Why does a hypertonic psoas restrict hip extension?

A muscle that is stuck contracted holds the joint in the direction it acts. The psoas is the chief hip flexor, so a hypertonic psoas holds the hip flexed and restricts the OPPOSITE motion, which is hip extension. The lost motion is always the antagonist of the tight muscle.

What is the classic presentation of psoas syndrome?

A forward-flexed antalgic posture with trouble standing erect, low back and groin or anterior thigh pain, sidebending toward the involved side, a positive Thomas test, and a tender point about two thirds of the way from the ASIS to the umbilicus. It is commonly paired with an L1 or L2 somatic dysfunction.

How do you treat a psoas tender point with counterstrain?

Place the patient in marked hip flexion with the trunk sidebent toward the tender point and slight external rotation of the hips to fine tune. Hold about 90 seconds and return slowly. This shortens the irritated psoas and resets the tender point.

What is the psoas sign and how does it differ from psoas syndrome?

The psoas sign is pain on passive right hip extension or resisted hip flexion when an inflamed retrocecal appendix irritates the psoas. It signals visceral irritation needing surgical evaluation, not the mechanical somatic dysfunction of psoas syndrome that responds to OMT.

OMM · Myofascial · Board Review

Psoas Syndrome & the Opposite-Motion Rule

One rule unlocks a whole category of board questions: a muscle that is stuck contracted holds the joint in the direction it acts, so it restricts the opposite motion. Learn it on the psoas, then watch it transfer.

A 10-year-old boy is brought to the office because of 3 days of difficulty walking after a weekend of soccer. There was no fall and no direct blow. He guards a slightly bent-forward posture and resists straightening up. Examination reveals a hypertonic, tender right psoas with a firm contracted band; hip and knee are neurovascularly intact and radiographs of the hip and pelvis are unremarkable. On motion testing of the right hip, one direction is clearly blocked. Which hip motion is most likely restricted?

A. Flexion

B. Extension

C. Abduction

D. Internal rotation

Extension. The psoas is the major hip flexor. A hypertonic psoas is stuck pulling the hip into flexion, so it physically holds the joint flexed. The motion it cannot allow is its own antagonist: hip extension.

Flexion is wrong because that is the direction the tight muscle is already pulling, so it stays free or even feels strong. Abduction and internal rotation are governed by other muscles, not the psoas. The lost motion is always the opposite of what the tight muscle does.

The engine of the whole topic

The opposite-motion machine

Pick a muscle. Watch which way it drags the hip, and watch the motion it steals. The green arrow is the pull. The red arc is the motion you lose.

The muscle pulls the joint into

Flexion

So the restricted motion is

Extension

A hypertonic psoas holds the hip flexed, so extension is the motion that disappears.

From the Attending

Stop memorizing lists of restricted motions. There is one move. A tight muscle is a rope pulled taut on one side of the joint. The joint sits where the rope drags it, and it cannot travel the way the rope refuses to lengthen. Flexor stuck on means flexion is the resting deformity and extension is the casualty. Name the muscle, name its action, flip it. That distinction drives every one of these questions.

Anatomy makes the rule unavoidable

Build the psoas, predict the deficit

If you know where the psoas starts, where it ends, and what it does, the restricted motion is not a fact to memorize. It is the only answer that fits.

Origin: the lumbar spine, bodies and transverse processes of T12 down through L5. It hugs the front of the vertebrae.

Insertion: it dives through the pelvis and grabs the lesser trochanter of the femur.

Nerve: direct branches of the lumbar plexus, L1 to L3 ventral rami.

Action: spanning spine to femur in front of the hip axis, it is the chief hip flexor (and bends the lumbar spine forward).

Stuck on: it shortens, tugs the upper lumbar spine, and holds the hip flexed. Extension cannot happen. A stubborn L1 or L2 dysfunction often rides along.

Anatomical drawing of the iliac and anterior femoral muscles showing psoas major and iliacus converging on the lesser trochanter of the femur

Psoas major and iliacus run from the lumbar spine and iliac fossa to the lesser trochanter. Anterior to the hip axis = flexor. (Gray's Anatomy, Wikimedia Commons)

Lumbar plexus diagram showing L1 through L4 nerve roots emerging around the psoas major muscle

The lumbar plexus (L1 to L4) is born inside the psoas. That is why an irritated psoas can refer pain to the groin and anterior thigh. (Wikimedia Commons)

From the Attending

Look at where it inserts. The lesser trochanter sits in front of the hip axis. Anything that crosses in front of a joint and pulls is a flexor. You do not need a chart. Front of the axis means flexor, flexor stuck means extension is gone. Find the insertion, find the answer.

Recognize it across the room

Psoas syndrome: the bent-forward patient

The whole syndrome is the rule playing out in a person. The psoas will not lengthen, so the body folds forward to live inside the deficit.

