Thoracic fibres of longissimus and iliocostalis lumborum arise from thoracic spine (Macintosh and Bogduk 1987) and span the entire lumbar spine forming the erector spinae aponeurosis
which moves freely over the lumbar erector spinae (Macintosh and Bogduk 1994), connecting to the sacrum and posterior superior iliac spine (Macintosh and Bogduk 1987).
The multifidus muscle, the largest of the lumbar back muscles, passes directly over the zygapophysial joints between them and the overlying erector spinae aponeurosis
. The larger fascicles of the multifidus muscle originate from the spinous process of the vertebrae at least three segments above their level of insertion, and run inferiorly, laterally and anteriorly to insert into the mamillary process and zygapophysial joint capsule (Lewin et al.
Access from a posterior approach requires palpation through the skin, a substantial amount of subcutaneous tissue, the thoracolumbar fascia, erector spinae aponeurosis
, and finally through the iliocostalis lumborum and quadratus lumborum muscles (Frazer 1940; Shellshear and Macintosh 1949) (Figure 4).