Anatomy of The Lumbar Plexus:
The lumbar plexus originates from the anterior primary rami of L1–4.
About 50% of subjects receive an additional contribution from T12. The lumbar plexus may be pre-ﬁxed, with its lowest contribution from L3, or post-ﬁxed, when it extends to L5.
Formation of the plexus:
The lumbar plexus lies in front of the transverse processes of the lumbar vertebrae within the substance of the psoas major.
L1, joined in 50% of cases by a branch from T12, divides into an upper and lower division.
The upper division gives rise to the iliohypogastric and ilio-inguinal nerves; the lower joins a branch from L2 to form the genitofemoral nerve. The rest of L2, together with L3 and the contribution to the plexus from L4, divide into dorsal and ventral divisions.
Dorsal divisions of L2 and 3 form the lateral cutaneous nerve of the thigh and L2–4 form the femoral nerve. The ventral branches join into the obturator nerve (L2–4) and, when present, the accessory obturator nerve (L3 and 4).
Summary of branches of the lumbar plexus:
(C)Genitofemoral L1, 2
1-Lateral cutaneous nerve of thigh L2, 3
2- Femoral nerve L2–4
1-Obturator nerve L2–4
2-Accessory obturator nerve L3, 4
(F)In addition, muscle branches are given to:
1- psoas major 3 -iliacus
2 -psoas minor 4 -quadratus lumborum
Distribution of the lumbar plexus
(a)The genitofemoral nerve: (L1, 2)
The genitofemoral nerve is mainly a sensory nerve. It divides into the genital and femoral branches at a variable distance above the inguinal ligament.
(b)The lateral cutaneous nerve of the thigh: (L2, 3)
The lateral cutaneous nerve sometimes arises from the femoral nerve and not as a separate branch of the lumbar plexus.
(c)The femoral nerve L2–4)
The femoral nerve is the largest nerve of the lumbar plexus.
Within the femoral triangle the nerve breaks up into its terminal branches which stem from an anterior and posterior division.
1- Muscular branches to:
(a) pectineus (b) sartorius
(a) intermediate cutaneous nerve of thigh
(b) medial cutaneous nerve of thigh.
1-Muscular branches to quadriceps femori
2-Cutaneous branch as saphenous nerve.
3-Articular branches to:
(a) hip (b) knee
(The saphenous nerve is the largest cutaneous branch of the femoral nerve.)
(d)The obturator nerve: (L2–4)
The nerve enters the obturator canal above and anterior to the obturator vessels, which are derived from the internal iliacs. Within the canal the nerve divides into its anterior and posterior branches.
1-The anterior branch passes into the thigh above the obturator externus ,
descends on adductor brevis, ﬁrst behind pectineus and then behind
adductor longus, to end as a ﬁlament which runs along the femoral
2-The posterior branch pierces and supplies obturator externus.