6 Lumbar Spine Anatomy

10.1055/b-0039-166415

Melissa G. Goczalk, Ankur S. Narain, Fady Y. Hijji, Philip K. Louie, Daniel D. Bohl, and Kern Singh

Anatomy and function:
- Lordotic curvature.
- Long transverse processes for muscle attachment.
- Lacks facets for rib articulation.
- Supports weight of trunk.
- Allow flexion, extension, lateral flexion, and rotation of spine.
Landmarks:
- L1: conus medullaris.
- L3: umbilicus.
- L4: iliac crests, aortic bifurcation.

Vertebral body:
- Cylindrically shaped and widest transversely.
Vertebral foramen:
- Triangular spinal canal.
Pedicles:
- Connect vertebral body to lamina.
- Directed posteriorly and located in the middle one-third of the transverse process.
Transverse processes:
- Thin and long from L1 to L4.
- Large and cone-shaped at L5 due to iliolumbar ligament attachment to pelvic bones.
Facet joints:
- L1–L4 facets are sagittally oriented to limit axial rotation.
- L5 facet is more coronal and resists anteroposterior movement.
- Prominent pars interarticularis.
Lamina:
- Connect spinous process to pedicles.
Spinous process:
- Broad and thick orientation.

Anterior longitudinal ligament:
- Located on the anterior surface of vertebral bodies.
- Functions include limiting spine extension and securing intervertebral disks.
Posterior longitudinal ligament:
- Located on the posterior surface of vertebral bodies.
- Limits spine flexion and secures intervertebral disks.
Ligamentum flavum:
- Spans posterior aspect of the inferior lamina to the anterior aspect of the superior lamina.
- Limits laminar flexion and separation.
Supraspinous ligament:
- Spans the tips of spinous processes; terminates at L3.
Interspinous ligament:
- Connect adjacent spinous processes; oriented obliquely.

**Table 6.1** Superficial extrinsic back muscles
Muscle	Origin	Insertion	Action	Innervation
Trapezius	Spinous processes of C7–T12	Clavicle, scapula	Rotate scapula	Cranial nerve XI
Latissimus dorsi	Spinous processes of T6–T12, lumbar spine, sacrum, iliac crests, ribs 9–12	Intertubercular sulcus of humerus	Extend, adduct, and medically rotate humerus	Thoracodorsal nerve
Levator scapulae	Transverse processes of C1–C4	Medial scapulae	Elevate scapula	Dorsal scapular nerve
Rhomboid minor	Spinous processes of C7–T1	Scapular spine	Adduct scapula	Dorsal scapular nerve
Rhomboid major	Spinous processes of T2–T5	Medial border of scapula	Adduct scapula	Dorsal scapular nerve
Serratus posterosuperior	Spinous processes of C7–T5	Upper border of ribs 2–5	Elevate ribs	Intercostal nerves T1–T4
Serratus posterior inferior	Spinous processes of T11–L3	Lower border of ribs 9–12	Depress ribs	Intercostal nerves T9–T12

**Table 6.2** Deep intrinsic back muscles: spinotransverse group
Muscle	Origin	Insertion	Action	Innervation
Splenius capitis	Ligamentum nuchae	Mastoid and nuchal line	Laterally flex and rotate ipsilateral neck	Dorsal rami of inferior cervical nerves
Splenius cervicis	Spinous processes of T1–T6	Transverse processes of C1–C4	Laterally flex and rotate ipsilateral neck	Dorsal rami of inferior cervical nerves

**Table 6.3** Deep intrinsic back muscles: sacrospinalis group
Muscle	Origin	Insertion	Action	Innervation
Iliocostalis lumborum	Sacrum, spinous processes of lumbar and lower thoracic vertebrae, supraspinous ligaments, and iliac crests	Lower six to seven ribs	Bilateral: vertebral column and head extension Unilateral: vertebral column lateral flexion	Dorsal primary rami
Longissimus thoracis	Transverse processes of lumbar vertebrae	Transverse processes of thoracic vertebrae	Bilateral: vertebral column and head extension Unilateral: vertebral column lateral flexion	Dorsal primary rami
Spinalis thoracis	Spinous processes of T10–L2	Spinous processes of T1–T8	Bilateral: vertebral column and head extension Unilateral: vertebral column lateral flexion	Dorsal primary rami

**Table 6.4** Deep intrinsic back muscles: transversospinales group
Muscle	Origin	Insertion	Action	Innervation
Semispinalis cervicis	Transverse processes	Spinous processes	Extend, rotate contralateral side	Dorsal primary rami
Semispinalis thoracic	Transverse processes	Spinous processes	Extend, rotate contralateral side	Dorsal primary rami
Semispinalis capitis	Transverse processes of T1–T6	Nuchal ridge	Extend, rotate contralateral side	Dorsal primary rami
Multifidus	Transverse processes of C2–S4	Spinous processes	Contralateral lateral flexion and rotation	Dorsal primary rami
Rotatores	Transverse processes	Spinous processes of superior vertebral level	Rotate contralateral superior vertebrae	Dorsal primary rami
Interspinales	Spinous processes	Spinous processes of superior vertebral level	Extend vertebral column	Dorsal primary rami
Intertransversarii	Transverse processes	Transverse processes of superior vertebral level	Lateral flex vertebral column	Dorsal primary rami

**Table 6.5** Anterolateral abdominal wall
Muscle	Origin	Insertion	Action	Innervation
Rectus abdominis	Pubic crest, pubic tubercle, pubic symphysis	Costal cartilages of ribs 5–7 and xiphoid process	Compress abdominal contents, flex vertebral column, tense abdominal wall	Anterior rami of T7–T12
External oblique	Anterior angles of ribs 5–12	Iliac crest and aponeurosis to linea alba	Compress abdominal contents, flex trunk	Anterior rami of T7–T12
Internal oblique	Thoracolumbar fascia, iliac crests, inguinal ligament	Inferior border of lower ribs, aponeurosis to linea alba, pubic crest, pectineal line	Compress abdominal contents, flex trunk	Anterior rami of T7–T12 and L1
Transversus abdominis	Thoracolumbar fascia, iliac crests, inguinal ligament, costal cartilages of ribs 7–12	Aponeurosis to linea alba, pubic crest, pectineal line	Compress abdominal contents	Anterior rami of T7–T12 and L1

**Table 6.6** Posterior abdominal wall muscles
Muscle	Origin	Insertion	Action	Innervation
Iliacus	Iliac fossa, anterior sacroiliac and iliolumbar ligaments, and sacrum	Lesser trochanter of femur	Flexion of thigh at hip	Femoral nerve
Psoas major	Vertebral bodies of T12 and L1–L5, transverse processes of lumbar vertebrae, and intervertebral disks of T12 and L1–L5	Lesser trochanter of femur	Flexion of thigh at hip	Anterior rami of L1–L3
Psoas minor	Vertebral bodies and intervertebral disks of T12 and L1	Pectineal line of pelvic brim and iliopubic eminence	Flexion of lumbar vertebral column	Anterior rami of L1
Quadratus lumborum	Transverse process of L5, iliolumbar ligament, iliac crest	Transverse process of L1–L4 and inferior border of rib 12	Depress and stabilize rib 12 and lateral bending of trunk	Anterior rami of T12 and L1–L4