Ans. d (H. influenzae) (Ref, Nelson pediatrics 18th/ 2843; Manual of orthopaedics by Marc, F. Swiontkowski p. 83)# S, aureus is the most common bacterial pathogen, followed by gram-negative rods, group A streptococcus, and H. influenzae (less likely now due to HIB vaccination).# Pseudomonas aeruginosa is most vital cause of osteomyelitis of foot, especially if there is a puncture wound.# Salmonella is the most common cause of osteomyelitis in patients with hemoglobinopathy.ACUTE OSTEOMYELITISOrganisms of the basis of patient age: a. Younger than 1 yearb. 1 to 4 year oldc. Older than 4 yearsd. Adolescenti. Staphylococcus aureusii. Group B streptococcusiii. Escherichia colii. S. aureusii. Haemophilus influenzaei. S.aureusi. S.aureusii. Neisseria gonorrhoeaeCommon organisms causing infections in a particular setting1.Most common clinical associationMicroorganism2.Frequent organism in any type of osteomyelitisS. aureus3.Most Frequent organism in acute osteomyelitis < 4 yrs ageS. aureus & H. influenzae4.Foreign body associated infectionCNS or Propionibacterium5.Common in nasocomial infectionEnterobacteriacea, P. aeruginosa, Candida6.Sickle cell diseaseSalmonella7.HIV infectionBartonella henselae8.Human or animal bitesPasturella multocidaRadiolgical investigations in acute osteomyelitisType of StudyCommentsPlain radiographs# Insensitive, especially in early osteomyelitis.# May show periosteal elevation after 10 days, lytic changes after 2-6 weeks.Three-phase bone scan (99mTc-MDP)# Characteristic finding in osteomyelitis: increased uptake in all three phases of scan.# Highly sensitive (~95%) in acute infection.67Ga-citrate, 111In-labeled WBCs scans# 111In-WBCs more specific than gallium but not always available.# Lack of consensus over role; often supplanted by MRI when the latter is available.MRI# As sensitive as 99mTc-MDP bone scan for acute osteomyelitis (~95%).# High specificity (~87%), with better anatomic detail than nuclear studies.