1. Osteomyelitis Osteomyelitis: Pathogenesis:
Osteomyelitis is the infection of the bone or bone marrow. It can be classified on the basis of the causative organism (pyogenic bacteria or mycobacteria), the route, duration and anatomic location of the infection.
Pathogenesis:
Microorganisms may infect bone through one or more of three basic methods: via the bloodstream, from local areas of infection (as in cellulitis), penetrating trauma, joint replacements or internal fixation of fractures or root-canaled teeth.

2. Osteomyelitis
Once the bone is infected, leukocytes enter the infected area, and engulf the infectious organisms, release enzymes that are associated with bone lyses.
Pus spreads into the bone's blood vessels, impairing their flow, and cause necrotic dead area of the bone called sequestra , form the basis of a chronic infection.
Often, the body will try to create new bone around the area of necrosis. The resulting new bone is often called an involucrum .

3. Osteomyelitis Causes of Osteomyelitis: Most common organisms Age group
S. aureus, Enterobacter species, and Group A and B Streptococcus species
Newborns (younger than 4 months)
S. aureus, Group A Streptococcus species, Haemophilus influenzae, and Enterobacter species
Children (aged 4 months to 4 years)
S. aureus and occasionally Enterobacter or Streptococcus species
Adult
Staphylococci (50%), and Tuberculosis (50%).
Vertebral osteomyelitis

4. Osteomyelitis
Osteomyelitis clinical picture:

5. Septic arthritis
Septic arthritis is: The invasion of a joint by an infectious agent which produces arthritis. People with artificial joints are more at risk than others. Septic arthritis is considered a medical emergency. If untreated, it may destroy the joint in a period of days. The infection may also spread to other parts of the body.

6. Septic arthritis Prevalence, and pathogenesis: Pathogenesis:
The incidence of septic arthritis has been estimated at 2 to 10 cases per 100,000 in the general population, and
as high as 30 to 70 cases per 100,000 in patients with rheumatoid arthritis.
Pathogenesis:
-Routes of Entry:
1- Dissemination of pathogens via the blood (hematogenous)
2- From contaminated needle.
3- Dissemination from soft tissue infection, entry via penetrating trauma.

7. Septic arthritis -Primary infection:
-The Synovial A cell (APC) engulfs the microbe.
- Production of TNF and IL-8.
- Chemotaxis, cellular infiltration, and edematous edema.
- Toxic free radicals production.
- Proteoglycan and collagen destruction, cartilage destruction.
- Direct pressure necrosis,
more cartilage destruction.
- Specific T-cell response,
and Polyclonal B
cell activation.
Secondary:
Osteomyelitis.

8. Septic arthritis
Bacteria that are commonly found to cause septic arthritis are: 1- Staphylococcus aureus - the most common cause in adults; (40-50% of cases). Others: 10-20%: 2- Streptococci - the second most common cause 3- Haemophilus influenzae - was the most common cause in children but is now uncommon in areas where Haemophilus vaccination is applied. 4- Neisseria gonorrhoea - in young adults 5- Escherichia coli - in the elderly, IV drug users and the seriously ill.

9. Septic arthritis Signs and Symptoms of Septic arthritis:
Patients with septic arthritis usually present with :
1- Joint pain.
2- Redness over the joint.
3- Joint inflammation and swelling.
4- Synovial fluid accumulation.
Synovial fluid analysis:
1- Physical examination:
The normal appearance of a sample of synovial fluid is usually:
A-Straw colored B-Clear C-Moderately Viscous.

10. Septic arthritis 2- Chemical examination:
Changes in the physical characteristics may provide clues to the disease present such as:
A- Less viscous fluid may be seen with inflammation.
B- Cloudy synovial fluid may indicate the presence of microbes,
white blood cells, or crystals.
C- Reddish synovial fluid may indicate the presence of blood.
2- Chemical examination:
A-Glucose—typically lower than blood glucose levels. May be
significantly lower with joint inflammation and infection.
B-Protein—increased with bacterial infection.
C- Lactate dehydrogenase—increased LD (LDH) level may be seen in
rheumatoid arthritis, infectious arthritis, or gout.
D-Uric acid—increased with gout.

11. Septic arthritis 3-Microscopic examination :
Normal synovial fluid has small numbers of white blood cells (WBCs) and red blood cells (RBCs) but no microorganisms or crystals present.
Specimens should be concentrated by centrifugation for:
A-Total WBCs count: WBCs count more than 50,000 cell.
B-Differential count: Neutrophils increased with bacterial infection.
Eosinophils elevated in Lyme disease.
C-Gram’s stain: for Gram-positive and negative bacteria, and fungi.
D-AFB (Z.N stain) smear: for Mycobacterium tuberculosis.
4-Culture and sensitivity test:
Specimens should be cultured on blood and chocolate agar and incubated at aerobic and anaerobic (10%CO2) conditions respectively.
Neisseria and Haemophilus species grow only on chocolate agar.