A biomechanical comparison of antegrade versus retrograde cannulated screw direction in suture-based tension band fixation of transverse patella fractures.

Abstract

The primary objective of this study was to determine if there is a difference in load to fixation failure when comparing antegrade or retrograde screw direction in tension band fixation of transverse patella fractures. A simulated fracture was created in 16 patellae with an oscillating saw, which was then reduced and fixed using two 4.0-mm headed partially threaded cannulated screws inserted in either an antegrade or retrograde fashion. FiberWire suture was passed through the screws in figure-of-eight fashion and tied. The quadriceps tendon was loaded in tension, and failure was defined by 2 mm of separation between the proximal and distal fragments. Loading was continued until catastrophic failure. Tension forces at 2 mm of fracture gapping and peak loads were recorded. The mean load at 2-mm fracture gapping was 715.8 and 701.9 N for the antegrade and retrograde screw configurations, respectively. Mean peak load was 1070.9 N for the antegrade group and 1166.8 N for the retrograde group. There was no significant difference between load to failure (<i>P</i> = 0.945) or peak load (<i>P</i> = 0.575) between the 2 tested configurations. Our biomechanical study demonstrates no significant difference in load to fixation failure between antegrade or retrograde cannulated screws in a suture-based anterior tension band for transverse patella fractures.