Lecture 7 - Bone and joint infections

Question 1

What is osteomyelitis?

Answer 1

It is an inflammatory process of bone secondary to bacterial infection

Question 2

How can osteomyelitis be classified?

Answer 2

Acute, subacute, chronic

Question 3

What are the two routes of infection for osteomyelitis?

Answer 3

Haematogenous (contiguous), or exogenous

Question 4

What are the two types of host responses to osteomyelitis?

Answer 4

Pyogenic or granulomatous

Question 5

What areas of the bone does can osteomyelitis affect?

Answer 5

May involve periosteum, medullary cavity, or compact/cancellous bone

Question 6

In which age group is osteomyelitis via haematogenous route of infection most common in?

Answer 6

In children who still have their growth plates ossifying. Beneath the growth plates the blood vessels are convoluted, and this causes vascular stasis, where the blood slows down. This makes it easier for microbes to proliferate and infect the bone.

Question 7

How can osteomyelitis via exogenous infection occur?

Answer 7

Osteomyelitis can occur via exogenous infection via direct inoculation of the bone (trauma, surgery) Or it can be contiguous, where the microbes from another infection spread to infect the bone (E.g. feet in diabetics, polymicrobial)

Question 8

What bacerium causes most of osteomyelitis infections?

Answer 8

Staph. aureus

90% in adults, 50% in children

Question 9

What are the risk factors for osteomyelitis?

Answer 9

• Immunosuppresion (Diabetes, HIV, Drugs, Cancer)
• Age (children, edlerly)
• PVD (Diabetes, smoking)
• IDU
• Chronic joint disease (rheumatoid arthritis)
• Recent bone surgery

Question 10

How do children present with osteomyelitis?

Answer 10

Often have infection in metaphysis of longbones, and will have severe local pain, accompanied by oedema, erythema, pseudoparalysis (not using affected limb), fever, nausea, vomiting.

Question 11

How do adults present with osteomyelitis?

Answer 11

Often with infection in spine & pelvis. They will often complain of back ache.

Question 12

What is the pathogenesis of osteomyelitis?

Answer 12

The inflammation causes increased pressued, and this causes vascular congestion. This causes oxygen deprivation, leading to ischaemia and necrosis. The immune cells from the inflammation will secrete collagenase and elastase, which causes osteolysis.

Suppuration occurs, which is when pus forms in the bone, leading to sinus formation.

Sequestrum forms, which is dead bone tissue due to the infection

Involcrum forms, this is a layer of new bone tissue on the existing dead bone. This new bone grows from the new periosteum.

Question 13

How can osteomyelitis be diagnosed?

Answer 13

Can do a Culture & Gram stain of aspirates, or bone biopsy

If its a haematogenous infection a blood culture can be done

Can using imaging - xray, CT, MRI

Question 14

What is the treatment for osteomyelitis?

Answer 14

Treatment starts with 4-6 weeks IV antibiotic (oral for children). When the patient first presents, we must use emperic treatment initially to reduce risk of further complications before exact organism is known from further tests. For the type of bacteria, always consider: Staph Aurues (MRSA), Streps, Gram negatives (E.coli, pseudomonas, haemophilus)

Also need to do surgical debridement to remove necrotic tissue.

Question 15

What is septic arthritis?

Answer 15

Septic arthritis is caused by the invasion of the joint space by a pathogen which produces arthritis

such as:

• Bacteria
• Fungi
• Viruses
• Acute or chronic disease

Question 16

What is the most common cause of septic arthritis? And what will have a higher chance of being the cause in younger, sexually active people?

Answer 16

Staph. Aureus

In sexually active consider Neisseria gonorrhoeae

Question 17

What happens to the synovial fluid and membrane in septic arhritis?

Answer 17

Colonisation of synovial fluid by a pathogen, which causes an influx of inflammatory & immune cells, which causes erosion of the synovial membrane

Question 18

What are some clinical symptoms of septic arthritis?

Answer 18

Acute, rapid onset of inflammation & swelling

Serve arthralgia

Mainly occurs in knee 40%, but also in hip 20%

Few systemic signs (low fever)

Pseudoparalysis

Question 19

What are some complications of septic arthritis?

Answer 19

Sepsis

Osteomyelitis

Joint destruction (loss of articular cartilage)

Question 20

How is setpic arthritis diagnoised?

Answer 20

• Aspiration of synovial fluid (arthrocentesis) - aspirate will be turbid, yellow, decreased viscosity
• Gram stain - specify organism and begin specific antimicrobial therapy
• Culture
  
  • Blood culture
• Xray, ultrasound

Question 21

What is the treatment for septic arthritis?

Answer 21

4-6 weeks of IV antibiotics, and when the patients first present we must give them empirical treatment, and then change to a more specific drug once the organism’s sensitivities are known.

Need to consider: Staph. Aureus (MRSA), streps (Enterococcus), gram negatives (E. coli, Pseudomonas), Neisseria gonorrhoeae

Always need to keep antibiotic resistnace in the back of mind whilst treating

After starting antimicrobial treatment, we need to do an aspiration of the infected synovial joint (and removed infected prosthesis if required)

Question 22

What is reactive arthritis?

Answer 22

It is an autoimmune inflammatory joint disease (unknown cause)

Question 23

When does reactive arthritis normally occur?

Answer 23

In sequelae (proceeding) to genitourinary infection (chlamydia), or GI infection (campylobacter, salmonella, shigella, yersinia, C. difficile

Question 24

What is the triad of symptoms that usually presents with reactive arthritis? (Not always present)

Answer 24

Urethritis/cervicitis

Conjunctivitis/uveitis

No symmetrical arthritis of large joints

Question 25

What gene is reactive arthritis strongly associated with?

Answer 25

HLA-B27 gene

Codes for a MHCl

Having this gene increased risk by 50x

Question 26

What groups in reactive arthritis groups most common in?

Answer 26

RA is most common in people aged 20-40, where the rates in men and women are similiar following an enteric infection. But following an STI, males have a rate 9 times higher than females.

Question 27

What is the pathogenesis of reactive arthritis?

Answer 27

Reactive arthritis occurs 1-6 weeks after initial infection, where the original infection is often asymptomatic

It causes inflammation of the joints, skin, mucous membranes and eyes

Question 28

How is reactive arthritis treated?

Answer 28

Reactive arthritis is typically self limiting, where it will take 3-12 months to resolve, but recurrence occurs 50% of the time.

We can use anti-microbials to remove the aetioloigcal agent, but this doesn’t change the course of the arthritis.

We can use DMARDs and NSAIDS for symptomatic treatment