Septic arthritis + Compartment syndrome

Question 1

What is septic arthritis?

Answer 1

Septic arthritis describes an infection of a joint.

Question 2

Which organisms cause septic arthritis?

Answer 2

Up to 90% of cases are caused by staphylococci or streptococci

• Staphylococcus aureus - most common cause in all age group
• Staphylococcus epidermidis - prosthetic joints
• Streptococcus pyogenes -children under 5 years old
• Neisseria gonorrhoeae - young, sexually active adults
• Pseudomonas aeruginosa - immunosupressed, elderly and IV drug abuse
• Escherichia coli - immunosupressed, elderly, and IV drug abuse

Question 3

Risk factors for septic arthritis

Answer 3

• Underlying joint disease: 10 fold increased risk; conditions such as rheumatoid arthritis, osteoarthritis and gout
• Intravenous drug use: transfer of pathogenic organisms into the blood stream
• Immunocompromised: elderly, diabetes, HIV
• Prosthetic joint

Question 4

Which joints are affected in septic arthritis?

Answer 4

The knee is the most commonly affected joint in adults. Other joints less commonly affected include the hip, shoulder, wrist and elbow joints.

Question 5

Clinical features of septic arthritis

Answer 5

Symptoms

• Difficulty weight bearing
• Fever

Signs

• Hot, tender, erythematous, swollen joint
• Very limited range of movement

Question 6

Primary investigations for septic arthritis

Answer 6

• Joint aspiration (arthrocentesis): definitive investigation ideally prior to commencing antibiotics; synovial fluid should be sent to the lab for microscopy and culture
• Blood cultures: should be performed on all patients before commencing antibiotics
• FBC: leukocytosis
• CRP and ESR: elevated due to inflammation and used for monitoring response to treatment
• Plain X-ray: not diagnostic but recommended as a baseline investigation to assess underlying joint disease. Early septic arthritis may show eveidence of a joint effusion

Question 7

What would you expect to see in the synovial fluid from a septic arthritis?

Answer 7

Colour: yellow and cloudy

WBC/ml: >50,000

Polymorphonuclear (PMN) cells: >50%

Culture: >50% positive

Crystals: None

Question 8

Which criteria is used to diagnose septic arthritis in children?

Answer 8

Kocher criteria

A score of 2 suggests a 40% probability and a score of 3 suggests a 93% probability.

• Non-weight bearing
• Temp >38.5
• ESR >40mm/hr
• WCC >12 x 10⁹/L

Question 9

Management of septic arthritis

Which antibiotics are used for:

Emperical therapy

Penicillin allergy

Suspected or confirmed MRSA

Gonococccal arthritis or gram-negative infection

Answer 9

Antibiotics as well as joint aspiration to dryness as often as required.

2 weeks of intravenous antibiotics followed by 4 weeks of oral.

Emperical therapy: flucloxacillin is first line

Penicilin allergy: clindamycin

Suspected or confirmed MRSA: vancomycin

Gonococcal arthritis or gram negative infection: cefotaxime or ceftriaxome

Question 10

Complications of septic arthritis

Answer 10

• Osteomyelitis (the spread of the infection from the joint to the surrounding bone)
• Permanent joint destruction
• Sepsis

Question 11

Differential diagnoses of someone presenting with a single, painful, swollen joint:

Answer 11

• Septic arthritis
• Flare of osteoarthritis
• Haemarthrosis
• Crystal arthropathies (gout and pseudogout)
• Rheumatoid arthritis (and other inflammatory arthropathies)
• Reactive arthritis
• Lyme disease (infection with Borrelia burgdoferi)

Question 12

Define compartment syndrome

Answer 12

Compartment syndrome is a critical pressure increase within a confined compartmental space.

Question 13

Which sites are affected by compartment syndrome?

Answer 13

Any fascial compartment an be affected. The most common sites are in the leg, thigh, forearm, foot, hand and buttock.

Question 14

Causes of compartment syndrome

Answer 14

• High energy trauma
• Crush injures
• Fractures that cause vascular injury
• Iatrogenic vascular injury
• Tight casts or splints
• Deep vein thrombosis
• Post-reperfussion swelling

Question 15

Pathophysiology of compartment syndrome

Answer 15

• Fascial compartments are closed and cannot be distended; any fluid deposited within them will cause an increase in the intra-compartmental pressure

As pressure increases:

• Veins will be compressed, increasing hydrostatic pressure within them, causing fluid to move down its gradient out of the veins, increasing intra-compartmental pressure further
• Traversing nerves are compressed; creating a sensory +/- motor deficit in the distal distribution
• Intracompartmental pressure reaches the diastolic blood pressure, arterial inflow will be compromised, leading to ischaemia

Question 16

Clinical features of compartment syndrome

Answer 16

Symptoms tend to present within hours, although it can develop up to 48 hours post insult.

• Severe pain, disproportionate to the injury, which is not readily improved with initial measures
• Pain is made worse by passively stretching the muscles within the affected compartment
• Parasthesia distally is a common feature
• The affected compartment may feel tense compared to the contralateral side , but generally will not be swollen
• If the disease progressed and the compartment syndrome is missed, the features of acute arterial insufficiency will subsequently develop:
  
  • Pain (disproportionate to the injury)
  • Pallor (or mottled which becomes non-blanching)
  • Perishingly cold
  • Paralysis
  • Pulselessness

Question 17

Investigations for compartment syndrome

Answer 17

Diagnosis is essentially clinical

Where there is clinical uncertainty: an intra-compartmental pressure monitor may be used

A creatinine kinase (CK) level may aid diagnosis , if elevated or trending upwards

Question 18

Definitive treatment of compartment syndrome

Answer 18

Emergency open fasciotomy

Question 19

Initial management of compartment syndrome, prior to definitive intervention, includes:

Answer 19

• Keep the limb at a neutral level with the patient (do not elevate or lower)
• Improve oxygen delivery with high flow oxygen
• Augment blood pressure with bolus of intravenous crystalloid fluids
• Remove all dressings/splints/casts down to the skin
• Treat symptomatically with opioid analgesia

Question 20

Complications of compartment syndrome

Answer 20

Monitor renal function closely due to potential effetes of rhabdomyolysis or reperfussion injury