Anatomical topography of the inferior lumbar triangle for transversus abdominis block.

BACKGROUND: Rapid development of anesthetic techniques of thoracic paravertebral block required to redefine anatomical landmarks of the inferior lumbar (Petit) triangle (ILT). Anesthesiologists are mainly interested in the ILT to perform the transversus abdominis plane (TAP) block. The aim of this study was to provide comprehensive information of the ILT to improve the success of TAP block.

METHODS: Descriptional anatomy of ILTs such as dimensions, space, area, and types was analyzed in 25 preserved adult male cadavers.

RESULTS: The ILT was identified in 100% out of all explored cadavers' lumbar regions. The predominant triangle was the acute-angled shaped (46%). The ILT in terms of the surface area was classified into four distinct types: Type I with a surface area <8 cm2 was identified in 50%. Type II or intermediate triangles with a surface area of 8-12 cm2 were detected in 36%. Type III or large triangles with a surface area >12 cm2 were found in 14%. Type 0 or no triangle did not exhibit a triangle. For the orientation zone over the posterior lumbar region, it was measured with the distances from the posterior median line (M) to the apex (A), medial point (B), and lateral point (C) of the triangle. MA; as M1A transverse line: 103.3 ± 21.3 mm (left) and 106.4 ± 18.4 mm (right), MB; as M2B transverse line; 102.4 ± 21.8 mm (left) and 105 ± 17.9 mm (right), MC; as M3C transverse line; 119 ± 20.5 mm (left) and 120 ± 19.2 mm (right) were measured. In addition, the measurements of the vertical lines were measured. M1A-M2B and M1A-M3C vertical lines were 20.1-22.8 mm (left-right) and 30-29 mm (left-right), respectively.

CONCLUSIONS: The shape, the size, useful points, geometry, and topography of the ILT are important to determine the orientation points during block procedures. It is possible to visualize the needle pathway in different shape of ILT to ultrasound-guided TAP block. Anesthetic intervention needs to be individualized, depending upon the size of the triangle. The findings may be useful in establishing the area with the highest probability of localization of the ILT which can improve both the safety and efficiency of TAP block.