Biomechanical evaluation of different surgical procedures in single-level transforaminal lumbar interbody fusion in vitro.

BACKGROUNDS: A variety of improved surgical methods were adopted in the transforaminal lumbar interbody fusion. A mechanical stability provides an ideal environment for the formation of a fusion mass and is the basis of their good outcomes. The object of this study is to evaluate the initial similarities and differences of four commonly-used posterior surgical procedures biomechanically.

METHODS: Biomechanical testing was performed at L3-4 motion segment in 6 fresh-frozen human cadaveric lumbar spines (L2-L5), including the following sequentially tested configurations: 1) intact motion segment; 2) bilateral pedicle screw fixation; 3) unilateral pedicle screw fixation; 4) unilateral pedicle screw plus contralateral translaminar facet joint screw fixation according to the Magerl technique; and 5) bilateral pedicle screw fixation with bilateral facetectomies. The range of motion, neutral zone and stiffness of each method and intact segment were collected and compared.

FINDINGS: All of four methods reduce the range of motion significantly in flexion and extension and lateral bending but not in axial torsion compared with the native segment. There is no significant difference among four procedures about the range of motion in all loading modes. All of methods increase the stiffness of segmental motion compared with intact segment in all loading modes, but only bilateral pedicle screw fixation showed significant increases in stiffness in flexion and extension(p=0.02) and lateral bending(p=0.023). The stiffness offered by instrumented constructs in different methods showed no significant difference in all loading modes.

INTERPRETATION: The stiffness offered by four different posterior fixations in single segmental transforaminal lumbar interbody fusion is not significantly different.