Updated: 1/20/2023

Hip Septic Arthritis - Pediatric

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  • SUMMARY
    • Pediatric Septic Hip Arthritis is an intra-articular infection in children that peaks in the first few years of life.
    • While diagnosis may be suspected by a combination of history, physical exam, imaging, and laboratory studies, confirmation requires a hip aspiration. 
    • Considered a surgical emergency and requires prompt recognition and urgent surgical I&D followed by IV antibiotics.
  • EPIDEMIOLOGY
    • Incidence
      • rare
        • affects 4-5 per 100,000 children annually
    • Demographics
      • peaks in the first few years of life
      • 50% of cases occur in children younger than 2 years of age
      • male > female (2:1 ratio)
    • 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
      • 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
  • Etiology
    • Mechanism
      • direct inoculation
        • from trauma or surgery (skin penetration)
      • hematogenous seeding
        • upper respiratory infection precedes about 80% of the cases
      • 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)
    • Pathophysiology
      • enzymatic 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
      • in up to 55% of cases, no organism is identified
      • organisms vary with age (see chart)
      • Microbiology by Organism
      • Group B streptococcus
      • most common in neonates with community-acquired infection
      • exposed during transvaginal delivery
      • most common in children over 2 years of age 
      • gram-positive cocci in clusters
      • most common in nosocomial infections of neonates
      • Neisseria gonorrhoeae
      • still the most common organism in adolescents 
      • gram negative diplococci, negative Gram stain a majority of the time
      • 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
      • 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 noted to be the most common organism in children < 4 years in some studies (best isolated on blood culture media)
  • 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
        • severe pain with logrolling of the hip
        • 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
      • 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
        • 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) is suggestive of an alternative diagnosis (i.e. transient synovitis)
          • 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
            • fever > CRP > ESR > refusal to bear weight > WBC
    • Hip aspiration
      • 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 recommended by some, but of questionable value
      • A septic joint aspirate will show
        • high WBC count (> 50,000/mm3 with >75% PMNs)
          • PMN percentage more sensitive than total WBC count
            • 85% PMNs correlates with an 88% sensitivity.
        • 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
    • Key Differential
      • transient synovitis
      • osteomyelitis
      • JRA
      • JIA
    • Additional Differential
      • Lyme Disease
      • SCFE
      • LCP
      • MED
    • Table - Differential diagnosis of Hip Pain in Children
  • Diagnosis
    • Diagnosis
      • made by a combination of history, physical exam, imaging, and laboratory studies
        • while the Kocher Criteria is commonly used, no one algorithm is diagnostic alone
    • Original Kocher Criteria
      • four criteria
        • WBC > 12,000 cells/µl of serum
        • inability to bear weight
        • fever > 101.3° F (38.5° C)
        • ESR > 40 mm/h
      • algorithm
        • probability of septic arthritis may be as high as 99.6% when all four criteria above are present
        • if none of the above predictors are present, probability of having septic arthritis is <0.2%
          • 3% incidence of septic arthritis if 1/4 criteria present, 40% incidence if 2/4 criteria present, 93% incidence if 3/4 criteria present
    • Modified Kocher Criteria
      • additional criteria
        • CRP
  • 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
  • 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
      • antibiotics
        • timing
          • perform joint aspiration, preferably before administration of empiric antibiotics
          • empiric IV antibiotics are started after samples are sent for culture
          • once cultures return follow with IV antibiotics targeting pathogens 
          • convert to PO antibiotics once the clinical picture improves and definitive sensitivities are obtained
            • current recommendation is a 2-7 day course of culture-specific IV antibiotics followed by a 2-3 week course of oral antibiotics
          • terminate antibiotics once the CRP or ESR normalizes, and clinical picture returns to normal
        • microbial coverage
          • based on age and medical comorbidities
          • immunization status determines whether empiric antibiotics should cover H influenzae
          • Septic Arthritis Antibiotic Treatment
          • Age
          • Organism
          • Antibiotics
          • < 3 months
          • group B streptococci, s. aureus, and gram-negative bacilli
          • 1st generation cephalosporin
          • 3 months to 5 years
          • S. aureus, Kingella, S. pneumoniae, group A streptococci, H. influenzae
          • 2nd or 3rd generation cephalosporin
            Kingella shown to be resistant to vancomycin and clindamycin 
          • 5-12 yrs
          • S. aureus
          • 1st generation cephalosporin
          • 12-18 yrs
          • N. gonorrhoeae, S. aureus
          • 2nd or 3rd generation cephalosporin
      • 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
        • treatment
          • salvage operations exist including varus/valgus proximal femoral osteotomies
    • Femoral neck deformity
      • physeal damage leads to late angular deformity and leg length discrepancy
    • Joint contracture
    • Growth disturbance
      • patients should be followed up for 1-2 years to monitor for physeal arrest
    • Limb-length discrepancy
    • Osteonecrosis
  • Prognosis
    • Overview
      • usually good unless diagnosis is delayed
        • delay in diagnosis may result in permanent joint damage, and long-term disability.
    • Prognostic indicators
      • poor
        • age < 6 months
        • associated osteomyelitis
        • delay >4 days until presentation
        • hip joint (versus knee)
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(OBQ18.56) A 5-year-old female presents to the emergency department with right hip pain. On exam, there is no skin discoloration but motion of the hip appears painful and she refuses to bear any weight on that side. A current radiograph is shown in Figure A. Initial set of vitals shows a body temperature of 37.8 degrees C, and his labs reveal a WBC count of 13K and ESR of 19. How many Kocher criteria are met, what is the corresponding likelihood of infection, and what is most likely causative organism?

