Septic arthritis is a surgical emergency — delay can rapidly result in cartilage destruction, joint damage, avascular necrosis of the femoral head, permanent disability and sepsis. The Kocher criteria (fever, non-weight-bearing, raised ESR, raised WBC) are a risk-stratification tool, mainly validated in children with suspected hip septic arthritis; published estimates vary by population and setting. They may support risk stratification but do not exclude septic arthritis — clinical concern overrides the score. A child who is systemically unwell, cannot weight-bear, has severe pain, fever or a hot joint requires same-day specialist assessment regardless of the score.

Malignancy: Leukaemia can present with musculoskeletal pain or limp, and blast cells may be absent on the initial blood film. Persistent or unexplained bone pain, pain at rest/night and constitutional symptoms are the alarm features. NICE NG12 (updated April 2026): very urgent FBC (within 48 hours) for pallor, persistent fatigue, unexplained fever, persistent infection, generalised lymphadenopathy, persistent or unexplained bone pain, unexplained bruising or bleeding; immediate specialist assessment for unexplained petechiae or hepatosplenomegaly; very urgent direct-access X-ray (within 48 hours) for unexplained bone swelling or pain where bone sarcoma is a concern, and very urgent referral if the X-ray suggests bone sarcoma.

NAI: Fractures are a recognised feature of physical abuse. A limp with no clear explanation, an inconsistent history, bruising in pre-mobile infants, delayed presentation or injury incompatible with developmental ability warrants safeguarding assessment — this does not automatically require same-day hospital admission in every case; act according to the level of concern. Document carefully; do not confront carers alone.

Age-related prevalence determines pre-test probability before any examination or investigation. Transient synovitis is a common cause of acute hip pain in younger children, but it is a diagnosis of exclusion — septic arthritis must be considered first on clinical assessment (Kocher criteria do not exclude it). SUFE is an important hip disorder in adolescents and may present with knee or groin pain — beware the referred pain pattern; the knee is examined but the hip is the problem. Delay in diagnosing SUFE leads to avascular necrosis. Perthes disease runs a prolonged course — early specialist referral supports management.

Referred pain is the most dangerous diagnostic pitfall: SUFE can present with isolated knee pain and a normal knee examination — clinicians who only examine the knee miss the diagnosis. Always examine the hip when a child complains of thigh or knee pain.

Morning stiffness >30 minutes is a JIA hallmark — children are often described as "warming up" over the morning. JIA requires 6 weeks of symptoms before formal diagnosis; early referral to paediatric rheumatology avoids joint damage.

Safeguarding: The limp consultation is a key opportunity — physically abused children may present with limb symptoms. The RCGP safeguarding competency requires GPs to consider abuse when injury doesn't fit the story.

Log-roll test: The hip is the single most important examination in a limping child. Loss of internal rotation is the earliest sign of Perthes disease and SUFE — often before the child is in severe pain. Marked or painful restriction of hip movement, particularly internal rotation, requires urgent assessment and imaging (AP and lateral hip) according to age, clinical context and local paediatric orthopaedic pathway.

Trendelenburg gait in a young child suggests hip dysplasia (DDH) or early Perthes — both require urgent paediatric orthopaedic referral.

Fever >38.5°C + restricted hip movement + refusal to weight-bear: Treat as suspected septic arthritis and arrange same-day paediatric/orthopaedic assessment — aspiration and definitive diagnosis are specialist-led. Do not be reassured by a normal inflammatory marker — early septic arthritis can have normal bloods.

The Kocher criteria (fever >38.5°C, non-weight-bearing, ESR >40 mm/h, WBC >12; Caird later added CRP >20) are a risk-stratification tool, mainly validated in suspected hip septic arthritis; published estimates vary by population and setting. They are not a standalone rule-in or rule-out test — a score of 2 indicates significant risk requiring assessment, not an automatic diagnosis. Clinical appearance and examination remain more important.

X-ray limitations: Early Perthes and SUFE may have normal plain films. A normal X-ray in a child with restricted hip movements and pain requires MRI. SUFE can only be confidently excluded on a lateral view (frog-leg, or cross-table lateral where an unstable slip is suspected) — an AP view alone can miss a slip.

Avoiding unnecessary radiation: Children are more radiation-sensitive than adults. Ultrasound is preferred for effusion detection; MRI for soft tissue and bony detail. Don't X-ray a toddler's "limp" if clinical features clearly point to Sever's or Osgood-Schlatter.

SUFE is a surgical emergency once confirmed: the child must be non-weight-bearing from the moment of suspicion and assessed same day; admission and operative management are according to the specialist team. Any delay risks further slip and avascular necrosis. Do not send home to await an outpatient appointment.

Perthes disease: Outcome correlates strongly with age of onset and degree of femoral head involvement. Younger children generally have a better prognosis; surgical decisions are specialist-led. Early referral preserves function.

Transient synovitis: A diagnosis of exclusion — do not label it as such where the child is febrile, toxic, non-weight-bearing or has marked restriction of movement. Manage in primary care only if systemically well, able to weight-bear and without red flags. Review within 24–48 hours; persistent or worsening symptoms require same-day paediatric/orthopaedic reassessment.

Ibuprofen in children: Anti-inflammatory and analgesic — useful for musculoskeletal pain. Regular dosing is not appropriate for every child or every pain presentation; use the lowest effective dose for the shortest appropriate period, dosed by age/weight per BNFC. Ibuprofen is not contraindicated in infection generally; avoid in dehydration and use caution in chickenpox or renal disease.

Codeine is contraindicated in children under 12 (MHRA restriction following deaths in codeine-morphine ultra-rapid metabolisers). Follow current MHRA advice and current paediatric prescribing guidance.

Transient synovitis can recur, and a small proportion of children later prove to have Perthes disease — this is why persistent or recurrent symptoms need reassessment. Natural history of TS is benign, but follow-up is mandatory.

Activity modification vs rest: Complete rest worsens outcomes in overuse injuries — bone requires mechanical loading to remodel. The British Journal of Sports Medicine recommends relative load management over complete cessation. Children respond better and faster than adults to structured physiotherapy.

Obesity and SUFE: SUFE is associated with childhood obesity, although obesity is not required — atypical age or body habitus should prompt consideration of endocrine/renal disease. Weight reduction reduces shear forces on the capital femoral epiphysis and may delay contralateral slip.

Vitamin D: Supplementation advice depends on age, season, diet and risk group — follow current NHS/UK government guidance and local prescribing arrangements. Do not routinely test vitamin D in every limping child; consider deficiency (e.g. rickets) only where there is a specific clinical indication.

The 1-week review for transient synovitis: true transient synovitis should have resolved. Any child still limping at 1 week has a diagnosis other than transient synovitis until proven otherwise — Perthes, reactive arthritis, and early JIA are the commonest alternatives. A normal X-ray at this stage does not exclude early Perthes — MRI is needed.

Contralateral SUFE risk: SUFE can be bilateral (sequential or synchronous). Children who have had one SUFE fixed must be counselled to return immediately with any new hip, groin, or thigh pain. GP follow-up has a critical role in detecting the contralateral slip early.

JIA uveitis: Anterior uveitis in JIA is often painless and can cause visual loss if undetected. Screening frequency is risk-stratified (JIA subtype, ANA status, age at onset, disease duration, previous uveitis) according to the local/RCPCH paediatric ophthalmology protocol — not a universal interval. GPs must ensure ophthalmology follow-up is active. This is an area where GP-initiated safety-netting prevents preventable visual loss.