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).
Tveit et al (1994), using magnetic resonance imaging, found that at the end range of lumbar flexion the lever arm of the upper erector spinae aponeurosis is reduced by between 10% and 20% throughout the lumbar spine when compared to a lordotic posture.
From superficial to deep these include the skin, subcutaneous tissue, the thoracolumbar fascia, the erector spinae aponeurosis
, and the multifidus muscle (Bogduk 1997) (Figures 1 and 2).
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).