QID: 212952
FIGURES:

1 of 4 Kocher criteria, <10%, Staphylococcus aureus

8%

(159/2055)

1 of 4 Kocher criteria, 40%, Neisseria gonorrhoeae

0%

(5/2055)

2 of 4 Kocher criteria, 40%, Staphylococcus aureus

78%

(1602/2055)

3 of 4 Kocher criteria, 93%, Group A streptococcus

11%

(234/2055)

3 of 4 Kocher criteria, 99%, Group B streptococcus

2%

(40/2055)

L 2 A

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(OBQ12.108) Which of the following is true regarding matrix metaloproteinases (MMPs)?

QID: 4468

They are activated by chelating agents

5%

(277/5042)

They mediate the destruction of cartilage in septic arthritis

76%

(3849/5042)

Toll-like receptors inhibit the formation of MMPs

6%

(327/5042)

They have a anabolic effect on cartilage

5%

(265/5042)

Stromelysin is an indirect antagonist of many MMPs

5%

(267/5042)

L 1 C

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(OBQ12.260) A 3-year-old presents with a 24-hour history of limping and progressive inability to bear weight. The parents recount no history of trauma, but note that he recently had an upper respiratory infection. A clinical photo is shown in Figure A. The patient’s vital signs are stable. Physical exam is limited because of pain. A hip ultrasound is shown in Figure B. Laboratory values are as follows: WBC-15.0 (97% PMN), ESR-120, CRP-5.0. What is the next best step for this patient?

QID: 4620
FIGURES:

Admit for observation

5%

(188/3704)

Repeat hip ultrasound

0%

(12/3704)

Obtain an MRI

5%

(181/3704)

Start the patient on IV antibiotics

3%

(127/3704)

Emergent hip arthrotomy with irrigation and debridement

86%

(3170/3704)

L 1 C

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(OBQ11.21) A 2-year-old child is diagnosed with a septic hip. Initially, no organisms grew on the standard blood agar plate. However, after 1 week, the offending organism was recovered in an aerobic blood culture medium. Which of the following organisms was the most likely cause?

QID: 3444

Kingella kingae

80%

(2524/3158)

Mycobacterium tuberculosis

6%

(180/3158)

Mycobacterium avium

2%

(78/3158)

Neisseria

7%

(211/3158)

E-coli

4%

(142/3158)

L 1 B

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(OBQ11.162) A 2-year-old boy is seen for evaluation of a limp. His history is significant for a left knee infection treated with IV antibiotics as a neonate and a family history of cancer. Laboratory testing demonstrates a normal ESR and CRP. The remainder of his workup is negative. An AP pelvis is seen in Figure A. What was the most likely etiology of his condition?

QID: 3585
FIGURES:

Untreated neonatal hip infection

91%

(2950/3236)

Chondrosarcoma

1%

(36/3236)

Legg-Calve-Perthes disease

6%

(192/3236)

Slipped capital femoral epiphysis

0%

(11/3236)

Osteosarcoma

1%

(27/3236)

L 1 B

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(OBQ10.243) An 8-day-old infant is admitted to the hospital for septic arthritis of the hip. He went home on day two after an uneventful vaginal birth. Which of the following will most likely be the causative organism by culture?

QID: 3342

Group B Streptococcus

78%

(2789/3586)

Staph Aureus

17%

(619/3586)

Staph Epidermidis

0%

(12/3586)

Haemophilus Influenzae

2%

(86/3586)

Neisseria Gonnorhea

2%

(55/3586)

L 1 A

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(OBQ10.255) A 7-year-old boy developed a limp with right leg pain five days ago, and today has trouble bearing weight. On exam, he is lethargic and has chills. His temperature is 38.4 degrees centigrade. He points to his right inguinal region as the source of the discomfort. He winces with compression of his pelvis. Lab studies reveal a white blood cell count of 11,400/ul, CRP of 0.9 mg/dL (normal < 1.0 mg/dL), and erythrocyte sedimentation rate of 55 mm/h. A pelvis radiograph is shown in Figure A. Ultrasound guided aspiration of the right hip joint yields 9,000 leukocytes per mL. What is the most appropriate next step in management?

