P11. Expansion trajectory of a lateral cage affects load distribution at the cage-endplate interface: a biomechanics study

• Published in: The spine journal 2023-09, Vol.23 (9), p.S113-S114
• Main Authors: Kusins, Jonathan, Uyekawa, Scott, Singh, Gurpreet, Peng, Yun, McQuarrie, Chase, Holman, Paul J., Cheng, Ivan, Jekir, Michael
• Format: Article
• Language: English
• ISSN: 1529-9430; 1878-1632
• DOI: 10.1016/j.spinee.2023.06.236

Early clinical outcomes associated with lateral expandable cages have been positive, but the risk of endplate violation and resultant subsidence remains. Particularly, during intraoperative expansion, edge loading of the cage should be avoided to reduce excessive stress at the vertebral endplate interface. While multiple lateral expandable cage designs exist, how the load distribution at the cage-endplate interface is impacted by specific cage expansion trajectories is not fully understood. Assess the impact of a lateral expandable cage's expansion trajectory on load distribution at the cage-endplate interface. Comparative biomechanics study using bone foam test blocks. Load distribution, max pressure. A custom experimental setup was fabricated to measure load distribution at the cage-test block interface arising from expansion of a lateral expandable cage under predefined expansion heights and test block lordotic angles. To perform testing, a lateral expandable cage was placed between two endplate-conforming bone foam test blocks and expanded under a constant 250N load. A calibrated pressure sensor measured the cage-test block load distribution. An expandable cage with cranio-caudal (CC) expansion was compared to a size-matched cage with independently-adjustable anterior and posterior (IAP) expanded heights at test block lordotic angles of 0 to 7.5º, 2.5º increments. In addition, a lateral cage with fixed-arc expansion was compared to a separate size-matched IAP expandable at test block lordotic angles of 7.5 to 15º, 2.5º increments. Each cage was expanded by 3.0 mm from the collapsed position, with measurements at 0.5-mm increments. The load distribution was characterized using anterior-posterior (AP) ratio and max pressure. AP ratio determined the symmetry of the loading profile, calculated by dividing the cumulative load on the anterior half of the cage by the total load; 50% indicates a perfectly balanced load distribution with no edge loading. A three-way ANOVA (n=10) determined the influence that expansion trajectory, lordotic angle, and expansion height had on load distribution. For an expandable cage with CC expansion, the load distribution was heavily dependent on the test block lordotic angle (p