Introduction
  • An intra-articular infection in children that is considered a surgical emergency and requires prompt recognition and treatment.  
  • Epidemiology
    • demographics
      • incidence
        • peaks in the first few years of life
      • age
        • 50% of cases occur in children younger than 2 years of age
    • location
      • hip joint involved in 35% of all cases of septic arthritis
      • knee joint involved in 35% of all cases of septic arthritis
    • risk factors for neonatal septic arthritis q
      • prematurity (relatively immunocompromised) 
      • Cesarean section 
      • patients treated in the NICU
      • invasive procedures such as umbilical catheterization, venous catheterization, heel puncture may lead to transient bacteremia
  • Pathophysiology
    • routes of inoculation
      • direct inoculation from trauma or surgery
      • hematogenous seeding
      • extension from adjacent bone (osteomyelitis) 
        • can develop from contiguous spread of osteomyelitis 
        • often from metaphysis
          • common in neonates who have transphyseal vessels that allow spread into the joint
        • joints with intra-articular metaphysis include
          • hip
          • shoulder
          • elbow
          • ankle
          • (NOT the knee)
    • mechanism of destruction
      • release of proteolytic enzymes (matrix metalloproteinases) from inflammatory and synovial cells, cartilage, and bacteria which may cause articular surface damage within 8 hours 
      • increased joint pressure may cause femoral head osteonecrosis if not relieved promptly
    • microbiology
      • organisms vary with age (see chart) 
      • neisseria gonorrhoeae
        • still the most common organism in adolescents
        • gram negative diplococci
        • patients usually have a preceding migratory polyarthralgia, multiple joint involvement, and small red papules
        • may treat with large doses of penicillin alone and usually does not require surgical debridement
      • group A beta-hemolytic streptococcus
        • most common organism following varicella infection
      • group B streptococcus 
        • most common in neonates with community-acquired infection
        • exposed during transvaginal delivery
      • staph aureus  
        • most common in children over 2 years of age 
        • gram positive cocci in clusters 
        • most common in nosocomial infections of neonates
      • HACEK organisms 
        • Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella
        • fastidious
        • Incidence of septic arthritis caused by H influenzae has markedly decreased since the advent of its vaccine
        • Kingella is best isolated on blood culture media 
  • Prognosis
    • usually good unless diagnosis is delayed
      • delay in diagnosis may result in permanent joint damage, and long-term disability. 
    • poor prognostic indicators 
      • age < 6 months
      • associated osteomyelitis
      • delay >4 days until presentation
      • hip joint (versus knee)
Presentation
  • History
    • recent local trauma or infections
    • vaccination history must be obtained, particularly with regard to vaccination against Haemophilus influenzae
    • recent or current antibiotics may mask symptoms
  • Symptoms
    • acute onset of pain
      • presents more acutely than osteomyelitis
    • systemic symptoms
      • often associated with fever and other systemic symptoms causing toxic appearance
    • limp or refusal to bear weight
  • Physical exam
    • vitals
      • temperature and vital signs to rule out hemodynamic instability
      • may show toxicity
    • inspection and palpation
      • localized swelling
      • effusion, tenderness, and warmth
      • hip rests in a position of flexion, abduction, and external rotation (FABER) 
        • hip capsular volume is maximized with flexion, abduction, and external rotation and is the position of comfort for hip septic arthritis
    • range of motion
      • severe pain with passive motion
      • unwillingness to move joint (pseudoparalysis)
      • examine adjacent joints and spine
        • must rule out adjacent joint involvement  
Imaging
  • Radiographs
    • recommended views
      • AP and frog-leg lateral pelvic x-rays, if hips can be put in frog leg position.
    • findings
      • may be normal, especially in early stages of disease
      • widening of the joint space
        • in infants, prior to ossification of the femoral head, widening of joint space can be seen by lateral displacement of the proximal femur  
        • this is a sign of significant pus in joint
      • subluxation
      • dislocation
      • bone lesions
        • may see bone involvement with associated osteomyelitis
  • Ultrasound
    • indications
      • neonate contralateral hip
        • in neonates ultrasound both hips if any septic joint is found, signs and symptoms of infection are muted in neonates, and a missed infection can be catastrophic.
      • can be used to guide aspiration
    • findings
      • may be helpful to identify effusion   
      • cannot differentiate between a septic and a sterile effusion
  • MRI
    • may be difficult to obtain expeditiously
