Limping Child

A limp is a presentation, not a diagnosis. It may come from pain, weakness, deformity, limb-length difference, neuromuscular control, inflammatory disease, infection, tumour, trauma or compensation. The safe clinician does not begin by reciting a long differential list. The safe clinician first asks: is this child sick, can they weight bear, is the limp painful, and what dangerous diagnosis must not be missed today?

Age is the strongest first organiser. Toddlers commonly present with occult trauma, infection, developmental hip issues, neuromuscular patterns or safeguarding concerns. School-age children raise the probability of transient synovitis, Perthes disease, infection, inflammatory disease and malignancy. Adolescents require a specific hip screen for slipped upper femoral epiphysis, even when the child points to the knee.

The hip deserves special attention because children localise pain poorly. Hip pathology may be felt in the thigh or knee. A teenager with knee pain and a normal knee examination may have SUFE. A younger child with a subtle limp and reduced hip abduction or internal rotation may have Perthes disease. A febrile non-weight-bearing child may have septic arthritis or osteomyelitis even if early radiographs are normal.

Observation is not a passive decision. Safe observation requires a well child, reassuring examination, improving symptoms, no red flags, a clear working diagnosis and explicit return triggers.

The gait pattern gives the first physiological clue. An antalgic gait shortens stance phase on the painful limb. Trendelenburg gait reflects hip abductor weakness, hip pain or altered femoral head mechanics. A short-leg gait suggests limb-length difference or pelvic obliquity. Circumduction, toe walking, spasticity, ataxia or foot drop move the differential toward neuromuscular disease.

The mechanism behind the limp differs by pathology.

History

The history should identify acuity, severity, red flags and the most likely anatomical source.

Examination

Observe before touching the child. A child who runs around the room is different from a child who lies still and refuses to move the hip. Note whether the gait is antalgic, Trendelenburg, short-leg, circumduction, toe-walking, spastic, ataxic or foot-drop pattern.

Examine from spine to foot.

Pain with passive hip motion, especially in a febrile or non-weight-bearing child, is a high-risk finding. Loss of internal rotation in an adolescent suggests SUFE until excluded. Reduced abduction and internal rotation in a school-age child raises concern for Perthes disease.

Investigations should answer the dangerous question still open after history and examination. Do not order the same panel for every child without deciding what you are trying to exclude.

Radiographs

• AP pelvis and lateral hip views for hip, thigh or knee pain when Perthes disease or SUFE is possible.
• Tibia radiographs for toddler fracture; repeat imaging may show periosteal reaction if early films are normal.
• Local radiographs for focal bony tenderness or trauma.
• Skeletal survey through the appropriate safeguarding pathway when non-accidental injury is suspected.

Blood tests

FBC, ESR, CRP and blood cultures support infection risk assessment. They are particularly useful in febrile, non-weight-bearing or systemically unwell children. Normal early markers do not overrule a concerning examination.

Septic hip risk stratification

Kocher-style criteria help separate septic arthritis from transient synovitis in a child with an acutely irritable hip, but they are not a substitute for clinical judgement, aspiration when indicated, or senior review.

Prediction rules perform differently across populations, organisms and joints. The CRP-containing (Caird) version discriminates better than the original Kocher rule and, in validation work, performs reasonably for large joints beyond the hip. Kingella infection and early disease may be less dramatic, with normal markers in a meaningful minority. If the child looks septic, has severe passive-motion pain, or deteriorates, escalate even if the criteria are incomplete.

Ultrasound

Hip ultrasound detects effusion but does not prove pus. It is most useful when interpreted with fever, weight-bearing status, pain with passive motion, inflammatory markers and clinical trajectory.

MRI

MRI is the escalation test when occult infection, abscess, tumour, stress fracture, discitis, early Perthes disease or unexplained persistent pain remains possible after initial assessment. MRI is also useful when symptoms are severe and the source is unclear.

If SUFE is possible, make the child non-weight bearing and obtain AP pelvis and appropriate lateral hip imaging. Do not force a painful frog lateral in a possible unstable slip.

Microbiology and empirical antibiotic cover

When septic arthritis or osteomyelitis is likely, empirical antibiotics should reflect the most probable organism for the child's age and host factors - a point examiners frequently push to after the Kocher/Caird discussion. Staphylococcus aureus is the commonest pathogen across all ages, but the differential cover changes with age, vaccination status and comorbidity.

Early

• Delayed septic arthritis diagnosis with cartilage injury.
• Missed SUFE with progression to unstable slip.
• Missed osteomyelitis with abscess formation.
• Inappropriate reassurance despite malignancy red flags.
• Unrecognised safeguarding concern.

Late

• Avascular necrosis or deformity from missed hip disease.
• Chronic osteomyelitis after delayed infection treatment.
• Growth disturbance from infection or physeal injury.
• Persistent gait abnormality due to missed neuromuscular or structural cause.
• Family loss of trust after vague safety-netting.

