01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Ask when the limp began, whether pain is in hip, groin, thigh or knee and whether symptoms vary with activity. Record fever, recent infection, trauma, night waking and morning stiffness to separate infection, tumour and inflammatory disease. Establish birth and developmental history, height, family skeletal disorders and previous transient-synovitis episodes. Parents may notice reduced running or a painless limp before the child reports discomfort. Bilateral symptoms and age at onset materially affect the differential and prognosis.
Observe walking, running only if comfortable, and single-leg stance for antalgia and abductor lurch. Compare leg length, thigh bulk and foot progression. Gently measure hip flexion, abduction and internal rotation; limitation can reflect synovitis early and deformation later. Examine knee, spine and abdomen because pain is referred. Fever or severe pain through all passive movement stops routine testing and triggers septic-arthritis assessment. Record height and other joints when dysplasia is possible.
Obtain AP pelvis and frog-leg lateral views of both hips in a stable child. Early signs include joint-space widening from effusion, a smaller dense ossific nucleus and subchondral fracture; fragmentation, lateral extrusion, flattening and later reossification follow. MRI detects marrow ischaemia and extent before plain change and evaluates cartilage and hinge mechanics, but it is not needed for every classic radiographic case. Ultrasound shows effusion but cannot stage femoral-head viability.
Describe stage and risk rather than only naming Perthes. Waldenström stage indicates biological phase. Herring lateral-pillar classification is applied during fragmentation and estimates preserved lateral height; Catterall describes head involvement. Younger age, limited necrosis, maintained range and containment favour spherical remodelling. An older child with extensive collapse, extrusion and stiffness has less growth time and a greater chance of residual asphericity.
Initial management preserves movement and keeps the vulnerable head covered. Explain the long fluctuating course, reduce running, jumping and contact impact during painful fragmentation and allow swimming or cycling when comfortable. Use short periods of crutches for pain rather than default years of non-weight-bearing. Physiotherapy restores abduction and internal rotation through gentle stretching and maintains gluteal strength. Treat adductor contracture before considering containment, sometimes with traction, casting or release in a specialist programme.
Containment means positioning the femoral head within the acetabulum so its cartilage moulds toward sphericity. Observation and motion work may achieve this in a young well-contained hip. Abduction bracing or casting is used selectively and requires adherence and skin monitoring. Femoral varus osteotomy redirects the head but shortens and alters gait temporarily; pelvic innominate or shelf procedures improve acetabular cover. Timing and operation depend on age, lateral pillar, extrusion and congruence.
Hinge abduction changes the goal. If the enlarged deformed lateral head cannot enter the acetabulum, forceful abduction increases edge pressure. Arthrogram or dynamic imaging defines congruence. Salvage options may include valgus osteotomy, shelf coverage, trochanteric procedures or later surgical dislocation and head-neck reshaping at expert centres. The objective becomes a painless mobile congruent-enough joint, not restoration of a normal radiograph at any cost.
Follow radiographs and function through reossification and healing. Measure range, gait, leg length and activity and support schooling and psychological wellbeing during a multi-year course. New acute pain requires fracture, infection or mechanical hinge reassessment. At maturity, Stulberg head shape and congruence predict arthritis risk. Residual impingement or labral symptoms can need hip-preservation surgery, while severe later degeneration may eventually require arthroplasty.
Key points
- Perthes disease is idiopathic osteonecrosis of the capital femoral epiphysis, classically presenting between four and eight years with limp and hip, thigh or knee pain.
- High-yield examination shows reduced hip abduction and internal rotation, an antalgic or Trendelenburg gait and possible thigh wasting.
- First-line imaging is bilateral AP pelvis and frog-leg lateral radiography; obtain MRI when early disease remains suspected despite normal films.
- Waldenström evolution moves through initial necrosis, fragmentation, reossification and healed remodelling over several years.
- Lateral-pillar height during fragmentation, age at onset, range and femoral-head containment are central prognostic variables.
- First-line treatment in a younger child with maintained containment is education, temporary impact reduction, analgesia and active restoration of abduction and rotation.
- Use protected loading for painful fragmentation, but avoid prolonged indiscriminate immobilisation that worsens stiffness and deconditioning.
- Older age, substantial lateral-pillar collapse or extrusion may justify femoral or pelvic containment surgery before fixed hinge abduction develops.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Idiopathic vascular interruption
Temporary loss of blood supply to the capital femoral epiphysis causes necrosis; the initiating vascular event remains uncertain in most children.
