L1 Nerve Root (L1)

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

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

Muscle	Origin	Insertion	Innervation	Action
Iliocostalis cervicis	Ribs 3-7	C4-C6 TP	Spinal nn. Posterior rami (lateral br.) C8 - L1	Bilateral: Extends spine Unilateral: Spine ipsilateral sidebend
Iliocostalis lumborum	Sacrum Iliac crest Thoracolumbar fascia (posterior layer)	Ribs 6-12 Upper lumbar TP Thoracolumbar fascia (posterior layer)	Spinal nn. Posterior rami (lateral br.) C8 - L1	Bilateral: Extends spine Unilateral: Spine ipsilateral sidebend
Iliocostalis thoracis	Ribs 7-12	Ribs 1-6	Spinal nn. Posterior rami (lateral br.) C8 - L1	Bilateral: Extends spine Unilateral: Spine ipsilateral sidebend
Psoas Major	T12-L4 and associated IV discs L1-L5 TP	Lesser Trochanter	Lumbar Plexus Direct Br. L1 - L3	Hip: Flexion, ER L/S (unilateral contraction with femur fixed): I/L spine sidebend L/S (bilateral contraction): Raises trunk from supine position
Psoas Minor	T12, L1 vertebrae (lateral aspect) and IVD	Pectineal Line Iliopubic ramus Iliac fascia Inguinal ligament	Spinal nn. L1 - L3	Trunk: Weak flexion

Dermatome

Figure 2: Dermatomal cutaneous distribution¹

Figure 3: Dermatomal cutaneous distribution (Posterior)¹

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 ankle²
• Dural signs of prone knee flexion
• SLR will occassionally be positive²
• ↓ Extension ROM
• Weakness
  • Slight weakness of iliopsoas²
  • Gross loss of quadriceps strength²
• Hypoesthesia of the medial aspect of the knee and lower leg²
• Patellar reflex Absent (0) or reduced (1)

References

1.

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

2.

Dutton M. Dutton’s Orthopaedic Examination, Evaluation, and Intervention. 5th ed. McGraw Hill Education; 2020.