Fractures located near the growth plate are a common cause of posttraumatic joint pain.

The growth plate is often the weakest portion of the joint in children. For this reason, in patients whose growth plates have not yet fused, it is difficult to diagnose anything other than the most minor joint injuries as “sprains.” Fractures near the growth plate can be classified by their radiographic appearance and severity.

Splinters, glass, or other foreign material located near a joint space can induce an inflammatory response, causing synovitis or tendonitis. This process can occur over a period of months, or it can develop earlier if complicated by infection.

Diagnosis is based on a high index of suspicion and a review of the history. Plain radiographs are helpful only with radiopaque foreign materials, such as glass.

The cause is predominantly bacterial, occurring by hematogenous delivery, by direct extension from osteomyelitis, or from a penetrating injury to the joint. Staphylococcus aureus and Streptococcus pyogenes are the most commonly involved organisms, though Kingella kingae has also been implicated in a significant portion of cases. Other bacterial causes to consider include group B streptococcus and Gram-negative organisms in neonates, Neisseria gonorrhoeae in adolescents, Salmonella in patients with SCD, and Haemophilus influenzae in unimmunized children. Pyogenic infection in the joint space causes increased pressure within the joint capsule, resulting in derangements of the vascular and lymphatic supply. Bacterial and leukocyte proliferation may also occur, causing the release of proteolytic enzymes. These changes can rapidly damage cartilage and bone tissue.

Most patients with septic arthritis develop fever within the first few days of infection. If the hip or shoulder joints are involved, the patient holds the extremity slightly flexed, abducted, and externally rotated to relieve the pressure within the joint. The knee and elbow, if affected, are slightly flexed, and the ankle is plantar flexed. The application of pressure to the joint or movement of the joint through almost any range of motion produces pain. This finding contrasts with that found in purely traumatic injuries, which may be asymptomatic through a limited range of motion. Erythema, heat, and swelling may be present but are difficult to detect in the hip and shoulder joints as these joints are relatively deep beneath the skin surface.

Neisseria infections can produce either monoarticular or polyarticular disease. Gonococcal arthritis may begin as polyarthralgia, with a progression to monoarticular arthritis within a few days. These symptoms begin within 2 to 4 weeks of the initial urethritis and commonly increase in severity 1 week following the menstrual period in girls. Acute cases may be associated with fever, malaise, or dermatitis. Tenosynovitis (painful tendon sheaths) may also be present.

Plain radiographs may not be helpful early in the course of illness, but they may reveal distortion of the normal fat pads and evidence of a joint effusion. Ultrasound can be useful to identify the presence of a joint effusion.

Although the peripheral leukocyte count alone is not often helpful, laboratory data including an elevated C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can be helpful in diagnosing septic arthritis. The joint fluid may appear turbid and reveals a large number of leukocytes and a low fluid-to-serum glucose ratio, as described in Table 47-1.

Joint fluid cultures identify the causative organism in about 60% of patients. In contrast, blood culture results are positive in only 30% of all patients. Joint fluid culture results are more likely to reveal the organism within the first week
of infection. Chronic meningococcemia presents a similar clinical picture to gonococcal joint disease; however, joint fluid cultures are usually sterile.