S1 Nerve Root (S1)

Authors

Affiliations

Nate Yomogida, PT, DPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, PT, DPT

Doctor of Physical Therapy

B.A. in Neuroscience

Figure 1: Nerve roots extending from the spinal cord¹

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
Abductor hallucis	Medial calcaneal tuberosity Plantar aponeurosis Flexor retinaculum	Medial aspect of 1st Proximal phalanx	Medial Plantar n. S1 - S2	1st Toe: MTP Flexion, MTP Abduction Arch support: Longitudinal arch support
Abductor digiti minimi	Medial tubercle of calcaneal tuberosity Cuboid Lateral cuneiforms 3-5th MTP joints Deep transverse metatarsal lig.	Base of 5th proximal phalanx Base of 1st proximal phalanx (via common tendon)	Lateral Plantar n. Lateral Plantar n. (Deep branch) S1 - S3	5th Toe: MTP Flexion 1st MTP: Flexion, Adduction Arch Support: *Transverse head* supports transverse arch, *Oblique head* supports longitudinal arch
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 hallucis brevis	Calcaneus (lateral dorsal)	1st Proximal phalanx	Deep Fibular n. L5 - S1	1st Toe: MTP 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
Flexor digitorum brevis	Medial tubercle of calcaneal tuberosity Plantar aponeurosis	Sides of middle phalanx 2-5	Medial Plantar n. S1 - S2	2nd-5th Toe: MTP Flexion, PIP Flexion Arch support: Longitudinal arch support
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 brevis	Cuboid Lateral cuneiforms Plantar calcaneocuboid lig.	Medial Sesamoid bone Lateral Sesamoid bone	Lateral Plantar n. Medial Plantar n. S1 - S2	MTP Flexion Supports Longitudinal Arch
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
Gastrocnemius	Superior-posterior aspect of Medial Femoral Condyle Lateral surface of Lateral Femoral Condyle	Calcaneal tuberosity via Achilles' Tendon	Tibial n. S1 - S2	TCJ: PF Knee: 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
Piriformis	Anterior Sacrum	Apex of the Greater Trochanter	Sacral Plexus Direct Br. S1 - S2	Hip (at <60° flexion): ER Hip: Abduction, Extension, Stabilization Hip (at ≥60° flexion): IR
Plantaris	Lateral epicondyle of Femur	Calcaneal tuberosity	Tibial n. S1 - S2	Knee: *negligble* Flexion TCJ: PF Proprioception: Organ of proprioception for the plantarflexors
Popliteus	Lateral Femoral Condyle Posterior horn of Lateral Meniscus	Posterior surface of Tibia	Tibial n. L4 - S1	Knee: Flexion, Unlocks the knee via knee IR
Quadratus femoris	Lateral border of Ischial tuberosity	Intertrochanteric crest	Nerve to Quadratus femoris L5 - S1	Hip: ER
Quadratus plantae	Calcaneal tuberosity (medial and plantar borders)	Tendons of FDL (lateral borders)	Lateral Plantar n. S1 - S3	Redirects and augments pull of the FDL
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
Soleus	Posterior Fibula Posterior Tibia	Calcaneal tuberosity via Achilles' Tendon	Tibial n. S1 - S2	TCJ: PF Lower leg: 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 Flexed knee: ER Extended knee: Locks out extension

Dermatome

Figure 2: Dermatomal cutaneous distribution¹

Figure 3: Dermatomal cutaneous distribution (Posterior)¹

Examination

DTR

• Achilles Reflex (S1, S2)

References

1.

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