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Health condition · Clinically reviewed

Legg-Calvé-Perthes disease, a child’s hip that softens - and reshapes.

An idiopathic avascular necrosis of the femoral head in a growing child. Managed patiently, most children do well - the goal is a round, contained hip for adult life.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against BSCOS, BOA and peer-reviewed paediatric orthopaedic sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK paediatric orthopaedic practice including containment surgery and hip preservation.

Key facts

Perthes at a glance.

The essentials, in plain English - what it is, who it affects, how it is staged and what treatment aims for.

  • What it is

    Idiopathic avascular necrosis of the femoral head in a growing child - the blood supply falters, the ball softens, then reshapes.

  • Who it affects

    Peak age 4 to 8 years, boys around four times more often than girls, occasionally bilateral but rarely at the same time.

  • How it evolves

    Four Waldenström stages - initial, fragmentation, reossification and healed - typically played out over 2 to 4 years.

  • Classification

    Herring lateral pillar grade A, B or C - the height of the outer pillar of the femoral head guides prognosis and treatment.

  • Aim of treatment

    Keep the softening femoral head contained within the acetabulum so it remodels into a round, congruent joint.

  • Long-term outlook

    Most children do well - some develop early hip osteoarthritis in adulthood and may need hip preservation or replacement.

Why this guide matters

A patient plan, over several years.

Perthes is not a quick fix - it is a slow, staged remodelling of the hip. The three points below shape everything else on this page.

  • Containment is the goal

    Keeping the softening femoral head inside the socket lets it reshape into a round, congruent joint.

  • Age and Herring grade guide care

    Younger children with lower lateral pillar grades often do well with observation; older children and higher grades may need surgery.

  • Follow-up runs into adulthood

    Even after healing, hip preservation and eventually hip replacement may play a role decades later.

How the diagnosis is made

From first limp to a staged plan.

The steps a UK GP and specialist paediatric orthopaedic team will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and red flags

    Gradual limp, hip, thigh or referred knee pain, no clear injury - and any fever, night pain or systemic upset flagged for urgent review.

  2. 02

    Assessing

    Paediatric hip examination

    Trendelenburg test, gait analysis, and a careful check of hip range - especially internal rotation and abduction.

  3. 03

    Assessing

    Differential diagnosis

    Distinguishing Perthes from transient synovitis, slipped upper femoral epiphysis, septic arthritis, hip dysplasia, JIA and bone tumours.

  4. 04

    Confirming

    Bilateral hip X-rays

    Antero-posterior and frog-leg views of both hips - the standard first-line imaging, staged and classified by a specialist paediatric radiologist.

  5. 05

    Confirming

    MRI scan

    The gold standard for early disease and staging - see our private MRI scan page for how a scan is arranged and reported.

  6. 06

    Planning

    Specialist paediatric MDT

    A specialist paediatric orthopaedic team, physiotherapist and radiologist agree the stage, Herring grade and containment plan.

  7. 07

    Planning

    Shared plan with the family

    Watchful observation, non-weight-bearing measures or containment surgery are set out clearly, with parents and child fully informed.

Typical timeline: from first limp to a shared plan in a few weeks, with follow-up over years.

Symptoms

What Perthes actually looks like.

A gradual limp, an ache in the hip, thigh or knee, and subtle changes in gait - and the features that mean it is time for a specialist opinion.

  • Gradual painless limp

    The classic first sign - an intermittent limp that worsens with activity and eases with rest.

  • Hip, groin or thigh pain

    Often mild, activity-related discomfort in the hip, groin or upper thigh - not always severe.

  • Referred knee pain

    Pain felt in the knee is a classic red herring - hip disease commonly presents as knee ache in children.

  • Reduced hip range

    Loss of abduction and internal rotation is typical - noticed on examination before X-ray changes.

  • Trendelenburg gait

    A drop of the opposite pelvis on standing on the affected leg - a sign of hip abductor weakness.

  • Muscle wasting

    Subtle wasting of the thigh and buttock muscles on the affected side after weeks of altered gait.

  • Bilateral, asynchronous disease

    About 10 to 20 percent of children develop Perthes in both hips - usually at different stages, months or years apart.

  • Red flag - fever or night pain

    Systemic illness, high fever or severe night pain points away from Perthes and towards septic arthritis or tumour.

Treatment

How Perthes is treated in the UK.

From watchful observation and specialist paediatric physiotherapy through to containment surgery, hip preservation and eventual hip replacement.

  • Observation and activity modification

    For younger children with good containment - regular review, reduced impact sport and specialist paediatric physiotherapy input.

  • Non-weight-bearing measures

    Crutches, traction or bracing to unload the femoral head during the fragmentation stage - specialist paediatric orthopaedic guidance.

  • Proximal femoral varus osteotomy

    Reshaping the top of the femur to tuck the ball deeper into the socket - a specialist commissioned containment operation.

  • Pelvic osteotomy (Salter, Pemberton, Chiari)

    Redirecting or reshaping the socket to cover the ball - specialist commissioned pelvic surgery for selected children.

  • Shelf acetabuloplasty

    Building a bony extension on the socket to improve cover of the femoral head - a specialist containment technique.

  • Hip arthrodiatasis

    External fixation across the hip to unload the joint while it heals - specialist commissioned, reserved for severe cases.

  • Hip preservation surgery (adolescent and adult)

    Surgical hip dislocation, femoral or periacetabular osteotomies for late deformity - specialist commissioned adult hip preservation.

