Septic Arthritis Flashcards by Caitlin McMullen

What is septic arthritis?

Inflammation of the joint space caused by infection

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What is the most common causative organism of septic arthritis in adults?

Staphylococcus aureus
(especially in the hip)

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Which bacteria was the most common cause of septic arthritis in children before vaccination?

Haemophilus influenzae - now rare

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What is the second most common bacterial cause of septic arthritis?

Streptococci

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Which bacteria can cause septic arthritis in young adults but is now rare in Western Europe?

Neisseria gonorrhoeae

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In which patients is Escherichia coli a cause of septic arthritis?

(1) Elderly
(2) IV drug users
(3) Seriously ill patients

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What is the most common way bacteria reach the joint in septic arthritis?

Haematogenous spread (bacteria enter blood from another infected site)

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Why is septic arthritis an orthopaedic emergency?

It causes rapid, irreversible damage to hyaline articular cartilage

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What are the main symptoms of septic arthritis?

Joint pain, Fever, Impaired range of motion

= means the affected joint has reduced ability to move due to pain, swelling, and inflammation

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How does septic arthritis typically present?

Acute monoarthropathy – a hot, red, painful joint with pain on movemen

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What is the key rule for diagnosing a red, swollen joint?

Any hot, red, tender joint is septic arthritis until proven otherwise – must aspirate

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What is the most commonly affected joint in septic arthritis?

Knee

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What are the key signs of septic arthritis?

(1) Impaired ROM +/- swelling
(2) Systemic fever
(3) Severe hip pain on passive movement

(4) Unable to weight bear with hip/groin pain

(5) Short duration of symptoms

(6) Hip positioned flexed & externally rotated

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What is the first-line investigation for septic arthritis?

Aspiration of joint fluid

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What percentage of blood cultures are positive in septic arthritis?

30-60%

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How do you differentiate transient synovitis from septic arthritis?

Aspiration

= normal in transient synovitis, abnormal in septic arthritis

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What is the first step in managing suspected septic arthritis?

Aspirate the joint BEFORE starting antibiotics

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When should empirical antibiotics be started?

If the patient is septic – otherwise, wait for culture results

What empirical antibiotic is used first-line for septic arthritis?

Flucloxacillin

What antibiotic is added if the patient is under 5 years old?

Ceftriaxone (for H. influenzae cover)

What surgical procedure may be required for septic arthritis?

Joint washout under orthopaedic review

How long is antibiotic therapy for septic arthritis?

1-2 weeks IV
(adjusted to culture results) → followed by oral antibiotics for a total of 6 weeks

How is response to treatment monitored?

Clinical improvement + serial CRP levels

What is septic arthritis of the hip?

Intra-articular infection of the hip joint

What is the most common causative organism in septic arthritis of the hip?

Staphylococcus aureus

Why are neonates at higher risk of septic arthritis spreading from osteomyelitis?

They have transphyseal vessels that allow bacteria to cross from the metaphysis into the joint

Which joints have an intra-articular metaphysis, making them prone to septic arthritis?

Hip Shoulder Elbow Ankle

What criteria help diagnose septic arthritis of the hip?

Kocher’s criteria.

What is the first-line surgical treatment for septic arthritis of the hip?

Open surgical washout

When should surgical washout be repeated in those wit septic arthritis of the hip?

If the patient is not improving

What approach is usually used for open washout in septic arthritis of the hip?

Anterior approach

When should antibiotics be started In septic arthritis of the hip?

After taking samples during washout

How long is the antibiotic course for septic arthritis of the hip?

6 weeks (6/52)

How are IV antibiotics delivered long-term in septic arthritis of the hip?

PICC line (Peripherally Inserted Central Catheter)

What are important differential diagnoses in a patient presenting with a painful joint?

1. Trauma 2. Inflammatory arthritis (rheumatoid, gout, pseudogout, vasculitis) 3. Osteoarthritis flare 4. Septic arthritis

Which form of imaging should be performed in septic arthritis initially?

Plain X-ray of the affected joint

What are the typical blood results in Septic Arthritis?

Raised white blood cell count and CRP

What are the classical features of joint fluid aspirate in septic arthritis?

1. Turbid yellow appearance on inspection 2. Extremely high WCC (>50,000/mm3) with >90% neutrophils 3. Bacteria visible on gram stain

What is the common pathogen associated with septic arthritis in intravenous drug users?

Pseudomonas aeruginosa

A 54-year-old man presents with an acute onset hot, red hip joint. The joint is tender and he is unable to move it due to severe pain. He is unable to tolerate passive movement of his hip joint. He is febrile and sweaty. Bloods reveal a raised white cell count and C-Reactive Protein (CRP). A joint aspiration of the hip is done, which shows pus in the joint. The synovial fluid is sent for urgent Gram stain and culture, which reveals Gram-negative intracellular diplococci. He denies any diarrhoea, penetrating wound injury or a cough. What is the next best step in the management of this patient?

Intravenous antibiotics for at least 2 weeks, then oral for 4-6 weeks

List in order the treatment/ mangement plan of those with septic arthritis

1. Joint aspirate 2. Antibiotics 3. washout

A 55-year-old man presents to the emergency department with a painful right knee. He has undergone knee replacement surgery on the same knee 2 weeks ago. He mentions having a fever that began yesterday evening and has a medical history of diabetes. On examination he is pyrexial at 38. His knee is hot to touch, visibly red and swollen. Flexion of the knee is significantly reduced. Why shouldn't you aspirate the joint for synovial fluid gram stain and culture?

He has a prosthetic joint = therefore It should be carried out by an orthopaedic surgeon in an operating theatre

A 22-year-old man presents to the emergency department with a painful left ankle. He reports that the pain started this morning and has progressively worsened such that he can no longer weight-bear. His past medical history is relevant only for a previous sexually transmitted infection found incidentally on screening and treated with ceftriaxone and azithromycin five days ago. He has no known drug allergies and takes no other regular medications. He reports no history of trauma. On examination, he appears flushed and systemically unwell. The left ankle appears swollen and erythematous; the range of movement is limited, and passive movement causes him severe pain. What is the most likely causative organism of this patient’s presentation?

Neisseria gonorrhoeae = Young patient, STI, septic arthritis symptoms

In young adults with septic arthritis, who are sexually active what is the most common organism found?

Neisseria gonorrhoeae - sexually