01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Start with physiology and function. Record temperature, heart rate, perfusion, interaction and whether the child can sit, crawl, stand or walk as usual. Ask onset, exact pain site, trauma, fever, recent infection, night waking, morning stiffness, rash, bowel or urinary symptoms and medicines. Explore weight loss, bruising and fatigue. In adolescents ask privately about activity and safeguarding where appropriate. Reconstruct whether a young child could have fallen unwitnessed.
Age changes probability. In toddlers consider transient synovitis, septic arthritis, osteomyelitis, discitis, toddler fracture and foreign body. In children around four to ten add Perthes and inflammatory disease. In adolescents prioritise SUFE, stress injury and overuse. Malignancy, infection, trauma and non-accidental injury cross all ages. A recent viral illness can precede transient synovitis but does not exclude sepsis.
Expose enough to compare both sides. Inspect skin, soles and nails, swelling, bruising, limb position and muscle bulk. Palpate systematically from spine and pelvis to toes and assess abdomen and groin. Move joints gently, using log roll for hip irritability and stopping at severe pain. Check leg length, power, tone, reflexes, sensation and pulses. Examine knee even when hip is suspected and hip whenever knee pain lacks a local explanation.
If safe, observe stance, foot progression, stride, pelvic level and trunk movement. An antalgic gait shortens painful stance; Trendelenburg pattern suggests abductor insufficiency; toe walking can compensate for shortening or reflect equinus or neurology. Ask the child to run, hop or squat only if fracture, SUFE and severe pain are not plausible. A normal gait after analgesia lowers but does not eliminate risk when history contains night pain or systemic features.
Target imaging to the likely site while remembering referred pain. Use AP and lateral radiographs for focal bone or joint concern and bilateral pelvis views for hip disorders. A toddler fracture or stress injury can be occult; immobilise and repeat imaging or obtain MRI when focal findings persist. Ultrasound identifies hip effusion and guides aspiration. MRI maps marrow, muscle, joint and spine and is preferred when infection, tumour or occult injury remains consequential.
Choose laboratory tests from risk. FBC, film, CRP and ESR support infection, inflammatory and haematological assessment; blood cultures precede antibiotics when possible in suspected sepsis. Renal, liver, calcium, phosphate, ALP and vitamin D address metabolic disease. Normal early markers do not exclude infection, and modest marker elevation does not distinguish septic from transient synovitis. Kocher variables structure probability but do not provide a discharge licence.
Management follows consequence. Resuscitate and treat sepsis, drain a septic joint and protect an infected or fractured limb. Make SUFE strictly non-weight-bearing and obtain same-day orthopaedic care. Immobilise an occult fracture when clinical localisation is convincing. Refer cancer warnings urgently under the suspected-cancer pathway and involve safeguarding specialists when injury history or interaction concerns arise. Use analgesia throughout rather than withholding it to preserve signs.
A well child with mild short-duration limp, no red flags and comfortable weight bearing can be observed with activity reduction and weight-based analgesia, but follow-up is active. Review within a defined interval and earlier for fever, worsening pain or reduced loading. Symptoms persisting beyond seven days, recurrence or loss of hip motion reopen Perthes, infection and inflammatory or malignant disease. Record who will check results and recovery.
Key points
- A limp is a presentation, not a diagnosis; first decide whether the child is systemically unwell, unable to bear weight or at immediate structural risk.
- Use age to prioritise without excluding: toddler fracture and infection in young children, Perthes in early school years and SUFE in adolescents.
- Ask the child to point with one finger, but examine the joints above and below, both hips, spine, abdomen, feet and skin because pain is often referred.
- Observe gait only when safe; never make a suspected SUFE, femoral-neck injury or severely painful child walk for diagnostic proof.
- No investigation may be reasonable in a well child with mild symptoms under seven days, comfortable weight bearing and a firm review plan.
- First-line tests for red flags are targeted radiographs and selected FBC, CRP, ESR and blood cultures; ultrasound detects effusion but not its cause.
- MRI is the reference investigation for occult fracture, osteomyelitis, pyomyositis, marrow tumour, early Perthes and spinal disease when localisation or radiographs are insufficient.
- Discharge only with a working diagnosis, permitted loading, analgesic dose, review time and explicit return advice for fever, worsening pain or reduced weight bearing.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Trauma and mechanical pain
Toddler fracture, stress injury, sprain, foreign body and overuse can alter stance even when trauma was unwitnessed or considered minor.
