Effect of thoracolumbar fascia morphology on lumbar stiffness and rotation under prescribed myofascial loading: A finite element analysis.

Abstract

The thoracolumbar fascia (TLF) helps stabilize the spine and provides a pathway for force transfer between connecting muscles and the lower back, but how its morphological changes affect this role remains unclear. This study examined how different TLF thicknesses and fiber volume fractions influence lumbar stiffness and static rotation under prescribed myofascial loading. A finite element model of the L1-S1 spine was created, including a TLF with a diamond lattice pattern of fibers inside a matrix. Twenty-five models were developed with varying thicknesses (1.0-2.5 mm) and fiber volume fractions (0.16-0.5). Under a 7.5 N m flexion moment and a 1000 N follower load, increased thickness and fiber volume fraction decreased lumbar rotation, indicating greater passive stiffness. Surface analysis through least-squares regression supported this trend, with a diminishing effect as the TLF became thicker or more fiber-dense. Through prescribed muscle-related loading conditions applied at the TLF, the transverse abdominis and gluteus maximus related loads reduced rotation, while, individually, the latissimus dorsi-related load increased it. The impact of each loading condition on changing spinal rotation decreased as the TLF became thicker and more fiber-dense. These findings suggest that TLF morphology affects passive stiffness and influences the static rotation of the lumbar spine under prescribed myofascial loading. As the TLF becomes thicker and more fiber-dense, the model suggests it may play a greater role in passive spinal stability; conversely, the same muscle-related loads result in smaller changes in lumbar rotation. These trends could lead to hypotheses for future research on LBP rehabilitation, such as examining the effects of reducing excessive TLF stiffening while improving the coordination and control of muscles interacting with the fascia.