MSK - Septic Arthritis

Question 1

Definition

Answer 1

Septic arthritis refers to infection inside a joint.
This can occur at any age, but is most common in children under 4 years.
Infection in a joint = emergency, as the infection can quickly begin to destroy the joint and cause serious systemic illness.

Question 2

Signs and symptoms

Answer 2

Usually only affects a single joint = often a knee or hip. It presents with a rapid onset of:
- Hot, red, swollen and painful joint
- Refusing to weight bear
- Stiffness and reduced range of motion
- Systemic symptoms such as fever, lethargy and sepsis
Septic arthritis can be subtle in young children, so always consider it as a differential when a child is presenting with joint problems.

Question 3

Common bacteria

Answer 3

• Staphylococcus aureus (MC)
• Neisseria gonorrhoea (gonococcus) in sexually active teenagers
• Group A streptococcus (Streptococcus pyogenes)
• Haemophilus influenza
• Escherichia coli (E. coli)

Question 4

Differential Diagnosis

Answer 4

• Transient sinovitis
• Perthes disease
• Slipped upper femoral epiphysis
• Juvenile idiopathic arthritis

Question 5

Management

Answer 5

Suspected arthritis = admission to hospital + orthopaedic team involvement
- Joint aspiration prior to Abx admission
= gram staining
= crystal microscopy
= culture
= antibiotic sensitivities
= the joint fluid
= the joint fluid may be purulent (full of pus)
- Empirical IV Abx = should be given until microbial sensitivities are known
- Abx usually continued for 3-6 weeks in total when septic arthritis confirmed.
- Px may require surgical drainage and washout of the joint to clear the infection in severe cases

Question 6

Definition

Answer 6

Osteomyelitis is an infection in the bone and bone marrow.
This typically occurs in the metaphysis of the long bones.
The infection may be introduced directly into the bone, for example during an open fracture. Alternatively it may have travelled to the bone through the blood, after entering the body through another route, such as the skin or gums.

Question 7

Chronic osteomyelitis

Answer 7

Deep seated, slow growing infection with slowly developing symptoms. Acute osteomyelitis presents more quickly with an acutely unwell child.

Question 8

Aetiology

Answer 8

Staphylococcus aureus

Question 9

Aetiology

Answer 9

Osteomyelitis is more common in boys and children under 10 years.

Question 10

Risk factors

Answer 10

There is often a risk factor that predisposes the child to developing osteomyelitis:
- Open bone fracture
- Orthopaedic surgery
- Immunocompromised
- Sickle cell anaemia
- HIV
- Tuberculosis

Question 11

Presentation

Answer 11

Osteomyelitis can present acutely with an unwell child, or more chronically with subtle features:
- Refusing to use the limb or weight bear
- Pain
- Swelling
- Tenderness
They may be afebrile, or may have a low grade fever. Children with acute osteomyelitis may have a high fever, particularly if it has spread to the joint causing septic arthritis.

Question 12

Investigations

Answer 12

FIRST LINE: Xrays
- can be normal in osteomyelitis.

GOLD STANDRARD: MRI
- A bone scan is an alternative.

Blood tests
- Raised CRP and ESR and white blood cells in response to the infection.

Blood culture is important in establishing the causative organism. A bone marrow aspiration or bone biopsy with histology and culture may be necessary.

Question 13

Treatment

Answer 13

Treatment requires extensive and prolonged antibiotic therapy. They may require surgery for drainage and debridement of the infected bone.