Abstract Background Data: Low back pain (LBP) is a common musculoskeletal disorder. In Egypt, patients with LBP constitute a high percentage of patients seeking medical care at outpatient clinics. Spinal fusion is a common treatment for spinal disorders such as disc degeneration, deformity, spondylolisthesis, or fracture. The minimally invasive lateral retroperitoneal transpsoas approach is a recent technique developed to avoid complications associated with traditional or minimally invasive anterior or posterior approaches to the lumbar spine. This technique provides a small incision that avoids significant abdominal muscle injury and lateral access to the disc space from L1-L2 to L4-L5. Purpose: To define a safe entry zone in the psoas muscle to prevent lumbar plexus injury during the transpsoas approach. Study Design: A descriptive cadaveric study. Material and Methods: A total of 30 cadavers were used in this study where each cadaver was dissected from both sides. Each cadaver was placed in lateral decubitus and a skin incision in the midaxillary line from the last rib to iliac crest was made. Then, the peritoneum was dissected, psoas muscle was exposed, and nerve roots were identified and reported at each disc space from L1-L2 to L4-L5. The safe entry zone was defined by the absence of crossing of a lumbar plexus branch. Results: Each disc space was divided into four zones: zone 1, the posterior quadrant; zone 2, the middle anterior quadrant; zone 3, the middle posterior quadrant; zone 4, the posterior quadrant. The safe working zone includes zones 2 and 3 at level L1-L2, zone 3 at level L2-L3, zone 3 at level L3-L4, and zone 2 at level L4-L5. There was no variance observed between either side regarding the relationships between the lumbar plexus and the intervertebral disc. Conclusion: Knowledge of the anatomy of lumbar plexus roots in psoas muscle is mandatory to prevent injury to lumbar plexus roots during entry of dilator through psoas muscle. This anatomical study suggests that there are certain safe zones at the lumbar disc spaces that allow passage of dilator inside psoas muscle to reduce direct nerve injury of the lumbar plexus. (2020ESJ200) Background data:
Low back pain (LBP) is a common musculoskeletal disorder. In Egypt, patients with LBP constitutes a high percentage of patients seeking medical care at outpatient clinics. Spinal fusion is a common treatment for spinal disorders such as disc degeneration, deformity, spondylolisthesis or fracture. The minimally invasive lateral retroperitoneal transpsoas approach is a recent technique developed to avoid complications associated with traditional or minimally invasive anterior or posterior approaches to the lumbar spine. This technique was popularized by Pimenta and Ozgur. This technique provides small incision that avoids significant abdominal muscle injury and provides lateral access to the disc space from L1–L2 to L4–L5.
Purpose:
This study aims to define safe entry zone in psoas muscle to prevent lumbar plexus injury during transpsoas approach.
Study design:
This study is descriptive cadaveric study.
Methods:
Cadavers number: 10 cadavers, each cadaver was dissected from both sides. Each cadaver is placed in lateral decubitus, skin incision in midaxillary line from last rib to iliac crest. Incision of abdominal muscle then retraction of peritoneum, psaos muscle exposed. The psoas muscle is dissected, and nerve roots are identified and reported at each disc space from L1_2 to L4_5. The safe entry zone is defined by the absence of crossing of a lumbar plexus branch.
Results:
Our results are comparable to previous anatomical studies. Each disc space divided into four zones; zone 1 the posterior quadrant, Zone 2 the middle anterior quadrant, Zone 3 the middle posterior Quadrant, Zone 4 the posterior quadrant. The safe working zone includes zones 2 and 3 at level L1L2, zone 3 at level L2L3, zone 3 at level L3L4, and zone 2 at level L4L5. There is no variance was observed between either side as regards the relationships between the lumbar plexus and the intervertebral disc.

Conclusion:

The tranpsoas approach is minimally invasive approach developed to prevent major complications of traditional approaches. However, the proximity of lumbar plexus is the main limitation of the approach. Knowledge of anatomy of lumbar plexus roots in psoas muscle is mandatory to prevent injury to lumbar plexus roots during entry of dilator through psoas muscle.