Psoas Minor

Origin, Insertion, Action & Nerve

Attachments explained

The Psoas Minor is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.

Action & function

When the Psoas Minor contracts, it produces the following movement: Weakly flexes the trunk (lumbar vertebral column).

As part of the Gluteal & Hip group of the Lower Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The Psoas Minor receives its nerve supply from the Anterior ramus of L1. This nerve carries fibres from spinal segment(s) L1.

Because a muscle can only contract when its nerve is intact, injury to the Anterior ramus of L1 or to its spinal roots (L1) can weaken or paralyse the Psoas Minor, impairing the movements it normally produces (weakly flexes the trunk (lumbar vertebral column)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Psoas Minor (the OIANS method)

Distinguish the psoas minor sharply from the psoas major: the minor lies in front of the major, ends on the pelvis at the pectineal line rather than the femur, and so never reaches the hip. Because it does not cross the hip joint, it is only a weak flexor of the lumbar spine, which is the key point that separates the two psoas muscles in memory.

Anchor two facts that make it distinctive: it is absent in a substantial minority of people, and it is supplied simply by the anterior ramus of L1. Remembering its high vertebral origin from T12 and L1 and its purely trunk-flexing role prevents it from being confused with the powerful hip flexor beside it.

Frequently asked questions

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