A new system to improve screw fixation to bones

Abstract

Plates and non-locked screws used in the treatment of osteoporotic bone fractures frequently become loose due to everyday mechanical demands. Currently, locking plates and screws are the gold standard treatment for these fractures. However, their use has several limitations and complications as they are technically demanding, and their cost is very expensive. To improve the fixation strength of traditional unlocked plate and screw constructs, we have developed a new fixation system based on a very old concept. The system consists of a screw locking element (SLE) manufactured from PEEK, which is attached to the end of the screw shaft once it has traversed both bone cortices. A specially designed tool is used to facilitate its attachment to the screw. This tool makes it possible for the screw to traverse an osteosynthesis plate or lockwasher as well as both bone cortices and to easily find the SLE, fixing it against the far cortex. We tested the pull-out strength of SLEs and compared the results with previously published data for human femoral cortex pull-out strength. Our laboratory tests demonstrate that the mean SLE pull-out strength was 3864 +/- 47.61 N, while that observed for a human femoral diaphysis cortex was 4071.54 +/- 1461.69 N. This difference was not significant (p > 0.05). This new system can easily be used with any type of osteosynthesis in osteoporotic or osteopenic bones, with the screws being placed on weakened areas of the bone (e.g., fissure lines, previous orifices, or thinned metaphyseal bone cortex), or to replace over-torqued screws. It is particularly suitable for veterinary trauma, where immediate weight-bearing protection after fracture treatment is nearly impossible. [DOI: 10.1115/1.4005227]