The surgical anatomy of the lumbosacroiliac triangle: a cadaveric study

Objective The anatomic area delineated medially by the lateral part of the L4-L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint, is of particular interest to spine surgeons. We are referring to this area as the lumbo-sacro-iliac triangle (LSIT). Knowledge of LSIT anatomy is necessary during approaches for L5 vertebral and sacral fractures, sacral and iliac tumors, and extraforaminal decompression of the L5 nerve roots. Methods We performed an anatomic dissection of the LSIT in 3 embalmed cadavers (6 triangles), using an anterior and posterior approach. Results We identified 3 key tissue planes: the neurological plexus plane, constituted by L4 and L5 nerve roots; an intermediate level constituted by the ileosacral tunnel; and posteriorly, by the lumbosacral ligament, and the posterior muscular plane. Conclusions Improving anatomic knowledge of the LSIT may help surgeons decrease the risk of possible complications. When LSIT pathology is present, a lateral approach corresponding to the tip of the L4 transverse process, medially, is suggested to decrease the risk of vessel and nerve root damage. OBJECTIVE: The anatomic area delineated medially by the lateral part of the L4-L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint, is of particular interest to spine surgeons. We are referring to this area as the lumbo-sacro-iliac triangle (LSIT). Knowledge of LSIT anatomy is necessary during approaches for L5 vertebral and sacral fractures, sacral and iliac tumors, and extraforaminal decompression of the L5 nerve roots. METHODS: We performed an anatomic dissection of the LSIT in 3 embalmed cadavers (6 triangles), using an anterior and posterior approach. RESULTS: We identified 3 key tissue planes: the neurological plexus plane, constituted by L4 and L5 nerve roots; an intermediate level constituted by the ileosacral tunnel; and posteriorly, by the lumbosacral ligament, and the posterior muscular plane. CONCLUSIONS: Improving anatomic knowledge of the LSIT may help surgeons decrease the risk of possible complications. When LSIT pathology is present, a lateral approach corresponding to the tip of the L4 transverse process, medially, is suggested to decrease the risk of vessel and nerve root damage.