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Goal of neuromonitoring for transpsoas lateral lumbar fusion surgery- to reduce the chances of injury to the nerves of the lumbar plexus.

Accomplished by utilizing:

S-EMG, T-EMG, SSEPs, MEPs.

Safe Passage to the disc spaces by lateral approach is based on an anatomical study of cadavers by Moro et al. 2003

Moro T, Kikuchi S, Konno S, Yaginuma H. An anatomic study of the lumbar plexus with respect to retroperitoneal endoscopic surgery. Spine 2003; 28:423-428.

CONCLUSIONS: The safety zone, excluding the genitofemoral nerve, is at L4-L5 and above.

http://www.ncbi.nlm.nih.gov/pubmed/12616150             These diagrams show the number of cadavers out of 12 subjects with a neural structure in each position.

The Genitofemoral nerve pierces the psoas from posterior to anterior between superior L3 and inferior L4 and extends along the anterior surface of the psoas in 95% of the population.

click to enlarge pics

This diagram includes the genitofemoral nerve

This diagram excludes the genitofemoral nerve

 

Cremaster Muscle- monitoring EMG activity in the cremaster muscle in males can provide information on the status of the genitofemoral nerve.  

 

The trans-psoas lateral lumbar fusion approach is retroperitoneal.

Retroperitoneal- Having to do with the area outside or behind the peritoneum (the tissue that lines the abdominal wall and covers most of the organs in the abdomen).
Situated behind the peritoneum.

 

Lumbar Nerves- taken from:http://www.med.mun.ca/anatomyts/nerve/lumbnerv.htm

The iliohypogastric nerve L1

The iliohypogastric nerve is formed by fibres from L1, with some contribution from T12. The nerve runs obliquely across the quadratus lumborum muscle behind the kidney. Close to the iliac crest the nerve pierces the transversus abdomins muscle. Its lateral branch pierces the muscle of the lateral abdominal wall to supply the skin over the lateral gluteal region. The anterior branch runs forwards and down wards between transversus abdominis and internal oblique to supply the skin above the pubis.
 

The ilioinguinal nerve L1

The ilioinguinal nerve is formed in common with the iliohypogastric nerve. The nerve lies on the quadratus lumborum muscle and the iliacus until it perforates the body wall near the anterior iliac crest. It lies between the internal and external oblique to pass through the superficial inguinal ring. It distributes sensory fibres to superomedial thigh, root of the penis and upper part of the scrotum in the male, or mons pubis and labium majus in the female.
 

The genitofemoral nerve L1-L2

The genitofemoral nerve is formed from L1,2 and passes through the psoas to emerge on its anterior surface. It runs down wards on the psoas and divides into genital and femoral branches. The genital branch enters the inguinal canal through the deep inguinal ring to supply the cremaster muscle and a small area of overlying skin. The femoral branch passes behind the inguinal ligament to enter the femoral sheath and supply the skin over the femoral triangle.
 

Lateral cutaneous nerve of the thigh

The lateral cutaneous nerve of the thigh emerges at the lateral body of the psoas muscle. It forms from the posterior branches of the L2,3 anterior primary rami. It crosses the iliacus muscle to emerge close to the anterior superior iliac spine. Its anterior and posterior branches supply the lateral thigh.

 

The femoral nerve

The femoral nerve arises from posterior branches of the L2,3,4 anterior primary rami. The nerve lies between psoas and iliacus and enters the thigh behind the inguinal ligament, lateral to the femoral artery.
 

The obturator nerve

The nerve arises from anterior branches of the L2,3,4 anterior primary rami. It emerges medial to the psoas muscle and curves around the lateral wall of the pelvis on the obturator internus muscle. The nerve leaves the pelvis through the obturator foramen as anterior and posterior branches. An accessory obturator nerve is sometimes present arising from L3,4. The nerve passes over the superior ramus of the pubis to enter the pectineus.

 

Nerve Segments Muscles Cutaneous
Genitofemoral Nerve L1-L2 Cremasteric Surface of the anterior labium majus or scrotum (genital branch) and the upper medial thigh (femoral branch)
Ilioinguinal Nerves L1 Muscles of the lower abdominal wall  Surface of the lower abdominal wall and the anterior labium majus or scrotum
Iliohypogastric Nerve L1 Muscles of the lower abdominal wall  Surface of the lower abdominal wall, upper hip and upper thigh
Obturator Nerve L2-L4 Adductor Longus, Adductor Brevis, Adductor Magnus, Gracilis and Obturator Externus Surface of the lower medial thigh
Femoral Nerve L2-L4 Sartorius, Rectus Femoris, Vastus Lateralis, Vastus Intermedius, Vastus Medialis and Pectineus Surface of the anterior thigh
Nerve to Quadratus Femoris L4-S1 Gemellus Inferior and Guadratus Femoris N/A
Superior Gluteal Nerve L4-S1 Gluteus Medius, Gluteus Minimus and Tensor Fasciae Latae Surface over tensor fasciae and capsule of the hip joint
Common Tibial Nerve (and Sciatic Nerve) L4-S3 Hamstrings, Gastronemius and Intrinsics of the Superior of the Foot medial sural cutaneous nerve posterolateral leg and foot
Common Fibular Nerve (and Sciatic Nerve) L4-S3 Short Head of the Bicepts, Anterior Tiberalis and Intrinsic of the Inferior of the Foot Lateral sural cutaneous nerve, medial and intermediate dorsal cutaneous nerve anteriolateral leg and foot
Nerve to Obturator Internus L5-S2 Gemellus Superior and Obturator Internus N/A
Inferior Gluteal Nerve L5-S2 Gluteus Maximus Inferior buttocks
Nerve to Piriformis S1-S2 Piriformis N/A
Pudendal Nerve S2-S4 bulbospongiosus, deep transverse perineal, ischiocavernosus, sphincter urethrae, superficial transverse perineal clitoris, penis, bowel and bladder
Coccygeal Nerve S4-Co1 N/A perineum

 

     Sensory Nerve Distribution - Lower Extremities-click to enlarge pic

 

Advantages of the Lateral Approach vs the Posterior & Anterior Approaches: 

Limitations of the Lateral Approach

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Advantages to using Attended Neuromonitoring vs. Nuvasive’s Approach: