Infections Flashcards
What is cellulitis?
infection of skin, subcutaneous fat, or connective tissue such as tendons/ligaments/muscle
What is osteomyelitis?
Infection of bone
What is septic arthritis?
infection of joint (synovial tissue/articular surfaces)
What are the at risk groups for infections?
- Immunosuppressed
- Diabetes
- Post-surgical
- Vascular insufficiency
- Sickle cell anemia
- IV drug users
- When conditions are right
What joints are drug addicts usually prone to infection in?
“S” Joints - spine, sacroiliacs, symphysis pubis, sternoclavicular
What is the most common organism for infection?
Staph aureus (90%)
What are the modes of infection?
- Trauma/post surgical
- Urinary tract infection
- Pneumonia
- Skin infections
- Open wound or cellulitis
- Heel sticks in infants
What are the route of dissemination of infection?
- Hematogenous
- Direct extension
- Direct implantation
- Postoperative
What is the most common route of dissemination of infection?
Hematogenous
What is the infantile pattern of vascular anatomy?
metaphyseal and diaphysral vessels may penetrate the physics (septic arthritis and osteomyelitis)
What is the childhood pattern of vascular anatomy?
1 year to physis closure, metaphyseal blood flow is slow and turbulent, metaphyseal vessels do not penetrate physics, separate epiphysis blood supply (tends to spare epiphysis and joint)
What is the adult pattern of vascular anatomy?
metaphyseal vessel penetrate the vanishing physics, establishing communication with the subarticular bone end (osteomyelitis and septic arthritis)
What are the most common locations for infections?
Knee Hip Ankle (distal tibia) Shoulder Spine
What are the two major categories for infections?
Suppurative (pus)
Non-suppurative (TB)
What is suppurative osteomyelitis?
Bone marrow infection by (pyogenic) non-tubular organism (anything but TB)
What is the most common suppurative organism of infection?
Staph. aureus
What are the clinical features of acute infection?
Edmea, lymphadenopathy, warm skin, cellulitis, joint pain
What are the 4 radiographic stages of infection?
- Latent/Hidden
- Early
- Middle
- Late
How long is the hidden/latent stage of infection?
1 to 10 days
How long is the early stage of infection?
10-21 days
How long is the middle stage of infection?
weeks
How long is the late stage of infection?
months
What radiographic features may be present during the early stage of infection
Soft tissue edema and osteopenia (micro holes). Edema displaces lucent fat planes and tends to obliterate soft tissue margins and become mass like
How long is the early stage of infection of spinal lesions?
3 weeks
What radiographic features may be present during the middle stage of infection?
Permeative or lytic moth-eaten destruction (may cross anatomical barriers), periosteal response, solid, codman’s triangle, laminated
What can the middle stage of infection look similar to?
Ewing sarcoma
What radiographic features may be present during the late stage of infection?
Cortical destruction Draining sinus Involucrum - bony collar Cloaca - big open sore Sequestrum - piece of dead bone inside bone Sclerosis Debris Loss of joint space - both sides Ankylosis Chronic incomplete resolution Immune deficient
What is a sequestrum?
Chalky, white area representing isolated dead bone and cortical and medullar infarcts
What can a sequestrum of infection look similar to?
Osteoid osteoma
What difference would there be between osteoid osteoma and sequestrum of infection?
Pain would be worse at night with osteoid osteoma and there would be a fever with infection
What is an involucrum of infection?
“bony collar” - chronic periosteal response, pus lifts the periosteum and causes new bone formation, trying to wall off the infection
What is the body’s attempt to wall things off during the late stages of infection?
Involucrum
What is a cloaca?
Ulcerative channel from bone to outside
What is Marjolin’s ulcer?
A rare complication of infection that is squamous cell carcinoma within the channel of cloaca
What stage of infection is cloaca associated with?
Late stage
What is a Brodie’s abscess formation?
Localized, aborted form of suppurative osteomyelitis
What does a Brodie’s abscess formation look similar to?
Giant cell tumor
What are the symptoms of a Brodie’s abscess formation?
Localized pain, worse at night relieved by aspirin
What symptoms of a Brodie’s abscess formation mimic?
Osteoid osteoma
What location is a Brodie’s abscess formation commonly found in?
Metaphyseal region, MC distal tibia (ankle)
What does a Brodie’s abscess formation look like?
Oval, elliptical or serpiginous (worm like) radiolucency with heavy reactive sclerosis
What are the differences between a tumor and infection?
Tumor respects growth plates and deflects fascial planes while infection has no respect for growth plate or joint spaces
What are features of septic arthritis?
Joint effusion, juxtaarticular osteoporosis, erosions, joint space loss, lytic destruction that crosses joint space
What is one sign of infection in the hip?
Increased teardrop distance
What distance is important regarding teardrop distance?
Greater than 11 mm or 2 mm difference from the opposite joint
What are the fat planes of the hip?
Gluteus medius, obturator internus and iliopsoas
Until what age is the intervertebral disc is still vascular?
20 years of age
How does infection spread in someone under age 20 if it is in the spine?
Infection starts in disc then spreads to adjacent bodies/endplates
How does infection spread in adults if it is in the spine?
Starts in anterior vertebral endplates then does to the disc with vertebral collapse and soft tissue paraspinal mass
What is the most common location for infection in the spine?
Lumbar spine
What is the most common location for infection in the spine in IV drug users?
Sacroiliac joints
How is infection in the spine spread?
Batson’s Venous Plexus
What are early radiographic features of infection in the spine?
Rapid disc space loss and endplate destruction
What are the limitations of plain films in regards to infection?
Not really a sensitive exam, must have significant loss in bone density before it is detected, other imaging studies are better for detection of early infection
Why is bone scintigraphy better for infection detection?
Maybe positive within hours, gallium for RBC, Indium for WBCs, very sensitive, often followed by MRI for evaluation of soft tissue
What are the advantages of CT in infection?
See findings earlier than plain films, good for hard to image areas (spine, pelvis, sternum), findings are more specific and suggestive of osteomyelitis (increase marrow density, demineralization, periosteal reaction)
What is another name for non-suppurative osteomyelitis?
TB
What is Pott’s Disease?
TB in the spine
What is referred to as the king of disease?
TB
What is the most common cause of infection related death worldwide?
TB
What is the most common secondary form of TB?
Skeletal involvement of TB
What is the most common location of TB in the spine?
Thoracolumbar junction
Where does TB like to spread under in the spine?
ALL
Where does TB infection typically start in the spine?
Anterior endplate region
What is the earliest radiographic finding of TB in the spine?
Disc space narrowing
What is a common result of TB in the spine?
Vertebral body collapse
What does TB look like on MRI?
Decreased T1 and increased T2
What percentage of TB skin tests are positive?
90-100%
What percentage of chest films are positive for granulomas?
50%
What are some clinical signs of TB?
Unexplained weight loss, fever, chills, night sweats, tenderness in the involved bones and joints
What is Gibbous formation?
Acute kyphotic angular deformity in the spine in a patient with TB
What is the Phemister’s Triad?
Tuberculosis septic arthritis - juxtarticular osteoporosis, marginal erosions (both sides of joint), slow joint space loss
What are treatment options for TB?
Chemo, debridement, arthrodesis, surgical
Which has a slower progression of joint destruction? Suppurative vs TB?
TB
Which has a slower response to therapy? Suppurative or TB?
TB