Osteomyelitis is an infection in a bone. 

Based on the duration of illness:

1. Acute osetomyelitis (days- weeks) - Absence of sequestra
2. Chronic osetomyelitis (months-years) - Presence of sequestra

Commonly organisms are Staphylococcus aureus, Enterobacter spp., Streptococcus spp., Pseudomonas spp., and gram negative bacilli