Bone & Joint Infections Flashcards
Define osteomyelitis. How is it often caused?
Infection of bones
Often caused by open fractures
Define septic arthritis.
Infection of joints
Define prosthetic joint infection.
Infection of an artificial joint replacements (may lead to another joint replacement)
What types of joint infections are more common and severe?
Prosthetic joint infections rather than native joint infections
What are the common microbes affecting bones and joints?
- Staphylococcus aureus (inc. MRSA) most commonly
- Streptococci (β-haemolytic Streptococci species + Strep. Pneumoniae)
- Enteric bacteria (E.Coli + Salmonella species)
- Coagulase-negative Staphylococci (+ other mycobacteria too)
- Others e.g. Lyme Borreliosis, Gonorrhoea, Brucellosis, TB, fungi and parasites
What are the risk factors for bone and joint infection?
- Direct inoculation via trauma, medial procedures or skin ulcers
- Contiguous spread from nearby skin of soft tissue infection (SSTI)
- Haematogenous dissemination from IV devices or drug abuse
- Immunosuppression e.g. in DM, renal failure and sickle cell disease
What is the step-by-step pathology of a microbe?
- Access into the body
- Adherence to suitable site
- Invasion/penetration of barriers
- Multiplication/replication
- Evasion of the host immune system
- Resistance to anti-microbial treatments
- Damage to host cells (directly/indirectly)
- Transmission to other hosts
How do bacteria interact with bone tissue?
Bacterial surface proteins e.g. SpA on S. Aureus or Lipase D on S. Epidermidis
How can acute osteomyelitis become chronic?
- Initial infection is localised to the cortical region of the bone creating a small abscess
- Infection progresses into the sub-periosteal space as the abscess enlarges lifting of the periosteum
- Diffuse infection occurs with further abscess enlargement causing sequestrum (avascular necrotic bone tissue)
- Biofilm form as bacteria present in an organic matrix on an inert surface
- Involucrum: new bone formation outside sequestrum
- Cloacae: pus from sequestrum escapes through involucrum via holes
- Infection and pus from cloacae causes skin necrosis (discharging sinuses)
Where else can biofilms form?
On prosthetic joints where they assist infection
What are the main clinical features of infection?
Inflammation: pain, swelling, redness, warmth and loss of function
What are the clinical features of osteomyelitis?
Inflammatory signs
Fever
Pathological fractures
Discharging sinuses
What are the clinical features of septic arthritis?
Inflammatory signs
Fever
Damage to articular surfaces
Presentations of infections can be confused. Why is this?
They can be gradual onset or mis-diagnosed
What are the common causes of osteomyelitis?
- Traumatic infections e.g. open fractures or penetrating wounds
- Operative infections e.g. total joint replacement, internal fixation of fractures or tumour resection with bone graft for limb salvage
- 2ndary to contiguous infections
- Contributing or predisposing factors e.g. haematoma or vascular insufficiency in DM/atherosclerosis
Why are people with diabetes mellitus (DM) more prone to osteomyelitis?
DM patients develop peripheral neuropathy meaning they have foot deformities (e.g. clawfoot) and lose lose sensation of their foot and the skin of the foot is of lower quality so they can wound their foot and because they do not notice, this wound gets worst, becomes infected and tracks deeper to the bone partly due to impaired immune response and poor perfusion
What blood tests would you run for a suspected bone or joint infection?
FBC
Inflammatory markers e.g. CRP
Other blood tests to look for evidence of severe sepsis e.g. renal function and lactate
Blood cultures (x2)
What skin sample test would run for a suspected bone or joint infection?
Skin/ulcer swabs inc. MRSA
What imaging would you rub for a suspected bone or joint infection? What would each show?
- Plain radiographs: shows late changes well but not early changes
- CT scans: show bone changes well but not as good for soft tissue changes
- MRI scans: shows soft tissue changes well but not at good for bone changes
What is the earliest visible sign of a bone or joint infection?
Periosteal reaction
Why might a patient get a pathological fracture around a prosthetic joint?
If the prosthetic has become loose
What can patients with tuberculosis (TB) get in terms of bone or joint infections?
Discitis where the IV discs of the vertebra become narrowed
When would you do a joint aspiration?
On the ward using local anaesthetic using aseptic technique unless the joint is prosthetic where the infection risk would be too high
What can you determine by looking at a joint aspiration sample?
- Fluid appearance
- Should be quite viscous and clear
- May look non-viscous, turbid/cloudy due to WBCs, purulent or blood-stained if there is a problem - Single sample may be taken for microscopy (WBCs, bacteria, crystals), culture and PCR tests
When would you do a bone biopsy?
In theatre using general anaesthetic so it is better to get answer from a blood culture instead
What would you look for in a bone biopsy?
Multiple samples should be taken for culture, PCR tests and histopathology
How should you treat bone and joint infections?
- Manage sepsis
- Obtain samples if possible before starting antibiotics
- Empirical antibiotics (IV Flucloxacillin/Benzylpenicillin)
- Targeted antibiotics depending on culture and sensitivities
- 2-6 week IV antibiotic course then 4-6 weeks PO
- Potentially surgery
When would surgery be needed to treat a bone or joint infection?
- Septic arthritis will require a joint washout in theatre (can get further diagnostic samples when doing this)
- Osteomyelitis requires surgery is chronic changes have developed
- Prosthetic joint infections require removal for a while and then replacement w/ antibiotics continued in between operations
How can you prevent bone and joint infections?
- Prompt diagnosis and treatment of predisposing conditions
- Strictest possible aseptic conditions for joint replacements
- Antibiotics embedded into cement used for prosthetic joints
