Biomechanical Effects of Cage Position in Full-endoscopic Trans-Kambin's Triangle Lumbar Interbody Fusion: A Finite Element Analysis

Full-endoscopic trans-Kambin's triangle lumbar interbody fusion is considered a minimally invasive procedure. The cage position in Kambin's triangle lumbar interbody fusion differs from that in other types of lumbar interbody fusion; the cage is inserted via the foramen and placed diagonally to the endplate. Therefore, the ideal cage position remains uncertain. This study evaluated the biomechanical effects of different cage positions in Kambin's triangle lumbar interbody fusion at L4/5. An intact lumbar-to-femur finite element model was constructed. A diagonal line was first set with the foramen as the starting point, and this was used as the reference line [K(0°)] for the cage insertion angle. Five insertion angles were set: 10° and 20° anteriorly [K(10°) and K(20°)], 0° [K(0°)], and 10° and 20° posteriorly [K(-10°) and K(-20°)]. Range of motion and von Mises stress at the endplate were measured with the cage placed anteriorly, in the middle, and posteriorly for each angle (15 cage positions total). The mean range of motion at L4/5 was smallest for the middle cage position at K(0°) [K(0°)-Middle], followed by K(10°)-Middle. Endplate stress at L5 was 25.2 and 23.3 MPa for K(0°)-Middle and K(10°)-Middle, respectively (83.5 and 77.1% of the average for the 15 cage positions). Considering the range of motion and endplate stress, a central cage position [K(0°)-Middle and K(10°)-Middle] can effectively enhance stiffness at the fused segment, thereby contributing to stability. Moreover, reducing endplate stress at L5 may lower the risk of endplate collapse and cage subsidence. Therefore, it is desirable to place the cage in the center or slightly anterior to the center.