23. Bone and joint infections (Robson) Flashcards
What is septic arthritis?
Inflammation to a joint caused by bacterial infection
Is septic arthritis typically mono or poly articular in nature?
Monoarticular - 90% of cases
Who does septic arthritis tend to occur in?
Tends to occur at either end of the age bracket - very young or very old
Poorer immune surveillance (older) or lack of immunisation (younger)
How does the presentation of acute and chronic septic arthritis differ?
Acute - usually be a mild fever i.e. pyrogenic
Chronic - this is a cold inflammation - no fever or signs of being unwell
Why can septic arthritis commonly occur at a growth plate?
Due to the tortuous course of the arteries here - can lead to a lodging of bacteria
What is the cause of septic arthritis?
Usually follows a haematogenous spread of e.g. infection from elsewhere
In what age group is septic arthritis most common and why?
Most common over the age of 50, especially over the age of 60 - these people are undergoing more procedures on their joints -greater risk of bacteria entering the joint
What are the five different ways that bacteria can enter the joint to form septic arthritis?
Haematogenous route - blood Dissemination from osteomyelitits (bone) Spread from adjacent soft tissues Penetrating damage or trauma Diagnostic or therapeutic measures
What are the three most common gram positive organisms causing septic arthritis?
Staphylococcus aureus
Streptococci pyogenes
Streptococci pneumoniae
What is the most common gram negative organism causing septic arthritis?
Neisseria gonorrhoea
In which age group is neisseria gonorrhoea the most common organism for septic arthritis?
In the sexually active age group - 16-50year olds
What is the most common joint affected by septic arthritis and why?
Knee
Very big joint - high blood supply
Which joints can potentially be infected by septic arthritis?
ANY JOINT
How will the synovial fluid appear in septic arthritis?
Lumpy
Slightly cloudy
Slightly red
Presence of bacteria and neutrophils
What is the glucose level in someone with septic arthritis and why?
Glucose level will be reduced - the bacteria are using up the glucose for proliferation
Why is radiology not useful in the early stages of septic arthritis?
The infection is inside the joint - hidden initially as the calcification appears normal
When will radiological changes start to appear from septic arthritis?
After about two weeks
What might be seen radiologically in septic arthritis? x6
Soft tissue swelling Joint capsule distension Joint space narrowing Effusion Erosion Cyst formation
What can be seen on an MRI for septic arthritis?
Increased signal will signify increased synovial effusion
How is septic arthritis treated?
Drainage and washout of the joint to remove as much bacteria as possible
(NB. do not put anything else back in - the articular capsule will reproduce the synovial fluid)
Antibiotics - start with broad spectrum and then specific
Why is there swelling in septic arthritis?
Synovial effusion
Other than the knee, what are the common joints affected by septic arthritis?
Hip, ankle, elbow
What are the differential diagnoses for septic arthritis and how do you rule these out?
Acute RA - polyarticular so if presenting as monoarticular then not this
Gout - usually in the big toe
Pseudogout - looking for presence of chondrocalcinosis (calcification of the cartilage)
What is reactive arthritits?
The joint is reacting to the presence of bacteria in the body - not necessarily in the joint itself
This is a sterile inflammatory process
What genetic predisposition is associated with reactive arthritis?
HLA-B27
What is Pott’s disease?
Form of TB outside of the lungs and in the vertebral joints i.e. the IV discs - bacteria lodged in the IV discs and bodies
Which regions of the vertebrae are typically affected by Pott’s disease?
Lower thoracic and upper lumbar
What is osteomyelitis?
Infection and inflammation of the bone
What are the three main routes by which osteomyelitis can occur?
Haematogenous spread from an infection elsewhere in the body
Contiguous spread from another infected focus
Direct trauma
Which route of osteomyelitis is more common in children?
Haematogenous spread
Which route of osteomyelitis is more common in young adults?
Direct trauma
How can osteomyelitis disrupt growth?
If the infection, once having entered the joint, spreads across the whole of the growth plate
What are the predisposing factors for the development of osteomyelitis?
Impaired immune surveillance e.g. malnutrition, extremes of age
Impaired local vascular supply e.g. diabetes, venous stasis, sickle cell
What is a Brodie’s abscess and why does this occur?
Walling off of localised bacteria in bone by formation of fibrous tissue and granulation tissue
Why does a Brodie’s abscess occur?
The bone attempts to wall off and hide the bacteria from the rest of the bone so that the infection cannot spread
When does a Brodie’s abscess typically occur?
In later stages of osteomyelitis
How can a Brodie’s abscess be recognised on an x-ray?
There is a sclerotic ring around it
How can you differentiate between a subchondral cyst and a Brodie’s abscess on an x-ray?
Subchondral cyst - at the EDGE of the bone margin
Brodie’s abscess - within the bone
What is the main complication of chronic osteomyelitis?
Local bone loss and resulting damage to the soft tissues
What is the relation of a squamous cell carcinoma to osteomyelitis?
Chronic, untreated osteomyelitis - can (rarely) result in the development of squamous cell carcinoma
What is the main investigation used for osteomyelitis?
Bone biopsy - see if you can find the bacteria
Why is a blood culture not useful for diagnosis of osteomyelitis?
The pathogen may not have gotten out of the bloodstream
How is acute osteomyelitis treated?
Same as septic arthritis - washout and provision of antibiotics
How is chronic osteomyelitis treated?
Surgical debridement to remove dead bone
Reconstruct the bone e.g. allograft or autograft
Antibiotics
How long should antibiotics be provided for when treating osteomyelitis?
For 4-6 weeks
What will be seen in the histology of a Brodie’s abscess?
Presence of neutrophils, macrophages and the bacteria
ESR in septic arthritis is?
Raised
Synovial fluid of septic arthritis described as? x2
Turbid
Purulent
Two factors commonly predisposing to reactive arthritis are?
STI - chlamydia
Enteritis - salmonella
Three presentations of osteomyelitis?
Abrupt fever - more common in children
Decreased limb movement
Local non-specific pain
Two signs of osteomyelitis?
Elevated neutrophil count
Elevated ESR
Two rare complications of osteomyelitis?
Squamous cell carcinoma
Amyloidosis
