Study design:

In-vitro cadaveric biomechanical study STUDY OBJECTIVE: The objective of this study was to characterize the biomechanical implications of spinous process compression, via in-situ shortening of a next-generation interspinous process fixation (ISPF) device, in the context of segmental fusion.

Methods:

Seven lumbar cadaveric spines (L1-L4) were tested. Specimens were first tested in an intact state, followed by iterative instrumentation at L2/3 and subsequent testing. Order: 1) stand-alone ISPF (neutral height); 2) stand-alone ISPF (shortened in-situ from neutral height; ‘shortened’); 3) lateral interbody cage (‘LLIF’)+ISPF (neutral); 4) LLIF+ISPF (shortened); 5) LLIF+unilateral pedicle screw fixation (PSF); 6) LLIF+bilateral PSF. A 7.5Nm moment was applied in flexion/extension (FE), lateral bending (LB), and axial rotation (AR) via a kinematic test frame. Segmental range-of-motion (ROM) and lordosis were measured for all constructs. Comparative analysis was performed.

Results:

Statistically significant FE ROM reductions: all constructs vs. intact condition (p<0.01); LLIF+ISPF (neutral & shortened) vs. stand-alone ISPF (neutral & shortened) (p<0.01); LLIF+USPF vs. ISPF (neutral) (p=0.049); BPSF vs. stand-alone ISPF (neutral & shortened) (p<0.01); LLIF+BPSF vs. LLIF+UPSF (p<0.01). Significant LB ROM reductions: LLIF+ISPF (neutral & shortened) vs. intact condition & stand-alone ISPF (neutral) (p<0.01); LLIF+UPSF vs. intact condition & stand-alone ISPF (neutral & shortened) (p<0.01); LLIF+BPSF vs. intact condition & all constructs (p<0.01). Significant AR ROM reductions: LLIF+ISPF (shortened) & LLIF+UPSF vs. intact condition & stand-alone ISPF (neutral) (p≤0.01); LLIF+BPSF vs. intact condition & all constructs (p≤0.04).

Conclusion:

In-situ shortening of an adjustable ISPF device may support increased segmental stabilization in comparison to static ISPF.