Bone Pathology Flashcards
What is the bone structure
Cortex - compact bone consisting of a parallel arrangement of osteons
Cancellous medullary - bone composed of sponge like trabecular bone
What is osteomyelitis
It is an infection of the bone and the bone marrow, most often caused by the bacteria S. aureus
What is the Haematogenous Spread
The condition where bacteria enter the bone via the bloodstream, causing infection
The primary manifestation or complication is from other organs or is systemic
What is the mechanism of Haematogenous Spread
Bacteria enter the bloodstream from a distant site and these bacteria start to seed in the bone marrow, especially in areas with rich blood supply
Why the metaphysis site of the bone for Haematogenous Spread
The blood flow in metaphysis is slow and turbulent, allowing bacteria to settle.
In children, metaphyseal vessels form loops close to the growth plate, a site where immune surveillance is lower.
What are the clinical features of Haematogenous Spread
Fever, localized bone pain, swelling.
What are the complications associated with Haematogenous spread
Abscess formation (Brodie’s abscess).
Spread into the joint space
Sequestrum (dead bone) and involucrum (new bone around sequestrum).
What is the Contiguous Spread of osteomyelitis
The spread of infection or disease from an adjacent area or source to another area that is in close proximity
- More common with adults in association with Diabetic foot ulcers, Post-surgical wounds, and pressure sores
What is the mechanism of Contiguous spread
From adjacent soft tissue or skin, directly to the underlying bone
The pathogen/inflammatory reaction permeates the periosteum or erods the articular surface and extends to cortex/medulla
What are the risk factors of Contiguous spread
- Diabetes mellitus
- Peripheral vascular disease
- Immunosuppression
What are the clinical symptoms of Contiguous spread
Local signs of infection (redness, warmth, discharge).
Chronic draining sinus can develop.
Systemic signs may be minimal.
How does direct implantation contribute to osetomyelitis
When organisms are introduced directly into bone
What is the mechanism of direct implantation
Trauma, Orthopaedic surgery, Penetrating wounds
What is the histopathology and imaging of osteomyelitis
- Acute osteomyelitis: Neutrophilic infiltrates, necrosis of bone (sequestrum), possible abscess
- Chronic osteomyelitis:
Fibrosis, lymphocytes, plasma cells, granulation tissue, and involucrum formation
What is the pathophysiology of bacterial osteomyelitis
The pathogen adheres to the collagen matrix and forms actively reproducing colonies; compromised blood flow by compression and thrombosis
This altered perfusion increases the chances of proliferation
What is the immune response to bacterial osteomyelitis
There is formation of abscess and granulation tissue (Suppurative inflammation) leading to intraosseous pressure, further hampering the perfusion
How would the bacterial osteomyelitis spread
1) Spread through the medulla
2) Spread along the Haversian Canals
3) Through the Cortex
4) To the Periosteum
5) Extension to the Soft Tissue or joints
What happens as the bacteria spreads through the Medulla
The medulla is the central cavity of the bone (where bone marrow is found)
The infection would begin here and the bacteria would multiply to provoke an inflammatory response that causes pus to accumulate
What happens as the infection spreads to the Haversian Canals
The Haversian Canals are the microscopic structure of the compact bone that carry blood vessels and nerves
The bacteria and pus use these canals as ‘highways’ to move through the dense bone matrix
What happens as it spreads through the cortex
The cortex is the hard outer layer of the bone
The infection travels from the medulla and Haversian canals outward through the cortex
The inflammation, pressure from pus, and enzymatic destruction from immune cells would lead to cortical bone necrosis - this sets the stage for sequestrum formation
What happens at the periosteum stage
The periosteum is the outer fibrous layer that covers bones, it contains blood vessels and nerves
As the pus accumulates under pressure, it may lift and separate the periosteum from the cortex
This disrupts blood supply even more, worsening necrosis
What happens as the infection spreads to soft tissue or joints
If the infection breaks through the periosteum, it can:
- Spread into the soft tissue, leading to abscesses
- Enter adjacent joints (especially if the bone is intra-articular) leading to septic arthritis
What is osteomalacia and rickets and what is the difference between the two
These are both metabolic bone diseases characterised by defective mineralization of the bone matrix, primarily due to vitamin D deficiency
Osteomalacia = Affects adults (mature skeleton)
Rickets = affects children (growing skeleton)
What are the two main components bone
1) Organic matrix (mainly collagen)
2) Mineral component (mainly calcium and phosphate)
