynamic compression plate (DCP) were evaluated. Six, 12-hole LC-DCP and DCP plates were applied to Delrin rods with a 1 cm gap located within the central portion of the plate. Six screw configurations were tested with the following variations: three proximal and three distal (six open), four proximal and three distal (five open), four proximal and four distal (four open), five proximal and four distal (three open), five proximal and five distal (two open), six proximal and five distal (one open). Three strain gauges were mounted on each plate within the gap (gauge three) and extended proximally. Additionally, three constructs (six, three, and one open hole) were tested to failure in cyclic loading. The strain measured within the gap (gauge three) was significantly greater than the strain at other gauges for each screw configuration. Strain within the gap did not significantly change with any screw configuration, but did significantly increase at other locations as screws were omitted. Overall, the DCP withstood significantly more cycles than the LC-DCP. Differences were noted within the DCP group with the 6/5 screw configuration lasting for significantly more cycles than the 5/4 and 3/3 constructs. Although overall strain at the gap did not significantly increase with screw omission, the clinical significance remains to be determined.