L5 Nerve Root (L5)

Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Figure 1: Nerve roots extending from the spinal cord¹

Peripheral Nerve Supply

Nerve	Roots	Motor Innervation	Cutaneous Innervation
Superior Gluteal N.	L4, L5, S1	Gluteus Medius Gluteus Minimus Tensor Fascia Latae (TFL)	None
Inferior Gluteal N.	L5, S1, S2	Gluteus Maximus
Posterior Cutaneous Nerve of the Thigh
Sciatic N.
Common Fibular N.	L4, L5, S1, S2
Tibial N.	L4, L5, S1, S2, S3

Muscle Supply

Motor Innervation

Muscle	Origin	Insertion	Innervation	Action
Biceps femoris long head	Ischial tuberosity Sacrotuberous lig. (Common head with semitendinosus)	Fibular head	Tibial n. L5 - S2	Hip: Extension Knee: Flexion, ER Pelvis: Sagittal stabilization
Biceps femoris short head	Lateral lip of Linea aspera	Fibular head	Common Fibular n. L5 - S2	Knee: Flexion, ER
Extensor digitorum brevis	Calcaneus (lateral dorsal)	Bases of middle phalanx 2-4	Deep Fibular n. L5 - S1	2nd-4th Toe: MTP Extension, PIP Extension
Extensor digitorum longus	Lateral condyle of Tibia Fibular head and medial surface IO membrane	Dorsal aponeurosis of 2-5th distal phalanges	Deep Fibular n. L4 - L5	TCJ: DF STJ: INV or EV (position dependent) 2nd-5th Toe: MTP Extension, PIP Extension, DIP Extension
Extensor hallucis brevis	Calcaneus (lateral dorsal)	1st Proximal phalanx	Deep Fibular n. L5 - S1	1st Toe: MTP Extension
Extensor Hallucis Longus	Fibula (middle 1/3 of medial surface) IO membrane	Dorsal aponeurosis of 1st distal phalanx	Deep Fibular n. L4 - L5	TCJ: DF STJ: Inversion 1st Toe: MTP Extension, IP Extension
Fibularis brevis	Middle lateral surface of Fibula	Base of 5th MT	Superficial Fibular n. L5 - S1	TCJ: PF STJ: Eversion
Fibularis longus	Proximal lateral surface of Fibula	Medial cuneiform Base of 1st MT	Superficial Fibular n. L5 - S1	TCJ: PF STJ: Eversion Arch: Transverse arch support
Fibularis tertius	Anterior border of Distal Fibula	Shaft or Base of 5th MT	Deep Fibular n. L4 - L5	TCJ: DF STJ: Eversion
Flexor digitorum longus	Middle 1/3 of posterior surface of Tibia	Bases of 2-5 Distal Phalanges	Tibial n. L5 - S2	TCJ: PF STJ: Inversion 2nd-5th Toe: MTP Flexion, PIP Flexion, DIP Flexion
Flexor hallucis longus	Posterior distal 2/3 of Fibula IO membrane	Base of 1st Distal Phalanx	Tibial n. L5 - S2	TCJ: PF STJ: Inversion 1st Toe: MTP Flexion, IP Flexion
Gluteus Maximus	Sacrum (dorsal surface, lateral part) Ilium (gluteal surface, posterior part) Thoracolumbar fascia sacrotuberous lig.	IT Band Gluteal tuberosity	Inferior gluteal n. L5 - S2	Entire mm.: Extension, ER (when <60° HF) Upper fibers: Abduction, IR (when &gt60° HF) Lower fibers: Adduction
Gluteus medius	Ilium	Greater trochanter (lateral surface)	Superior gluteal n. L4 - S1	Entire mm.: Abduction, Frontal stabilization Anterior fibers: Flexion, IR Posterior fibers: Extension, ER (when <60° HF), IR (when &gt60° HF)
Gluteus Minimus	Ilium gluteal surface (inferior to gluteus medius origin)	Greater trochanter (anterolateral surface)	Superior gluteal n. L4 - S1	Entire mm.: Abduction, Frontal stabilization Anterior fibers: Flexion, IR Posterior fibers: Extension, ER (when <60° HF), IR (when &gt60° HF)
Inferior Gemellus	Ischial tuberosity	Medial surface of greater trochanter via obturator internus tendon	Nerve to Quadratus femoris L5 - S1	Hip: ER, Extension, Abduction
Obturator Internus	Obturator membrane and its bony boundaries	Medial surface of Greater Trochanter	Nerve to Obturator internus L5 - S1	Hip: ER, Extension, Abduction, Stabilization
Popliteus	Lateral Femoral Condyle Posterior horn of Lateral Meniscus	Posterior surface of Tibia	Tibial n. L4 - S1	Knee: Flexion, Unlocks the knee via femoral ER
Quadratus femoris	Lateral border of Ischial tuberosity	Intertrochanteric crest	Nerve to Quadratus femoris L5 - S1	Hip: ER
Semimembranosus	Ischial tuberosity	Medial tibial condyle Oblique popliteal lig. Popliteus fascia	Tibial n. L5 - S2	Hip: Extension Knee: Flexion, IR Pelvis: Sagittal stabilization
Semitendinosus	Ischial tuberosity Sacrotuberous lig. (common head with biceps femoris long head)	Pes anserine	Tibial n. L5 - S2	Hip: Extension Knee: Flexion, IR Pelvis: Sagittal stabilization
Superior gemellus	Ischial spine	Medial surface of greater trochanter via obturator internus tendon	Nerve to Obturator internus L5 - S1	Hip: ER, Extension, Abduction
Tensor Fascia Latae	ASIS	IT Band	Superior gluteal n. L4 - S1	Tenses fascia latae Hip: Abduction, Flexion, IR
Tibialis Anterior	Tibia (Upper 2/3 of lateral surface) IO membrane Superficial crural fascia	Medial cuneiform (Medial & plantar surface) 1st Metatarsal (medial base)	Deep Fibular n. L4 - L5	TCJ: DF STJ: Inversion
Tibialis posterior	IO membrane Adjacent Tibia Adjacent Fibula	Cuneiforms 2-4 MT bases	Tibial n. L4 - L5	Knee: *negligble* Flexion TCJ: PF Arch support: Transverse arch, Longitudinal arch

