A child who is refusing to walk, limping, or holding one leg differently is telling you something. Small children often cannot localise or describe pain accurately — hip pain can present as knee pain, and back pain as leg pain. The key is not to dismiss a limp as nothing because the child looks fairly comfortable.
The decision that matters most in evaluating a childhood limp is ruling out septic arthritis. Infection in a hip joint is a medical and surgical emergency: the pressure from the infected effusion can cut off blood supply to the femoral head and cause permanent avascular necrosis within hours to days. A comfortable-looking child can still have septic arthritis, and the clinical and laboratory parameters used to assess the probability are not perfect.
Healthbooq (healthbooq.com) covers common presentations in children including musculoskeletal symptoms.
Transient Synovitis (Irritable Hip)
Transient synovitis is the most common cause of acute hip pain in children, predominantly affecting those aged three to eight years (median age five). It is a reactive inflammation of the hip joint synovium, typically following a viral illness by one to two weeks. The child usually presents with a sudden onset of hip or groin pain, sometimes referred to the inner thigh or knee, and a limp or refusal to weight-bear.
On examination, the hip is held in slight flexion and external rotation (the position that maximises joint volume and therefore minimises pain from the effusion). Internal rotation of the hip is the most limited and painful movement. The child is typically afebrile or mildly febrile (below 38.5°C), and appears generally well.
Inflammatory markers (CRP, ESR) are usually normal or minimally elevated. Hip ultrasound shows a joint effusion in most cases.
Transient synovitis resolves spontaneously within one to two weeks. Management is rest (non-weight-bearing when in pain), NSAIDs for comfort, and monitoring to ensure resolution and that the diagnosis does not change.
Septic Arthritis
Septic arthritis is bacterial infection within a joint. In the hip, it most commonly affects infants and young children under five. Staphylococcus aureus is the most common causative organism at all ages; in neonates, Group B Streptococcus is also important. Haematogenous spread (bacteria seeding the joint from the bloodstream) is the usual route.
The child with septic arthritis typically appears unwell and febrile, is in significant pain, and holds the hip in the position of comfort (flexion, external rotation). Weight-bearing is usually impossible. However, early or partially treated cases can look deceptively mild.
The Kocher criteria (Kocher et al., Journal of Bone and Joint Surgery 1999) use four variables to estimate the probability of septic arthritis versus transient synovitis: fever above 38.5°C, non-weight-bearing, raised ESR (>40mm/hour), and raised white blood cell count (>12,000/mm³). The more criteria present, the higher the probability of septic arthritis.
Septic arthritis of the hip requires urgent surgical washout of the joint under general anaesthetic, combined with intravenous antibiotics. Delay increases the risk of avascular necrosis of the femoral head and permanent hip damage.
Toddler's Fracture
A toddler's fracture is an undisplaced spiral fracture of the tibia (lower leg bone), usually following minor trauma — a stumble, a small fall, stepping off a kerb — that the parent may not have noticed or may have thought insignificant. The child refuses to walk or limps markedly. There is no deformity and minimal swelling.
X-ray may not show the fracture acutely — it can be invisible on initial plain films and only visible on follow-up films at ten to fourteen days when callus (healing bone) forms. Management is a below-knee cast or supportive splinting, and the fracture heals well.
Perthes Disease
Perthes disease (Legg-Calvé-Perthes disease) is avascular necrosis of the femoral head — the blood supply to the ball of the hip joint is disrupted, causing the bone to die and then gradually remodel. It presents in children aged four to ten years (peak age five to seven), more commonly in boys. The presentation is an intermittent limp, often without significant pain, sometimes noticed after activity.
Early investigation requires plain X-ray and occasionally MRI. Management ranges from observation to bracing to surgery depending on the child's age, the degree of involvement, and the stage of disease. Specialist orthopaedic management is required.
When to Seek Urgent Assessment
Any child with a limp should be assessed on the same day. The urgency is higher if: the child appears unwell or febrile, pain is severe, the child is completely refusing to weight-bear, or there is recent significant trauma.
Key Takeaways
A limp in a young child is always worth investigating, even if the child appears relatively comfortable. The most common cause in toddlers and young children is transient synovitis (irritable hip) — a self-limiting inflammation of the hip joint following a viral illness. However, the most important diagnosis to exclude is septic arthritis (infection in a joint), which is a surgical emergency that can permanently damage the joint within hours if not treated. The Kocher criteria help differentiate septic arthritis from transient synovitis. Other important causes include toddler's fracture (undisplaced tibial fracture from minor trauma), developmental dysplasia of the hip, and Perthes disease (avascular necrosis of the femoral head).
