A three-dimensional mathematical model of the thoracolumbar fascia and an estimate of its biomechanical effect.

The thoracolumbar fascia (TLF) provides a means of attachment to the lumbar spine for several muscles including the transverse abdominis, and parts of the latissimus dorsi and internal oblique muscles. Previous biomechanical models of the lumbar spine either tend to omit the TLF on the assumption that its contribution would be negligible or incorporate only part of the TLF. Here, a three-dimensional model of the posterior and middle layers of the TLF is presented to enable its action to be included in future three-dimensional models of the spine. It is used illustratively to estimate the biomechanical influence of this structure on the lumbar spine. The formulation of the model allows the lines of action of the fibres comprising the fascia to be calculated for any posture whilst ensuring that anatomical constraints are satisfied. Application of the model suggests that the TLF produces moments primarily in flexion and extension. The simulated results demonstrate that the abdominal muscles, acting via the TLF, are capable of contributing extension moments comparable to those produced by other smaller muscles associated with the lumbar spine. Crown