3 Other investigation techniques
OTHER INVESTIGATIONS
More often than not the diagnosis can be established from the clinical assessment and imaging studies without the aid of other special investigations. In any case the possibilities should be narrowed down to as few as possible before such investigations are ordered. If doubt then exists, appropriate tests are ordered to support or weaken each possible diagnosis.
MICROBIOLOGICAL TESTS
The diagnosis of musculoskeletal infection is often challenging for a number of reasons.
1 Bacteria such as the normal skin flora are grown as contaminants from specimens such as sputum. However, in orthopaedics these same organisms can be pathogens and the cause of musculoskeletal infections. To distinguish between a growth of, for example, Staphylococcus epidermidis, which is a contaminant as opposed to one which is a pathogen, it is vital to obtain multiple samples. At operation of a patient with suspected musculoskeletal infection, at least five samples should be obtained under sterile conditions. If two or more of these multiple specimens grow the same bacteria, it is likely that this is a true pathogen rather than a contaminant.
2 The swabs from sinus tracts are often misleading and do not accurately reflect the true deep organisms that are causing the infection. However, aspiration of fluid from the depth of a sinus is worthwhile and often will give a more accurate picture of the true range of causative organisms.