Age and sex pattern
Presentation clusters between four and eight years and is more common in boys, although younger and older children can be affected.
Constitutional associations
Smaller body size, delayed skeletal maturation, thrombophilic factors and tobacco-smoke exposure have associations but do not provide a diagnostic test.
Bilateral susceptibility
Both hips are affected in a minority, often at different stages; synchronous symmetrical disease should trigger an alternative systemic differential.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Epiphyseal avascular necrosis
Loss of perfusion kills ossified femoral-head bone while overlying articular cartilage initially remains viable and continues growing.
- 2Resorption and fragmentation
Necrotic trabeculae are removed before replacement is strong enough, creating the period of greatest mechanical vulnerability and collapse risk.
- 3Lateral extrusion
Synovitis, head enlargement and abductor forces push the softened epiphysis beyond acetabular coverage, exposing it to edge deformation.
- 4Reossification and remodelling
New bone gradually restores density, while the growing acetabulum can reshape a contained congruent head over several years.
- 5Loss of spherical congruence
Flattening, enlargement and neck shortening create hinge abduction, impingement and concentrated cartilage loading that persists into adulthood.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Parents may first notice reduced stride or abductor lurch before the child localises hip, thigh or knee pain.
Progressive restriction allows lateral extrusion and is a modifiable target during the early vulnerable stages.
Painful or mechanical loss of rotation is common and can precede obvious femoral-head flattening.
Early radiographs may show sclerosis and reduced apparent ossific-nucleus size before fragmentation becomes pronounced.
Loss of lateral epiphyseal height during fragmentation indicates weaker containment support and a worse shape prognosis.
The deformed lateral head rides against the acetabular rim rather than entering it as the hip abducts.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
First-line bilateral AP pelvis radiographFirst stepFirst line - Why
- Identify epiphyseal density, collapse, extrusion, acetabular coverage and bilateral or alternative disease.
- Interpretation and limitations
- Normal early radiographs do not exclude Perthes when limp and restricted rotation persist.
- 02
Frog-leg lateral radiograph - Why
- Show anterior or posterior head contour, subchondral fracture and fragmentation not fully seen on AP imaging.
- Interpretation and limitations
- Use only when the child is stable and infection or unstable SUFE is not suspected; never force a painful hip.
- 03
MRI for occult or complex disease - Why
- Detect early perfusion-related marrow change and map cartilage, necrotic extent and femoral-head containment.
- Interpretation and limitations
- MRI is the reference sensitive test before radiographic change and helps resolve atypical bilateral or hinge mechanics.
- 04
Arthrogram for operative congruence - Why
- Assess cartilaginous head shape, reducibility and hinge abduction during planned treatment under anaesthesia.
- Interpretation and limitations
- A head that cannot enter the acetabulum safely should not undergo forced conventional containment.
- 05
Targeted blood tests for alternatives - Why
- Investigate infection, inflammation or systemic skeletal disease when age or symptoms are atypical.
- Interpretation and limitations
- Routine Perthes bloods are often normal; abnormal CRP, cytopenia or metabolic pattern redirects the diagnosis.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Transient synovitis
Short-duration limp after viral illness in a well child usually resolves, but persistence or recurrence requires imaging for evolving Perthes disease.
Septic arthritis
Fever, inability to move the hip, systemic illness and raised inflammation require urgent aspiration and source control.
Slipped upper femoral epiphysis
An older heavier child with external rotation and physeal widening needs immediate non-weight-bearing and fixation assessment.
Juvenile idiopathic arthritis
Prolonged morning stiffness, several joints, uveitis risk and synovial thickening suggests inflammatory disease rather than epiphyseal fragmentation.
Skeletal dysplasia
Bilateral symmetrical head changes, short stature and abnormalities at several epiphyses indicate a generalised developmental bone disorder.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01SuspectImage the persistent childhood limpFirst stepA young child has ongoing limp, referred knee pain or loss of abduction and internal rotation.+
- 1Assess fever, systemic state, weight-bearing ability and red flags before performing gentle bilateral hip examination.
- 2Obtain AP pelvis and safe frog-leg lateral views of both hips and review previous transient-synovitis episodes.
- 3Use MRI when radiographs are normal but compatible restriction or limp persists.
- 4Refer confirmed or strongly suspected disease to paediatric orthopaedics for stage and containment assessment.