  • Total hip replacement

    Eventual option for end-stage hip osteoarthritis in adulthood - see our hip replacement surgery page for more detail.

Related resources: specialist physiotherapy, private MRI scan, hip replacement surgery and factor V Leiden thrombophilia. Emerging options - including bisphosphonates - remain specialist commissioned and are used selectively.

What this guide is based on

The sources behind every claim on this page.

UK paediatric orthopaedic society standards and peer-reviewed literature, 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 GP or specialist paediatric orthopaedic team knows your child and can tell you which parts apply. If in doubt, get seen.

  • British Society for Children’s Orthopaedic Surgery (BSCOS). Consensus statements on Perthes disease.

  • British Orthopaedic Association (BOA). Paediatric hip standards.

  • NICE Clinical Knowledge Summaries. Hip pain in children.

  • Herring JA et al. The lateral pillar classification and prognosis in Legg-Calvé-Perthes disease.

Red flags

When a limping child needs urgent attention.

Most childhood limps are transient and benign. These are the situations that are not - and where a specialist paediatric opinion is essential.

  • Fever with hip pain

    Refusal to weight bear with fever suggests septic arthritis - a paediatric emergency needing same-day assessment.

  • Sudden severe pain after minor injury

    Especially in an overweight adolescent - consider slipped upper femoral epiphysis and refer urgently.

  • Night pain and systemic upset

    Persistent night pain, weight loss or fatigue - always investigate to exclude bone tumour or infection.

  • Bilateral symmetrical hip disease

    Perthes is usually asymmetric - simultaneous, symmetrical changes point to a skeletal dysplasia mimicking Perthes.

  • Rapid loss of range of motion

    A sudden, stiff, guarded hip during watchful observation deserves prompt specialist review and re-imaging.

  • Progressive femoral head extrusion

    The ball drifting laterally out of the socket is a strong signal that containment surgery may be needed.

  • Delayed presentation in an older child

    Perthes appearing over the age of 8 has a poorer prognosis - specialist paediatric input should be arranged early.

  • Concerning family or thrombophilia history

    Some children have an underlying clotting tendency - see our factor V Leiden thrombophilia guide for context.

  • Psychological impact

    Long treatment, crutches and time off sport take a toll - mental-health support for the child and family matters.

Living with it

A slow condition, with a clear plan.

Four things that make the biggest difference day to day - a steady rhythm, patience, gentle movement and knowing when to escalate.

A quiet reminder

Small, steady weeks add up to years of good hip.

Perthes rewards a consistent routine and honest conversations at every follow-up, over quick fixes.

  1. 01 Rhythm

    Keep a steady routine

    Regular reviews, gentle range of motion exercises and school-friendly activity plans give the hip its best chance to remodel.

  2. 02 Patience

    Think in years, not weeks

    Perthes runs its course over 2 to 4 years - progress is measured on X-ray as much as on how the child feels.

  3. 03 Movement

    Swim, cycle, protect impact

    Low-impact activity keeps the hip mobile and the child strong - contact sport is usually restricted during active disease.

  4. 04 Escalate

    Speak up if things change

    New pain, a worsening limp or loss of movement should trigger an earlier specialist review, not the next scheduled one.

Frequently asked

Everything parents ask about Perthes.

Quick answers on stages, imaging, containment surgery and long-term outlook.

  • What is Legg-Calvé-Perthes disease?

    Perthes is an idiopathic avascular necrosis of the femoral head in a growing child. The blood supply to the ball at the top of the thigh bone falters, the bone softens, fragments and then gradually reossifies over 2 to 4 years. It typically affects children aged 4 to 8, boys around four times more often than girls, and is occasionally bilateral but rarely at the same time.

  • What causes Perthes disease?

    The exact cause is unknown. Suggested factors include thrombophilia (an inherited clotting tendency, discussed on our factor V Leiden page), genetic influences, subtle skeletal differences and vascular anatomy. Most affected children have no identifiable underlying condition.

  • How is Perthes different from an irritable hip or SUFE?

    Transient synovitis (irritable hip) usually settles in days and is discussed in our irritable hip in children guide. Slipped upper femoral epiphysis (SUFE) typically affects heavier adolescents. Septic arthritis is a paediatric emergency with fever. Hip dysplasia is a structural problem - see our hip dysplasia page. Perthes is diagnosed on X-ray and MRI by a specialist paediatric team.

  • How is Perthes disease diagnosed?

    Assessment starts with a careful history and paediatric hip examination, including Trendelenburg testing and range of motion. Bilateral hip X-rays (AP and frog-leg views) are the first imaging. MRI is the gold standard for early disease and staging - our private MRI scan page explains how this is arranged. A specialist paediatric orthopaedic team then agrees the Waldenström stage and Herring lateral pillar grade.

  • What treatments are available?

    Treatment ranges from watchful observation, activity modification and physiotherapy in younger children with good containment, through non-weight-bearing measures with crutches or bracing, to specialist containment surgery. Options include proximal femoral varus osteotomy, pelvic osteotomies (Salter, Pemberton, Chiari), shelf acetabuloplasty and hip arthrodiatasis. In adulthood, hip preservation surgery and eventual total hip replacement may be needed for end-stage osteoarthritis.

  • What is the long-term outlook?

    Most children with Perthes go on to lead active lives. Younger children with good containment and lower Herring grades tend to do best. A proportion develop early hip osteoarthritis in adulthood, sometimes leading to hip preservation surgery or eventual hip replacement. Regular specialist follow-up through growth and into early adulthood is important.

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