5. A biomechanical investigation of the sacroiliac joint in the setting of lumbosacral fusion: the impact of pelvic fixation vs sacroiliac joint fixation

Proceedings of the 34th Annual Meeting of the North American Spine Society / The Spine Journal 19 (2019) S1−S58 5. A biomechanical investigation of the sacroiliac joint in the setting of lumbosacral fusion: the impact of pelvic fixation vs sacroiliac joint fixation Harry M. Mushlin, MD1, Gerald Hayward, BS2, Daina M. Brooks, BS3, Bryan Ferrick, BS4, Stephen Carbine5, Brandon Bucklen, PhD2, Charles A. Sansur, MD6; 1 University of Maryland School of Medicine, Department of Neurosurgery, Baltimore, MD, US; 2 Globus Medical Inc., Audubon, PA, US; 3 Medstar Union Memorial Hospital, Baltimore, MD, US; 4 Drexel University School of Biomedical Engineering, Philadelphia, PA, US; 5 Baltimore, MD, US; 6 University of Maryland, Towson, MD, US BACKGROUND CONTEXT: The sacroiliac (SI) joint is a known source of lower back pain. Randomized clinical trials support sacroiliac fusion over conservative management for sacroiliac joint dysfunction. Clinical experience suggests degeneration of the sacroiliac joint in the setting of lumbosacral fusions. However, there are limited biomechanical studies to understand the effect of lumbosacral fusion on the sacroiliac joint. This study is a biomechanical investigation to understand the effect of pelvic vs sacroiliac joint fixation on the sacroiliac joint in lumbosacral fusion. Furthermore, researchers studied the effect of lumbosacral fixation on the SI joint in the absence of pelvic and SI joint fixation. PURPOSE: To determine the immediate stability of various lumbopelvic fixation constructs. STUDY DESIGN/SETTING: In-vitro biomechanical range of motion testing. METHODS: Seven fresh-frozen human cadaver specimens were used. There was one intact and 6 operative constructs: (1) posterior pedicle screws and rods from T10−S1 (PS); (2) PS+bilateral iliac screw fixation (BIS); (3) PS+unilateral iliac screw fixation (UIS); (4) PS+UIS+3 contralateral unilateral SIJ screws (UIS+3SIJ); (5) PS+3 unilateral SIJ screws (3SIJ); and (6) PS+6 bilateral SIJ screws (6SIJ). A custom-built 6 degreesof-freedom (6DOF) testing apparatus was used to simulate 3 bending modes: flexion extension (FE), lateral bending (LB), axial rotation (AR). Range of motion was recorded at L5−S1 and sacroiliac joint. RESULTS: All 6 operative constructs had significantly reduced ROM at L5−S1 compared to the intact specimen in all 3 bending modes (p<0.05). In FE, BIS had significant reduction in L5−S1 ROM compared to all specimens (p<0.05). SIJ ROM was greatest in FE bending mode. FE did not show statistically significant differences in the SIJ ROM across constructs, but there were appreciable differences. PS construct had the highest SIJ ROM. BIS construct reduced bilateral SIJ ROM by 44%. BIS and 6SIJ showed nearly equal reduction in SIJ ROM compared to PS. UIS and 3SIJ showed appreciable reduction in the unfused SIJ compared to PS. CONCLUSIONS: This biomechanical investigation demonstrated the effects of various fusion constructs using pelvic and sacroiliac fixation in lumbosacral fusion. It adds biomechanical evidence to the literature showing adjacent segment stress in the SIJ in fusion constructs to S1. Unilateral pelvic fixation or SIJ fusion led to appreciable but nonsignificant reduction to the unfused contralateral SIJ. Finally, bilateral pelvic fixation showed the greatest significant reduction of movement at L5−S1 and was equivalent to bilateral sacroiliac fusion in reducing SIJ motion. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. https://doi.org/10.1016/j.spinee.2019.05.018

6. Biomechanical investigation of the potential development and prevention of scoliosis following various sizes of chest wall resection Zackery W. Witte, MD1, Jonathan M. Mahoney, BS2, Jonathan Harris2, Hassaan P. Sheikh, BS2, Brandon Bucklen, PhD2, Rex A. Marco, MD3, Varan Haghshenas, MD4; 1 Houston, TX, US; 2 Globus Medical Inc., Audubon, PA, US; 3 Houston Methodist Orthopedics & Sports Medicine, Houston, TX, US; 4 Houston Methodist Hospital, Houston, TX, US BACKGROUND CONTEXT: Chest wall resection is used to treat several thoracic disorders including tumor removals. A well-known

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problematic sequela of chest wall resections is development of scoliosis. Literature shows that the degree of the induced curvature correlates to the number of resected ribs. Despite the seriousness and frequency of scoliosis following chest well resection, the etiology and biomechanical information needed to understand this deformity development are not well-known. PURPOSE: The objective of the present study was to investigate the effect of chest wall resections, ranging in size from 1 to 6 ribs, on the biomechanical stability of the spine. Further, the study compared anterior-only fixation with a combined anterior-posterior approach in reducing range of motion (ROM) following chest wall resection. STUDY DESIGN/SETTING: Biomechanics/laboratory. METHODS: The range of motion (ROM) of six specimens (C7−L2) was captured using a custom-built six degrees-of-freedom machine in each of three physiological rotation axes: flexion extension (FE), lateral bending (LB), and axial rotation (AR). Left posterior ribs were sequentially resected 7 cm from the rib head, starting at the 5th rib and continuing until the 10th rib. Injured specimens were instrumented first with unilateral anterior rod fixation (UA) and then with additional unilateral posterior fixation (UA+UP), each starting at T4 and then extended distally as ribs were resected. Relative motion between the proximal and distal ends of the construct was measured in all three axes for the intact, injured, UA, and UA +UP constructs. RESULTS: Raw ROM of the injured specimen increased in a stepwise manner as additional ribs were resected, with an average increase of 0.90˚§0.52˚ in FE, 0.98˚§0.40˚ in LB, and 2.75˚§1.50˚ in AR. No statistically significant differences in ROM normalized to the intact specimen were found between operative constructs for any injury size (p>.05). Across all injury sizes, the UA construct reduced motion, and the UA+UP construct further reduced motion in all FE (22.0§12.3% vs 58.4§13.2%), LB (51.0§9.8% vs 74.4§9.0%), and AR (25.4§9.0% vs 58.7§11.2%). The impact of fixation was slightly greater as more ribs were resected. CONCLUSIONS: The stepwise ROM increase for the injured model as more ribs were resected can likely be attributed to the additional motion segment, suggesting that the etiology of scoliosis following chest wall resection may not be purely biomechanical in nature. Overall, the UA+UP construct may be a more optimal construct than UA in reducing motion and potentially assisting in limiting the risk of scoliosis development. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. https://doi.org/10.1016/j.spinee.2019.05.019

7. Eccentric kinematic patterns of the sacroiliac junction following lumbopelvic reconstruction Daina M. Brooks, BS1, Bryan W. Cunningham, PhD1, P. Justin Tortolani, MD2; 1 MedStar Union Memorial Hospital, Baltimore, MD, US; 2 Baltimore, MD, US 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.

Refer to onsite annual meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosure and FDA device/drug status at time of abstract submission.