<prompt> Most common cause of osteomyelitis below 4 years of age?PneumococcusE. coliSalmonellaH. influenzae  <response>: 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. 