Other investigation techniques

Published on 11/03/2015 by admin

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Last modified 11/03/2015

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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.

Tests commonly employed in orthopaedic diagnosis include haematological studies; biochemical tests upon urine, faeces, plasma, and cerebrospinal fluid; serological and bacteriological tests; electrical tests; arthroscopy; and histological examination of specimens excised at biopsy or at definitive operation.

BLOOD TESTS

Haematology

Full blood count. Assessment of the haemoglobin is of great value after trauma and post-operatively, as it gives an indication as to how much blood has been lost. The white cell count is usually, but not always, raised when an infection is present. The ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein) are more sensitive tests for revealing systemic inflammation. The CRP is particularly useful, as it rises rapidly when there is an infective process. The ESR and CRP are also helpful in distinguishing septic and aseptic loosening of total joint replacements. If these tests are normal on two occasions, it is unlikely that the loosening is as a result of an infection.

Biochemistry

If there are concerns about organ dysfunction, liver function tests and renal function tests are of value and part of the pre-operative work-up. Similarly, routine electrolytes can also be of value, particularly if the patient is on drugs such as diuretics.

The biochemical tests that are of particular value for assessing bone function are the plasma levels of calcium, phosphate and alkaline phosphatase. Derangements in the calcium and phosphate balance can confirm the diagnosis of rickets and osteomalacia.

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.
3 In 10–20% of cases with established musculoskeletal infection, despite optimum culture techniques, it may not be possible to grow an organism. Thus, it is vital to obtain material for histological analysis as well as for microbiological culture where infection is suspected (see below).

ELECTRICAL TESTS (ELECTRODIAGNOSIS)

The two most common electrodiagnostic techniques used in orthopaedic practice are nerve conduction studies and electromyography.

Nerve conduction studies

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