What usually causes hip pain in childrenStrong evidence
The NHS says irritable hip is the most common cause of hip pain in children: the hip joint becomes sore and inflamed, and it usually gets better by itself. Less common but more serious causes include an infected hip joint, an injury such as a broken bone, and Perthes disease. The NHS limping page adds a slipped growth plate, juvenile arthritis and, rarely, a cancer such as leukaemia, and asks parents not to self-diagnose: a limp with no obvious cause should always be checked by a GP.
NHS inform says a hip problem in a child can be felt in the bottom, the groin, the back, the thigh or the knee. Age is the best clue to the likely cause, and the map above sorts them.
Sources 1, 2, 3
Irritable hip (transient synovitis)Emerging evidence
A short-lived inflammation of the lining of the hip joint that causes pain and a limp. In Merseyside, 25.1 children in every 100,000 aged up to 14 were diagnosed with it each year, boys 3.2 times as often, at an average age of 5.4.
The NHS limping page links it with sudden hip, knee or thigh pain sometimes after a viral infection, and guidance for doctors says it is thought to follow one; but the Merseyside study found no seasonal pattern, which casts some doubt on the virus idea. Either way, a recent cold doesn't rule out an infection in the joint, which is why it is checked first.
Sources 1, 4, 5, 6, 7, 2
A joint or bone infection: what doctors rule out firstStrong evidence
An infected joint needs treating in hospital straight away, and the British Orthopaedic Association's standard asks for it to be drained, ideally within 24 hours of diagnosis. Young children don't always get a high temperature with a bone infection, the NHS says. The National Institute for Health and Care Excellence (NICE) asks clinicians to consider a joint or bone infection in a child under 5 with a fever who has a swollen limb or joint, isn't using a limb, or won't put weight on a leg.
Doctors weigh a history of fever, whether the child will bear weight and blood tests. In 11 studies of 1,810 children, four things separated infection from irritable hip: a history of fever (an odds ratio of 6.04), not bearing weight (5.23), and two blood tests, the erythrocyte sedimentation rate or ESR (3.98) and the white cell count (2.73). A third blood test, C-reactive protein (CRP), didn't reach significance there, though it was a strong sign in a smaller prospective study. The original prediction rule worked less well when tested in a new group of 154 children, and the standard says no single set of tests is completely reliable. These are hospital tools, not a checklist for parents: a fever with a limp is a reason to get help, not to score.
Sources 8, 9, 10, 11, 12, 13, 14, 15
Perthes diseaseStrong evidence
The blood supply to the ball of the hip is disrupted for a while, so the bone softens and can change shape before it heals and regrows, NHS inform says. It is commonest at 4 to 9 and in boys, with pain in the groin, thigh or knee, especially after activity, a limp, and a stiff hip. In Great Britain it starts in about 2.48 in 100,000 children aged up to 14 each year, and a national study found its effect on children's quality of life was marked and lasted at least 2 years.
Sources 16, 17
A slipped growth plate (SUFE)Strong evidence
In a slipped upper femoral epiphysis (SUFE), the ball of the hip slips at its growth plate, usually between 12 and 14 (range 11 to 16), NHS inform says. It can feel like a pulled muscle in the hip, knee or thigh; there is pain in the hip, groin, thigh or knee and a limp, and the leg may look shorter. It is linked with being overweight, being less active and the start of puberty, and every child with it needs an operation.
In Great Britain it starts in about 3.34 in 100,000 children aged 6 to 18 each year. In the national study, delays in diagnosis were common and the slip got worse the longer it took, and children who couldn't walk when they reached hospital had 4.4 times the odds of losing the blood supply to the ball of the hip. Knee pain first leads to longer delays: in 290 matched children, about 92 days longer to a hip X-ray.
Sources 18, 19, 20, 21
Teenagers: hip dysplasia, sports injuries and growth-area painEmerging evidence
Hip dysplasia, a shallow hip socket, is usually found in babies, but a mild case may not cause symptoms until late childhood, puberty or adulthood, as hip or groin pain, sometimes with clicking, the NHS says. A sudden pull in sport can tear a piece of growth plate off the pelvis (an avulsion fracture): in 14 studies of 596 adolescents, the average age was 14.3, three in four were boys, and the commonest places were the bony points at the front of the hip and the sitting bone.
A gradual ache where a tendon pulls on growing bone during a growth spurt, worse with activity and eased by rest, is traction apophysitis, NHS inform says, and a click or snap that can be painful, felt at the outside or front of the hip, is a snapping hip.
Sources 22, 23, 24, 25
Rarer causes: arthritis, tumours and leukaemiaStrong evidence
Painful, swollen joints that last more than 6 weeks can be juvenile arthritis, the NHS says, often with stiffness and a limp that are worse in the morning; in England it starts in about 6.2 per 100,000 white children a year and 2.7 to 3.0 per 100,000 in other ethnic groups. A lump on the leg, weight loss or pain at night can, rarely, be a cancer such as leukaemia, and bone cancer can cause pain worse at night and a limp. NICE asks GPs to arrange a very urgent blood count for a child with persistent or unexplained bone pain. These are rare, but they need early treatment.
Sources 2, 6, 26, 27, 28, 29
Age is a clue: under 3 and over 9Emerging evidence
A guide for GPs reports NICE's advice to refer a child with an acute limp urgently to the emergency department if they're under 3, or over 9 with painful or restricted hip movement, can't bear weight, have a fever or other warning signs. A teaching resource for clinicians lists the very young child for same-day assessment, and an NHS pathway asks for a same-day hip X-ray when a slipped growth plate or Perthes disease is suspected. We couldn't open the NICE summary itself, so our under 3 and over 9 warning lines are our suggestions from this guidance.
Sources 6, 30, 7
Tests and scansStrong evidence
At an appointment, a doctor or nurse may look at and feel the hip, leg and knee, gently move the leg, ask about recent injuries or illnesses and arrange an X-ray, sometimes with a blood test or other scans, the NHS says. When infection is possible, hospital teams take blood tests and X-rays, with an ultrasound and a magnetic resonance imaging (MRI) scan ideally within 48 hours. A slipped growth plate is confirmed by examining hip movement and an X-ray, and older children with suspected hip dysplasia have X-rays rather than an ultrasound.
Sources 1, 11, 18, 22, 7
How it usually goesEmerging evidence
Irritable hip usually gets better in 1 or 2 weeks and doesn't cause lasting problems, the NHS says. In 25 studies, almost all children were free of symptoms at 2 weeks, it came back in up to 26.3%, and children whose symptoms lasted more than a month were more likely to have another hip condition such as Perthes disease, so follow-up for at least 6 months is advised.
In 596 adolescents with avulsion fractures, 80% of those treated without surgery and 92% of those treated with it returned to their sport, in low-quality studies. Most new hip problems in children improve within 6 weeks, with the biggest change in the first couple of weeks, NHS inform says. No one can promise a date.
Sources 1, 5, 17, 19, 23, 3
