[Diagnosis of periprosthetic hip infections].

The diagnosis of periprosthetic infection requires a clear definition itself and structured procedure concerning anamnesis, clinical examination, laboratory findings, puncture and imaging diagnostics. The clinical presentation may vary considerable due to the time of their occurrence as early, delayed, or late infection. Recognition of risk factors and knowledge of differential diagnoses facilitate and confirm the diagnosis. The synovial fluid is assessed with regard to leukocyte count, protein content, and glucose. Intraoperative tissue specimen sampling has to be performed correctly; the histopathological and microbiological studies must be assessed using specific criteria. The examination and classification of periprosthetic membranes make discrimination of the causal pathological mechanism possible, especially distinction between septic and aseptic loosening. In this manner statements with regard to etiology and prosthesis durability are possible. Different causative microorganisms appear postoperatively at specific times. Pathogens that grow as biofilms are of great significance, as they may compound diagnosis and therapy. Early infections are often caused by virulent microorganisms (S. aureus) with acute onset. Delayed (low grade) infections are usually caused by less virulent microorganisms, such as S. epidermidis or coagulase-negative staphylococci. Many diagnostic imaging methods have been used in the assessment of periprosthetic infection: plain radiographs, arthrography, ultrasonography, computed tomography, and magnetic resonance imaging. Nuclear medicine with bone scintigraphy or positron-emission tomography enhance diagnostic capabilities. Cultures of samples obtained by sonication of prostheses are more sensitive than conventional periprosthetic tissue culture. Multiplex PCR of sonication fluid is a promising test for diagnosis of periprosthetic joint infection. The promising diagnostic accuracy for interleukin-6 and procalcitonin has yet not been affirmed.