Biomechanical comparison of two tension band wiring techniques for transverse patella fracture fixation: an in vitro study of 3-D printing models

Patella fractures are relatively rare, though effective treatment of these fractures is essential. Screws and cerclage cable have been proposed to treat displaced patellar fractures to overcome the disadvantages of the modified tension band technique. The aim of the present study was to compare the in vitro biomechanical behaviour of a surgical construct consisting of screws and cable cerclage figure-of-eight tension band against the classic tension band technique using a specifically designed 3-D printed model of patella fracture. The patellar-fracture fixation systems tested in the current study consisted of screws and cerclage cable tension band compared to a conventional modified AO (Association of Osteosynthesis) tension band. Each system was tested in ten 3D- printed patella – fracture models. Two trials were designed to reproduce the forces the patella withstands throughout the range of knee motion. Differences between forces and displacement were explored with the Student t test. In the extension test, the between-group difference of the force required for failure was 1455,9 N greater in the screw cerclage cable setup in the flexion test, the screw cerclage group showed lower fracture displacement (1,42 mm less displacement) at higher forces (more than 244,9 N) compared to the Modified AO tension band. Differences were found to be statistically significant. Screws and cerclage cable are an alternative to conventional surgical procedures for transverse patellar fractures. Further research must establish if this setup and new non metallic materials should become the surgical treatment gold standard.