The osteomyelitis diagnosis score should help to avoid the false description of a clinical presentation as "osteomyelitis". A safe diagnosis is essential for the aetiology, treatment and outcome studies of osteomyelitis.

Acute septic arthritis is a surgical emergency because rapid septic destruction of articular cartilage can lead to impairment or even loss of joint function. Diagnosis consists of patient history, clinical examination, laboratory results, (sonography- guided) joint aspiration and radiography. Emergency therapy is based on arthroscopic or open joint debridement and lavage combined with systemic antibiotic therapy. No data are available for the recommendation of local antibiotics but antiseptic solutions are not recommended because of cartilage damage. New trends in diagnostics are positron emission tomography/computed tomography (PET/CT), urine sticks for analysis of joint fluid and molecular pathology. Chronic joint empyema is more diagnostically demanding and is difficult to treat. In cases of necrotic and infected articular cartilage, joint resection has to be performed for quiescence of infection. Options following successful treatment of empyema are arthroplasty, arthrodesis or permanent resection.

A classification of osteomyelitis must reflect the complexity of the disease and, moreover, provide conclusions for the treatment. The classification is based on the following eight parameters: source of infection (OM [osteomyelitis]/OT [post-traumatic OM]), anatomic region, stability of affected bone (continuity of bone), foreign material (internal fixation, prosthesis), range of infection (involved structures), activity of infection (acute, chronic, quiescent), causative microbes (unspecific and specific bacteria, fungi) and comorbidity (immunosuppressive diseases, general and local). In the long version of the classification, which was designed for scientific studies, the parameters are named by capital letters and specified by Arabic numbers, e.g., an acute, haematogenous osteomyelitis of a femur in an adolescent with diabetes mellitus, caused by Staphylococcus aureus, multi-sensible is coded as: OM2 Lo33 S1a M1 In1d Aa1 Ba2a K2a. The letters and numbers can be found in clearly arranged tables or calculated by a freely available grouper on the internet (www.osteomyelitis.exquit.net). An equally composed compact version of the classification for clinical use includes all eight parameters, but without further specification. The above-mentioned example in the compact version is: OM 3 S a Ba2 K2. The short version of the classification uses only the first six parameters and excludes causative microbes and comorbidity. The above mentioned example in the short version is: OM 3 S a. The long version of the classification describes an osteomyelitis in every detail. The complexity of the patient's disease is clearly reproducible and can be used for scientific comparisons. The for clinical use suggested compact and short versions of the classification include all important characteristics of an osteomyelitis, can be composed quickly and distinctly with the help of tables and provide conclusions for the individual treatment. The freely available grouper (www.osteomyelitis.exquit.net) creates all three versions of the classification in one step.

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