Introduction: A cadaveric biomechanical evaluation of a novel rigid interspinous process fixation (ISPF) device was performed. The ISPF device, which can be incrementally shortened/extended in-situ, allows for optimization of spinous process compression/distraction without device substitution/re-positioning (Figure 1). This study sought to explore what translated effects in-situ device shortening may have on lordotic correction and segmental stability. It is hypothesized that resultant facet locking with in-situ ISPF device shortening may provide enhanced sagittal correction and rigidity; similar to that of pedicle screw fixation (PSF).
Methods: Five ligamentous lumbar cadaveric spines (L1-L4) were tested. Osseous integrity was confirmed via DEXA scans and radiographs. The L1 and L4 vertebral bodies were potted. Each spine was first tested in an intact state, followed by sequential iterative construct instrumentation (L2/3) and testing (see Results for sequence). Neutral ISPF device height and subsequent shortening was dictated by specimen anatomy. Lateral interbody cage (L.Cage) placement was performed via a standard lateral discectomy.
A 7.5Nm moment was applied in flexion/extension (FE), lateral bending (LB), and axial rotation (AR) using a six degree-of-freedom kinematics system. Segmental range-of-motion (ROM) was tracked using a motion analysis system. Mean ROM reduction and change in lordosis was calculated.
Results: (See Table 1.)
L2/3 ROM Reduction (FE; LB; AR) / Mean Lordotic Angle:
ISPF (Neutral): 33; 88; 88% / 6.9deg
ISPF (Compressed in-situ; Mean: 3.0mm): 31; 79; 77% / 8.7deg
L.Cage +ISPF (Neutral): 12; 58; 85% / 6.7deg
L.Cage +ISPF (Compressed in-situ; Mean: 3.1mm): 11; 56; 70% / 8.8deg
L.Cage +Unilateral PSF: 17; 39; 49% / 9.6deg
L.Cage +Bilateral PSF: 10; 14; 34% / 9.9deg
Conclusions: The novel ISPF device afforded segmental lordosis and sagittal stability (FE) comparable to that of PSF. However, ROM reduction in AR and LB was greater with PSF. Supplemental anterolateral plating may augment this difference while maintaining the less invasive posterior approach of the ISPF device.
Patient Care: It aids in further characterizing the benefits and limitations of ISPF in providing segmental stability and sagittal balance. Current biomechanical data around ISPF, particularly the novel technology discussed in this presentation, is limited.
Learning Objectives: Session participants should be able to:
1.Understand the translated effects of fixation with a novel ISPF device on segmental stability and sagittal restoration
2.Discuss how in-situ spinous process compression/distraction may or may not be advantageous
3.Identify (if any) patient cohorts for which spinous process compression/distraction with a minimally invasive ISPF approach may be beneficial