Limp in children: Differentiating benign from dire causes

A mother brings her 4-year-old son to the office because he has been limping. She isn’t aware of a specific trauma. But the boy and his twin brother, while recovering from “colds,” were rough-housing in their room when this son complained of pain. He is afebrile and points to his knee as the area of pain.

Although limping in children is common—the incidence is roughly 2 per 1000¹—it is never normal. It indicates pain, weakness, or structural abnormality.² Most cases result from trauma.¹ Limp usually resolves with little intervention and no sequelae. However, the differential diagnosis is broad and daunting (TABLE 1), and some causes of limp are associated with significant morbidity.

TABLE 1
Possible causes of limp in a child^1-3,17

Helpful tips for your initial assessment

Many textbook authors have described some causes of limp as “painless.” However, truly painless limp is rare, seldom acute, and usually the result of mechanical or neuromuscular disorders.¹ A more likely explanation for acute “painless” limp is that a young child with pain is unable to express pain or accurately identify its location. Further, the child may instinctively avoid painful positions or movements and, thus, may present only with decreased movement of an extremity or refusal to bear weight.³

With a child who has knee pain, remember the pediatrics maxim: “Knee pain equals hip pain,”³ underscoring the diagnostic difficulty with limp.

Also bear in mind that children of different ages tend to have different etiologies of limp (TABLE 2). For example, septic arthritis, osteomyelitis, and transient synovitis occur more commonly in children under 10 years. Legg-Calve-Perthes disease and leukemia are more common in children between the ages of 4 and 10. Slipped capital femoral epiphysis (SCFE) is more common in boys over the age of 11.

TABLE 2
Common causes of limp according to child’s age¹

Fracture
Fracture is a possibility across all age ranges, necessitating radiographs if suspected. Beyond detecting fractures, x-ray films can identify bony changes associated with disease (eg, Legg-Calve-Perthes disease, SCFE). Radiographs can also identify a clinically significant joint effusion at the hip.⁴ However, x-ray results may be falsely negative for some fracture types.

Salter-Harris Type I fractures are transverse fractures through the growth plate with epiphyseal separation from the metaphysis.⁵ Typical findings are a history of trauma and point tenderness over the epiphyseal plate. Type I fractures are radiographically occult, making the injury easy to mistake as a sprain. Nonetheless, growth plate injuries are common in children, requiring immobilization.

Toddler’s fracture was first described as a spiral, oblique undisplaced fracture of the distal tibial shaft in children from 9 months to 3 years of age.⁶ It results from a rotational or twisting force through the tibia while the leg rotates internally on a planted foot.^7,8 This is the most common tibial fracture in infants and young children.⁹ The incidence has been reported as 0.6 to 2.5 per 1000 pediatric visits.¹⁰ Accurate diagnosis is important because current treatment recommendations suggest a long leg cast for 3 to 5 weeks, followed by a short leg cast for a total of 6 weeks.¹¹

Despite being the most common tibial fracture, toddler’s fracture is easily missed. Initial radiographs are only 53% sensitive.^7,10 This implies that nearly 50% of children with tibial fracture will have an initially negative x-ray result. However, nearly 94% of children with a confirmed toddler’s fracture have been unable to bear weight.¹² Evidence suggests that despite negative radiographs, patients with point tenderness over the tibia and an inability to bear weight should be treated for presumed toddler’s fracture.¹²