Dermatome

Figure 2: Dermatomal cutaneous distribution¹

Figure 3: Dermatomal cutaneous distribution (Posterior)¹

Overview

“L5 root involvement causes lower back, buttock, lateral thigh, and anterolateral calf pain. Sensory signs and symptoms occur on the lateral leg, the dorsomedial foot, and the large toe. Paresis occurs in the gluteus medius, gluteus minimus, tensor fasciae latae (adduction and internal rotation of thigh), semimembranosus and semitendinosus (knee flexion), tibialis posterior (plantar flexion and inversion of foot), tibialis anterior (dorsiflexion and inversion of foot), peronei (foot plantar flexion and eversion), flexor digitorum longus (plantar flexion of foot and all toes except the large toe), extensor digitorum brevis (extension of the large toe and three medial toes), extensor hallucis longus (extension of great toe and foot dorsiflexion), and extensor digitorum longus (extension of four lateral toes and foot dorsiflexion). With L5 root lesions, both the patellar (L2 L4) and Achilles (S1 S2) reflexes are spared.”²

Examination

SLR

“The straight leg raise, also called Lasègue sign, Lasègue test or Lazarevi sign, is a test done during the physical examination to determine whether a patient with low back pain has an underlying herniated disk, often located at L5 (fifth lumbar spinal nerve). With the patient lying down on his or her back on an examination table or exam floor, the examiner lifts the patient’s leg while the knee is straight. If the patient experiences sciatic pain when the straight leg is at an angle of between 30 and 70 degrees, then the test is positive and a herniated disc is likely to be the cause of the pain. A meta-analysis reported the accuracy of the straight leg test as 91% sensitive and 26% specific [7]. If raising the opposite leg causes pain (cross or contralateral straight leg raising), the sensitivity is 29% and the specificity is 88% [7]. The straight leg raising test and the cross straight leg raising test are two tests based on stretching of the nerves in the spine. The diagnostic accuracy of the straight leg raising test is thus limited by its low specificity [7].”²

Sensation

• 1st 2 toes

DDX

• Superficial fib
  • Doesnt innervate cleft between toes #1 and #2

References

1.

Gray H. Anatomy of the Human Body. 20th ed. (Lewis WH, ed.). Lea & Febiger; 1918. https://www.bartleby.com/107/

2.

Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8th ed. Wolters Kluwer Health; 2022.