Muscle fibre direction of longissimus, iliocostalis and multifidus: landmark-derived reference lines.

Considerable inter-individual variations in the fibre direction angles of the iliocostalis lumborum, longissimus and multifidus were observed, thus bringing the applicability of a two dimensional fixed angle grid system for fibre direction determination into question. However, the angulation of the fibres of the multifidus and iliocostalis lumborum were found to be easily identifiable by the use of three surface anatomical landmarks: the caudal tip of the superior iliac spine, the lateral border of the iliocostalis at the twelfth rib and the L1-L2 interspinous space. No reliable index was found for the longissimus. Suggested electrode placement sites for the electromyographic study of the iliocostalis lumborum and the multifidus are at the levels of the L2-L3 and the L4-L5 interspinous spaces respectively.