Infection Flashcards
Pathways of spread?
Haematogenous – via blood stream, affected area will follow blood vessels
Contiguous spread – spread into bone from adjacent contaminated site (cutaneous, sinus and dental infections are
common primary sites).
Direct spread – from penetrating injuries or wounds – open fractures, knife or nail wound, implantation of prosthesis/wire/ screw.
Bone spread patterns?
Infantile – cartilaginous vascular barrier at the epiphyseal plate does not from till between 8-18 months, haematogenous spread across epiphysis can easily occur (explains high incidence of septic arthritis in this age group)
Childhood – occurs between 1yr and the time the physis fuses, no metaphyseal vessels penetrate the physis so epiphyseal blood is separate and distinct. Metaphyseal blood flow is slow and turbulent giving good environment form microbe proliferation hence the common site for infection
Adult – after physeal plate closure, metaphyseal blood supply is re-established across to epiphysis. Organisms can now access the subarticular bone and the joint. Resulting in the increase of septic arthritis in adults.
Types of periosteal reactions?
Solid – slow growing, benign → benign tumour, fracture, slow growing infection
Laminated – onion-skin layered→malignant tumour, infection
Spiculated – sunburst, hair on end, new bone orientated perpendicular to bone→malignant
tumour
Codman’s triangle – often malignancy but can occur in many lesions
What is a Sequestrum?
Inflammatory exudate→compression of capillaries→marrow, fate and bone infarction.
Periosteal and subperiosteal involvement causes a loss of blood supply to the cortical bone resulting in necrosis. Cortical and medullary infarcts result in the formation of an area of necrotic bone.
What is a Involucrum?
As oedema lifts the periosteum, it causes a modest degree of new bone proliferation
Periosteal new bone is an attempt of the body to wall off the infective process
Starts as laminated periosteal reaction but progresses to a solid periosteal reaction forming new
bone growth around the bone
Often affects whole diameter of the shaft
What is a Cloaca?
Drainage defects may develop in the involucrum to allow for continued discharge
(decompression) of the inflammatory exudate
May traverse the soft-tissues and communicate with the skin, particularly in chronic
osteomyelitis
Rarely these sinuses may develop a squamous cell carcinoma within the channel of the cloaca
Chronic drainage allows infection to form in soft tissues
Radiographic Signs of Early Infection
latent period (10 days for extremities)
moth-eaten or permeative medullary and cortical destruction
periosteal new bone – solid or laminated periosteal reaction, occasionally Codman’s triangle appearance
red, hot, and shiny skin, very painful
lytic bone
Radiographic Signs for Late Infection
bone → destruction of adjacent cortex, involucrum, sequestrum (by 3-6 weeks), cloaca
joint→may spread into the joint and cause septic arthritis, loss of joint space, healing by bony ankylosis
soft tissue→drainage sinus, Marjolijn’s ulcer (aggressive ulcerating squamous cell carcinoma)
lytic change but sometimes can only visualise healing response, bony destruction, solid periosteal reaction
Suppurative osteomyelitis
Demographics Affected
- Most comon between 2 and 12 years of age
- > in makles
- can occur at any age
Causative agent
- Staphylococcus aureus
Distirbutiuon
- Lumbar, thoracic, cervical, SIJ
Calinical Features
- Infants/young: acute fever, chills, pain, swelling, loss of limb function.
- Adults: more chronic w/ fever, malaise, pain and swelling
Radiographic Features
- Subperiosteal abcess (cervical)
- Periostial Reaction - laminated, solid, Codmans triangle
- Focal bony lytic area or cortical loss
- Loss of trabecular bone architecture
- New bone appostion
DDx
- Septic arhritis
- Early stage malignant bone tumour - Ewing sarcoma, osteosarcoma, lymphoma, multiple myeloma
- Metastases
Appendicular osteomyelitis
Demographics Affected
- Most common between 2 and 12 years of age.
- > in males.
- Can occur any age
Causative Agent
- Staphylococcus Aureus
Distribution
- Femur (most common), tibia, humerus and radius
Clinical Features
- Infants/young: acute fever, chills, pain, swelling, loss of limb function.
