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.

side view

Watch the muscle pull first. Then test the opposite motion and see where the red barrier stops it.

Muscle action

Flexion

Resting drag

Hip held flexed

Lost motion

Extension

A hypertonic psoas holds the hip flexed. The motion that would lengthen it is extension, so extension 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: the psoas itself gets direct L1 to L3 branches. The lumbar plexus forms inside the psoas, so its named branches explain the groin and thigh symptoms.

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 (T12 to L4) is born inside the psoas. Its branches leave around the muscle, which is why psoas spasm can send pain into the groin and anterior thigh. (Wikimedia Commons)

Name the nerves, not just the plexus

Iliohypogastric + ilioinguinalL1. Lower abdomen and inguinal region.

GenitofemoralL1-L2. Groin, upper anterior thigh, genital branch.

Lateral femoral cutaneousL2-L3. Lateral/anterior thigh sensory track.

FemoralL2-L4. Anterior thigh plus quadriceps and patellar reflex.

ObturatorL2-L4. Medial thigh and adductor compartment.

Clinical rulePsoas spasm lives where these nerves travel, so symptoms can look neural without a root deficit.

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 through the psoas-adjacent lumbar plexus: genitofemoral/ilioinguinal for groin, femoral/lateral femoral cutaneous for anterior thigh.
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.

Osteopathic (OMM) treatment

Counterstrain, psoas tender point. The physician shortens the angry muscle until the tender point goes quiet. With the patient supine, the physician supports the thigh and knee, brings the treated hip into marked flexion, lets the trunk sidebend toward the point, and uses only a tiny external-rotation fine tune if it softens the point. Hold about 90 seconds, then return the patient slowly to neutral. This should feel like ease, not torque or a forced stretch.

Iliacus tender point sits medial to the ASIS in the iliac fossa. The physician supports both legs, brings both hips and knees into flexion, then lets the knees fall outward into external rotation.

Psoas tender point position

Schematic: the physician monitors the psoas tender point, located about two thirds of the way from the ASIS to the umbilicus, while supporting the thigh and knee into ease. Hold about 90 seconds only after the point softens.

Psoas: physician flexes the patient's hip and knee, supports the leg, sidebends the trunk toward the point, then fine tunes gently only if the tender point softens.

Iliacus tender point position

Schematic: supine frog-leg. The physician supports both legs, flexes both hips and knees, and lets the knees fall outward into external rotation, shortening the iliacus in the iliac fossa.

Iliacus: physician flexes both hips and knees, externally rotates so the knees fall outward, and crosses the ankles. The tender point is medial to the ASIS in the iliac fossa.

Then address the partner. Treat the L1 or L2 dysfunction (muscle energy or HVLA as indicated) and recheck the piriformis. Counsel against the sustained-flexion habit that fed it, or it returns.

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. The classic bedside psoas sign is right lower quadrant pain when the clinician passively extends the right hip; resisted right hip flexion can reproduce the same irritation. On the right, that 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)

Psoas sign: stretch the muscle, irritate the appendix

Labeled anatomy of the anterior hip showing the psoas major and iliacus muscles crossing the front of the pelvis and femur, where an inflamed retrocecal appendix can lie against the right psoas and hurt when the hip is extended

What the clinician does: extend the right hip behind the patient, stretching the right psoas.
Why it hurts: a retrocecal appendix can lie directly against that psoas. Stretching the muscle tugs on the inflamed organ.
What it means: right lower quadrant pain during the maneuver is a positive psoas sign and supports appendicitis, especially with fever, anorexia, guarding, and leukocytosis.

Imaging clue. Do not diagnose appendicitis by staring at an unlabeled crop. In a board stem, the CT report tells you appendicitis; the psoas sign explains why hip extension hurts. Surgical evaluation, not psoas counterstrain.

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 the physician reaches for the treatment 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. 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.