Essentials I. Ilioinguinal nerve • Exits the pelvis over the inguinal ligament to the superior-medial portion of the thigh. II. Femoral nerve • Exits the pelvis, passes in between the psoas and iliacus muscles, underneath the inguinal ligament, down the anterior thigh to innervate the anterior compartment muscles. III. Obturator nerve • Descends medial to the femoral nerve, anterior to the sacrospinous ligament and exits via the obturator canal, down the medial aspect of the thigh to innervate the medial compartment muscles. IV. Sciatic nerve • Exits the pelvis anterior and inferior to the piriformis via the greater sciatic foramen and then descends posterior to the femur. • At the inferior femur, it divides into: - The tibial nerve, which continues down the posterior tibia to innervate the posterior leg and plantar foot. - The peroneal nerve, which wraps around the fibular neck and innervates the anterior and lateral leg and dorsal foot. V. Superior gluteal nerve • Exits the greater sciatic foramen superior to the piriformis muscle. Hip and pelvis innervation: essentials • Spinal nerves L1 – S4 innervate the hip and pelvis. • The sciatic nerve is derived from L4 – S3. - It innervates the hamstrings, which provide hip extension. • The femoral and obturator nerves are derived from L2 – L4. - The femoral innervates iliopsoas, which provides hip flexion; it is key to climbing upstairs or rising from a low chair. thigh innervation: essentials • The femoral nerve innervates the anterior compartment. • The obturator nerve innervates the medial compartment. • The sciatic nerve innervates the posterior compartment. - The "one compartment — one nerve" principle helps us remember each compartments' innervation and function. Muscle Groups • Femoral nerve - Quadriceps • Gluteal nerves - Gluteal muscles • Obturator nerve - Adductor muscles • Sciatic nerve - Extrinsic foot muscles • Sciatic nerve - Hamstrings • Sciatic nerve - Intrinsic foot muscles • Short rotators of the hip Advanced Innervation Inferior gluteal nerve (L5 – S2) • Innervates gluteus maximus, which provides provides hip extension. Superior gluteal nerve (L4 – S1) • Innervates gluteus medius, gluteus minimus, and tensor fasciae latae; all of which provide hip abduction – tensor fasciae latae does when the hip is in flexion. Iliohypogastric and ilioinguinal nerves (L1). • Both nerves provide motor innervation to the internal oblique and transversus abdominis muscles. • Iliohypogastric nerve provides sensory coverage to the suprapubic and upper-lateral gluteal areas. • Ilioinguinal nerve provides sensory coverage to the superior-medial portion of the thigh and proximal external genitalia. Genitofemoral nerve (L1–L2) • Genital branch innervates the cremaster muscle. - Provides sensory coverage to the scrotum or labia. • Femoral branch is purely sensory. - Provides sensory coverage to the femoral triangle. Lateral cutaneous nerve of the thigh (aka lateral femoral cutaneous nerve) (L2 and L3) • Provides sensory coverage to the lateral thigh. Posterior cutaneous nerve of the thigh (aka the posterior femoral cutaneous nerve) (S1 – S3) • Provides sensory coverage to the midline back of the thigh. Pudendal nerve (S4 + S2 and S3) • Branches into the inferior rectal nerve, perineal nerve, and dorsal nerve to the penis or clitoris. • Provides motor innervation to the external urethral and anal sphincters and external genitalia and it provides sensory coverage to the anus and external genitalia. Short rotators of the hip (L5 – S2) • Provide external rotation of the hip when it is in extension and hip abduction when it is in flexion. - The nerve to quadratus femoris innervates quadratus femoris and gemellus inferior; the nerve to obturator internus innervates obturator internus and gemellus superior; the nerve to piriformis innervates piriformis; and the obturator nerve innervates obturator externus (note that obturator externus is supplied by L3, L4).