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 Staph aureus 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 the Kocher criteria are only sensitive for diagnosing pediatric septic arthritis of the hip and should not be inappropriately applied to other locations such as the knee 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 cephalosporinKingella 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)