Attenuation of Proximal Junctional Kyphosis Using Sublaminar Polyester Tension Bands: A Biomechanical Study.

OBJECTIVE

To investigate the effect of sublaminar polyester tension bands on the biomechanics of the motion segments proximal to a long fusion construct.

METHODS

This was a human cadaveric biomechanical study. Pure moments of 4 Nm and 8 Nm were applied to the native spine and the instrumented spine, respectively (n = 8). The test conditions included native spine (T7-L2), fused (T10-L2), fused + bilateral tethers tensioned to 250 N at T9-T10 (tethers 250 N), fused + tethers tensioned to 350 N (tethers 350 N), fused (T11-L2) + tethers tensioned to 250 N at T9-T10 and 350 N at T10-T11 (2-level tethers), fused (T10-L2) + hand-tied suture loop through the spinous processes at T9-T10 (suture loop), and fused (T10-L2) with the T9-T10 interspinous and supraspinous ligaments cut (cut ISL/SSL).

RESULTS

The flexion range of motion (ROM) at T9-T10 of the fused spine, loaded at 8 Nm, increased to 162% of the native spine loaded at 4 Nm. The average flexion ROM at T9-T10 for tethers 250 N, tethers 350 N, 2-level tethers, suture loop, and cut ISL/SSL were 85% (P < 0.0001), 70% (P < 0.0001), 93% (P < 0.0001), 141% (P = 0.13), and 177% (P = 0.66) of the native spine at 4 Nm, respectively (P values vs. fused).

CONCLUSIONS

Sublaminar polyester bands can modulate the biomechanical flexion ROM as a function of the band pretension and provide a more consistent and tunable technique than hand-tying a suture loop between the spinous processes.