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Chapter: Medicine and surgery: Musculoskeletal system

Septic arthritis - Bone and joint infections

Inflamed painful joint caused by infection with a pyogenic organism. - Definition, Incidence, Aetiology, Pathophysiology, Clinical features, Complications, Investigations, Management, Prognosis.

Septic arthritis

 

Definition

 

Inflamed painful joint caused by infection with a pyogenic organism.

 

Aetiology

 

Joint infection arises most commonly from haematogenous spread. Other mechanisms include local trauma or an adjacent infective focus such as osteomyelitis. It can also occur as a complication of joint surgery, although this is minimised by the use of laminar flow theatres and sterile techniques. The commonest causative organism is Staph. aureus.

 

·        Toddlers and children: Staph. aureusStreptococci,

 

·        Haemophilus (rare since vaccination).

 

·        Adults: Staph. aureusStreptococciNeisseria gonorrhoea.

 

·        Immunosuppressed: Gram-negative bacteria, mycobacterium, fungi.

 

·        Patients with sickle cell anaemia are particularly prone to infections with Salmonella.

 

Pathophysiology

 

Bacteria are initially found in the synovial membrane but quickly spread to the synovial fluid. Cytokine-mediated inflammation and a rise in intra-articular pressure follow the spread of bacteria. The pressure may cause compression of the blood vessels leading in the hip to avascular necrosis of the femoral head especially in young children. Erosion of the articular cartilage results from the release of proteolytic enzymes from neutrophils within the inflammatory exudate. Prolonged exposure to these enzymes can result in chondrocyte and bone damage. Pus may find its way out of the joint causing an abscess, which may drain via a sinus.

 

Clinical features

 

The classical features of septic arthritis are a red, hot, painful monoarthritis associated with fever. Overall the knee is the most commonly affected joint, but hips are often the site in children. There may be evidence of the source of infection such as a urinary tract infection, skin or respiratory infection. On examination the joint is held immobilised in the position that maximises the intra-articular volume (e.g. a hip is usually held flexed, abducted and externally rotated). Movement of the joint is very painful and often prevented by pain and muscle spasm (pseudoparesis).

 

Complications

 

If treatment is delayed there is severe articular destruction, which may heal by fibrosis with permanent restriction of movement, deformity or bony union.

A tense joint effusion may result in dislocation.

 

In children extensive destruction of the epiphysis may occur causing growth disturbance and deformity.

 

Investigations

 

X-ray of the affected joint may show widening of joint space and soft tissue swelling but are of little diagnostic value.

 

Blood tests may reveal a leucocytosis, raised ESR and CRP. Blood cultures should be taken and may be positive in a third of cases.

 

Diagnosis is confirmed by aspiration of joint fluid for urgent microscopy, culture and sensitivities. The fluid often appears purulent at time of aspiration. Depending on the joint involved and available facilities, aspiration may be blind, ultrasound guided, CT guided or surgical.

 

Management

 

Patients require adequate analgesia.

 

Antibiotics should start immediately after synovial fluid and blood cultures have been taken. Initial therapy is dependent on the suspected organism. In previously healthy children and adults, penicillin (Streptococcus cover) and flucloxacillin (Staphylococcus cover) are used. A third-generation cephalosporin is used if gonococcus is suspected and in the immunocompromised gentamicin is added to cover for anaerobic organisms. Antibiotic therapy is reviewed in the light of culture and sensitivities.

 

Splintage and resting of the joint is essential. If the hip is infected it should be held abducted and 30 flexed. Drainage of pus and arthroscopic joint washout under anaesthesia can be performed.

 

Surgical drainage may be indicated if the infection does not resolve with appropriate antibiotics or if percutaneous drainage is not possible. Arthroscopic procedures allow visualisation of the interior of the joint, drainage of pus and debridement.

 

Surgery may also be required for the removal of foreign bodies or infected prosthetic material.

 

If there is no cartilage damage, gentle mobilisation should begin once inflammation has settled.

 

Prognosis

 

Outcome is related to immune status of the host, virulence of the organism and the speed at which adequate antibiotic therapy is started. In Staphylococcal infections involvement of multiple joints carries a significant mortality (>90% if more than three joints involved).

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Medicine and surgery: Musculoskeletal system : Septic arthritis - Bone and joint infections |

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