Infection and inflammation
Septic arthritis, osteomyelitis, pyomyositis, transient synovitis and inflammatory arthritis produce overlapping pain, stiffness and reduced loading.
Developmental hip disease
DDH, Perthes disease and SUFE present at different ages and may refer pain to thigh or knee rather than hip.
Malignant or neurological disease
Leukaemia, bone tumour, spinal compression and neuromuscular disorders can first present as limp before systemic or focal signs become obvious.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Antalgic load avoidance
Pain shortens stance time on the affected side and shifts the trunk to reduce force through the symptomatic structure.
- 2Abductor insufficiency
Hip displacement, proximal-femoral deformity or muscle weakness permits contralateral pelvic drop and a compensatory trunk lean.
- 3Restricted joint excursion
Effusion, synovitis, deformity or contracture reduces motion and creates circumduction, toe walking or externally rotated progression.
- 4Limb-length compensation
True or apparent shortening produces pelvic tilt, toe walking on the short side or vaulting on the opposite limb.
- 5Neurological gait failure
Weakness, spasticity, ataxia or sensory loss alters selective control and balance rather than simply reducing painful stance.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Shortened stance on one side identifies pain but not its anatomical source, which can be above or below.
Refusal or inability to load is a high-consequence sign requiring infection, fracture and SUFE exclusion.
Hip disease commonly presents at the knee, especially SUFE and Perthes, despite a normal local knee examination.
Night waking, weight loss, bruising, pallor or fever moves malignancy and infection ahead of benign mechanical causes.
Weakness, spasticity, ataxia, sensory loss or bladder change indicates cord, nerve or brain assessment rather than isolated limb imaging.
An injury unexplained by the child's mobility or inconsistent accounts raises a safeguarding concern requiring structured escalation.
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 targeted plain radiographsFirst stepFirst line - Why
- Identify fracture, SUFE, Perthes, tumour, deformity and late infection at the clinically localised site.
- Interpretation and limitations
- Obtain appropriate orthogonal and bilateral hip views; normal early films do not exclude toddler fracture, stress injury or early Perthes.
- 02
FBC, CRP, ESR and blood cultures - Why
- Assess infection, inflammation, cytopenia and bacteraemia when systemic or severe features exist.
- Interpretation and limitations
- Interpret trends and clinical state; normal early results cannot safely clear a concerning child.
- 03
Ultrasound of a suspected joint - Why
- Detect effusion and guide aspiration without ionising radiation.
- Interpretation and limitations
- Fluid is non-specific and cannot distinguish transient synovitis from septic arthritis without sampling and context.
- 04
Reference MRI of localised region - Why
- Find occult fracture, osteomyelitis, pyomyositis, marrow tumour, early Perthes or spinal disease.
- Interpretation and limitations
- Use urgently when the result changes source control or protection; image the correct anatomical field rather than only the reported pain site.
- 05
Bone scan or whole-body MRI when unlocalised - Why
- Survey for multifocal or occult skeletal disease when examination and initial imaging cannot localise persistent symptoms.
- Interpretation and limitations
- Choice depends on age, availability and suspected disease; focal uptake still requires anatomical correlation.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Age-specific hip disorder
Transient synovitis and Perthes dominate younger childhood, while SUFE becomes critical in the adolescent growth period.
Occult fracture
Toddler tibial fracture, foot injury or stress fracture can have normal early radiographs and little swelling despite focal pain.
Bone or joint infection
Fever may be absent early, particularly with Kingella, so weight-bearing loss, focal tenderness and trajectory remain important.
Inflammatory or malignant disease
Morning stiffness and multiple joints suggest arthritis, whereas night pain, bruising, cytopenia or mass requires cancer investigation.
Referred abdominal or spinal pain
Appendicitis, psoas disease, discitis and spinal tumour can limit hip movement and gait without primary limb pathology.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01EmergencyTreat the dangerous limp firstFirst stepThe child is unwell, non-weight-bearing or has severe joint pain, neurovascular change or neurological findings.+
- 1Assess ABCDE, observations and analgesia and stop unsafe walking or provocative testing.
- 2Obtain urgent paediatric and orthopaedic input, cultures and targeted radiographs, ultrasound or MRI.
- 3Immobilise fracture, make SUFE non-weight-bearing and start sepsis antibiotics without delay when indicated.
- 4Drain septic joint or abscess and protect neurological or vascular structures through the relevant emergency pathway.
02LocaliseExamine beyond the painful siteThe child is stable but the cause and anatomical origin remain uncertain.+
- 1Use age, tempo and one-finger pain localisation, then inspect skin, foot, joints, spine and abdomen systematically.
