Osteomyelitis

Question 1

Definition

Answer 1

Inflammation of the bone or bone marrow typically from an infection (staphylococcus aureus)

Question 2

Aetiology

Answer 2

Microorganisms such as bacteria (staphylococcus aureus), reaches the bone to cause infection.
Bacteria reaches the bone via the blood stream (hematogenous spread)
Organisms can reach specific places:
- older adults- vertebrae (vertebral osteomyelitis)
- children- metaphysis of long bones

Using contaminated needles

Haemodialysis

Dental extraction of an infected tooth

Trauma:
– open fracture from trauma, the bone may come into direct contact with bacteria

Surgery:
– infection being introduced to the bone through surgery

Contiguous spread:
– spread from one area of the body to an adjacent area

Prosthetic joint

People with diabetes mellitus:
– can lead to peripheral or autonomic neuropathy, this can eventually lead to osteomyelitis through contiguous spread

Question 3

Risk factors:

Answer 3

High risk individuals:
– weak immune system (HIV)
– poor blood circulation due to uncontrolled diabetes

Question 4

Pathophysiology

Answer 4

When bacteria reaches the bone, they start to proliferate
– alerts the nearby immune cells to try and fight off the infection
– this triggers the acute phase of the disease (happens over a course of weeks)

Acute phase:
– immune cells release chemicals and enzymes that break down bone and cause destruction
– acute osteomyelitis eventually comes to a resolution, meaning that the immune system destroys all the remaining bacteria
—- if the lesion is not that extensive, then the osteoblasts and osteoclasts begin to repair the damage over a period of weeks

Chronic phase (lasts months-years):
– affected bone can become necrotic, and separate from the healthy bone (sequestrum)
– osteoblasts may wrap the sequestrum in place, causing an involucres

In both acute and chronic osteomyelitis the inflammation may inolve the periosteum:
– the periosteum is loosely attached to the compact bone (especially in children)
– so the 2 layers can separate, allowing an abscess to form between them.
—- the abscess will track along the periosteum, lifting it up away from the contact bone

Infection can spread to other areas:
– nearby joint (knee or hip in young children)
– overlying muscle
– skin
– blood vessels (thrombophlebitis)

Question 5

Microorganisms that can cause osteomyelitis:

Answer 5

Staphylococcus aureus:
– can live in the skin
– can invade the skin and spread contiguously to the bone

Salmonella:
– particularly affects individuals with sickle cell
—- therefore, individuals with sickle cell, are more at risk for staphylococcus aureus and salmonella infections

Pasteurella multocida:
– usually spread through cat or dog scratch/bite

Question 6

Clinical presentation

Answer 6

Acute osteomyelitis:
– pain at the site of infection
– fevers
– depending on the location, may affect the use of the bone

Chronic osteomyelitis:
– prolonged fevers
– weight loss
—- due to the chronic inflammatory state

Question 7

Investigations

Answer 7

CBC (complete blood count):
– increased WBC
– increased ESR
– increased CRP

X-ray:
– thickening of the cortical bone and periosteum
– elevation of the periosteum
– loss of normal architecture of the bone
—- especially the trabecular architecture
– osteopenia (loss of bone mass)
—- become evident when over half of the bone matrix is destroyed

Bone scan or MRI:
– Can confirm the presence of osteomyelitis
– also can help identify an abscess

Bone biopsy:
– to help identify the pathogen responsible
– and confirm the diagnosis

Question 8

Treatment

Answer 8

Weeks of antibiotics direct at the organism causing the infection

Surgery:
– if there’s an abscess, particularly a vertebral abscess causing neural compression, surgery may be required
– needed to remove any necrotic bone
—- particularly in osteomyelitis where the sequestrum has to be removed