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Flashcards in Infection Deck (17)
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1

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.

2

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.

3

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

4

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.

 

5

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

6

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

7

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

8

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

9

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 

10

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

 

 

 

11

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 

12

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 

13

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 

14

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

 

15

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 

16

Non-suppurative Osteomyelitis (TB)

 

Demographics 

  • Immunosuppresed and <30 years 

Aetiology 

  • Myobacterium tuberculosis (TB)

Distribution

  • Thoracic and lumbar spine 
  • KNee and hip are common appendicular sites 

Clinical Features 

  • Insidious onset, chronic course, symptomatic months before diagnosis
  • Very destructive and resistant to control
  •  Mild pain and stiffness, decreased ROM, focal tenderness, swelling
  • Neurologic involvement with spinal TB
  •  Pus draining sinus tract in advanced stage

Radiographic Features 

  • Will be same as TB spondylitis just relevant features in appendicular skeleton

17

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.)