Septic Arthritis

Epidemiology

0.25% of the hospitalizations among children.

Most of the pediatric septic arthritis patients (50%) are < 2y.

More common in boys than girls (2/1).

Hip>knee>ankle>elbow>wrist>shoulder

Staph. Aureus is the most common pathogen. Other possible pathogens: Group B streptococcus, K.kingae, H. influenzae, N. gonorrhea

Table 1: Common organisms in septic arthiris, by age, and their treatment choices

Pathophysiology

Hematogenous seeding is the most common cause. Especially upper respiratory tract illnesses, sinusitis, otitis media.

Other causes are penetrating injuries (direct inoculation) and extension from adjacent bone (osteomyelitis)

                  In neonates, transphyseal vessels allow the spread of microorganisms into joints with intraarticular metaphysis (hip, elbow, shoulder, ankle, NOT knee)

Bacterial entry to the joint causes an inflammatory cascade which eventually destructs the articular cartilage. Macrophages, neutrophils, cytokines such as IL-1, IL-6 and TNF-α causes cartilage damage starting from 2 to 5 days of the onset.

Evaluation

History:

Acute onset of pain, atraumatic limitation of the extremity

Ill appearing, “septic” child

Physical examination:

Vitals – to rule out hemodynamic instability

Swelling, erythema, tenderness to touch, warmth

Range of motion – pain with passive motion, the patient doesn’t want to actively move the extremity

The presence of warm joint which is painful during passive ROM suggests septic arthritis, while passive ROM doesn’t cause symptoms for osteomyelitis.

Lab tests and imaging:

CBC, CRP, ESR, procalcitonin, blood cultures

WBC – elevated, with >80% neutrophil rate

ESR – elevated, >40 mm/hr

CRP - >20 mg/l for septic patients; if <20, alternative diagnosis is possible

X-rays – septic arthritis may cause joint space widening

USG – can be used for the patients with hip symptoms, to evaluate hip effusion

MRI – demonstrates joint effusion

Kocher criteria are used for the diagnosis of pediatric septic arthritis. ESR, fever, non-weight bearing and higher WBC count are the components.

Table 2: Kocher criteria and the possibility of the diagnosis for the number of predictors present

Hip aspiration:

Definitive modality for the diagnosis

Blind aspiration is not suggested. Aspiration should be performed with ultrasonography or an arthrogram.

The aspiration material should be sent for Gram stain, culture, cell count, glucose and protein studies

WBC>50000/mm3, neutrophil predominance, high protein content, low glucose content (< 33% of serum glucose) are found in septic arthritis.

Differential diagnosis:

Transient synovitis – previous URTI/GI infection history, no fever, acute joint pain and inability to bear weight, no toxic appearance, CRP<20mg/L

Osteomyelitis – fever, pain with weight bearing, no pain with joint ROM, x-ray findings

JIA, rheumatic fever, Kawasaki syndrome, avascular necrosis, SCFE, trauma, Lyme arthritis, Legg-Calve-Perthes syndrome

Treatment:

Antibiotic treatment:

For Neisseria infections, antibiotic treatment (ceftriaxone) without debridement can be used for app. 4 weeks.

Surgery: Debridement & irrigation

Aspiration and lavage/repeated aspiration/arthroscopy/open arthrotomy with iv antibiotics

Arthroscopy – ability to see the joint space, remove synovitis, easier rehab as it is a minimal invasive approach

Arthrotomy – most commonly used

Better results – debridement in the first 4 days

Complications:

Sepsis, premature arthritis, femoral head destruction, physeal arrest, growth disturbance, joint stiffness, persistent infection

Delay in treatment – the most important factor for the prognosis

Poor results are associated with delay in definitive treatment >5 days, osteomyelitis of the proximal femur

References:

1-       Herring JA. Tachdjian’s Pediatric Orthopedics from the Texas Scottish Rite Hospital for Children. 5th ed. Philadelphia: Elsevier Saunders; 2013

2-       Miller MD, Thompson SR, editors. Miller’s review of orthopaedics. 7th ed. Philadelphia: Elsevier; 2016.

3-       Pääkkönen M. Septic arthritis in children: diagnosis and treatment. Pediatric Health Med Ther. 2017 May 18;8:65-68. doi: 10.2147/PHMT.S115429. PMID: 29388627; PMCID: PMC5774603.