- 2Examine both hips for any thigh or knee complaint and assess neurology and leg length.
- 3Observe gait only if safe and distinguish antalgic, abductor, short-limb and neurological patterns.
- 4Select investigations from the most consequential remaining differential rather than ordering a universal panel.
03Low riskObserve with a failsafeA well child has mild symptoms under seven days, walks comfortably and has no red flags or concerning examination.+
- 1Provide short activity reduction and correctly prescribed paracetamol or ibuprofen.
- 2Name the working diagnosis and explain uncertainty and the expected recovery trajectory.
- 3Arrange a definite review and immediately reassess fever, worsening pain, night symptoms or reduced weight bearing.
- 4EscalationEscalate persistence or recurrence to repeat examination, radiographs or MRI rather than renewing reassurance indefinitely.
04SafeguardingProtect the child while investigatingMechanism, development, delay, injury pattern or interaction creates concern for inflicted harm or neglect.+
- 1Treat pain and injury and document exact accounts separately, developmental ability and full skin and musculoskeletal findings.
- 2Follow the local safeguarding pathway and involve senior paediatrics without confronting or investigating independently.
- 3Obtain imaging and other assessments through the specialist child-protection plan.
- 4Ensure immediate safety and information sharing before discharge while continuing ordinary differential diagnosis.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Paracetamol during limp assessment
Prescribe the current BNFC age- and weight-based dose, recording exact milligrams, formulation volume, dosing interval and 24-hour maximum.Check weight, liver risk and other paracetamol products; analgesic response alone does not exclude infection, fracture or malignancy.
Ibuprofen for a selected low-risk child
Use the current BNFC age- and weight-specific oral regimen for a short course when hydration, kidney function, gastrointestinal risk and NSAID-sensitive asthma history permit.Avoid in dehydration or renal disease and do not use symptomatic improvement as a reason to cancel follow-up or loading restrictions.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Delayed septic source control
Missed joint or bone infection causes irreversible cartilage destruction, growth disturbance, systemic sepsis and chronic osteomyelitis.
Progression of SUFE
Continued weight-bearing through an unrecognised slip substantially increases displacement, proximal-femoral deformity and subsequent femoral-head osteonecrosis risk.
Displaced occult fracture
Failure to protect a subtle femoral-neck, tibial or physeal injury can convert stable damage into deformity or surgery.
Delayed cancer diagnosis
Repeated benign labels for night pain or cytopenic symptoms can postpone staging and permit tumour progression or fracture.
Safeguarding failure
Ignoring developmental mismatch or inconsistent history can leave a child exposed to recurrent injury and escalating harm.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Repeat observations, perfusion, pain, neurological status and weight-bearing ability when the child remains under assessment.
- Track every imaging, culture and blood-film result to named clinical ownership after discharge or transfer.
- For observation, document the review date and confirm resolution of gait and joint range rather than symptoms alone.
- Escalate persistent fever, CRP rise, night pain, cytopenia or new focal swelling immediately.
- Maintain visible non-weight-bearing or immobilisation instructions across radiology and inter-hospital transport.
- Record growth and recurrence over time when Perthes, inflammatory, metabolic or neuromuscular disease remains possible.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Age ranks but never excludes
A diagnosis may be typical at one age yet infection, fracture and malignancy remain possible throughout childhood.
Pain travels along the limb
Hip pathology commonly presents at thigh or knee, making examination above and below mandatory.
Analgesia improves examination
Treating pain is humane and can clarify function; it does not erase fever, structural signs or a dangerous history.
Normal radiographs have timing
Toddler fracture, early Perthes, stress injury and osteomyelitis can be invisible before later change or MRI.
An effusion is a finding
Ultrasound locates fluid but does not label it transient, septic, inflammatory or haemorrhagic.
Reassurance needs an owner
A low-risk diagnosis is safe only when worsening advice and a defined clinician-led review close the loop.
11Common pitfallsFrequent interpretation and management errors.
- 01
Making a suspected SUFE walk to demonstrate gait or sending the child home after normal knee imaging.
- 02
Calling a sonographic effusion transient synovitis without assessing infection risk.
- 03
Using normal early radiographs or inflammatory markers to clear a persistently concerning child.
- 04
Examining only the reported painful joint and missing spine, abdomen, foot or referred hip disease.
- 05
Withholding analgesia to preserve signs or using response to analgesia as a diagnostic test.
- 06
Discharging a low-risk limp without a review date, loading plan and red-flag return advice.