Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Recognise childhood femoral-head osteonecrosis, preserve hip motion and containment during biological fragmentation and select reconstruction by age, head involvement and mechanical congruence.
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.
Temporary loss of blood supply to the capital femoral epiphysis causes necrosis; the initiating vascular event remains uncertain in most children.
Presentation clusters between four and eight years and is more common in boys, although younger and older children can be affected.
Smaller body size, delayed skeletal maturation, thrombophilic factors and tobacco-smoke exposure have associations but do not provide a diagnostic test.
Both hips are affected in a minority, often at different stages; synchronous symmetrical disease should trigger an alternative systemic differential.
Loss of perfusion kills ossified femoral-head bone while overlying articular cartilage initially remains viable and continues growing.
Necrotic trabeculae are removed before replacement is strong enough, creating the period of greatest mechanical vulnerability and collapse risk.
Synovitis, head enlargement and abductor forces push the softened epiphysis beyond acetabular coverage, exposing it to edge deformation.
New bone gradually restores density, while the growing acetabulum can reshape a contained congruent head over several years.
Flattening, enlargement and neck shortening create hinge abduction, impingement and concentrated cartilage loading that persists into adulthood.
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.
Short-duration limp after viral illness in a well child usually resolves, but persistence or recurrence requires imaging for evolving Perthes disease.
Fever, inability to move the hip, systemic illness and raised inflammation require urgent aspiration and source control.
An older heavier child with external rotation and physeal widening needs immediate non-weight-bearing and fixation assessment.
Prolonged morning stiffness, several joints, uveitis risk and synovial thickening suggests inflammatory disease rather than epiphyseal fragmentation.
Bilateral symmetrical head changes, short stature and abnormalities at several epiphyses indicate a generalised developmental bone disorder.
An enlarged flattened head loses spherical congruence and produces edge loading, reduced motion and later degenerative change.
Physeal disturbance shortens the femoral neck, reducing abductor lever arm and contributing to limp and trochanteric impingement.
A deformed lateral head catches on the acetabular rim during abduction, making forced containment ineffective and painful.
Head collapse and neck shortening can create measurable limb discrepancy, pelvic compensation and gait disturbance during growth.
Residual asphericity damages labrum and cartilage, causing adult impingement, stiffness and possible reconstructive or replacement surgery.
Referred pain makes bilateral hip examination essential in a young child with unexplained knee symptoms and limp.
Resorption temporarily outpaces reconstruction, so extrusion and edge loading during this phase drive permanent shape loss.
Younger children usually have more growth available to restore a contained femoral head toward sphericity.
A stiff adducted hip cannot be placed safely under the acetabular mould and may need range restoration first.
The lateral head catches on the rim, so more abduction increases focal damage instead of improving coverage.
Symptoms fluctuate while necrotic bone fragments and reossifies, requiring sustained education rather than repeated emergency explanations.
Calling recurrent or persistent limp transient synovitis without repeat examination and imaging.
Investigating referred knee pain without assessing both hips.
Using normal early radiographs to exclude Perthes despite continuing restricted internal rotation.
Prescribing prolonged complete inactivity that causes stiffness, weakness and family disengagement.
Forcing abduction when hinge mechanics prevent the head entering the acetabulum.
Discussing prognosis from stage alone without age, lateral pillar, extrusion, motion and congruence.
Your practice draft is saved in this browser.
A six-year-old remains limping with reduced hip abduction and internal rotation three weeks after a presumed transient synovitis. Initial radiographs were normal. What is the best next investigation?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
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.
Check weight and liquid strength, avoid dehydration and kidney disease and do not use analgesia to justify painful impact or forced range.
Check combination products and liver risk; renewed night pain, fever or inability to bear weight requires reassessment rather than repeated dosing.