Updated: 7/24/2021

Septic Arthritis - Adult

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  • summary
    • Septic Arthritis is the inflammation of the joints secondary to an infectious etiology, most commonly affecting the knee, hip, and shoulder. 
    • Diagnosis is made with an aspiration of joint fluid with a WBC count > 50,000 being considered diagnostic for septic arthritis. Lower counts may still indicate infection in the presence of positive gram stains or cultures results. 
    • Treatment is usually urgent surgical irrigation and debridement followed by culture directed IV antibiotics.
  • Epidemiology
    • Anatomic location
      • most commonly affected joints in descending order
        • knee (~ 50% of cases) >
        • hip >
        • shoulder >
        • elbow >
        • ankle >
        • sternoclavicular joint
          • found in IV drug users
          • pseudomonas aeruginosa was most common pathogen in 1980's
          • staphylococcus aureus is now the most common pathogen in all patients, including IV drug users
          • advanced imaging (CT/MRI) should be obtained preoperatively to rule out retrosternal abscess or chest wall phlegmon 
    • Risk factors
      • age > 80 years
      • medical conditions
        • diabetes
        • rheumatoid arthritis
        • cirrhosis
        • HIV
      • history of crystal arthropathy
      • endocarditis or recent bacteremia
      • IV drug user
      • recent joint surgery
  • Etiology
    • Pathophysiology
      • pathoanatomy
        • 3 etiologies of bacterial seeding of joint
          • bacteremia
          • direct inoculation
            • from trauma or surgery
          • contiguous spread
            • from adjacent osteomyelitis
      • cellular biology
        • septic arthritis causes irreversible cartilage destruction in an involved joint
          • cartilage injury can occur by 8 hours
        • caused by release of proteolytic enzymes from inflammatory cells (PMNs)
      • microbiology
        • most common pathogens is staphylococcus aureus (accounts for >50% of cases)
        • see Classification below
    • Associated conditions
      • prosthetic implant infection
  • Classification
    • By organism
      • staphylococcus species
        • staphylococcus aureus
          • most common and accounts for >50% of cases
        • MRSA
        • staphylococcus epidermis
      • neisseria gonorrhea
        • account for ~20% of cases
        • most common organism in otherwise healthy sexually active adolescents and young adults
        • manifests as a bacteremic infection
          • arthritis-dermatitis syndrome in ~60% of cases
          • localized septic arthritis in ~40% cases
      • gram-negative bacilli
        • account for 10-20% of cases
        • pathogens include
          • E coli, proteus
          • klebsiella
          • enterobacter
        • risk factors
          • neonates
          • IV drug users
          • elderly
          • immunocompromised patients with diabetes
      • streptococcus
        • streptococcus pyogenes (Group A)
          • most common
        • Group B streptococcus (e.g., agalactiae)
          • predilection for infants, elderly and diabetic patients
      • propionibacterium acnes
        • associated with shoulder surgery
      • salmonella or streptococcus pneumoniae
        • seen in patients with sickle cell disease
      • bartonella henselae
        • seen in patients with HIV
      • pseudomonas aeruginosa
        • seen in patients with history of IV drug abuse
      • pasteurella multocida
        • seen in patients after dog or cat bite
      • eikenella corrodens
        • seen in patients after human bite
      • fungal/candida
        • found in immunocompromised host
  • Presentation
    • Symptoms
      • pain in affected joint
      • fevers (only present in 60% of cases)
      • may appear toxic
    • Physical exam
      • inspection
        • erythema
        • effusion
        • extremity tends to be in position of maximum joint volume
          • hip would be in FABER position (flexed, abducted, externally rotated)
      • palpation
        • warmth
        • tender
      • motion
        • inability to bear weight
        • inability to tolerate PROM
  • Imaging
    • Radiographs
      • recommended views
        • AP and lateral of the joint in question
      • findings
        • may show joint space widening or effusion
        • periarticular osteopenia
    • Ultrasound
      • indications
        • may help in confirming joint effusion in large joint such as hip
          • can be used in guiding aspirations
    • MRI
      • indications
        • detects joint effusion, and may detect adjacent bone involvement such as osteomyelitis
  • Studies
    • Serum labs
      • WBC >10K with left shift
      • ESR >30
        • ESR is often elevated but may be normal early in process
          • rises within 2 days of infection and can rise 3-5 days after initiation of appropriate antibiotics, and returns to normal 3-4 weeks
      • CRP >5
        • most helpful
        • best way to judge efficacy of treatment, as CRP rises within few hours of infection, and may normalize within 1 week of treatment
    • Joint fluid aspirate
      • gold standard for treatment and allows directed antibiotic treatment
      • should be analyzed for
        • cell count with differential
        • gram stain
        • culture
        • glucose level
        • crystal analysis
          • septic arthritis occurs concurrently with gout or pseudogout in < 5% of cases
      • characteristic findings
        • joint fluid appears cloudy or purulent
        • cell count with WBC > 50,000 is considered diagnostic for septic arthritis, however lower counts may still indicate infection
        • gram stains only identifies infective organism 1/3 of time
        • glucose less than 60% of serum level
        • negative "string" sign
          • septic synovial fluid has low viscosity compared to normal synovial fluid (high viscosity)
    • Saline load test
      • utilized to determine if wound near a joint communicates with the joint
      • for the knee
        • 155 mL of saline is needed to reach 95% sensitivity
        • 175 mL of saline is needed to reach 99% sensitivity
  • Differential
    • Crystal arthropathy
      • gout
      • pseudogout
    • Cellulitis
    • Bursitis
      • prepatellar bursitis
  • Treatment
    • Operative
      • IV abx, operative irrigation and drainage of the joint
        • indications
          • considered an orthopaedic surgical emergency
        • IV antibiotic therapy
          • initiate empiric therapy prior to definitive cultures based on patient age and or risk factors
            • young, healthy adults
              • staphylococcus aureus and neisseria gonorrhea
            • immunocompromised patients
              • staphylococcus aureus and pseudomonas aeruginosa
          • transition to organism-specific antibiotic therapy based once obtain culture sensitivities
        • outcomes
          • treatment can be monitored by following serum WBC, ESR, and CRP levels during treatment
  • Technique
    • Operative irrigation and drainage of the joint
      • approach
        • can be performed open or arthroscopically (depending on joint)
      • irrigation
        • remove all purulent fluid and irrigate joint
      • debridement
        • synovectomy can be performed as needed
      • cultures
        • obtain joint fluid and tissue for culture
  • Complications
    • Arthritis
    • Fibrous ankylosis
    • Osteomyelitis
  • Prognosis
    • Delayed diagnosis can lead to profound, extensive cartilage damage within hours
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Questions (12)
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(SBQ18TR.9) Which of the following describes the most common organism cultured from septic olecranon bursitis?

