Infection Flashcards
Name 4 local factors that increase susceptibility to infection of bones and joints
Trauma Articular steroid injection Large wound area and depth Poor perfusion Distal anatomical location Necrotic tissue Foreign body Chronic bone or joint disease
Name 4 systemic factors that increase susceptibility to infection of bones and joints
Age: children and elderly Malnutrition General illness Anaemia Diabetes mellitus Sickle-cell anaemia* Alcohol excess Rheumatoid disease Immunosuppression IVDU
Describe the features of acute pyogenic infection
Formation of pus often localised in an abscess
Abscess may extend infection along tissue directly, or spread via lymphatics (lymphangitis and lymphadenopathy) or blood (bacteraemia and septicaemia).
Systemic reaction due to enzymes and toxins.
Describe the features of chronic infection
May occur after acute infection
Less acute systemic effects, but may be more debilitating
Lymphadenopathy, splenomegaly, and tissue wasting
Outline the treatment principles of bone and joint infections
Analgesia and supportive measures Rest the affected part Initiate antibiotics Drainage of pus and debridement of necrotic tissue Stabilise bone if fractured Maintain soft tissue and skin cover
What is typically the causative organism of acute osteomyelitis?
Staph aureus
Less often: Strep pyogenes, Strep pneumoniae, or H. influenzae (children)
If sickle-cell: Salmonella typhi
Which patient group is most affected by acute osteomyelitis?
Children over age of 4 years
What is the most common location of acute osteomyelitis in children?
Metaphysis of long bones
Most often at the proximal or distal end of the femur, or the proximal end of the tibia
N.B. in infants, acute osteomyelitis can also reach the epiphysis due to presence of anastomoses.
Describe the pathological changes of acute osteomyelitis
- Acute inflammation: intense pain, obstructed blood flow
- Suppuration: subperiosteal abscess formation
- may spread along shaft and re-enter bone, or spread to soft tissues
- infants: may spread to epiphysis and joint - Necrosis: usually seen by 1 week
- stasis, periosteal stripping, thrombosis
- bone fragments can act as foreign bodies - New bone formation: involucrum encases infection
- if infection persists ➔ chronic osteomyelitis - Resolution
- requires infection to be controlled and intraosseous pressure to be release at an early stage
- may result in overall thickening of bone
Describe the clinical features of acute osteomyelitis in children
Severe pain: limb held still
Systemic: fever, malaise, irritability, lethargy
Tenderness over involved bone
Decreased range of motion in adjacent joints
Later: red, swollen, warm ➔ pus formation (suppuration)
Describe the clinical features of acute osteomyelitis in infants and neonates
Infants and neonates may present with misleadingly mild symptoms: failure to thrive, drowsy, irritable
May have metaphyseal tenderness and resistance to joint movements
Always look at other sites, as multi infection is not uncommon.
Name 2 aspects of the history that would increase suspicion of acute osteomyelitis in neonates
Birth difficulties
Umbilical artery catheterisation
Name and explain 2 consequences of acute osteomyelitis in infants within 1st year of life
Growth retardation and deformity
Metaphysis-epiphysis anastomoses present in 1st year of life, allow haematogenous spread to epiphysis.
Where is the commonest location of acute osteomyelitis in adults? What clinical features would suggest this?
Spine
Suspicious features: back pain and a mild fever
How is acute osteomyelitis confirmed?
Fine needle aspiration and culture
How is acute osteomyelitis investigated?
Aspirate pus from subperiosteal abscess or joint* Culture for cells and organisms Raised WBC and ESR MRI*: 90-100% sensitivity X-ray: normal for first 2 weeks
Explain the treatment of acute osteomyelitis
Blood and aspirate samples sent for culture
Supportive: bed rest, splint, analgesia
Prompt antibiotics if pus found on aspiration
Empirical antibiotics: Flucloxacillin or clindamycin
Continue antibiotics for 4-6 weeks
Children should initially receive 2 weeks of IV antibiotics
Abscess drainage
Surgical debringement
Outpatient follow-up*: crucial to check for recurrence
State 3 complications of acute osteomyelitis
Spread: septic arthritic or metastatic osteomyelitis
Pathological fractures
Growth disturbance/deformity if epiphysis involved
Persistent infection ➔ chronic osteomyelitis
Describe the clinical features of subacute osteomyelitis
Common in distal femur, and proximal and distal tibia
Pain near one of larger joints for several weeks
What classic radiographic sign is indicative of subacute osteomyelitis?
Brodie abscess: small oval cavity surrounded by sclerotic bone
Most be explored as can be mistaken for osteoid osteoma or bone tumour if large
What is the commonest causative organism of post-traumatic osteomyelitis?
Staph aureus
Others: E. coli, Proteus mirabilis, Pseudomonas aeruginosa
Describe the clinical features of post-traumatic osteomyelitis
Fever
Pain and swelling over fracture site
May have purulent discharge
What are the common causes of chronic osteomyelitis?