- Adults: more chronic w/ fever, malaise, pain and swelling
Radiographic Features
- Brodies abscess
- Eventual sclerosis
- Periosteal reaction→laminated, solid or even Codman’s can occur
- Focal bony lytic area or cortical
- Loss of trabecular bone architecture
- New bone apposition
DDx
- Suppurative osteomyelitis
- Septic arthritis
- Early stage malignant bone
- Tumour→Ewing sarcoma, osteosarcoma, lymphoma, multiple myeloma
- Metastases
Septic arthritis
Demographics
- Greatest incidence <30 years
Distribution
- Knee and hip common sites. Metaphysis due to rich blood supply
Clinical Features
- Restricted ROM secondary to severe pain and swelling, chills, fever, purulent synovial fluid.
Radiographic Features
- soft tissue – swelling, elevation or displacement of fat planes, obliteration of fat planes, increased density of soft tissue shadows.
- Joint – distention of joint capsule, widening of joint space early. Narrowing of joint space late with complete loss within a few weeks
- Bony change - Loss of normal subchondral and cortical bone, medullary moth eaten destruction. Complete resorption of articular ends of bone. Laminated periosteal reaction. Possible ankylosis. Deformation of joint as healing occurs
DDx
- Osteomyelitis
- Suppurative Osteomyelitis
- Transient Synvitis
Chronic Osteomyelitis
Demographics
- Increased in males and can occur at any age
Aetiology
- Unresolved Osteomyelitis
Distribution
- Any bone, typically long portion into diaphysis
Radiographic Features
- Increased bone density: sclerosis, cortical thickining, periosteal new bone, areas of destruction, dense sequestra
- Clocoa
- Large potion of the long bone is involved
- Periosteal reaction - laminated, solid, or even Codmans trangle can occur, will most likely be solid in a chronic case
- Focal bony lytic area or cortical loss
- Loss of trabecular bone architecture
- New bone apposition
DDx
- Spetic arthritis
Brodies Abscess
Demographics
- Increased in male children
Aetiology
- Recent infection or surgery (form of osteomyelitis - Staph A)
Distribution
- Metaphysis of tibia, femur, fibula, radius
Radiographic Features
- Localised area of lucency
- Drainage tract (cloaca)
- Large are of sclerosis around lesion
DDx
- Osteoid Osteoma
- Stress fracture
Supperative Spondylitis
Demographics
- Highest incidence in debilitated patients in 5th to 6th decade
- Females over males
Aetiology
- Staph A 90% of cases
- Contiguous spread – initial infection in adjacent disc.
- Spread via UTI via Batson’s venous plexus – haematogenous.
Distribution
- Lumbar spine most common
- Thoracic spine 2nd most common
Clinical Features
- Recent primary infection, recent surgery, or instrumentation
- High association with UTI’s
- Back pain – insidious and constant
- Local tenderness
- Decreased motion
- Fever is infrequent
Radiographic Features
Latent for 3 weeks on radiograph
- Discitis
- Disc space narrowing
- Paraspinal abscess
- Vertebral body destruction
- Spondylodiscitis
- Anterior superior vertebral body destruction
- Paraspinal abscess
- Involvement og neighbouring vertebra
- decreased disc height
- Abscess may displace paraspinal lines and psoas shadow (best depicted in T2 weighted MRI
- Possible ankylosis eventually
DDx
- Degeneration
- Osteomyelitis
- Septic arthritis
- Tubercular spondylitis
Mainliner’s Syndrome
Demographics
- Heroin users, diabetics, sterioids, immunosuppresed, haemodialysis patients
Distribution
- Unusual predilection for axial skeleton, “S” joints, especially spine, SIJ, pubic symph, SCJ
Features
- Mimics supperastive osteomyelitis
- This type of infection cannot occur in healthy people
Tuberculer Spondylitis (Pott’s Disease)
Demographics
- Immunosuppresed and <30 years
Aetiology
- TB
Distribution
- TL junction
Clinical features
- Pott’s paraplegia→collapse of multiple vertebrae narrows spinal canal
Radiographic Features
- Abscess
- Dsiplacment of paraspinal line
- Psoas abscess: pear shaped and often calcifies
- Osteolytic destruction of vertebral bodies
- Disc degeneration and vertebral collapse
- Gibbus deformity - one or more adjacent vertebrae become wedged anteriorly
DDx
- Fungal infection
- Sarcoidosis
- Metastases
- Pyogenic infection (puss producing – usually strains of staph A.)
