Health condition · Clinically reviewed
Irritable hip in children, the common cause of a sudden limp, and the mimic you must exclude.
Transient synovitis is the usual answer when a well child aged 3 to 8 wakes up limping. Septic arthritis is the answer no one wants to miss.
Why trust this guide
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Clinically reviewed
Written by our editorial team and reviewed by a registered UK clinician before publication.
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Sourced from guidance
Checked against NICE CKS, BOAST and BOA paediatric orthopaedic standards you can see at the end.
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Current for 2026
Reflects modern UK paediatric orthopaedic practice including Kocher criteria and ultrasound-first assessment.
Key facts
Irritable hip at a glance.
The essentials, in plain English - what it is, who gets it, and why the difference from septic arthritis matters so much.
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What it is
Transient synovitis - a short-lived aseptic inflammation of the hip synovium in an otherwise well child.
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Who gets it
Most common cause of hip pain in children aged 3 to 8, more often boys, frequently after a viral illness.
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How it feels
Sudden limp, hip or groin pain, sometimes referred to the knee, with reluctance to weight-bear.
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The critical mimic
Septic arthritis of the hip - a surgical emergency that must be excluded before a child is sent home.
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How it is confirmed
A careful history and examination, temperature, blood tests and hip ultrasound to look for an effusion.
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How it resolves
Conservative care, rest and simple analgesia - most children are back to normal within one to two weeks.
Why this guide matters
A common story, with an uncommon shadow.
Most limping children have a mild, self-limiting problem. A small number have something that needs the operating theatre tonight. Three principles keep the two apart.
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Rule out septic arthritis first
Fever, weight-bearing status, white cell count and ESR - the Kocher criteria - drive every decision.
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Ultrasound is the workhorse
A quick, radiation-free hip ultrasound confirms an effusion and guides aspiration if needed.
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Follow-up catches the rest
Perthes, SUFE and JIA can start looking like an irritable hip - a planned recheck is not optional.
How the diagnosis is made
From a sudden limp to a clear answer.
The pathway UK paediatric teams follow, in order - so parents know what to expect and why each step matters.
Phase 1 · Assessing
History, examination and vitals
Phase 2 · Confirming
Bloods and imaging
Phase 3 · Escalating
Specialist review if needed
- 01
Assessing
History and red-flag screen
Fever, recent viral illness, trauma, night pain, weight loss, tick exposure and rash - each points toward a different cause.
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Assessing
Focused examination
Range of movement, guarding, position of comfort, neurovascular check and a look at the knee and spine.
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Assessing
Weight-bearing and vitals
Temperature, ability to bear weight and general appearance - the well child versus the toxic-looking child is a crucial distinction.
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Confirming
Bloods - WBC, CRP, ESR
Inflammatory markers help separate transient synovitis from septic arthritis using the Kocher criteria.
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Confirming
Hip ultrasound
Sensitive for a hip effusion - the workhorse test for the irritable hip. See our guide on private ultrasound scans.
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Confirming
Hip X-ray
Looks for Perthes, slipped upper femoral epiphysis, fracture or a bone lesion when the picture is atypical.
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Escalating
Specialist review or aspiration
If septic arthritis cannot be ruled out, urgent paediatric orthopaedic review and hip aspiration under anaesthetic.
Typical timeline: from arrival to a settled plan in the same visit for most children.
Symptoms
What an irritable hip looks like.
A well child, a sudden limp and a restricted hip - and the features that mean it is not a simple transient synovitis at all.
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Sudden limp
A previously well child who wakes up limping, often after a cold or sore throat a week or two before.
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Hip or groin pain
Discomfort felt in the front of the hip, groin or upper thigh, worse on movement.
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Referred knee pain
Hip pathology often refers pain to the knee - always examine the hip when a child complains of knee pain.
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Reluctance to weight-bear
The child avoids putting weight on the leg or refuses to walk altogether - a key sign to take seriously.
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Reduced range of movement
Internal rotation and abduction are typically the first movements to become uncomfortable and restricted.
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Position of comfort
The hip is often held in slight flexion and external rotation to reduce pressure in the joint capsule.
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Otherwise well child
A child who is playing, eating and only mildly unwell fits transient synovitis. A toxic-looking child does not.
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Red flag - fever and unwell
High fever, systemic upset or refusal to move the leg at all raises concern for septic arthritis - an emergency.
Management
How an irritable hip is managed in the UK.
Conservative care for transient synovitis, and a clear ladder up to emergency care or specialist review when the picture changes.
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Rest and reduced activity
A few days off sport and rough play - most children self-limit anyway. Gradual return as symptoms settle.
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Simple analgesia
Weight-based paracetamol and ibuprofen (if no contraindication) - enough to keep the child comfortable and mobilising.
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Safety-net advice
Written return criteria - fever, worsening pain, refusal to weight-bear or a systemically unwell child means straight back to hospital.
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Follow-up review
A planned recheck within one to two weeks to confirm resolution and a low threshold for repeat imaging if symptoms persist.
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Emergency admission - septic
Suspected septic arthritis is a surgical emergency - IV antibiotics and urgent washout by paediatric orthopaedics.
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Referral - Perthes or SUFE
Perthes disease or SUFE need paediatric orthopaedic management, sometimes including surgery. See our Perthes guide.
