Biomechanical analysis of tension band wiring (TBW) of transverse fractures of patella.

PURPOSE: Tension band wiring is commonly used for fixation of simple transverse fractures. The popular configuration is parallel Kirschner wires (K-wires) and a stainless steel wire loop placed in a vertically oriented figure-of-8.

METHODS: We used a wooden model of a patella with a midway transverse fracture and compared four different types of fixation. The first construct had a vertical figure-of-8 with one twist of wire. The second contained a vertical figure-of-8 with two twists of wire. The third was a vertical figure-of-8 with two twists of wire placed at adjacent corners while the last one had a horizontal figure-of-8 with two twists of wire placed at adjacent corners. Interfragmentary compression at the point of wire breakage was measured for each construct as well as permanent displacement on cyclic loading.

RESULTS: Placement of the figure-of-eight in a horizontal orientation with two wire twists at the corner improved interfragmentary compression by 63% (p < 0.05, Tukey post hoc test). On cyclic loading, all the constructs with vertical figure-of-eight but none with a horizontal construct failed (p=0.01; Fisher's exact test). Permanent fracture displacement after cyclic loading was 67% lower with horizontal figure- of-eight constructs (p < 0.05; t test).

CONCLUSION: Placing wire twists at the corner and a horizontal placement of figure-of-8 improves stability of the construct.