OSTEOMYELITIS.
Definition.
Osteomyelitis is the inflammation of the bone and marrow; and the common use of the term virtually always implies bone infection. Therefore OSTEOMYELITIS literally means bone infection.
Aetiology.
Pathogenic microorganisms are the causes of Osteomyelitis.
Bacteria:
- Staphylococcus aureus (Pyogenic osteomyelitis).
- Streptococcus pyogenes.
- Mycobacterium tuberculosis (Bone tuberculosis).
- Pseudomonas aureginosa.
- Escherichia coli.
- Salmonella species.
- Treponema pallidum (bone syphilis).
- Anaerobic bacteria-Bacteroides species, Clostridium species e.t.c
Note:
- Staphylococcus aureus is the most common isolate in haematogenous osteomyelitis.
- E.coli, S.Pyogenes, and S.aureus are the common isolates in neonates.
Fungus:
- Actinomyses species (Actinomycosis)
- Blastomycoces (Blastomycosis).
Note: Fungal infections are uncommon.
Pathogenesis.
Pathogenic microorganisms can spread to a bone by one of the three routes:
- Haematogenous spread (through blood).
- Direct extension from a contagious site.
- Direct introduction.
Haematogenous osteomyelitis occurs mostly in the region of most rapid growth and greatest vascularity;and in this case in the ends of long bones(epiphysis,physeal area and metaphyseal area) in children and before the epiphyseal closure( between the age of 16 and 25 years); and in adults occurs in the vertebrae which are generally vascular.
Contagious osteomyelitis occurs due to burns, periodontal infections, soft tissue infections, skin ulcers and peripheral vascular disease (arteosclerosis, diabetes, and vasculitis) which are among the adjoining sites of microbial infection that may spread to the bone.
Direct introduction of pathogen means introducing a pathogen through penetrating wounds, compound fractures, simple fractures treated surgically with open reduction and internal fixation, prosthetic joint replacements, and other orthopedic appliances (plates, nails, screws, pins).
In either way the microorganism will reach the bone. Once localized in bone, bacteria proliferate and induce an acute inflammatory reaction and cause cell death.
The inflammation may percolate throughout the harvesian system to reach the peritoneum. The peritoneum become loose and detach from the bone cortex (this impairs further blood supply) and may rupture leading to an abscess in the surrounding soft tissue and the eventual formation of draining sinus into the soft tissue or extend to the skin surface. The elevated periosteum is stimulated to form new bone (this new bone is called involucrum).
Clinical forms of osteomyelitis.
The clinical course of osteomyelitis depends on the characteristics of the causative organism, the route of the infection and the age of the patient. In this case there are two main clinical forms in which the disease (osteomyelitis) presents itself:
- Acute osteomyelitis and Chronic osteomyelitis.
Acute osteomyelitis.
Occurs relatively rapid; and in most cases is due to hematogenous spread of bacteria; and is seen more commonly in children than in adults (where it is often insidious).
The symptoms of acute osteomyelitis include those of infection and inflammation:
- Fever.
- Bone pain.
- Local erythema.
- Swelling.
Gross pathological features of acute osteomyelitis include
- Inflammatory exudates in medullary bone and other sites.
- Evidence of bone destruction.
Microscopic features acute osteomyelitis include
- Unorganized medullary trabeculae.
- Presence of polymorphonuclear inflammatory cells (neutrophils).
- Presence of Woven bone.
Radiographic features acute osteomyelitis.
- Normally nothing can be appreciated in acute cases of the disease. Generally osteomyelitis has to be present for at least 4 to 7 days before there are significant radiological changes.
Chronic Osteomyelitis.
The course of chronic osteomyelitis is insidious; and normally is due to contagious infections, Mycobacterium tuberculosis and Treponema pallidum infections.Chronic osteomyelitis may progress from an acute form of the disease. It is believed that about 5% to 25% cases of acute osteomyelitis fails to resolve and persist as a chronic infection.Chronicity may develop from acute disease when there is delay in diagnosis, extensive bone necrosis, abbreviated(shortened) antibiotic therapy, inadequate surgical debridement and weakened host defenses(i.e. compromised host fails to contain the infection).
Clinical signs and symptoms of chronic osteomyelitis:
- Progressive pain.
- No systemic signs like fever etc.
- Draining sinuses from the lesion may be seen.
- Other complications associated with chronic osteomyelitis include the following:
-Pathologic fractures.
-Tumor (cancer) development in the affected site, normally squamous cell carcinoma has a tendency to develop from an osteomyelitic lesion.
Gross pathological features of chronic osteomyelitis:
· Dead bone tissue (sequestra) clearly separated from a viable bone segment is clearly seen. A sequestrum is a piece of dead bone that has become separated during the process of necrosis from normal/sound bone.
- Involucrum (reactive new bone formation) may be seen
- An abscess usually is seen in metaphysis, occuring as a pus filled cavity, surrounded by a wall of dense fibrous tissue and reactive bone. This abscess is known as Brodie's abscess. Brodie's abscess is a chronic abscess of bone and is an indication of chronic osteomyelitis, which may persist for years before converting to a frank osteomyelitis.
Microscopic features of chronic osteomyelitis:
- Chronic inflammatory cells are present in the tissue. These cells include
-Lymphocytes.
-Plasma cells.
-Giant cells.
-Fibroblasts.
- Reactive new bone formation may be noticed.
Radiographic features of chronic osteomyelitis:
- There is Irregular bone destruction.
- Dead bone tissue is seen as patchy areas of radiolucency.
- Brodie's abscess is seen as a well demarcated lucent area surrounded by radiodense sclerotic bone in the metaphysis of affected bone (normally tibia).
Diagnosis.
· Radiography.
· MRI.
· Bone scan-not specific.
· Bone biopsy for microbial culture (Confirmatory t
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