The extensive differential diagnosis of the child with a limp may be approached from several angles: disease category, location of pathology, or age of the child Table 46.1 presents the differential diagnosis by disease category; Table 46.2 organizes the differential diagnosis by age and the location of pathology This section reviews the differential diagnosis within the framework of an algorithmic approach ( Fig 46.1 ) The most common cause of limping in all ages is trauma, either acute or repetitive microtrauma (e.g., stress fractures) Older children who limp as a result of trauma can generally describe the mechanism of injury and localize pain well The toddler and preschool age groups, with their limited verbal ability and cooperation skills, often provide a diagnostic challenge A common type of injury in this population (often not witnessed) is the aptly named “toddler’s fracture,” a nondisplaced spiral fracture of the tibial shaft that occurs as a result of torsion of the foot relative to the tibia Occult fractures of the bones in the foot also occur in young children Initial plain radiographic findings may be subtle, or at times nonexistent, but will become apparent in to weeks Another fracture often lacking initial radiographic confirmation is a Salter–Harris type I fracture, which presents as tenderness over a physis after trauma to a joint area Stress fractures may also lack overt radiographic findings Common sites for overuse injury include the tibial tubercle (Osgood–Schlatter disease), the anterior tibia (shin splints), and the calcaneus at the insertion of the Achilles tendon (Sever disease) More information on the subject of fractures is found in Chapter 111 Musculoskeletal Trauma Trauma may also induce limping as a result of soft tissue injury Although young children are more likely to sustain fractures than sprains and strains, the latter can occur Joint swelling and pain out of proportion to the history of injury raises the possibility of a hemarthrosis as the initial presentation of a bleeding disorder (see Chapter 93 Hematologic Emergencies ) Severe soft tissue pain and swelling in the setting of a contusion or crush injury suggests possible compartment syndrome With compartment syndrome, pain is exacerbated by passive extension of the affected part; pallor and pulselessness are late findings Severe pain of an entire limb out of proportion to the history of injury suggests complex regional pain syndrome In pediatrics, this entity is most common in young adolescent girls It may be accompanied by mottling and coolness of the extremity, presumably as a result of abnormalities in the peripheral sympathetic nervous system A limp that is accompanied by a history of fever or recent systemic illness is likely to be infectious or inflammatory in origin However, the absence of fever