02Early conservativePreserve motion and containmentThe child is younger, the head remains contained and abduction is recoverable.+
- 1Explain the prolonged course and reduce high-impact activity during pain and fragmentation.
- 2Use short-term crutches and age-appropriate analgesia for symptoms while retaining safe low-impact conditioning.
- 3Provide supervised gentle abduction and rotation work plus hip and core strengthening.
- 4EscalationRepeat clinical range and radiographs at the specialist interval and escalate extrusion or deteriorating motion.
03Operative containmentImprove cover before deformation fixesOlder age, extrusion, lateral-pillar loss or inadequate containment makes poor remodelling likely.+
- 1Restore enough range for containment and define cartilage congruence with MRI or arthrogram when needed.
- 2Select femoral varus or pelvic containment surgery from age, anatomy, head involvement and surgeon expertise.
- 3Protect loading and maintain motion through postoperative healing while monitoring alignment and leg length.
- 4Continue surveillance through reossification because surgery redirects mechanics but does not shorten biology.
04Hinge or healedManage residual mechanicsAspherical head, hinge abduction, impingement or leg-length difference persists despite healing.+
- 1Avoid forcing an incongruent head into abduction and define the impingement or cartilage lesion anatomically.
- 2Consider valgus, shelf, trochanteric or head-neck procedures only in a specialist hip-preservation pathway.
- 3Use lifts, strength and activity adaptation for smaller functional discrepancies.
- 4Counsel regarding adult arthritis surveillance and investigate new mechanical symptoms early.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Ibuprofen for painful inflammatory phases
Use the current BNFC age- and weight-specific oral dose for a short course with food when the child is hydrated and has no renal, gastrointestinal or NSAID-sensitive asthma contraindication.Check weight and liquid strength, avoid dehydration and kidney disease and do not use analgesia to justify painful impact or forced range.
Paracetamol as alternative or adjunct
Prescribe the BNFC dose for the child's age and weight with the exact formulation volume, interval and 24-hour maximum recorded for carers.Check combination products and liver risk; renewed night pain, fever or inability to bear weight requires reassessment rather than repeated dosing.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Coxa magna and plana
An enlarged flattened head loses spherical congruence and produces edge loading, reduced motion and later degenerative change.
Coxa breva
Physeal disturbance shortens the femoral neck, reducing abductor lever arm and contributing to limp and trochanteric impingement.
Hinge abduction
A deformed lateral head catches on the acetabular rim during abduction, making forced containment ineffective and painful.
Leg-length difference
Head collapse and neck shortening can create measurable limb discrepancy, pelvic compensation and gait disturbance during growth.
Premature osteoarthritis
Residual asphericity damages labrum and cartilage, causing adult impingement, stiffness and possible reconstructive or replacement surgery.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Measure abduction and internal rotation consistently because deteriorating range can precede radiographic extrusion.
- Record limp, pain during daily activity, school participation and need for crutches at each stage.
- Use serial AP and lateral imaging to follow fragmentation, lateral-pillar height, containment and reossification.
- After osteotomy, monitor wound, alignment, union, leg length and safe progression of loading and motion.
- During bracing or casting, inspect skin, nerve function, adherence and psychological and family burden.
- At maturity, review residual head shape, congruence, impingement and arthritis symptoms when clinically indicated.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
The knee can report the hip
Referred pain makes bilateral hip examination essential in a young child with unexplained knee symptoms and limp.
Fragmentation is mechanically vulnerable
Resorption temporarily outpaces reconstruction, so extrusion and edge loading during this phase drive permanent shape loss.
Age represents remodelling time
Younger children usually have more growth available to restore a contained femoral head toward sphericity.
Containment needs motion
A stiff adducted hip cannot be placed safely under the acetabular mould and may need range restoration first.
Hinge abduction resists containment
The lateral head catches on the rim, so more abduction increases focal damage instead of improving coverage.
Healing takes years
Symptoms fluctuate while necrotic bone fragments and reossifies, requiring sustained education rather than repeated emergency explanations.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling recurrent or persistent limp transient synovitis without repeat examination and imaging.
- 02
Investigating referred knee pain without assessing both hips.
- 03
Using normal early radiographs to exclude Perthes despite continuing restricted internal rotation.
- 04
Prescribing prolonged complete inactivity that causes stiffness, weakness and family disengagement.
- 05
Forcing abduction when hinge mechanics prevent the head entering the acetabulum.
- 06
Discussing prognosis from stage alone without age, lateral pillar, extrusion, motion and congruence.