📝 STANDARD DESCRIPTION:
High-Yield Points:
• Lie on the ventral surface of lumbar vertebrae — form roof of abdomen with vertebrae.
• Psoas Major + Iliacus = Iliopsoas — main flexor of hip (cattle 'tenderloin').
• Psoas Minor — flexes the lumbar spine and inserts on the psoas minor tubercle/iliopubic eminence of the ilium.
• Quadratus Lumborum — between transverse processes; stabilises spine.
• Innervated by ventral branches of lumbar nerves.
• Important to the meat industry: 'Tenderloin'/'Fillet' = the psoas group.
📚 DETAILED DESCRIPTION:
SUBLUMBAR (HYPAXIAL) MUSCLES
This group lies on the ventral aspect of the lumbar vertebrae, between the bodies of vertebrae and the abdominal cavity. Together with the lumbar vertebrae, they form the roof of the abdomen.
1. Psoas Major:
• Origin: Ventral surfaces of lumbar transverse processes and last ribs.
• Insertion: Lesser trochanter of femur (joins iliacus → 'iliopsoas').
• Action: Flexes hip joint, rotates femur outward; flexes lumbar spine.
• Tenderloin / fillet of beef = bovine psoas major + minor.
2. Iliacus:
• Origin: Ventral surface of ilium.
• Joins psoas major distally to form 'iliopsoas'; common insertion at lesser trochanter.
• Action: Flexes the hip (works with psoas major).
3. Psoas Minor:
• Origin: Bodies of last 2 thoracic + first 4-5 lumbar vertebrae.
• Insertion: Tubercle of psoas minor on shaft of ilium.
• Action: Flexes lumbar spine; absent in some species.
4. Quadratus Lumborum:
• Lies between lumbar transverse processes.
• Stabilises lumbar spine, fixes ribs.
Innervation: Ventral rami of lumbar nerves (lumbar plexus branches).
Clinical importance: The lumbar plexus emerges between psoas muscles → these muscles can compress nerves causing 'paralumbar paresis' in down cows. Sublumbar abscesses are diagnosed by per-rectum palpation.
// COMPARATIVE ANALYSIS
| OX |
Tenderloin = psoas group; most expensive cut. Iliopsoas weakness in downer cows. |
| HORSE |
Same arrangement. Psoas plays major role in flexing hindlimb forward during stride. |
| DOG |
Iliopsoas strain ('groin pull') common in agility/working dogs. |
CLINICAL RELEVANCE
Iliopsoas Strain (dog): Lameness, painful hip flexion. Sublumbar Abscess: Sublumbar abscesses may arise from local or haematogenous infection and can be palpable per rectum; a routine migration route from rumen through diaphragm and mediastinum should not be assumed. Downer Cow Syndrome: Prolonged recumbency can injure the obturator or sciatic nerves and cause ischaemic damage to the iliopsoas and other muscles, contributing to inability to rise.
