Approaching The Interspace Between Multifidus And Longissimus Accurately In Lumbar Surgery: An Anatomically Based Study Of The Wiltse Approach

Background and aim: The Wiltse approach is a common approach to the lumbar spine. However, it has remained difficult to approach the interspace, even while strictly following instructions and methods introduced by Wiltse et al. This is mainly due to the sacrospinalis aponeurosis covering the interspace between multifidus and longissimus. This study aimed to explore the anatomical basis and methods to improve the reliability and feasibility of lumbar Wiltse approach. Methods: Twenty embalmed cadavers were dissected, bilaterally, to observe anatomical characteristics and the relationship between sacrospinalis aponeurosis and the two muscles (multifidus and longissimus). Results: Multifidus was seen as independent from the sacrospinalis aponeurosis, although few fibers existed. Longissimus formed enthesis from sacrospinalis aponeurosis in the lumbar region. The enthesis extended from central-superficial to inferior-lateral and formed a septum stretching to facet joints and accessory process making up the native interspace between multifidus and longissimus. Taking this septum as an anatomical sign, successful blunt dissections were performed to expose facet joints directly in all cadavers. Other special anatomical signs to locate the interspace between multifidus and longissimus were not found, either on the surface or in the inferior part of sacrospinalis aponeurosis. In the interspace, segmental nerves and concomitant blood vessels could be seen inside the longissimus. Conclusion: The longissimus forms an enthesis and septum from sacrospinalis aponeurosis in the lumbar region. Making a sacrospinalis aponeurosis incision inside the interspace between multifidus and longissimus, the septum can easily be found after the sacrospinalis aponeurosis is pulled outside. The Wilste approach is feasible and safe if based on a comprehensive understanding and knowledge of the lumbar muscle septum.