Lumbar plexus and psoas major muscle: not always as expected

Area of Science:

• Anatomy
• Surgical anatomy

Background:

• Conflicting definitions exist regarding the precise anatomical location of the lumbar plexus.
• Variations in the topographical relationship between the lumbar plexus and the psoas major muscle have been reported.

Purpose of the Study:

• To investigate anatomical variants of the lumbar plexus.
• To determine the topographical relationship between the lumbar plexus and the psoas major muscle.
• To describe lumbar plexus anatomy at the L4-L5 vertebral level.

Main Methods:

• Dissection of 63 lumbar plexuses from 32 embalmed cadavers.
• Assessment of the topographical relationship between the lumbar plexus and the psoas major muscle.
• Description of the variability in the course of the femoral and obturator nerves at the L4-L5 levels.

Main Results:

• The lumbar plexus was located within the psoas major muscle in 61 out of 63 cases.
• In 2 cases, the lumbar plexus was found posterior to the psoas major muscle.
• Nerve emergence from the plexus within the psoas major muscle typically occurred on the posterior or posterolateral surface.

Conclusions:

• Both intraparenchymal and posterior locations of the lumbar plexus relative to the psoas major muscle can be encountered clinically.
• The intraparenchymal location is the predominant variant.
• The femoral and obturator nerves, with significant branching of the femoral nerve, are predominantly situated within the psoas major muscle at the L4-L5 level.