CHAPTER 60 ■ PAIN: JOINTS RICHARD J SCARFONE, AARON E CHEN INTRODUCTION Arthritis and arthralgia are common reasons for children to seek care in the emergency department (ED) Arthritis is joint inflammation marked by swelling, warmth, and limitation of motion; arthralgia is joint pain without inflammation Establishing a diagnosis for the child with joint pain is challenging because the differential diagnosis is lengthy ( Table 60.1 ), clinical and laboratory findings are rarely specific for a particular disease, and disease patterns for many of the etiologies are often highly variable among different patients Among the most common causes of joint pain in children are infections, trauma, and postinfectious conditions ( Table 60.2 ), whereas those most likely to be life-threatening are due to systemic disease and malignancy ( Table 60.3 ) This chapter serves as a guide to the approach to the child with arthritis or arthralgia, with an emphasis on historical points and physical examination findings that can serve to narrow the diagnostic possibilities DIFFERENTIAL DIAGNOSIS The initial differential diagnosis usually focuses on the most common or potentially serious etiologies ( Tables 60.2 and 60.3 ) Children from to 24 months of age have the highest incidence of nongonococcal bacterial (septic) arthritis, which results primarily from the hematogenous dissemination of an organism The diagnosis of septic arthritis of the hip should not be delayed because pressure in the joint space will compromise the vascular supply to the femoral head, leading to necrosis (see Chapter 94 Infectious Disease Emergencies ) Osteomyelitis involving the distal end of long bones may manifest as arthralgia with or without objective signs of joint inflammation Children with sickle cell anemia and Type diabetes mellitus are at higher risk Onset of symptoms is typically more indolent compared to septic arthritis In the first 10 days of illness, children with Kawasaki disease may have arthritis or arthralgia, often involving smaller joints in the hand Beyond that time, involvement of larger joints of the lower extremities is more common If an arthrocentesis is performed, the synovial fluid analysis resembles that seen with