Osteomyelitis
- Inflammation of the bone and marrow
Pyogenic osteomyelitis
- Almost always cause by bacteria. Organisms can reach the bones via;
- Haematological spread
- Extension from a continguous site
- Direct implantation
- Haematological spread
- Most cases are haematogenous anddevelop in the long bones or vertebral bodies
- Initial bacteraemia can be due to;
- Injury to the intestinal muscosa
- Vigorous chewing of hard food
- Minor infection of skin
- Injury to the intestinal muscosa
- Most commonly caused by Staph aureus
- E.coli, pseudomonas and klebsiella are more frequently isolated from patients with genital tract infections and those who are I.V drug abusers
- Mixed bacterial infections are seen in the setting of surgery or open fractures
- In the neonatal period, patients are most susceptible to Haemophilus and Group B strep
- Patients with Sickle cell have an increased predisposition for salmonella infection
- In almost 50% of cases no organism can be detected
- The location of the lesion depends upon the vascular circulation which varies with age
- In the neonate the metaphyseal vessels penetrate the growth plate resulting in frequent infection of the metaphysis, epiphysis or both
- In children infection of the metaphysis is common
- After growth plate closure the metaphyseal vessels unite with their epiphyseal vessels and provide a route for bacteria to seed the epiphyses and the subchondral regions
Morphology
- Once localised in the bone, the bacteria proliferate and induce necrosis of the bone ]the bacterial and inflammation can then spread throughout the shaft and may percolate throughout the Haversian system to reach the periosteum
- Subperiosteal abscesses may form which can track for long distances along the bone
- Lifting of the periosteum impairs the blood supply to the affected region increasing necrosis
- The dead piece of bone is known as the sequestrum
- Rupture of the periosteum leads to an abscess in the surrounding tissue and the formation of a draining sinus
- In infants but less commonly adults, epiphyseal infection spreads through the articular surface to reach the joint and produces a septic arthritis
- Over time, a chronic inflammatory response develops. The release of cytokines stimulates osteoclast reabsorption, growth of fibrous tissue and deposition of reactive bone in the periphery.
- When a sleeve of living tissue forms around a segment of devitalised bone it is known an involucrum
Clinical course
- Acute systemic illness with malaise, fever, chills, leukocytosis and throbbing pain over affected area
- Characteristic x-ray findings of lytic focus of bone destruction surrounded by a zone of sclerosis
- Blood cultures are generally positive
- Treatment is via antibiotics and surgical drainage
- In 5-25% may develop into a chronic infection where acute flare-ups mark the clinical course
- Other complications of chronic osteomyelitis are;
- Pathological fracture
- Secondary amyloidosis
- Endocarditis
- Sepsis
- Development of squamous cell carcinoma in the sinus tract
- Rarely sarcoma of the infected bone
- Pathological fracture