Acute osteomyelitis - Bone and joint infections

Bone and joint infections

Acute osteomyelitis

Definition

Acute bacterial infection of bone.

Age

Normally seen in children and adults over 50 years.

Aetiology

Most infections result from haematogenous spread of organisms. Local spread from a soft tissue infection may also occur. Acute osteomyelitis is normally seen in children but may also occur in malnourished or immunocompromised adults.

·        Haematogenous spread: Staphylococcus aureus and Streptococci are the common organisms. Previously Haemophilus influenzae was seen in young children, but it is now rare due to vaccination. Patients with sickle cell anaemia are prone to osteomyelitis due to

·        Salmonella.

·        Direct spread from local infection may occur with

Streptococcus, Staphylococcus, anaerobes and gramnegative organisms.

Pathophysiology

In children the long bones are most often involved; in adults, vertebral, sternoclavicular and sacroiliac bones are more commonly involved than are long bones. In-fections from a distant focus spread via the blood stream and settle in the bone. In children the organisms usually settle in the metaphysis because the growth disc (physis) acts as a barrier to further spread. In infants the infection tends to spread to the epiphysis and in adults the infection may occur anywhere in the bone.

Acute inflammation occurs accompanied by a rise in pressure leading to pain and disruption of blood flow. Pus forms within the medulla of the bone and forces its way to the surface along the Volkmann’s canals forming a subperiosteal abscess. The infection then spreads locally and in infants may enter the joint. In children the physis acts as a physical barrier to intraarticular spread. Necrosis of the bone due to pressure and disrupted blood supply may cause pieces of bone to separate (sequestra).

Clinical features

Presentation ranges from an acute illness with pain, fever, swelling and acute tenderness over the affected bone, to an insidious onset of non-specific dull aching and vague systemic illness. A history of preceding infection may indicate the source and suggest the organism.

Complications

·        As the bone heals and new bone is formed, infected tissue and sequestrated bone fragments may be enclosed.

·        Sinuses form in the presence of continuing infection, resulting in a chronic osteomyelitis.

·        In children growth disturbance may result if the physis is damaged with resultant limb shortening or deformity.

·        Infection may spread to the joint causing a septic arthritis or to other bones causing metastatic osteomyelitis.

Investigations

The X-ray finding may take 2–3 weeks to develop. A raised periostium is an early sign that may be seen before any abnormality of the underlying bone. Later there is rarefaction (diminution in the density) of the metaphysis. With healing there is sclerosis and sequestrated bone fragments may be visible.

CT scanning (MRI in spine) is accurate at demonstrating cortical damage and periosteal reaction to infection.

There may be a leucocytosis and raised inflammatory markers (ESR, CRP). Blood cultures are positive in 50%.

Radioisotope bone scanning can show increased activity before X-ray changes are evident.

Management

Surgical drainage should be used if there is a subperiosteal abscess, if systemic upset is refractory to antibiotic treatment or if there is suspected adjacent join involvement.

Antibiotics: Initially treat on the basis of likely pathogen then change depending on sensitivity. Parenteral treatment is often required for a prolonged period (2–4 weeks) prior to a long course of oral antibiotics to ensure eradication. All antibiotic therapies should be rationalised once culture and sensitivity are known.

i.            Infants and young children may need treatment with a third-generation cephalosporin to cover for Haemophilus infection.

ii.            Older children and previously fit adults are treated with flucloxacillin and fucidic acid (Staphylococcus).

Adequate analgesia is essential and may be improved with splints to immobilise the limb (which also helps to avoid contractures). Physiotherapy is required early to reduce associated muscle disuse atrophy and to maintain joint mobility.