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Rheumatology - JIA
Recurrent or bilateral joint symptoms, morning stiffness or a rash prompt a paediatric rheumatology opinion.
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MDT paediatric orthopaedics
Complex, atypical or persistent cases benefit from a shared plan between orthopaedics, radiology and paediatrics.
What this guide is based on
The sources behind every claim on this page.
UK national guidance and paediatric orthopaedic standards, current at the time of last review.
Key references
Guidelines and standards we relied on.
A quiet reminder
This guide is for information, not medical advice.
Your child’s GP or paediatric team knows the full story and can tell you which parts apply. If in doubt, get seen the same day.
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NICE CKS. Hip pain - children.
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British Orthopaedic Association (BOA) and British Society for Children’s Orthopaedic Surgery (BSCOS). Paediatric orthopaedic standards.
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BOAST. Management of the child with an irritable or septic hip.
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Kocher MS et al. Differentiating septic arthritis from transient synovitis of the hip in children.
Red flags
When a limp is not just a limp.
Most children with an irritable hip do very well. These are the features that change the plan - and where a specialist opinion is needed the same day.
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Fever with an unwell child
Temperature over 38.5°C with systemic upset raises the suspicion of septic arthritis - urgent hospital review.
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Refusal to move the leg
Pseudoparalysis - a child who will not move the leg at all - is a septic joint until proven otherwise.
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Night pain and weight loss
Bony pain waking a child at night with weight loss or fatigue must prompt urgent investigation for malignancy.
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Trauma or bruising
A clear history of significant trauma, or bruising out of keeping with the story, warrants imaging and a safeguarding review.
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Persistent symptoms
Symptoms that do not settle within two weeks need re-imaging - Perthes and other structural conditions can hide behind a synovitic picture.
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Bilateral or migratory pain
Two joints involved, or pain moving from joint to joint, suggests juvenile idiopathic arthritis or a reactive arthritis.
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Rash - HSP or Lyme
Purpuric rash on the legs suggests HSP - a tick bite and expanding rash raises Lyme. See our HSP guide.
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Adolescent - think SUFE
In older or overweight children with a limp, slipped upper femoral epiphysis must be excluded on frog-leg X-rays.
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Neurovascular compromise
Cold, pale or numb leg is a vascular emergency, not an irritable hip - straight to hospital.
Recovery
A short illness, with a clear finish line.
Four things that make the biggest difference at home - short rest, simple analgesia, clear return criteria and a planned recheck.
A quiet reminder
Trust your instincts as a parent.
If something feels wrong between visits, do not wait. A same-day review is always the right call.
- 01 Rest
A short pause, not a long one
A few quiet days at home is usually enough - most children are back to school and light play within a week.
- 02 Analgesia
Keep the child comfortable
Regular paracetamol, and ibuprofen if suitable, help mobilising and sleep. Give it time to work before escalating.
- 03 Watch
Know when to come back
Fever, worsening pain, refusal to weight-bear or a systemically unwell child means the same-day emergency department.
- 04 Follow-up
Recheck, don’t assume
A planned review at one to two weeks catches Perthes, SUFE and other diagnoses that transient synovitis can mimic.
Frequently asked
Everything parents ask us about the irritable hip.
Quick answers on transient synovitis, septic arthritis, tests and recovery.
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What is transient synovitis of the hip?
A short-lived, aseptic inflammation of the lining of the hip joint - the most common cause of hip pain and limp in children aged 3 to 8. It often follows a viral illness and settles by itself over one to two weeks.
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How do doctors tell it apart from septic arthritis?
Using a combination of temperature, refusal to weight-bear, white cell count and ESR - the Kocher criteria. The more of these that are positive, the higher the probability of septic arthritis, which is a surgical emergency needing urgent aspiration and washout.
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Why does my child’s knee hurt if the problem is the hip?
Nerves from the hip and the knee share pathways, so hip pathology often refers pain to the knee or thigh. Any child with unexplained knee pain and a limp should have the hip examined and, when indicated, imaged.
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What tests will be done?
A clinical assessment, temperature and vital signs, blood tests including white cell count, CRP and ESR, and a hip ultrasound to look for a joint effusion. An X-ray is added when Perthes, SUFE or a bone lesion is a concern.
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How long does an irritable hip take to settle?
Most children improve within a few days and are back to normal within one to two weeks. Persistent symptoms beyond that need repeat review and imaging to look for another diagnosis such as Perthes disease.
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When should I bring my child back to hospital?
Return the same day if there is a high fever, a systemically unwell child, refusal to move the leg, worsening pain or new symptoms such as a rash. Between visits, trust your instincts - if something feels wrong, get seen.
Related content
Keep reading.
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Perthes disease
Avascular necrosis of the femoral head in children.
Learn more -
Hip dysplasia
Developmental dysplasia of the hip in children.
Learn more -
Hip and groin pain
A broader guide to hip and groin pain.
Learn more -
Growing pains in children
Benign musculoskeletal pain of childhood.
Learn more -
Henoch–Schönlein purpura
A vasculitis that can mimic joint pain.
Learn more -
Hip arthroscopy
Related surgical procedure for the hip.
Learn more -
Private MRI scan
Detailed imaging when the picture is atypical.
Learn more -
Private ultrasound scan
The workhorse test for the irritable hip.
Learn more