Following open fracture or operation
Less common nowadays after acute osteomyelitis
Name 2 typically causative organisms of chronic osteomyelitis
Staph aureus E. coli Strep pyogenes Proteus mirabilis: soil Pseudomonas aeruginosa Strep epidermidis: surgical implants
Describe the clinical features of chronic osteomyelitis
Recurrent pain, redness, and tenderness at affected site
Healed and discharging sinus
What x-ray features are seen with chronic osteomyelitis?
Bone rarefaction (thinning) surrounded by dense sclerosis and cortical thickening
Outline the treatment options for chronic osteomyelitis
If seldom relapses: conservative management
-Rest, dressing, and antibiotics for 4-6 weeks
Drainage of any acute abscess
Refractory or frequent relapses: surgery
- excision of infected/devitalised bone
- Ilizarov method after bone transport ➔ bone union
What is the usual causative organism of septic arthritis?
Staph aureus
Children aged 1-4: H. influenzae if not vaccinated
Explain the pathology of septic arthritis
Joint invaded by:
- a penetrating wound
- eruption of adjacent bone abscess
- distal haematogenous spread
Describe the clinical features of septic arthritis in children
Acute severe pain and swelling of single joint
-Commonly hip (children)
-Unable to weight bear
Tachycardia
Swinging fever
Red, swollen, tender joint: often flexed
Restricted movement due to pain and spasm
Describe the clinical features of septic arthritis in infants
Emphasis on septicaemia rather than joint pain
Irritable and refuses to feed
Rapid pulse +/- fever
Local warm, tender joints: resistant to movement
Examine umbilical cord and IV access sites
Describe the clinical features of septic arthritis in adults
Acute severe pain and swelling of single joint -Commonly knee (adults) -Unable to weight bear Tachycardia Mild fever Red, swollen, tender joint: often flexed Restricted movement due to pain and spasm Unable to weight bear
How does the presentation of septic arthritis differ in adults with rheumatoid arthritis?
Patients with rheumatoid arthritis, especially on corticosteroids, may develop a ‘silent’ joint infection.
Suspect septic arthritis if unexplained deterioration in patient’s general condition.
What x-ray changes are seen with septic arthritis?
First 2 weeks of bacterial arthritis:
Soft-tissue swelling
Widening of joint space
Periarticular osteoporosis
Later: joint space narrowing and signs of bone destruction
How is a diagnosis of septic arthritis confirmed?
Joint aspiration and culture*
Blood culture positive in 50%
WBC, CRP, and ESR are suggestive
Name 3 differentials of septic arthritis
Osteomyelitis near joint: may be indistinguishable, safest to assume both osteomyelitis and septic arthritis present
Acute haemarthrosis (trauma or haemophilia): blood on joint aspiration
Transient synovitis: clinical features less acute
Gout/CPPD: presence of urate or pyrophosphate crystals
Name 2 complications of septic arthritis
Dislocation Avascular necrosis Epiphyseal destruction ➔ pseudoarthrosis Growth disturbance/deformity Ankylosis: stiffening and immobility due to fusion
What is the treatment for septic arthritis
Joint aspiration and examination Antibiotics STAT: flucloxacillin 4-6 weeks Joint rested and splinted -if hip: abducted and 30 degrees flexed Drainage and wash-out of joint
Encourage movement afterwards if cartilage intact
Otherwise, immobilise joint in optimum position whilst ankylosis occurs
What percentage of TB patients present with skeletal involvement?
5%
Which patient groups are most commonly affected by skeletal TB?
Endemic: pulmonary TB in children and young adults
Non-endemic: chronic disease, or immunosuppressed
Explain the pathology of skeletal TB
Infection reaches the skeleton by haematogenous seeding from lungs or intestine.
Chronic inflammation ➔ caseating granuloma
Cold abscess
Chronic sinus, may have secondary pyogenic infection
Describe the progression of vertebral TB
Vertebral TB usually begins in the anterior part of the vertebral body near the intervertebral disc.
Later invasion into intervertebral disc, with subsequent collapse forwards ➔ sharp angulation of spine (gibbus deformity)
Describe the progression of joint TB
Joint TB may start in synovium or nearby metaphysis. If untreated, it will destroy the articular cartilage and cause fibrous ankylosis.
Describe the clinical features of skeletal TB
Tuberculosis arthritis (1%): affects spine (50%), hip or knee (30%). Fever, night sweats, weight loss.
Pott’s disease (TB spondylitis): Back pain, lower limb weakness, kyphosis. Fever, night sweats, weight loss.
How is skeletal TB treated?
Anti-tubercular drugs:
2 months: Rifampicin, Isoniazid (+pyridoxine), Pyrazinamide, Ethambutol
Additional 4 months: Rifampicin, Isoniazid (+pyridoxine)
Dose is weight-dependent
What monitoring is required whilst on anti-tubercular treatment?
LFTs: ‘R.I.P.’ all can cause hepatitis
Visual acuity: ‘E.’ can cause optic neuritis
