Bone and joint infection basics
by Michael Held & Maritz Laubscher
Learning objectives
- Know the pathophysiology and differences between children and adults.
- Know the risk factors.
- Understand the most common pathogens and know how to approach
Introduction
Bone and joint infections can be acute or chronic. Acute infections should be treated as orthopaedic emergency. Especially for children and immunocompromised patients infections, acute infections can lead to severe systemic illness and can have detrimental long term morbidity if not treated urgently. Osteomyeltits (infection of bone) can be divided into acute, sub-acute and chronic. In sub-acute osteomyelitis, infection lasts from one to several months, after which chronicity begins. Chronic osteomyelitis is characterised by progressive bone destruction and new bone apposition.
Pathophysiology
Hematogenous
Compared to children, adult osteomyelitis is rarely hematogenous, i.e. originated or transported by blood. When it occurs, it usually affects the spine. It is caused by microorganisms that seed the bone in the event of bacteremia. The most common organism found in hematogenous spread is Staphylococcus aureus. Hematogenous infections are most common in children. The metaphysis is the most common site because it is rich in blood supply (although this has sluggish flow) and is an actively growing part of bone. It also has relatively fewer phagocytes than the physis or diaphysis.
Contiguous spread
This mode of contamination can be associated with previous surgery, an old non healing wound (diabetic foot, neuropathic ulcer) or a previous trauma. Infection spread by contiguity from adjacent tissue to bone.
Direct inoculation
Open fractures, penetrating injuries or bone surgeries can be a direct source of infection, resulting in osteomyelitis.
Risk factors
- Recent trauma or surgery
- Immunocompromised patients
- IV drug use
- Poor vascular supply
- Systemic conditions such as diabetes and sickle cell anaemia
- Peripheral neuropathy
Classification
Osteomyelitis may be classified based on the duration of illness (acute versus chronic) and the mechanism of infection (haematogenous versus non- haematogenous).
Bacteriology and antibiotics
The most common infecting organism is staphylococcus aureus in all age groups, which accounts for 80–90% of positive cultures. The table below shows common organisms of different age groups and patient populations with antibiotic choice, but this should be guided by local authorities.
| Patient cohort and bacteriology | Antibiotics | |
|---|---|---|
| Neonates | S. aureus (MRSA), Group | Cloxacillin (Fusidic Acid) |
| B strep | 3rd gen cephalosporin | |
| Gram negatives | ||
| 6 months – 4 years | S. aureus, K. kingae, H. | Cloxacillin |
| influenzae (rare) | + Ampicillin/3rd gen cephalosporin | |
| > 4 years | S. aureus | Cloxacillin |
| Adults (acute) | S. aureus | |
| Penicillin allergy | Clindamycin | |
| immunocompromised | S. aureus, S. pneumoniae, | Cloxacillin + 3rd gen cephalosporin |
| pseudomonas, fungal | Cloaxillin + 3rd gen cephalosporin | |
| Cefazolin is an alternative to Cloxacillin | ||
| Sickle cell disease | S. aureus, Salmonella | (if not available) |
| contiguous chronic | The most common causative | Common organisms of different age |
| osteomyeliti | organisms are: | groups and patient populations with |
| Enterobacteriaceae sp. | antibiotic choice | |
| Staphylococcus sp. | ||
| Pseudomonas aeruginosa | ||
| Enterococcus sp. | ||
| In 45% of infections multiple | ||
| organisms cultured | ||
| heamatogenous chronic | Staphylocossus aureua is | |
| osteomyelitis | the most common organism involved in adults (60-90%) |