A small child who suddenly limps, refuses to walk, or holds one leg differently is telling you something — but they often can't tell you what. Toddlers refer pain badly: hip pain often shows up as knee pain, back pain as leg pain. Don't dismiss a limp because your child still looks fairly comfortable.
The single most important call when assessing a childhood limp is ruling out septic arthritis. Infection inside a hip joint is a surgical emergency: pressure from the infected fluid can cut off blood supply to the femoral head and cause permanent damage within hours to days. A child with septic arthritis can occasionally look deceptively well early on. That's why every limp in a young child gets seen the same day.
Healthbooq covers common childhood presentations including musculoskeletal symptoms.
Transient Synovitis (Irritable Hip)
The most common cause of acute hip pain in children. Peak ages 3-8, median age 5. It's a reactive inflammation of the hip joint synovium that follows a viral illness — usually a cold or upper respiratory infection — by 1-2 weeks. The child wakes up limping or refusing to walk on what was a normal leg yesterday.
Typical picture:
- Sudden hip or groin pain, often referred to the inner thigh or knee
- Hip held in slight flexion and external rotation (the position that gives the inflamed joint the most room — and therefore hurts least)
- Internal rotation of the hip is the most limited and most painful movement on examination
- Afebrile or low-grade fever (under 38.5°C)
- Otherwise well — playing on the sofa, eating, normal mood
Bloods (CRP, ESR, white cells) are normal or minimally elevated. Hip ultrasound shows a small effusion in most cases.
It resolves on its own within 1-2 weeks. Management: rest from weight-bearing while painful, ibuprofen for comfort, and a follow-up to confirm it's getting better — because transient synovitis is a diagnosis of exclusion, and the diagnosis can change.
Septic Arthritis — The One You Can't Miss
Bacterial infection inside the joint. In the hip it most often hits children under 5; Staphylococcus aureus is the most common organism at all ages, with Group B Strep also relevant in neonates. The bug usually arrives via the bloodstream from somewhere else.
Typical picture:
- Looks unwell. Often febrile, sometimes high (>38.5°C)
- Significant pain, usually obvious distress
- Refuses any weight-bearing — won't even crawl on that side
- Holds the joint in the position of comfort and resists any movement of it
The Kocher criteria (Kocher et al., Journal of Bone and Joint Surgery, 1999) estimate the probability of septic arthritis versus transient synovitis using four predictors:
- Fever above 38.5°C
- Non-weight-bearing
- ESR above 40 mm/hour
- White cell count above 12,000/mm³
Probability of septic arthritis: roughly 3% with one criterion, 40% with two, 93% with three, 99% with four. The criteria are useful but not perfect — early or partially treated infection can look mild, and clinical concern alone is enough to escalate.
Treatment is urgent surgical washout of the joint under general anaesthetic plus IV antibiotics. Delay measured in hours matters. Outcomes are excellent when caught early and progressively worse the longer it sits.
Toddler's Fracture
An undisplaced spiral fracture of the tibia (lower leg bone), usually after minor trauma — a stumble, a small fall, stepping awkwardly off a kerb. The trauma is often so unremarkable the parent didn't notice it. The child refuses to walk or limps heavily, with no deformity and minimal swelling.
The catch: the fracture is often invisible on the initial X-ray and only becomes visible at 10-14 days, when callus (healing bone) shows up on follow-up films. Treatment is a below-knee cast or supportive splint. Heals well, no long-term consequences.
Perthes Disease
Legg-Calvé-Perthes disease — avascular necrosis of the femoral head. The blood supply to the ball of the hip joint is disrupted, the bone dies, and over months to years it gradually rebuilds. Affects children aged 4-10, peak 5-7, four to five times more common in boys.
Typical picture:
- Intermittent limp, often without much pain
- Sometimes worse after activity, better with rest
- Can be missed for weeks because the child is otherwise fine
Diagnosis is X-ray and sometimes MRI. Management depends on age, the extent of head involvement, and the stage when it's caught — options run from observation through bracing to surgery. Always under specialist orthopaedic care.
Developmental Dysplasia of the Hip
DDH — abnormal development of the hip joint, present from birth or early infancy. Usually picked up before walking through routine newborn checks (Barlow and Ortolani manoeuvres) or with ultrasound for at-risk infants. Occasionally presents later as a limp, leg-length difference, or asymmetric thigh creases. Covered in more detail in a separate article.
When to Seek Same-Day Assessment
Any child with a limp gets seen the same day. The threshold is lower — i.e. emergency department, not a GP appointment in two days — if any of these apply:
- Looks unwell or febrile
- Severe pain
- Completely refusing to bear weight
- Recent significant trauma
- Limp that has been there longer than a week without explanation
Don't wait to see if it improves. Septic arthritis cannot wait, and the cost of an unnecessary check is far smaller than the cost of a missed one.
Key Takeaways
Any limp in a young child needs same-day medical assessment, even if they look comfortable — the priority is excluding septic arthritis, which can permanently damage a joint within hours. Transient synovitis is the most common cause overall (ages 3-8, after a viral illness), but it is a diagnosis of exclusion. The Kocher criteria (fever >38.5°C, non-weight-bearing, ESR >40, WBC >12,000) help estimate the probability of septic arthritis but are not perfect — clinical concern alone is enough to investigate.
