L1 Nerve Root (L1)

Authors
Affiliations

Nathaniel 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

Peripheral Nerve Supply

Peripheral Nerves Originating from L1 Nerve root
Nerve Roots Motor Innervation Cutaneous Innervation
Ilioinguinal N.

L1

Iliohypogastric N.

L1

Genitofemoral N.

L1, L2

Motor Innervation

L1 Nerve Root Skeletal Muscle Innervations
Muscle Origin Insertion Innervation Action
Psoas Major

  • [T12-L4 and associated IV discs](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#origin) [@gilroyAtlasAnatomy2020]

  • [L1-L5 TP](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#origin) [@bogdukAnatomyBiomechanicsPsoas1992]
  • [Lesser Trochanter](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#insertion) [@gilroyAtlasAnatomy2020]


L1 - L31

  • [Lumbar Plexus Direct Br.](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#nerve) [@gilroyAtlasAnatomy2020]

[L1](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#nerve) - [L3](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#nerve) [@gilroyAtlasAnatomy2020]

 Hip

  • [Flexion](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#action) [@gilroyAtlasAnatomy2020]
  • [ER](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#action) [@gilroyAtlasAnatomy2020]

L/S (bilateral contraction)

  • [Raises trunk from supine position](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#action) [@gilroyAtlasAnatomy2020]

L/S (unilateral contraction with femur fixed)

  • [I/L spine sidebend](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_major_muscle.qmd#action) [@gilroyAtlasAnatomy2020]
Psoas Minor
  • [T12, L1 vertebrae (lateral aspect) and IVD](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#origin) [@gilroyAtlasAnatomy2020]

  • [Pectineal Line](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#insertion) [@gilroyAtlasAnatomy2020]

  • [Iliopubic ramus](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#insertion) [@gilroyAtlasAnatomy2020]

  • [Iliac fascia](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#insertion) [@gilroyAtlasAnatomy2020]

  • [Inguinal ligament](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#insertion) [@gilroyAtlasAnatomy2020]


L1 - L31

  • [Spinal nn.](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#nerve) [@gilroyAtlasAnatomy2020]

[L1](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#nerve) - [L3](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#nerve) [@gilroyAtlasAnatomy2020]

 Trunk

  • [Weak flexion](/The Archive/Anatomy/Skeletal Muscles/Lower limb muscles/Iliopsoas muscles/psoas_minor_muscle.qmd#action) [@gilroyAtlasAnatomy2020]

Compression

Compression of L3 nerve root includes:

  • Pain in the middle lumbar spine, upper buttock, whole anterior thigh and knee, medial knee, and just above the ankle3
  • Dural signs of prone knee flexion
  • SLR will occassionally be positive3
  • ↓ Extension ROM
  • Weakness
    • Slight weakness of iliopsoas3
    • Gross loss of quadriceps strength3
  • Hypoesthesia of the medial aspect of the knee and lower leg3
  • Patellar reflex Absent (0) or reduced (1)

References

1.
Gilroy AM, MacPherson BR, Wikenheiser JC, Voll MM, Wesker K, Schünke M, eds. Atlas of Anatomy. 4th ed. Thieme; 2020.
2.
Bogduk N, Pearcy M, Hadfield G. Anatomy and biomechanics of psoas major. Clinical Biomechanics. 1992;7(2):109-119. doi:10.1016/0268-0033(92)90024-X
3.
Dutton M. Dutton’s Orthopaedic Examination, Evaluation, and Intervention. 5th ed. McGraw Hill Education; 2020.

Citation

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