QuestionSBA
QuestionChoice
This would appear as Gram-positive elongated diplococci
32215
c
Streptococcus pneumoniae
QuestionChoice
This would appear as Gram-negative intracellular diplococci. It is associated with young sexually active adults
32214
b
Neisseria gonorrhoeae
QuestionChoice
This would appear as Gram-negative intracellular diplococci. It is associated with young sexually active adults
32216
d
Escherichia coli
QuestionChoice
This would appear as Gram-negative bacilli. It is an uncommon cause of septic arthritis
32217
e
Pseudomonas aeruginosa
QuestionChoice
This would appear as Gram-positive diplococci in clusters. This is seen as purple staining cocci that appear similar to "bunches of grapes". S. aureus is a common cause of septic arthritis in otherwise healthy adults and may be associated with prosthetic joint infections
32213
a
Staphylococcus aureus
Concept
Chapter
# Summary

Septic arthritis is an infection of the joint characterized by acute inflammation and swelling. It is caused by a bacterial or viral pathogen that infects the synovial fluid. The most commonly implicated organism is Staphylococcus aureus. Noteworthy clinical signs include a tender, swollen joint with reduced mobility, often accompanied by systemic illness. Key investigations include joint aspiration for Microscopy Culture and Sensitivity, along with blood tests showing increased white blood cell count and elevated ESR/CRP. Management typically involves IV antibiotics, joint washout under general anaesthesia, and physiotherapy once the acute infection has resolved.

# Definition

Septic arthritis is an infection of the joint, specifically the synovial fluid. It is typically caused by a bacterial or viral pathogen and necessitates prompt medical intervention due to the high risk of joint damage and other severe complications.

# Epidemiology

Septic arthritis has an annual incidence of 4-10 cases per 100,000 patients in Western Europe. It can affect individuals of any age, though certain populations are at a higher risk due to underlying conditions.

# Aetiology

The most prevalent organism implicated in septic arthritis is Staphylococcus aureus. Other responsible organisms include:

-   Gonococcus: primarily in sexually active individuals
-   Streptococcus spp.
-   Gram-negative bacilli

Risk factors contributing to septic arthritis include:

-   Pre-existing joint diseases such as rheumatoid arthritis
-   Chronic kidney disease
-   Immunosuppressive states
-   Presence of prosthetic joints

# Signs and Symptoms

The clinical presentation of septic arthritis usually involves:

-   Acute onset of tender, swollen joint
-   Reduced range of joint movement
-   Systemic symptoms such as fever, malaise, or chills

# Differential Diagnosis

Differential diagnoses for septic arthritis include:

-   Gout and pseudogout: characterized by intense joint pain, redness, and swelling, often in the big toe or knee.
-   Osteoarthritis: presents with joint pain, stiffness, and sometimes swelling, generally improving with movement.
-   Rheumatoid arthritis: marked by joint pain, swelling, and stiffness, often symmetrical and worse after rest.
-   Lyme disease: may show erythema migrans rash, flu-like symptoms, and possibly migratory joint pains.

# Investigations

Diagnostic investigations for septic arthritis include:

-   Joint aspiration for Microscopy, Culture, and Sensitivity: The aspirate usually appears turbid and yellow, resembling pus.
-   Blood tests: elevated white cell count, high ESR/CRP
-   Blood cultures: to identify causative organisms
-   Imaging: X-ray of the joint may be performed to evaluate for osteomyelitis or other complications.

# Management

The treatment of septic arthritis involves:

-   IV antibiotics guided by local antibiograms and susceptibilities
-   Consideration of joint washout under general anaesthesia to remove infected material
-   Physiotherapy following the resolution of acute infection to restore joint function

Complications of septic arthritis can include:

-   Osteomyelitis: infection of the bone
-   Chronic arthritis: persistent joint inflammation
-   Ankylosis: joint fusion resulting in immobility

# References

[Click here for the BNF Treatment Summary for Musculoskeletal infections](https://bnf.nice.org.uk/treatment-summary/musculoskeletal-system-infections-antibacterial-therapy.html)

[Click here for the BMJ Best Practice Summary of Septic Arthritis](https://bestpractice.bmj.com/topics/en-us/486)
438
2658
Septic Arthritis
Topic
37
Orthopaedics
Staphylococcus aureus
6443
Staphylococcus aureus is the most common causative organism of septic arthritis.
Picture
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+xcCBYAfj4anVqiUlcVBlPydb9tw
Topic
54
Rheumatology
A 40 year old gentleman is admitted to the acute medical unit with a 1 day history of sudden onset right ankle pain and swelling. He has no other past medical history.



On examination, his right ankle is erythematous, warm and tender on palpation. There is limited active and passive range of movement in the ankle joint due to pain.



Observations:



  - Temperature 38.5°C
  - pulse 90
  - BP 110/70
  - respiratory rate 18
  - SpO<sub>2</sub> 100% on room air



Initial blood tests are as follows:



||||
|--------------|:-------:|---------------|
|Haemoglobin|142  g/L|(M) 130 - 170, (F) 115 - 155|
|White Cell Count|16.1x10<sup>9</sup>/L|3.0 - 10.0|
|Platelets|210x10<sup>9</sup>/L|150 - 400|
|Neutrophils|13x10<sup>9</sup>/L|2.0 - 7.5|



Joint aspiration is done which shows a cloudy yellow fluid with a predominance of neutrophils. The following is seen on Gram stain:



  [lightgallery]



Which is the most likely causative organism?
a