A limping child is a safety diagnosis until the dangerous causes are excluded. The first decision is not the final diagnosis; it is whether the child is systemically unwell, unable to weight bear, has severe pain, has a septic joint risk or has a non-orthopaedic emergency.

The assessment should use age bands. Toddlers commonly have occult trauma, toddler fracture or infection. Children aged four to eight need careful assessment for Perthes, transient synovitis and infection. Adolescents need slipped upper femoral epiphysis considered even when pain is felt in the knee. Any age can present with malignancy, inflammatory disease, discitis or non-accidental injury.

Transient synovitis is a diagnosis of recovery, not a label for every painful hip. A child who remains febrile, cannot weight bear, has rising inflammatory markers, severe passive-motion pain or persistent symptoms needs reassessment for septic arthritis, osteomyelitis, abscess or another diagnosis.

Do not start with a long list of diagnoses. Start with the child status: sick or well, weight bearing or not, painful or painless, and age band. This immediately separates septic arthritis and major red flags from the more common benign causes.

Transient synovitis is common, but the diagnosis should include why septic arthritis is unlikely. A well child who can weight bear, has mild symptoms after a viral illness, has improving pain and has reassuring inflammatory markers is very different from a febrile child who refuses to move the hip.

A normal X-ray is not the same as a normal child. Early osteomyelitis, tumour, toddler fracture, stress fracture and early Perthes disease can have subtle or normal radiographs. If the story remains concerning, escalate to MRI, repeat imaging or senior review rather than discharging on the basis of one normal film.

Non-accidental injury is not an accusation; it is a safety diagnosis that must be considered when the history, developmental stage and injury pattern do not match. The orthopaedic role is to recognise the mismatch, document carefully and activate the correct safeguarding pathway.

The discharge plan should sound precise: "This is the most likely diagnosis, these are the dangerous diagnoses we do not currently think are present, this is the follow-up plan, and these symptoms should bring you back urgently."

Common pitfalls

• Calling it transient synovitis before assessing septic arthritis risk.
• Forgetting that hip disease can present as knee pain.
• Relying on ultrasound effusion alone to diagnose septic arthritis.
• Missing SUFE because the child points to the knee.
• Ignoring night pain or systemic symptoms.
• Not considering safeguarding in a non-walking child with fracture.

The limping child is a worldwide presentation, but the diagnostic emphasis and available tools vary by setting. The core safety logic, separating sepsis and red flags from benign causes, is universal.

Global epidemiology

• Limp is a common paediatric emergency presentation; transient synovitis is the single most frequent cause of acute non-traumatic hip pain in children, typically aged 3 to 8 years.
• Septic arthritis of the hip is uncommon but time-critical, with the highest incidence in infants and young children.
• Kingella kingae is now recognised as the leading cause of osteoarticular infection in children under 4 years where molecular diagnostics are used; in settings reliant on conventional culture, a high proportion of these infections are reported as culture-negative.
• Perthes disease peaks at roughly 4 to 8 years with a male predominance; reported incidence varies several-fold between populations and is higher in some northern European cohorts.
• SUFE incidence tracks childhood obesity and is rising in many regions; bilaterality is common, which is why both hips are imaged and monitored.

Side-by-side guidance

Registry and surveillance notes

• Unlike arthroplasty, the limping child has no single implant registry; evidence comes from prospective cohorts (Kocher, Caird), classification studies (Loder, Herring) and national infection surveillance.
• SUFE and Perthes outcomes are tracked through paediatric orthopaedic networks and multicentre studies rather than device registries, which is why classification-based prognosis (lateral pillar, stable/unstable) remains central.

High- versus limited-resource practice

• Where MRI and molecular testing are readily available, occult infection, early Perthes disease and Kingella can be confirmed earlier and aspiration targeted more precisely.
• In limited-resource settings, serial clinical examination, repeat plain radiographs, ultrasound and empirical pathways carry more weight, and a lower threshold for senior review and joint aspiration compensates for diagnostic uncertainty.
• The universal safety rule holds everywhere: a febrile child who will not weight bear is treated as a possible septic joint until excluded, regardless of the imaging available.

• Prediction rules versus clinical judgement. Kocher and Caird criteria stratify risk but were derived in specific hip cohorts and perform variably elsewhere. They support, never replace, aspiration and senior review when a child looks septic.
• The Kingella era. The rise of Kingella kingae, which often produces mild markers and negative cultures, blurs the line between transient synovitis and true infection in toddlers and challenges scores built before molecular testing.
• Imaging escalation thresholds. When to move from radiograph and ultrasound to MRI, and how quickly, is debated and resource-dependent; MRI is the most sensitive escalation test but access and the need for sedation in young children constrain its use.
• Perthes containment. The benefit of operative containment is concentrated in older children with more severe lateral pillar grades; for younger or milder hips, observation may match surgery, so management remains individualised.
• Antibiotics before aspiration. Balancing prompt empirical antibiotics in a septic-looking child against obtaining diagnostic cultures first is a recurring judgement call, guided by how unwell the child is.