Childhood Hip and Leg Disorders

Introduction

A limping child is one of the most common paediatric musculoskeletal presentations and one of the highest-stakes, because the differential ranges from a self-limiting viral synovitis to septic arthritis, leukaemia and non-accidental injury. Around 1.5 to 3% of children present with a limp at some point.¹

The most efficient way through it is by age, because the four conditions that dominate the topic occupy almost non-overlapping age bands. Layered on top of that are two questions asked of every child regardless of age: is the child febrile and systemically unwell, and can the child weight bear? Those two questions identify almost everyone who needs urgent action.

The third principle is anatomical: hip pathology refers to the knee via the obturator nerve. A child brought with knee pain and a normal knee has a hip problem until the hip has been examined and, if necessary, imaged. Missing a slipped upper femoral epiphysis for this reason remains one of the classic avoidable errors in orthopaedics.

The limping child: a framework

Developmental dysplasia of the hip

DDH describes a spectrum from a shallow, dysplastic acetabulum through subluxation to frank dislocation. It affects 1 to 3 per 1000 live births in its more severe forms, is around six times more common in girls, involves the left hip more often (reflecting the usual intrauterine position), and is bilateral in about a fifth.

Risk factors

• Breech presentation - the strongest risk factor, particularly breech at or after 36 weeks or at delivery, regardless of eventual mode of delivery
• A first-degree family history of DDH
• Female sex and being firstborn
• Oligohydramnios, multiple pregnancy and high birth weight - all reducing intrauterine space
• Other packaging deformities - congenital torticollis, talipes, plagiocephaly
• Swaddling with the legs extended and adducted, which is a modifiable risk factor worth advising against

Detection

The UK Newborn and Infant Physical Examination (NIPE) programme screens all babies at birth and again at 6 to 8 weeks, using two manoeuvres performed on a relaxed infant:³

• Ortolani's test - the hip is flexed and gently abducted while lifting the greater trochanter forwards; a palpable clunk indicates a dislocated hip relocating into the acetabulum
• Barlow's test - the flexed hip is adducted with gentle posterior pressure; a clunk indicates a located but dislocatable hip

Both tests become unreliable after about 3 months as soft tissues tighten. Later presentations are detected by asymmetric skin creases in the thigh or groin, limited abduction in flexion (often the most reliable sign after infancy), apparent limb shortening with the knees at unequal heights when the hips and knees are flexed (Galeazzi sign), and, once walking, a painless limp, toe walking or a waddling Trendelenburg gait.

Management

• Under 6 months - a Pavlik harness, holding the hips flexed and abducted so the femoral head is directed into the acetabulum, worn for several weeks with regular ultrasound monitoring. Success rates are high when started early.⁴
• 6 to 18 months, or failed harness - closed reduction under anaesthetic with adductor tenotomy and a hip spica cast, sometimes with arthrogram
• Older children - open reduction, often with femoral shortening or a pelvic (Salter or Pemberton) osteotomy
• The major complication of treatment is avascular necrosis of the femoral head, which is why the harness must not force excessive abduction, and why the position is checked on ultrasound

Transient synovitis and septic arthritis

Transient synovitis (irritable hip) is the commonest cause of hip pain in children aged 3 to 10. It is a self-limiting sterile inflammation of the synovium, typically occurring 1 to 2 weeks after a viral upper respiratory tract infection. The child limps or refuses to walk, holds the hip flexed and externally rotated, and has restricted internal rotation - but is systemically well, with at most a low-grade temperature.

It is a diagnosis of exclusion, and the condition that must be excluded is septic arthritis, which shares the presentation and destroys a joint within days. The Kocher criteria were developed precisely to separate them.²

Once septic arthritis is genuinely excluded, transient synovitis is managed with rest, simple analgesia and NSAIDs, and it settles within one to two weeks. Arrange follow-up: a proportion of children initially labelled irritable hip turn out to have early Perthes' disease, and persistence beyond a couple of weeks warrants repeat radiographs.

Perthes' disease

Legg-Calve-Perthes disease is idiopathic avascular necrosis of the proximal femoral epiphysis, followed by revascularisation and remodelling over a period of two to four years. It typically affects children aged 4 to 8 (range 3 to 12), is four to five times commoner in boys, and is bilateral in 10 to 15% - though bilateral simultaneous involvement should prompt consideration of a skeletal dysplasia or hypothyroidism instead.

Associations include low birth weight, short stature and delayed bone age, passive smoking, socioeconomic deprivation and hyperactivity. The underlying cause remains unclear, and is probably a combination of a precarious epiphyseal blood supply and repeated minor insults.⁵

Presentation and stages

• Insidious onset over weeks to months of a limp, which may be painless, with hip, groin, thigh or knee pain
• Restricted abduction and internal rotation on examination, with muscle spasm, and eventually thigh wasting and limb shortening
• Waldenstrom's stages describe the natural history: initial necrosis, then fragmentation, then reossification, then remodelling - the whole process taking 2 to 4 years

Radiographs (AP and frog-leg lateral) may be normal early on. The earliest changes are widening of the joint space and increased density of the epiphysis, followed by a subchondral fracture line (the crescent sign), then fragmentation, and later flattening and broadening of the head (coxa plana and coxa magna). MRI or bone scan detects the disease before radiographic change appears, and is used where the diagnosis is suspected but the film is normal.

