284 - Eccentric Kinematic Patterns of the Sacroiliac Junction following Lumbopelvic Reconstruction

Abstract

BACKGROUND CONTEXT The unique biomechanical properties of the sacroiliac joint (SIJ) presents formidable challenges in spinal reconstructive surgery. Controversy exists as to effective surgical management of this joint. Abnormal motion across the joint is believed to lead to pain, dysfunction and instrumentation complications, but few data are available on the kinematic response. This investigation was performed to quantify and compare the sacroiliac kinematics of lumbosacral fixation and unilateral and bilateral iliac screw configurations. PURPOSE Hypermobility or aberrant kinematics of the SIJ has been suggested to cause SIJ pain. The current study investigates the biomechanical properties of symmetric and asymmetric posterior lumbopelvic instrumentation on motion of the left and right SIJ using an in vitro cadaveric model. It is postulated that unilateral iliac screw fixation predisposes the SIJ to asymmetric biomechanical loading and subsequent may serve as a causative factor in SIJ dysfunction. STUDY DESIGN/SETTING In vitro human cadaveric model and multidirectional flexibility testing. METHODS A total of 15 cadaveric lumbopelvic spines (mean age 52.0 years, range 22-74) were utilized in this investigation. Multidirectional flexibility testing was performed at ±12.5Nm in flexion-extension, lateral bending, and axial rotation using a 6-degree-of-freedom spine simulator. Bilateral L1-Iliac (bilateral), left L1-Iliac and right L1-sacrum (unilateral), and bilateral L1-sacrum (sacral) instrumented reconstructions were tested. Range of motion (ROM) of the right and left SIJ was quantified and compared. RESULTS The intact ROM for the left SIJ was 1.3±0.09°, 0.7±0.4°, and 0.9±0.5° in flexion-extension, lateral bending, and axial rotation, respectively. Right SIJ motion during flexion-extension, lateral bending, and axial rotation was 1.3±1.0°, 0.6±0.5°, and 0.9±0.5°, respectively. SIJ ROM increased above the intact condition following sacral fixation with a statistically significant increase observed for the right SIJ (p≤0.05) and a trend toward significance for the left SIJ. Both the bilateral and unilateral constructs reduced motion, across the left and right SIJ, when compared to the sacral construct (p≤0.05). However, the right SIJ demonstrated significantly greater motion in flexion-extension compared to the left SIJ for the unilateral construct only (p≤0.05). CONCLUSIONS This serves as a comprehensive biomechanical evaluation of SIJ ROM following lumbopelvic fixation. Sacral instrumentation without iliac fixation increased motion at the SIJ and may lead to clinical dysfunction. Asymmetric iliac fixation - unilateral vs bilateral - results in a compensatory increase in contralateral SIJ motion and may predispose spinal instrumentation to altered loading conditions and instrumentation complications. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.