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Background: A child who has an acutely irritable hip can pose a diagnostic challenge. The purposes of this study were to determine the diagnostic value of presenting variables for differentiating between septic arthritis and primary psoas abscesses in children who present with hip pain.
Purpose: This study was to determine the diagnostic value of the clinical presentations in children for differentiating between septic arthritis of the hip joint and psoas abscess.
Methods: The cases of children evaluated for an acutely irritable hip at a university hospital between 1984 and 2001 were reviewed retrospectively. Diagnoses of septic arthritis of the hip joint and psoas abscess were defined by the presence of pus in the hip joint or in the psoas muscles, results of cultures of the joint fluid, blood and pus, and the clinical course. The clinical presentations were used to differentiate between septic arthritis and psoas abscesses; univariate and multiple logistic regression analyses were used to assess their statistical significance.
Study design: Case-control study
Setting: Department of Orthopedics, Faculty of Medicine, Khon Kaen University
Results: Thirty-seven patients, 13 girls and 24 boys, had septic arthritis of the hip joint and ten, 4 girls and 6 boys, had a psoas abscess. The mean age of the septic hip and psoas abscess groups were 9.7± 3.6 years (range, 4 to14 years) and 8.3±4.2 years (range, 5 months to 14 years) respectively. The left hip joint was affected in 21 cases, the left psoas muscle in 7. Staphylococcus aureus was the causative pathogen in 25 cases of the septic hip group and 6 of the psoas abscess group. Most of the psoas abscess group (90 percent, 9/10 cases) presented with a lower abdominal mass whereas none were found in the septic hip group (p<. 001). All of patients in the psoas abscess group experienced abdominal pain, while none in the septic hip group did (p<. 001). None of the patients in the septic hip group was able to walk but all of the psoas abscess group was able to do so (p<. 001). All cases in both groups presented with fever and hip flexion contracture except one in the septic hip group. Results of other laboratory investigations were similar for both groups, except that ultrasound of abdomen revealed abscesses inside affected psoas muscles. The mean duration of symptoms was 9.5 ± 8.8 days and 31.6±35.2 days in the septic hip and psoas abscess groups, respectively (p<. 001). The multiple logistic regression indicated that lower abdominal mass and pain, and ability to bear weight were significant variables only in the psoas abscess group.
Conclusions: Pyogenic psoas abscess is the most likely diagnosis in children who present with fever, hip pain and flexion contracture of the hip joint, but can bear weight, and have clinical findings that include lower abdominal masses and pain.