5 - Infection of Bone and Joint

Osteomyelitis definition

Inflammation of bone(osteo-) and it’s marrow(myel-), almost always by bacterial infection

Bone infection pathology

1. When an infection happens, neutrophils come, and pus forms as usual.

2. However, the pus has nowhere to go, since the bone is an unexpandable cavity → increase in pressure which leads to blood supply being cut off

3. The part of bone that has it’s supply cut off is the sequestrum and this means that antibiotics can’t get to the sequestrum and bacteria form a biofilm there and survive even more

4. When the infection grows more, it can push through and lift the periosteum, causing it to lay down new bone around the bacteria called an involucrum

3 main routes of osteomyelitis

1. Hematogenous

2. Direct penetration

3. Contiguous from nearby structure

Why is a foreign body bad in terms of osteomyelitis, and what are some examples?

It’s bad because it is a place where bacteria can grow

1. Any surgical implants or screws

2. Dirt or other materials entering an open wound

3. Dead bone itself(Like a sequestrum) is also a foreign body

Acute hematogenous osteomyelitis

• Common demographic

• Common location of infection

• Children

• A single location, typically metaphysis of tibia, femur, humerus

Most common site of hematogenous osteomyelitis in adults

Vertebral bodies

Most common cause of hematogenous osteomyelitis

S. aureus

How long does it take for X-ray results to show in osteomyelitis?

10-14 days+

Septic arthritis

An infected joint, usually bacteria

• Can occur together with osteomyelitis

Why is septic arthritis an emergency?

Because articular cartilage has no blood supply, so if the cells there die, it can’t regenerate and the pt. is left with a stiff/painful joint for life

Septic arthritis symptoms

1. Severe pain even with small movements

2. Red, hot, swollen joint

3. Fever over 38.5C

4. WBC 12k, ESR > 40

5. Monoarthritis

Viral arthritis will usually be ___

polyarthritis

Main causative organism of nongonococcal arthritis

S. aureus

Investigation of

• Osteomyelitis

• Septic arthritis

• Young sexually active adult with joint pain/skin pustules

• Osteomyelitis: Blood culture

• Septic arthritis: Joint aspiration

• Young sexually active adult with joint pain/skin pustules: NAAT swab from urethra/cervix

Tuberculous osteomyelitis

• Origin

• Lungs(usually)

Pott disease

• What is it

• Other name

• Symptoms

• Inflammation of vertebrae from TB

• TB spondylitis

• Weight loss, night sweats, low-grade fever, back pain and stiffness

Pott abscess

• What is it

• When does it form?

• Most dangerous symptom

• TB abscess of the spine, a complication of Pott disease

• It forms when the infected vertebrae produces too much caseous material

• Can press back into the spinal cord → leg weakness, numbness, bladder/bowel issues

Tuberculous arthritis

• What it is

• Timeline

• Most common location

• TB infection of a joint

• Joint pain that develops over months, along w TB symptoms(Weight loss, night sweats, low grade fever)

• Hips, knees, ankles, but usually monoarticular