| Discussion: |
Osteomyelitis is a progressive infection of the bone marrow and cortex resulting in inflammatory destruction of the bone, bone necrosis and ultimately the formation of new bone, resulting in bone remodelling and often deformity. Before antibiotics, mortality and amputation rates were high. Antibiotic therapy has virtually eliminated mortality but osteomyelitis is still a serious infection with potentially severe consequences. Certain patients are at particular risk from osteomyelitis.
High-risk patients include:
· The immunocompromised
· Drug addicts
· Patients with a catheter related bloodstream infection. Haematogenous spread can result in deep-seated infection with virulent organisms such as Staphylococcus aureus (including MRSA).
Diagnosis of osteomyelitis:
Clinical manifestations vary depending on the type of osteomyelitis and the location of the infection. There may be a recent history of infection (eg. respiratory tract, urinary tract, skin/soft tissue) or of blunt trauma to the affected area. The presentation can range from insidious onset with localised signs and symptoms to acute systemic toxicity. Acute haematogenous osteomyelitis is primarily a disease of children. Signs and symptoms can include:
· Abrupt onset of high fever and systemic toxicity.
· Local signs of infection including inflammation of the affected part.
· Sympathetic effusion in neighbouring joints.
· Patients commonly present with sinus formation and drainage of pus, but there may be just local pain and swelling in an otherwise asymptomatic patient.
· Relapse or persistence of acute osteomyelitis after treatment is classed as chronic.
Imaging in osteomyelitis:
· The changes in radiographs are not seen for up to two weeks after the disease process starts and can be difficult to interpret. Early radiographs show haziness and loss of density of the affected bone, and may also show soft tissue swelling, periosteal thickening and/or elevation and focal osteopenia. The lytic changes which are diagnostic for osteomyelitis tend to occur later.
· Radionucleotide scans, CT and MRI may be required when the diagnosis is equivocal and can also be used to determine the extent of the infection. Radionucleotide scans may be positive in as little as two days after the onset of infection, but are not highly specific. Impaired blood supply may reduce the effectiveness of technetium Tc 99 polyphosphate scans and gallium scans do not distinguish well between bone and soft tissue inflammation. MRI has very high sensitivity and specificity for osteomyelitis (88% and 93%, respectively) compared with radioisotope scans (61% and 33%, respectively).
Imaging in chronic osteomyelitis:
· There is subperiosteal reaction and later sequestrum and involucrum. Cancellous bone shows less change on x-ray than vascular bone.
Cierny-Mader classification of osteomyelitis:
The Cierny-Mader staging system is determined by the status of the disease process regardless of its aetiology, regionality or chronicity.
Stage 1: Medullary osteomyelitis (Infection confined to the intramedullary surfaces of the bone)
Stage 2: Superficial osteomyelitis (A true, contiguous-focus infection of bone. Occurs when an exposed infected, necrotic surface of bone lies at the base of a soft tissue wound)
Stage 3: Localised osteomyelitis (A full thickness cortical sequestration which can be removed surgically without compromising the stability of the bone)
Stage 4: Diffuse osteomyelitis (A comprehensive process that results in a loss of stability of the bone either before or after surgical debridement).