Septic arthritis in the pediatric hip is an emergent surgical condition that if not rapidly treated, can lead to the rapid destruction of the hip, sepsis and even death. Septic arthritis of the pediatric hip needs to be differentiated from transient synovitis of the hip. Transient synovitis is a non-emergent and non-surgical condition that can resolve with symptomatic pain management and observation. It is important to recognize that that significant morbidity may result from the improper diagnosis of either of these conditions. Proper diagnosis includes identification of the infecting organism. The organism will vary depending on the age and comorbidities of the patient.
The hematogenous spread of bacteria into the hip joint is the most common mechanism for the development of pediatric septic arthritis. An upper respiratory infection precedes about 80% of the cases. The bacteria involved in about 70% of the cases are a gram-negative coccobacillus, Kingella kingae. Staphylococcus organisms account for 10% of the reported cases. In the past, Haemophilus species were the most common organism causing septic arthritis of the hip in children younger than two years of age.
The pooling of blood in the metaphyseal vessels of long bones allows for bacterial seeding into this area. Bacteria can then spread through the physical blood vessels of the pediatric bone into the bony epiphysis and result in an intracapsular infection of the hip joint hip.
About 50% of children presenting with septic arthritis of the hip is younger than two years of age. It has been reported to occur twice as often in males as in females. Children who are immunocompromised, have sickle cell disease, or who have hemophilia are more likely to develop septic arthritis of the hip than other children. In areas where Lyme disease is endemic, this condition should be considered as part of the differential diagnosis. This is true especially if other signs of Lyme disease (transient poly-arthralgia, typical erythema migrans (bull's eye rash), heart palpitations and irregular heartbeat) are present. Serological testing (Lyme titer /western blot) should be ordered to confirm a diagnosis of Lyme disease.
The release of cytokines contained in the pus within a septic joint leads to hydrolysis of proteoglycans and collagen in the hyaline cartilage covering the end of the bones within the joint. This leads to the destruction of the hyaline cartilage and articular bone resulting in deformity, chronic loss of function, and pain. If left untreated, septicemia and death can occur.
Children who have septic arthritis of the hip usually present with acute onset of hip joint pain. If they walk, they may be limping and resist weight bearing on their affected leg. Children who do not walk will lie in bed holding their hip in the most comfortable position which is flexed and abducted. This is a position which allows the hip capsule to be laxer, and therefore, decrease any pressure from an intraarticular effusion that may be causing pain. They are usually febrile. There may be a history of a recent oropharyngeal infection.
When the children are in bed, log rolling of the child will produce severe pain in the hip. Any passive motion of the hip joint is very painful.
The process of differentiating a patient who presents with acute hip pain and has septic arthritis from those who have acute pain from transient synovitis of the hip is difficult. The most definitive method of making this differentiation is the aspiration of the hip. The Kocher Criteria for diagnosing septic arthritis of the hip can be used to determine if an aggressive approach to management of the patient should be started. The four criteria used in order of sensitivity in the Kocher criteria are, fever higher than 38.5 C (101.3 F), ESR more than 40. Weight-bearing status (non-weight bearing), and white blood cell (WBC) count more than 12,000. Children who meet one out of four of these criteria have a 3% incidence of septic arthritis, two out of four have a 40% incidence, three-quarters have a 93% incidence, and four out of four have a 99% incidence.
X-ray examination of the hip should be done in older children to rule out any possibility of Perthes disease or a slipped femoral capital epiphysis.
Children who have hip pain but only meet one out of the four Kocher criteria should be observed and watched for further progression of the condition. Children who have two or more of the criteria should have the aspiration of their hip with a gram stain and cell count. If bacteria are identified or if the cell count reveals a WBC count over 50,000 WBC/mm3 with greater than 75% PMN cells and a glucose more than 50 mg/dl less than that of the serum level the hip joint should be opened and irrigated with an antibacterial agent.
The synovial fluid WBC differential is considered more sensitive than the WBC count when diagnosing septic arthritis. A finding of 85% PMNs correlates with an 88% sensitivity.
Recommendations for the length of use of intravenous (IV) antibiotic therapy vary. 2 days of IV antibiotics followed by a 3-week course of oral antibiotics has been found to be adequate. Other authors have recommended one week of IV antibiotic therapy followed by 2 additional weeks of oral antibiotics. Kingella kingae has been shown to be resistant to vancomycin and clindamycin. Management with IV beta-lactamase antibiotics and then their oral forms have been used in the treatment of these infections. The sooner treatment is initiated the better the results and fewer long-term complications.
Surgical approaches to the hip used in these cases are either anterior or anterior lateral. Recent literature documents similar surgical results when comparing open drainage of the hip to arthroscopic drainage.
Long-term follow-up is necessary to look for complications of septic arthritis of the hip. These complications can include avascular necrosis of the femoral head, growth disturbances of the hip, and the development of post-infection arthritis of the hip.
The management of transient synovitis is much less aggressive, and progression should be observed in children who are suspected of having transient synovitis. They can also receive non-steroidal anti-inflammatory medication or oral non-narcotic pain medication for pain management of pain associated transient synovitis. Most cases will resolve within five days.