    • identifies a joint effusion and possible adjacent osseous involvement which can guide operative treatment
Studies
  • Serum labs
    • helpful to distinguish from transient synovitis 
      • probabilty of septic arthritis may be as high as 99.6% when all four criteria below are present (Kocher Criteria) q q
        • WBC > 12,000 cells/µl of serum
        • inability to bear weight
        • fever > 101.3° F (38.5° C)
        • ESR > 40 mm/h
      • if none of the above predictors are present, probability of having septic arthritis is <0.2%
      • WBC
        • is elevated in 30-60% of patients with a left shift in 60%
        • neonates may have leukopenia
      • ESR
        • often elevated but may be normal early in the course of infection
      • CRP ***The most important of the labs
        • may rise as soon as 6-8 hours after injury or infection
        • CRP > 2.0 (mg/dl) is an independent risk factor (not included in studies of the previous 4 criteria)
        • CRP > 2.0 (mg/dl) in combination with refusal to bear weight yields a 74% probability of septic arthritis
      • order of sensitivity of above criteria q
        • fever > CRP > ESR > refusal to bear wieght > WBC 
  • Hip aspiration q 
    • may confirm diagnosis of septic arthritis  
    • fluid samples should be sent for
      • WBC count with differential
      • Gram stain, culture, and sensitivities
      • Glucose and protein levels have been recomended by some, but of questionable value
    • A septic joint aspirate will show
      • high WBC count (> 50,000/mm3 with >75% PMNs)
      • glucose 50 mg/dl less than serum levels
      • high lactic acid level with infections due to gram positive cocci or gram negative rods
  • Blood cultures
    • should be performed if the patient is febrile, as they are often positive, even when local cultures are negative
  • Lumbar puncture
    • consider in a septic joint caused by H. influenzae due to risk of meningitis IF there are clinical signs of meningitis
Differential Diagnosis
  •  Table - Differential diagnosis of Hip Pain in Children
Treatment
  • Nonoperative
    • antibiotics alone
      • rarely indicated
        • adolescent Neisseria gonorrhoeae infection
          • in some cases can be treated with large doses of penicillin alone and usually does not require surgical debridement
  • Operative
    • urgent surgical I&D followed by IV antibiotics
      • indications
        • standard of care for septic hip joints
          • if possible in septic arthritis it is better to err on the side of surgical drainage 
        • considered a surgical emergency in the hip due to chondrolytic effect of pus
          • removes damaging enzymes which are chondrolytic
        • reduces intraarticular pressure and decreases epiphyseal ischemia
      • antibiotics
        • timing
          • perform joint aspiration, preferably before administration of empiric antibiotics 
          • empiric IV antibiotics are started after samples are sent for culture and are usually continued for 3 weeks
          • once cultures return follow with IV antibiotics targeting pathogens 
          • convert to PO antibiotics once the clinical picture improves and definitive sensitivities are obtained
          • duration of antibiotic therapy is generally 3-4 weeks
          • terminate antibiotics once the CRP or ESR normalizes, and clinical picture returns to normal
        • microbial coverage
          • empiric antibiotics
            • based on age and medical comorbidities
            • immunization status determines whether empiric antibiotics should cover H influenzae
Septic Arthritis Antibiotic Treatment
Age
Organism
Antibiotics
<12 mos staphylococcus sp., group B streptococci, and gram-negative bacilli  1st generation cephalosporin
6 mos to 5 yrs S. aureus, S. pneumoniae, group A streptococci, H. influenzae 2nd or 3rd generation cephalosporin
5-12 yrs S. aureus 1st generation cephalosporin
12-18 yrs N. gonorrhoeae, S. aureus

oxacillin/cephalospori

 
 
Surgical Techniques
  • Septic Hip Irrigation and Debridement 
    • approach
      • most commonly one of the following approaches is utilized
        • anterolateral approach to the hip 
        • anterior approach through the Smith-Peterson interval
        • drainage of the shoulder, elbow, knee, and ankle may be open or arthroscopic
    • technique
      • arthrotomy is performed to remove all purulent fluid and to irrigate the joint
      • consider removal of 1cm by 1cm hip capsule to minimize chances of re-accumulation
      • consider synovial culture 
      • intra-articular drain placement is recommended
    • postoperative care
      • range of motion exercises of the affected joint may be started within the first few days after surgery
Complications
  • Femoral head destruction
    • complete destruction of the femoral head and neck, easily visible on x-ray 
    • salvage operations exist including varus/valgus proximal femoral osteotomies 
  • Deformity
    • physeal damage leads to late angular deformity and leg length discrepancy
  • Joint contracture
  • Hip dislocation
  • Growth disturbance
  • Limb-length discrepancy
  • Gait abnormalities
  • Osteonecrosis