QID: 211199
1

Gram positive cocci in chains

15%

(269/1783)

2

Gram positive bacilli in branches

2%

(39/1783)

3

Gram positive cocci in pairs and clusters

80%

(1430/1783)

4

Gram negative diplococci

1%

(17/1783)

5

Gram negative bacilli with thin rods

1%

(10/1783)

L 2 A

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(OBQ17.72) A 55-year-old man presents with pain in his great toe that began 2 days ago. On physical exam, his first metatarsophalangeal (MTP) joint is red, warm, and tender to palpation (Figure A). His skin is intact with no evidence of ulceration. He reports pain with range of motion. He denies recent fevers and his admission temperature is 37.9°C. Labs are drawn and significant for a WBC of 15K (reference range [rr], 4500-11000 µL), ESR of 90 (rr, 0-20 mm/h), and CRP of 6.5 (rr, 0.08-3.1 mg/L). A radiograph of his foot is shown in Figure B. Which of the following is the next best step?

QID: 210159
FIGURES:
1

Joint aspiration

73%

(1153/1588)

2

Joint irrigation and debridement

3%

(48/1588)

3

Outpatient oral antibiotics for 14 days

1%

(15/1588)

4

Oral indomethacin for 3 to 5 days

19%

(299/1588)

5

MRI of the foot

3%

(52/1588)

L 2 A

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(OBQ10.114) When performing a saline load test to evaluate for a traumatic arthrotomy of the knee, a minimum of how much saline should be utilized to obtain a 95% diagnostic accuracy?

QID: 3208
1

30 mL

1%

(44/3059)

2

50 mL

5%

(162/3059)

3

75 mL

6%

(174/3059)

4

100 mL

10%

(298/3059)

5

155 mL

77%

(2368/3059)

L 3 C

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(OBQ06.249) Which of the following is true regarding the use of the saline injection load test to diagnose traumatic knee arthrotomies?

QID: 260
1

Addition of methylene blue to the saline load test increases the sensitivity of the test

18%

(265/1498)

2

Injection of 110ml of saline will diagnose 95% of knee arthrotomies

12%

(185/1498)

3

Injection of 175ml of saline will diagnose 99% of knee arthrotomies

60%

(904/1498)

4

A superomedial injection location requires significantly less fluid than a inferoeromedial injection location

1%

(16/1498)

5

A history and physical exam by an orthopaedic surgeon has equivalent sensitivity to saline load test at detecting a traumatic arthrotomy

8%

(120/1498)

L 3 C

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(OBQ06.63) A 20-year-old man presents with erythema, swelling, and pain at the left sternoclavicular joint shown in Figure A. His temperature is 38.9 degress Celsius, serum WBC is 14,000, and his C-reactive protein is elevated. He reports that he uses IV heroin. A coronal 3D CT scan of the left clavicle is shown in Figure B. Joint aspiration shows many grams stain positive organisms. Which of the following organisms is the most likely pathogen?

QID: 174
FIGURES:
1

Propionibacterium acnes

2%

(31/1505)

2

Staphylococcus aureus

91%

(1365/1505)

3

Group B streptococcus

5%

(70/1505)

4

Neisseria gonorrhea

2%

(24/1505)

5

Enterococcus coli

1%

(8/1505)

L 2 C

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(OBQ04.24) A 45-year-old IV drug abuser has sternoclavicular (SC) joint pain for the past 2 weeks. He is afebrile and physical exam findings include point tenderness and swelling. He most likely has septic arthritis of the sternoclavicular joint. If so, what is the most likely infecting organism?

QID: 135
1

Streptococcus pneumoniae

1%

(6/591)

2

Staphylococcus aureus

79%

(467/591)

3

Pseudomonas aeruginosa

11%

(65/591)

4

Staphylococcus epidermis

7%

(41/591)

5

Propionibacterium acnes

2%

(9/591)

L 2 D

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