Introduction: Pedicle screw and rod insertion (PS, Fig. 1) is a common construct fusion spine surgery. A recently developed alternative is the spinous process plate (SPP, Fig. 2). Advantages of SPP over PS include significantly less lateral muscle dissection and the elimination of the risk of nerve root injury. One criticism of SPP is possible inferior rigidity compared to PS, which could potentially lead to decreased fusion rates. The purpose of this study is to biomechanically compare posterior lumbar interbody fusion (PLIF) supplemented with SPP versus PS.

Methods: Thirteen human cadaveric specimens from seven donor spines were implanted with either SPP or PS. Functional spinal unit (FSU) test specimens consisted of two vertebrae, the intervertebral disc and associated ligaments. The specimens were tested in four states: (1) intact, (2) after removal of ligaments and disruption of facet joints (destabilized), (3) after placement of interbody grafts (PLIF), and (4) after fixation with either SPP or PS. A pure bending moment was applied to each FSU using a load frame (Fig. 3) to assess: (1) flexion, (2) extension, and (3) lateral bending. Deformation of the FSU was measured utilizing photogrammetry.

Results: The stiffness of the implanted FSU (SPP or PS) was found to be greater than the intact, destabilized or PLIF states. SPP and PS behaved similarly in flexion and extension, with PS having a slightly higher but statistically nonsignificant average modulus than SPP. SPP was statistically not as stiff as PS in lateral bending, but it was still as stiff as the intact FSU. (Table 1).

Conclusions: SPP performed comparably to PS in flexion and extension but was inferior in lateral bending stiffness. SPP might be a reasonable and safer alternative to PS in lumbar fusion, and further investigation of its overall performance is warranted.

Patient Care: This biomechanical study demonstrates that spinous process plate fixation performs similarly to pedicle screws and rods with regard to flexion and extension. Spinous process plating may be a feasible, safer alternative to traditional pedicle screw fixation in lumbar spine surgery.

Learning Objectives: Biomechanical evaluation of two lumbar spine fusion constructs: bilateral pedicle screws and rods versus spinous process fixation with plating.

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