Biomechanical Comparison Of The Combined Partially Threaded Cancellous Lag Screw And Partially Threaded Cancellous Lag Screw

The partially threaded cancellous lag screw (PTLS) is the standard screw for establishing rigid fixation in intra-articular fractures. However, its use in the clinical setting is associated with difficulties in obtaining the optimal compressive force (CF) and screw purchase (pullout strength [POS]) for rigid fixation. In the present study, we investigated whether the combined PTCLS (CPTLS) outperforms the PTLS in creating CF and maintaining POS. The CF and POS were measured after the PTLS and CPTLS were tightened manually for compression by a surgeon using surrogate cancellous blocks of three different densities: 0.12, 0.16, and 0.20 g/cm(3). The CF and POS of the CPTLS were significantly higher than those of the PTLS (P < 0.001). The CPTLS outperformed the PTLS in terms of the coefficient of variance of CF. CF and POS were affected by the bone mineral density and screw design (P < 0.001), and there was no interaction between these two factors (P = 0.872 for CF and P = 0.909 for POS). Our results demonstrate that the CPTLS is better than the PTLS for creating compression, as its use improved the compressive ability, resulted in better screw purchase, decreased compression-induced damage to the surrounding cancellous bone, and reduced the possibility of inadvertent incomplete tightening, overtightening, and screw stripping.