Infection of bones and joints Flashcards
What are the common causative agents of joint infection?
- Usually bacterial
- Rarely fungal
Some viruses (rubella, mumps and Hep. B) are associated with a mild self-lijmiting arthritis but this is not due to direct joint involvement
What is the predominant causative organism of septic arthritis?
Staph. aureus
What are the risk factors for the development of septic arthritis?
- RA
- OA
- Joint prostheses
- IV drug abuse
- Alcoholism
- Diabetes
- Recent intra-articular corticosteroid injection
- Presence of cutaneous ulcers
What organisms may cause septic arthritis in specific patient groups?
- In sexually active patients, gonococcal arthritis may be suspected
- In older and immunocompromised people, gram-negative organisms are more common than among young people (although staph./strep. still predominate)
What causative organism might be suspected in a patient presenting with septic arthritis who has recently been discharged from hospital, or in nursing home residents or patients with in dwelling urinary catheters?
MRSA
What might cause septic arthritis in immunocompromised patients?
Tuberculous arthritis
How might a joint become infected?
By direct injury or by blood borne infection from an infected skin lesion or another site
How does septic arthritis present?
A hot, swollen, tender restricted joint which has developed acutely. There may be evidence of infection elsewhere e.g. fever.
How might septic arthritis present in a patient who has a prosthetic joint?
May be early (within 3 months of surgery) or late
Early infection presents with wound inflammation or discharge, joint effusion, loss of function and pain
Late disease presents with pain or mechanical dysfunction
What investigations might be done if a patient is suspected of having septic arthritis?
- Synovial fluid gram stain and culture
- Synovial fluid white cell count
- Blood culture
- ESR and CRP
What is the appearance and white cell count of normal synovial fluid?
Appearance: straw-coloured
WCC: <3000 WCC/mm3
What is the appearance and white cell count of inflammatory synovial fluid?
Appearance: cloudy
WCC: >3000 WCC/mm3
What is the appearance and white cell count of septic synovial fluid?
Appearance: opaque
WCC: up to 75,000 WCC/mm3
How is acute septic arthritis managed in confirmed Staph. aureus infection?
Flucloxacillin + fusidic acid
Add gentamicin in immunosuppressed patients to cover gram-negative agents
Antibiotic therapy should be IV for 2 weeks, then oral for a further 4 weeks
The joint should be aspirated to dryness as often as necessary
How should acute septic arthritis be managed in confirmed staph aureus infection in a penicillin allergic patient?
Replace IV flucloxacillin with IV clindamycin or ceftriaxone for 2 weeks
Oral clindamycin or ceftriaxone for a further 4 weeks
How should acute septic arthritis be managed in confirmed MRSA infection?
Replace IV flucloxacillin with IV vancomycin
What is the most common cause of septic arthritis in previously fit young adults?
Gonococcal arthritis
What concomitant symptoms may be seen with gonococcal arthritis?
It occurs secondary to genital, rectal or oral infection although this is often asymptomatic
Concomitant skin infection is common- maculopapular pustules are seen
How is gonococcal arthritis treated?
Penicillin, ciprofloxacin or doxycycline for 2 weeks and joint rest
How is meningococcal arthritis treated?
Penicillin
What bones/joints are most commonly affected in tuberculous arthritis?
Hip knee and spine
What are the symptoms of tuberculous arthritis?
Insidious onset of pain, swelling and dysfunction
Patient is febrile, has night sweats and loses weight
How is tuberculous arthritis treated?
As for tuberculosis infection elsewhere (i.e. rifampicin, pyrazinamide, ethambutol, isoniazid) but with treatment extended to 9 months
What is osteomyelitis?
Infection of bone marrow which may spread to the bone cortex and periosteum via the Haversian canals. It results in inflammatory destruction of the bone and, if the periosteum becomes involved, necrosis.
What is the most common causative agent of osteomyelitis?
Staphylococcus aureus is the most common causative organism accounting for 90% of cases.
Other organisms involved are haemophilus influenza and Strep. species
In 5% of cases, more than one organism is involved
What is a sequestrum?
Necrotic bone which has become detached from healthy bone. A large sequestrum that remains in situ acts as a focus for ongoing infection
What is the most common site of osteomyelitis in adults and children?
Adults: cancellous/trabecular bone (softer/more flexible bone found at the ends of long bone, proximal to the joints and within the interior of the vertebra)
Children: distal femur and proximal tibia
How is osteomyelitis categorised?
Haematogenous osteomyelitis: an infection resulting from a haematological bacteria seeing from a remote source. More commonly associated with children where it tends to occur in the rapidly growing and highly vascular metaphysis of growing bones. Also seen in patients with distant foci of infection e.g. those with infected urinary catheters
Direct/contiguous osteomyelitis:
This type of infection occurs where there is direct contact of infected tissue with bone, as may occur during a surgical procedure or following trauma Clinical signs tend to be more localised and there are often multiple organisms involved
What conditions predispose to osteomyelitis?
DM
Peripheral vascular disease
What are the risk factors for osteomyelitis?
- Trauma
- Posthetic orthopaedic device
- DM- osteomyeloitis is frequent in persisting diabetic foot ulcers and is a high risk factor for adverse outcome. Early diagnosis is crucial to ensure correct management
- Peripheral arterial disease
- Chronic joint disease
- Alcoholism
- IV drug abuse
- Chronic steroid use
- Immunosupression
- TB
- HIV
- Presence of catheter-related bloodstream infection
- Sickle cell disease
How does acute, haematogenous osteomyelitis of a long bone present?
The acutely febrile and bacteraemic patient presents with a markedly painful, immobile limb. There may be swelling and tenderness over the affected area, with associated erythema and warmth. Pain is exacerbated by movement.
How does acute, haematogenous osteomyelitis of the spine present?
Presents insidiously following an acute septicaemic episode. There may be localised oedema, erythema and tenderness, chronic back pain or night pain.
What is Pott’s disease?
Vertebral osteomyelitis resulting from the haematogenous spread of TB. There is damage to the bodies of two neighbouring vertebrae leading to vertebral collapse and subsequent abscess formation. Pus can track out from there into adjacent structures leading to systemic symptoms of malaise, fever and night sweats
What symptoms are seen in chronic osteomyelitis?
All or only a few of the following:
- Previous acute infection
- Localised bone pain
- Erythema and swelling over the affected area
- Non-healing ulcer
- Draining sinus tracts
- Decreased range of motion of adjacent joints
- Chronic fatigue
- General malaise
What are the differential diagnoses for suspected osteomyelitis?
- Cellulitis
- Trauma
- Gout
- Spinal cord neoplasm
- Acute sickle cell disease crisis
What is the image modality of choice for investigation of acute osteomyelitis?
MRI
What is the first line treatment of acute osteomyelitis?
Flucloxacillin for 6w + fusidic acid for the inital 2w
How is acute osteomyelitis managed in penicillin allergic patients?
Clindamycin for 6w + fusidic acid for the inital 2w
How is acute osteomyelitis managed if MRSA is suspected?
Vancomycin for 6w + fusidic acid for the inital 2w
What is done in addition to antibiotic prescription in the management of chronic osteomyelitis?
Surgical debridement of necrotic tissue
