Septic hip arthritis usually develops in children, but not adults. Septic hip arthritis typically results from direct inoculation of bacteria into the joint or its surroundings or seeding from a distant site. Therefore, adult ONFH combined with hip infection is rarely encountered in clinical practice. A search of the English literature revealed 7 relevant studies from 1978 to 2011[5–11], which reported on a total of 18 patients with concomitant ONFH and septic arthritis. In a study by Lee et.al , one patient who underwent internal fixation for femoral neck fracture was excluded because the infection was attributed to the process of internal fixation. The study ultimately included 17 patients (Table 1 and Table 2). In 11 cases, a bodily focus of infection was identified. 7 patients were immunocompetent (Table 1), and 10 were immunocompromised (Table 2). Therefore, ONFH combined hip infection is rare, especially in immunocompetent patients with no risk of infection. We encountered two patients who were diagnosed as having ONFH and concomitant septic arthritis of the hip without any risk of infection or immune-related compromise (Table 3).
The clinical symptoms of septic arthritis and of ONFH may be similar, and early diagnosis of septic arthritis is difficult . Septic hip arthritis in patients with ONFH is rarely encountered in clinic. 12 of the 17 patients were reported to have symptoms of fever when admitted to hospital, nine of whom were immunocompromised (Table 1, 2). None of the remaining patients had local or systemic symptoms of hip infection [5–11]. The only symptom reported by the three patients at the time of admission to the hospital was fever. Diagnosis of ONFH combined with septic arthritis is often difficult, especially in early-stage and immunocompetent patients.
WBC count may be of minimal help in diagnosis of hip infection, but the ESR and CRP are extremely sensitive for diagnosis of hip infection . WBC count was confirmed in 11 of 17 cases in the literature, but leukocytosis was confirmed in only 6 cases. ESR and CRP were significantly increased in all cases included in the study. This finding supports previous reports that measurements of ESR and CRP are good indices for detection of hip infection . ESR and CRP were significantly elevated in all cases for which measurements were obtained. The two cases seen at our institution involved leukocytosis. If no inflammatory etiology associated with elevated CRP and ESR is identified through diagnostic work, in patients without leukocytosis, the surgeon should rule out sepsis of the hip joint prior to THA.
MRI is a good tool with which to diagnose hip infection in an ONFH patient with elevated CRP and ESR . Specific MRI findings indicative of septic hip include alterations in signal intensity of bone marrow of both the proximal femur and acetabulum and strong enhancement in soft tissue surrounding the hip joint . Alteration of signal intensity of soft tissue around the hip joint seldom occurs in ONFH. Of the 17 cases described in the literature, MRI of the hip was performed in six and three of them showed signs of hip infection. MRI results for the 2 patients in our study indicated ONFH with septic hip arthritis.
Although organism culture is the gold standard for diagnosis of septic hip arthritis , organism identification may not always be possible. Patients may have received treatment with antibiotics before organism culture . Although culture was successful in 1 of 2 cases in our department, culture of joint fluid was negative for 4 of 17 patients described in the literature.
In recent years, the most common approaches to treatment of septic hip have been surgical debridement with arthrotomy combined with irrigation or arthroscopic debridement combined with irrigation and intravenous antibiotics [6–8, 11, 20]. Although arthroscopic debridement combined with irrigation is less invasive than open arthrotomy [20, 21], irrigation after surgery poses a challenge for patients. The cases seen at our institution were treated with spacers made of bone cement containing vancomycin. Spacers were used to replace the femoral head and were implanted in the hip. With this approach to treatment, the patient can move freely with the help of a walking stick. Postoperative irrigation was not necessary, as the spacer was designed for sustained release of vancomycin. This approach to treatment yielded excellent results in our patients.