Biomechanical Evaluation of a Less Invasive Technique for Midline Lumbar Decompression and Fusion

Malloy J.P.1, Chaput C.D.2, Soriano-Baron H.E.3, Rodriguez-Martinez N.G.3, Crawford N.R.3, Newcomb A.G.3, Ferrara L4
1Broward Health North, Pompano Beach, FL
2Scott & White Healthcare, Temple, TX USA
3Barrow Neurological Institute, Spinal Biomechanics, Phoenix, AZ
4OrthoKinetic Technologies, Southport, NC USA

The purpose of the study was to evaluate the biomechanical stability of a less invasive midline lumbar fixation (MLF) device that utilizes crosslinked transfacet pedicle screws (TFPS) in conjunction with a facet/pars buttress plate.

Segmental flexibility testing was conducted to compare the performance of the MLF device to TFPS and pedicle screw and rod constructs (PSR) utilizing eight human cadaveric specimens with intact discs following complete laminectomies. Load to failure was compared between the MLF and traditional stand alone TFPS.

Cyclical load testing was also conducted to evaluate the performance under repetitive loads. Pre- and post-cyclical segmental range of motion (ROM) and stiffness values were recorded following non-destructive cyclic loading, initially in flexion-extension followed by lateral bending coupled with axial torsion over a total of 5,000 cycles.

During segmental flexibility testing, ROM with the MLF device trended towards greater stability compared to PSR during flexion, extension and axial rotation, but this did not reach statistical significance (p>0.3, Fig 1). During lateral bending, bilateral PSR demonstrated statistically significant reduction in ROM compared to TFPS alone and the MLF device (p<0.02). The load to failure analysis showed that the MLF device withstood significantly higher loads (30%) compared to TFPS alone (p=0.01, Fig 2). During cyclical load testing, the MLF device demonstrated greater long-term stability than traditional TFPS (Fig 3, 4).

The MLF device demonstrated initial stability similar to standard lumbar instrumentation, statistically improved load to failure, with greater stiffness and stability after cyclical loading. A potential advantage is that the MLF device can be placed through the same small midline approach used for lumbar laminectomy, sparing the additional lateral soft tissue dissection that would be necessary to implant conventional PSR instrumentation.

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