Unilateral vs. Bilateral iFuse (Lindsey - JNS Spine 2018)

Biomechanics of Unilateral and Bilateral Sacroiliac Joint Stabilization: Laboratory Investigation

Lindsey DP, Parrish R, Gundanna M, Leasure J, Yerby SA, Kondrashov D.
J Neurosurg Spine. 2018 Mar;28(3):326-332. [Epub 2018 Jan 5]. doi: 10.3171/2017.7.SPINE17499


Objective: Bilateral symptoms have been reported in 8%-35% of patients with sacroiliac (SI) joint dysfunction. Stabilization of a single SI joint may significantly alter the stresses on the contralateral SI joint. If the contralateral SI joint stresses are significantly increased, degeneration may occur; alternatively, if the stresses are significantly reduced, bilateral stabilization may be unnecessary for patients with bilateral symptoms. The biomechanical effects of 1) unilateral stabilization on the contralateral SI joint and 2) bilateral stabilization on both SI joints are currently unknown. The objectives of this study were to characterize bilateral SI joint range of motion (ROM) and evaluate and compare the biomechanical effects of unilateral and bilateral implant placement for SI joint fusion.

Methods: A lumbopelvic model (L5-pelvis) was used to test the ROM of both SI joints in 8 cadavers. A single-leg stance setup was used to load the lumbar spine and measure the ROM of each SI joint in flexion-extension, lateral bending, and axial rotation. Both joints were tested 1) while intact, 2) after unilateral stabilization, and 3) after bilateral stabilization. Stabilization consisted of lateral transiliac placement of 3 triangular titanium plasma-sprayed (TPS) implants.

Results: Intact testing showed that during single-leg stance the contralateral SI joint had less ROM in flexion-extension (27%), lateral bending (32%), and axial rotation (69%) than the loaded joint. Unilateral stabilization resulted in significant reduction of flexion-extension ROM (46%) on the treated side; no significant ROM changes were observed for the nontreated side. Bilateral stabilization resulted in significant reduction of flexion-extension ROM of the primary (45%) and secondary (75%) SI joints.

Conclusions: This study demonstrated that during single-leg loading the ROMs for the stance (loaded) and swing (unloaded) SI joints are significantly different. Unilateral stabilization for SI joint dysfunction significantly reduces the ROM of the treated side, but does not significantly reduce the ROM of the nontreated contralateral SI joint. Bilateral stabilization is necessary to significantly reduce the ROM for both SI joints.

KEYWORDS: ODI = Oswestry Disability Index; ROM = range of motion; SI = sacroiliac; TPS = titanium plasma sprayed; biomechanics; degenerative sacroiliitis; fusion; minimally invasive surgery; sacral; sacroiliac joint disruption

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