Management

• The goal is containment - keeping the softened femoral head within the acetabulum so that it remodels into a spherical shape
• Younger children (under about 6) with limited involvement are managed conservatively: analgesia, activity restriction, physiotherapy to preserve range of movement, and regular review. Most do well.
• Older children and those with extensive head involvement or loss of containment may need bracing in abduction or surgical containment with a femoral varus or pelvic osteotomy
• Maintaining hip range of movement is the single most important part of conservative treatment, and losing abduction is the trigger for escalation

Prognosis depends chiefly on age at onset - children under 6 do substantially better - together with the extent of epiphyseal involvement (classified by the Herring lateral pillar system) and the range of movement maintained. A deformed, non-spherical head predisposes to femoroacetabular impingement and to osteoarthritis in early adulthood.

Slipped upper femoral epiphysis

SUFE (also called SCFE) is displacement of the femoral head through the growth plate. The epiphysis stays in the acetabulum while the metaphysis and neck displace anteriorly and rotate externally - so relative to the neck, the head slips posteriorly and inferiorly. It is essentially a Salter-Harris type I fracture through a physis weakened during the adolescent growth spurt.

Who gets it

• Age 10 to 16 - typically boys aged 12 to 15 and girls aged 10 to 14, corresponding to the growth spurt
• Boys more than girls, roughly 2 to 1
• Obesity - the single strongest modifiable risk factor, present in the majority
• Bilateral in 20 to 40%, often sequentially, with the second slip usually within 18 months of the first
• Endocrinopathy - hypothyroidism, growth hormone deficiency or its treatment, hypogonadism, panhypopituitarism and renal osteodystrophy. Screen for these if the child is outside the usual age range, is short or underweight, or if the slip is bilateral at presentation.

Presentation and examination

• Usually insidious over weeks, with a limp and vague groin, thigh or knee discomfort; sometimes acute-on-chronic after minor trauma
• Around a quarter present with knee pain alone and a completely normal knee - the reason the hip must always be examined
• Loss of internal rotation is the earliest and most consistent sign
• Obligatory external rotation on passive hip flexion (Drehmann's sign) - as the hip is flexed the leg swings involuntarily into external rotation and abduction. This is close to pathognomonic and easy to elicit.
• In severe or unstable slips the leg lies shortened and externally rotated, and the child cannot weight bear

Imaging

Request AP and frog-leg lateral views of both hips. The lateral is essential because a mild slip, which displaces posteriorly, may be entirely invisible on the AP film - and imaging both hips allows comparison and detects an asymptomatic contralateral slip.

• Trethowan's sign - Klein's line, drawn along the superior border of the femoral neck on the AP view, normally intersects part of the epiphysis. In SUFE it passes above it without intersecting.
• Widening and irregularity of the physis, and loss of epiphyseal height on the AP view
• The classic description of the appearance is "ice cream slipping off the cone"
• MRI detects a pre-slip or an early slip where radiographs are equivocal

Management

1. Stop weight bearing immediately - a stable slip can become unstable, and that transition dramatically worsens the prognosis. Admit the child and use a wheelchair or bed rest; do not send them home to await an outpatient appointment.⁷
2. Urgent orthopaedic referral
3. Surgical fixation in situ with a single cannulated screw across the physis, which prevents further slip and promotes physeal closure
4. Do not attempt to reduce a chronic slip - forcible reduction disrupts the remaining blood supply and precipitates avascular necrosis. Severe slips may later need a corrective osteotomy once healed.
5. Consider prophylactic fixation of the contralateral hip in younger children, in those with an endocrinopathy, and where follow-up is likely to be unreliable

Complications include avascular necrosis, chondrolysis (acute loss of articular cartilage with a stiff painful hip), femoroacetabular impingement from the residual deformity, limb length discrepancy, and osteoarthritis in early adult life.

Other conditions worth knowing

Assessment and investigation

• History - age, onset and duration, trauma, fever and systemic symptoms, recent viral illness, ability to weight bear, night pain, weight loss, developmental milestones and birth history including breech presentation
• Observe the gait before touching the child - antalgic, Trendelenburg, toe walking, or a circumducting gait
• Examine the whole child - both hips, knees, ankles and feet, the spine, and the abdomen; look for rash, bruising, lymphadenopathy and organomegaly; measure and plot height and weight
• Bloods - FBC with film, CRP, ESR and blood cultures if infection or malignancy is a possibility. A film is important: leukaemia can present with bone pain and limp before the count is obviously abnormal.
• Radiographs - AP pelvis and frog-leg lateral of both hips for any adolescent hip presentation, and for suspected Perthes'
• Ultrasound - for a hip effusion, and for DDH in infants
• MRI - for early Perthes', osteomyelitis, a suspected tumour, or an equivocal slip
• Joint aspiration - urgently where septic arthritis is suspected, before antibiotics

Comparing the three hip conditions

Prognosis

Transient synovitis resolves completely within one to two weeks in the great majority, with a small recurrence rate and no long-term sequelae - provided the diagnosis was correct.

DDH treated early with a Pavlik harness has excellent outcomes, with normal hip development in most; late diagnosis requires more extensive surgery and carries a substantially higher risk of residual dysplasia, avascular necrosis and early osteoarthritis. This is the entire rationale for newborn screening.

Perthes' disease in a child under 6 with limited head involvement usually results in a well-remodelled hip; older children and those with extensive involvement frequently develop a deformed head, with symptomatic osteoarthritis in the fourth or fifth decade. SUFE treated promptly while stable does well, with over 90% of hips remaining satisfactory; an unstable slip carries up to a 50% risk of avascular necrosis, and both groups have an increased lifetime risk of impingement and arthritis. In all of these, the determinant of outcome is how early the diagnosis was made - which is a reasonable summary of the whole topic.