Limping child
“Irritable hip” describes a presentation, not a final diagnosis. Differential diagnoses include:
- transient synovitis
- septic arthritis
- osteomyelitis
- Perthes disease
- SUFE in older children
- occult fracture
- inflammatory arthritis
- malignancy
Transient synovitis
Typical features:
- child otherwise reasonably well
- acute limp or hip/thigh/knee pain
- mild or no fever
- restricted internal rotation/abduction
- sometimes a recent viral illness
Treatment is usually analgesia, relative rest and review. Failure to improve as expected requires reassessment rather than repeated reassurance.
A well child with improving symptoms, low inflammatory markers and preserved ability to weight bear is more compatible with transient synovitis, but follow-up is needed if symptoms persist or change.
Septic arthritis
A child with systemic illness, fever, inability to bear weight and severe restriction of hip movement must be treated as possible septic arthritis.
Investigations
- FBC
- CRP and ESR
- blood cultures
- ultrasound for effusion
- radiographs to assess alternative pathology
- MRI when osteomyelitis or deep infection is suspected
Clinical prediction tools such as Kocher/Caird criteria help estimate probability but are not sufficiently accurate to replace judgement.
Joint aspiration
Aspiration can provide:
- cell count
- Gram stain
- culture
- molecular testing where available
Aspirate before antibiotics when safe, but do not delay antibiotics in a septic or unstable child.
Treatment
The principles are:
- urgent source control when septic arthritis is suspected/confirmed
- appropriate intravenous antibiotics with microbiology input
- culture-directed treatment thereafter
- identify associated osteomyelitis
Hip drainage may be arthroscopic or open depending on age, severity, surgeon expertise and local practice.
Complications
Delayed treatment may cause:
- cartilage destruction
- growth disturbance
- avascular necrosis
- subluxation/dislocation
- chronic infection
The younger the child, the lower the threshold for urgent specialist assessment.
The key diagnostic problem
A child with a painful hip may have transient synovitis, septic arthritis, osteomyelitis, trauma, Perthes disease, SUFE or other pathology.
The dangerous diagnosis to miss is septic arthritis because delay can rapidly damage cartilage and growth structures.
History
Ask about:
- fever
- recent infection
- duration and progression
- ability to weight bear
- night pain
- trauma
- antibiotic exposure
- age-specific alternative diagnoses
Examination
A child with septic arthritis often holds the hip in a position of comfort and resists movement in all directions.
Assess:
- general appearance
- temperature
- weight bearing
- hip motion
- adjacent joints
- abdomen
- spine
- skin and infection source
Blood tests
Use:
- inflammatory markers
- full blood count
- blood cultures when indicated
No single blood result safely excludes septic arthritis.
Clinical prediction rules can support assessment but should not override a concerning clinical picture.
Imaging
Ultrasound can detect an effusion but cannot reliably distinguish sterile from infected fluid.
Radiographs exclude alternative bony pathology and establish a baseline.
MRI is valuable when osteomyelitis, pyomyositis or deep infection is suspected, but should not delay drainage of a clinically septic joint.
Aspiration
Joint aspiration provides:
- appearance of fluid
- cell count where used
- Gram stain
- culture
Ideally samples are obtained before antibiotics in a stable child, but antibiotics should not be delayed in a systemically unwell child.
Treatment of septic arthritis
Urgent drainage plus intravenous antibiotics is required. Drainage may be arthroscopic, open or by repeated aspiration in selected joints/settings, but the hip is commonly managed surgically because complete clearance is important.
Monitor clinical response and inflammatory markers.
FRCS synthesis
The safest approach is septic until reasonably excluded in a febrile, non-weight-bearing child with a very irritable hip.