The limping child: evaluation and diagnosis.

A limp is a common reason for a child to present to the orthopaedist. Because of the long list of potential diagnoses, some of which demand urgent treatment, an organized approach to evaluation is required. With an understanding of normal and abnormal gait, a directed history and physical examination, and the development of a differential diagnosis based on the type of limp, the patient's age, and the anatomic site that is most likely affected, the orthopaedist can take a selective approach to diagnostic testing. Laboratory tests are indicated when infection, inflammatory arthritis, or a malignant condition is in the differential diagnosis. The C-reactive protein assay is the most sensitive early test for musculoskeletal infections; an abnormal value rapidly returns to normal with effective treatment. Imaging should begin with plain radiography. Ultrasonography is particularly valuable in assessing the irritable hip and guiding aspiration, if necessary.