Posture: stands forward-flexed, sidebent toward the tight side, cannot straighten fully.
Pain: deep low back, often radiating to the groin or anterior thigh (the L1 to L3 territory).
Trigger: follows prolonged sitting, a flexion strain, or sustained hip flexion.
Tender point: deep in the lower quadrant, about two thirds of the way from the ASIS to the umbilicus.
Partner dysfunction: a nonneutral L1 or L2 dysfunction; the piriformis on the same side often gets irritated too.
Confirm: a positive Thomas test.

Clinical photograph of the Thomas test: patient supine, one hip fully flexed to the chest while the opposite thigh lifts off the table revealing a tight hip flexor

Thomas test. Patient supine, one knee hugged to the chest to flatten the lumbar lordosis. If the opposite thigh rises off the table, that hip flexor is shortened. (Wikimedia Commons)

Why the Thomas test works

When the patient flattens the back by pulling one knee up, gravity should let the other leg lie flat. A shortened psoas will not allow its hip to extend onto the table, so that thigh floats. The test is just the opposite-motion rule, measured. The muscle that flexes refuses to extend.

Same muscle, different alarm

When the psoas is irritated, not tight

The psoas does not only get stuck. It can get irritated from the outside by an inflamed organ lying against it. The exam looks similar. The disposition could not be more different.

A retrocecal appendix sits directly on the right psoas. When it inflames, every stretch of that muscle hurts. So extending the right hip, or resisting hip flexion, lights up the right lower quadrant. That is the psoas sign, and on the right it points at the appendix.

Notice the rule still holds: the inflamed psoas hates the motion that lengthens it (extension), just like the tight one. The difference is the source. One is a mechanical muscle problem. The other is a visceral emergency wearing the same coat.

Plain AP abdominal radiograph showing the normal psoas shadow outlining the lateral border of the psoas muscle

The psoas shadow on a plain film. Retroperitoneal irritation (appendicitis, abscess, bleed) can blur or erase that line. (Wikimedia Commons)

Sort the two before you treat

Psoas syndrome (somatic)

Days of mechanical back or groin pain, no fever.
Hypertonic, ropey, tender muscle band; positive Thomas test.
Normal white count, soft non-tender belly.
Disposition: OMM, stretch, habit change.

Psoas sign positive (visceral)

Hours of RLQ pain, fever, anorexia, nausea.
Pain on passive right hip extension; RLQ guarding, rebound.
Leukocytosis; imaging shows appendicitis.
Disposition: surgery, not the table.

From the Attending

Before you reach for the table, ask one question: is this muscle tight or is it irritated. A fever and a high white count beside a positive psoas sign is not a tender point, it is an appendix on your hands. Find the source first. Every time.

One rule, every joint

Carry it off the hip

Tap each card to flip it. Front is the tight muscle and its action. Back is the motion it steals. Same logic, new joint.

Piriformis

Action: external rotation of the hip

Tap to reveal the lost motion

Restricted

Internal rotation

Stuck in external rotation, the hip cannot turn inward. Deep buttock pain plus a foot that points out is the look. Watch the sciatic nerve.

Hamstrings

Action: knee flexion (and hip extension)

Tap to reveal the lost motion

Restricted

Knee extension

A short hamstring holds the knee bent, so the knee cannot straighten. This is the contracture that keeps a bedbound or post-stroke knee flexed.

Pectoralis major

Action: internal rotation, adduction, flexion of the shoulder

Tap to reveal the lost motion

Restricted

External rotation & extension

A tight pec pulls the arm forward and inward, so reaching back and turning the palm out is lost. The rounded-shoulder desk posture, mapped onto one muscle.

Anatomy image highlighting the piriformis muscle running from the sacrum to the greater trochanter, the deep external rotator of the hip

Piriformis (highlighted), sacrum to greater trochanter. An external rotator, so when it is tight, internal rotation is what you lose. (Wikimedia Commons)

Rapid drill

Which motion is lost?

A muscle is hypertonic. Name the motion it can no longer allow. Predict before you tap.

Prove it under pressure

Board-style walkthrough

One vignette at a time. Right-click or long-press a choice to cross it out. Double-click or double-tap to highlight. The clues glow after you answer.

Vignette 1 of 7

Medically reviewed by Fatima Ali, DO and Kaitlyn Cocuzzo, MD.

Piriformis & deep rotatorsThe buttock pain that mimics sciatica Low back pain workupSort mechanical from red-flag back pain Pelvis & lumbar counterstrainTender points and treatment positions

Sources: Greenman, Principles of Manual Medicine; Nicholas, Atlas of Osteopathic Techniques; Chila, Osteopathic Medicine; Savarese, OMT Review; Gray's Anatomy. Images courtesy of Wikimedia Commons. For education only, not a substitute for clinical judgment.