QID: 3357
FIGURES:

Further imaging of the pelvis

48%

(1451/3033)

Open drainage and irrigation of the right hip joint

28%

(854/3033)

Repeat aspiration of the hip joint

3%

(103/3033)

Percutaneous screw fixation of the proximal femoral physis

1%

(23/3033)

Nonsteroidal antiinflamatory medications and observation

19%

(589/3033)

L 4 D

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(OBQ09.151) An 18 month-old child has been brought to the emergency room by his mother. He had the sudden onset of hip pain 3 days ago and now won't put weight on the affected limb. The child is febrile and an ultrasound (longitudinal view of the proximal femur) shown in Figure A shows the unaffected hip on the left and affected hip on the right. The patient is taken to the operating room for hip aspiration which reveals 60,000 leukocytes with 95% polymorphonucleocytes. What is the most likely diagnosis?

QID: 2964
FIGURES:

Traumatic effusion

1%

(16/1938)

Toxic synovitis

3%

(49/1938)

Acute rheumatic fever

1%

(12/1938)

Juvenille rheumatoid arthritis (JRA)

1%

(10/1938)

Septic arthritis

95%

(1837/1938)

L 1 C

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(OBQ09.158) An 8-month old infant is brought by his parents to your office for fever and malaise. Your inspection of the patient is detailed in Image A. An oral temperature of greater than 38.5 has been found to be the best predictor of this child's condition. What is the second best predictor?

QID: 2971
FIGURES:

Elevated neutrophil count

7%

(182/2724)

Elevated ESR

13%

(357/2724)

Elevated rheumatoid factor

1%

(17/2724)

Elevated CRP

76%

(2066/2724)

Presence of bacteria on CSF gram stain

3%

(86/2724)

L 2 B

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(OBQ08.180) A 3-year-old boy presents with his caregiver with concerns regarding a long-standing gait disturbance. The birth history is unknown except for a prolonged ICU stay for sepsis. A pelvic radiograph is shown in Figure A. What is the most likely cause for this child's limp?

QID: 566
FIGURES:

Slipped capital femoral epiphysis

1%

(32/3689)

Legg-Calve-Perthes disease

7%

(245/3689)

Developmental dysplasia of the hip

6%

(239/3689)

Residual effects of previous untreated septic hip arthritis

85%

(3142/3689)

Acute femur fracture secondary to child abuse

0%

(7/3689)

L 2 C

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(OBQ08.68) A 6-week old boy refused to move his left hip. The patient was delivered by C-section 4 weeks premature, but otherwise is healthy. He has been afebrile. Examination reveals some mild, diffuse swelling about the left proximal thigh. Passive motion of the hip elicits discomfort. An AP pelvis radiograph is shown in Figure A. What is the most appropriate next step in management?

QID: 454
FIGURES:

MRI

20%

(347/1695)

CT scan

1%

(11/1695)

Observation

5%

(80/1695)

Aspiration

52%

(886/1695)

Pavlik Harness

21%

(361/1695)

L 3 B

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(OBQ06.121) Which of the following Gram stain images most accurately represents the primary causative organism for pediatric osteomyelitis and septic arthritis?

QID: 307
FIGURES:

Figure A

16%

(365/2286)

Figure B

2%

(46/2286)

Figure C

2%

(49/2286)

Figure D

2%

(53/2286)

Figure E

77%

(1754/2286)

L 1 A

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(OBQ04.159) In differentiating pediatric septic hip from transient synovitis, an elevated ESR (>40), history of fever, refusal to bear weight and what other finding has been identified as predictive of a septic hip?

QID: 1264

Elevated absolute neutrophil count

3%

(48/1635)

Serum white blood cell count > 12,000 cells/cubic millimeter

89%

(1452/1635)

Positive blood cultures

5%

(89/1635)

Pain with hip extension

1%

(15/1635)

Symptoms greater than 3 days

1%

(22/1635)

L 1 B

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(OBQ04.242) A 10-month-old infant is brought to the emergency department for fevers, irritability, and avoidance of motion in the right leg. On physical exam, passive motion of the right hip elicits crying. An AP pelvis and an ultrasound of the right hip are shown in Figures A and B respectively. A hip aspiration yields 82,000 WBC with >80% PMNs. Which of the following is the strongest predictor of a poor prognosis?

QID: 1347
FIGURES:

CRP > 5mg/L

4%

(46/1182)

Delay in treatment >4 days

92%

(1090/1182)

Age > 6 months

1%

(10/1182)

Absence of associated osteomyelitis

0%

(4/1182)

ESR > 40mm/hr

2%

(23/1182)

L 2 D

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