Acute osteitis and septic arthritis.
The majority develop from haematogenous spread of circulating organisms to the bone or joint, but a minority arise from direct contamination by penetrating wounds or surgery. Most haematogenous bone infections develop in bone with a good blood supply, usually the metaphyses of long bones in children (commonly the hip and knee), or the vertebrae in adults. The vascularity of joints allows septic arthritis to develop at any age.
Not only the virulence and circulating load of the infecting bacteria are important, but also the host factors that reduce the immune response to infection. In South Africa, the high incidence of HIV/AIDS has resulted in atypical infections, which must be considered in the diagnosis of any musculoskeletal pathology in adults. Diabetes mellitus, malnutrition and steroid medication are other important factors.
Acute infections are most often caused by Staphylococcus aureus, less commonly group B streptococci. Osteitis in infants is often caused by Escherichia coli or other Gram-negative bacteria. Haemophilus influenzae infects children up to 5 years of age who are not immunised. Gonococcal arthritis may affect multiple joints and should be considered in adults.
Acute osteitis and septic arthritis occur in or close to major joints, and may be difficult to distinguish from each other or from pyomyositis. Cellulitis is rare in children. The limb is swollen, inflamed and very painful. Movement and use of the limb are resisted. Septic arthritis typically causes an effusion in the knee and more severe loss of movement of the affected joint than osteitis. Osteitis may lead to secondary arthritis in the hip and knee. Patients have a fever and are ill. Infection is confirmed by a raised neutrophil count, and by determining the ESR and C-reactive protein. Radiographs are of no use for diagnosing osteitis in the first week, but will exclude a fracture in patients with a confusing history of minor trauma. Ultrasound is useful to confirm the presence of fluid in an inaccessible joint such as the hip.
All patients should be referred to an orthopaedic surgeon, as the majority will require emergency surgical drainage.
If referral is impossible the diagnosis is confirmed by aspiration of the joint or bone under anaesthesia, and pus is sent for microbiological examination before antibiotics are started. Blood cultures may also be taken.
Neonatal osteitis may be undramatic and present with pseudoparalysis or failure to use a limb.
Intravenous cloxacillin is the initial antibiotic of choice. It has to be started immediately after specimens are taken for microbiology, and changed later according to bacterial culture and sensitivity. The joint or subperiosteal abscess should be drained and washed out under general anaesthesia. In the case of osteitis, one or two drill holes should be made in the metaphysis to drain the medullary cavity. Wounds should be closed over suction drains, and the limb immobilised in a cast or by traction.
Septic arthritis of the hip should always be drained on the grounds of a clinical diagnosis alone as aspiration for confirmation of the diagnosis is unreliable.
It is preferable to perform drainage unnecessarily than to risk the possibility of even a few hours of continuing damage to the bone or joint.
Intravenous antibiotics are continued until the pyrexia subsides, after which they should be administered orally for a total of 6 weeks, or until infective markers have normalised. If clinical infection persists, re-exploration is required to drain recurrent collections of pus. Joints should be mobilised within the patient's pain tolerance after about a week, and weight bearing restricted for 4-6 weeks by using crutches.
Very early or subacute cases of osteitis may require an MRI scan to confirm the diagnosis. If only intraosseous oedema, but no pus, is demonstrated, such patients may be treated by intravenous antibiotics initially and, if they respond well, surgery may be avoided.
Long-term problems are joint stiffness, chronic osteitis with persistent drainage from sinuses, fracture because of weakened bone, and limb shortening. Long-term follow-up is necessary to manage these complications.
J A SHIPLEY, MB ChB, MMed(Orth) Professor, Department of Orthopaedics, University of the Free State, Bloemfontein
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|Title Annotation:||More about ... Orthopaedics|
|Publication:||CME: Your SA Journal of CPD|
|Date:||Aug 1, 2008|
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