What are the characteristics of bone infections that are fundamental differences from other infections?
Blood supply is not as rich as other systmes
Mechanical function is disturbed by infection in bone and worsens with longevity (Treat ASAP)
Surgical implants increase risk of infection
What is the most common organism responsible for orthopedic infections?
S. Aureus
Initially binds to host extracellular matrix proteins
Release of toxins damages host cells and elicits
Describe the virulence of S. Aureus
50% have a plasmid mediated resistance to antimicrobials
Excretion of Protein A that inactivates IgG
Production of a capsular polysaccharide that inhibits phagocytosis
Produces a biofilm to seclude the organism
Describe the diagnostic modalities for Ortho infections?
CBC with differential ESR (inc. for 1st days) CRP (inc. within 6 hrs) Blood Culture Tissue Culture
Prior to treating a suspected ortho infection, what must the physician do?
Get a blood culture for a definitive dx prior to treatment
What is the earliest finding seen in imaging of patients with ortho infections?
soft-tissue swelling evident on radiograph
What types of bone scanning are indicated for the dx of osteomyelitis?
Standard is the Three Phase bone scan (Technetium [Tc99]), and sometimes Indium 111 leukocyte labeled
What does bone scanning detect that allows for dx of an infection?
Bone scans reflect inflammatory changes and reaction in the bone.
Describe the uptake and excretion of Tc99
Uptake related to osteoblastic activity/regional blood flow (increased = show up on scan = inflammation)
Excreted by the kidneys (notable in pt with renal issues)
Describe the 3 phases of a Tc99 bone scan
Flow phase: demonstrates blood flow
Eq. phase: distribution of istope in extracellular space
Delayed phase: osteoblastic activity (positive in osteomyelitis, tumors, DJD, post-surgical, trauma
Describe the changes in activity in the certain phases of triple phase scanning for osteomyelitis, cellulitis, and DJD.
Cellulitis: increased flow and eq./ decreased delay
Oseomyelitis: increased all phases
DJD: increased in delayed/not in flow or eq
Describe how indium bone scans differ from Tc99.
Indium are costly and complex
Blood removed at 2, 4, and 24 hours and indium is mixed with the blood sample
It is the most sensitive modality
What is an MRI used for in dx of a bone infection?
To assess the extent of marrow involvement
What is the conclusive course of modality recommended in dx of bone infections?
Radiographs followed by Triple Phase bone scan and MRI if available.
Describe osteomyelitis in general.
Inflammation of bone caused by infecting organism
Can involve marrow, cortex, periosteum, and surrounding tissue.
Describe the 3 classes of osteomyelitis.
Based on pathogenesis: Hematogenous, Traumatic, Contiguous
Based on duration; Acute, subacute, chronic
Based on age: Adult or Ped
Describe Acute Hematogenous osteomyelitis
Most common in children (due to slowed blood flow in metaphyseal arteries)
Caused by bacteremia (bacteria in the blood)
Involves metaphysis of growing long bones
Can erode cortex, causing subperiosteal abscess and eventual sequestra and chronic osteomyelitis
Where does hematogenous osteo most commonly occur in the body?
Hip
Describe the most common causative pathogens for osteomyelitis
Staph aureus in older children and adults
Pseudomonas - in IV drug usuers and puncture wounds
Fungal infections common in patients on long term pickline
Salmonella in patients with hemoglobinopathy (e.g. sickle cell)
Describe subacute osteomyelitis
insidious onset, fever and systemic symptoms
WBC normal, ESR elevated
Brodie Abscess - localized osteomyelitis with metaphyseal and epiphyseal involvement
Lytic lesion with rim of sclerotic bone
Often confused with a neoplasm
A small round dark spot surrounded by bright white bone on xray is known as?
Brodies abscess - localized osteomyelitis
Describe the erradication of osteomyelitis once its reached its chronic fomr
Usually cant be erradicated unless surgical intervention is done.
Define the terms involucrum and sequestrum.
Sequestrum; dead bone or purulent matter where bone should be
Involucrum: dead bone around a sequestrum
What bug has a high correlation with osteomyelitis resulting from a puncture wound?
Pseudomonas
What is the significance of sequestrum with regard to treatment of bone infections.
The sequestrum is separated from the living bone and haversian canals are blocked making antibiotics unable to penetrate.
How are sequestra formed
Infections leads to an increased in intramedullary pressure from inflammatory exudates
Periosteum becomes stripped from osteum, and leads to vascular thrombii
Necrosis due to lack of blood supply
Describe an involucrum and its significance.
it is bone formed around a sequestrum, can form a sinus or sinuses that may allow dead bone and pus to pass out of the sequestrum
What is the term for sequestrum removal surgery?
saucerization
What is the most common cause of septic arthritis in adults?
Neisseria gonorrhoeae
Mycobacterium or fungal infections in immunocomprimised.
What value is commonly indicative of an infection in the bone?
40-60% PMNs
Describe transient synovitis of the hip
Age 3-8 years
Presents with acutely irritable hip, presentation my be indistinguishable from septic arthritis
WBC>12,000, ESR >40mm/h are diagnositc
Describe the course of tuberculosis and why it can be associated with orthopedic infections.
TB affects every organ system
50% with osseous involvement
Where in the skeleton does a TB infection most commonly show bone effects?
The lumbar and lower thoracic spine (Pott’s Disease)
MRI of the spine to help confirm dx
Describe the effects of syphillis on the MSK system
T. Pallidum
Causes chronic arthralgias, development of charcot neuroarthropathy
Treatment - penicillin benzanthine
Describe the 3 possible types of necrotizing fasciitis.
Flesh eating disease caused by bacterial infections in the deeper layers of skin and subcutaneous tissue, eats through fascial layers
Type I - polymicrobial
Type II - monomicrobial (S. Pyogenes)
Type III - gas gangrene (clostridia)
REVIEW SLIDE ON LAYERS OF SKIN W/ INFECTION TYPES @ EACH LEVEL
Name some causative agents of necrotizing fasciits.
Strep A, Strep Pyogenes, Recently MRSA
Release exotoxins which activates T-cells and cytokines
Aggressive debridement and removal of infected tissue necessary (amputations are very common)
What is diskitis?
Hematogenous infection of disk and vertebral body
Presents with severe pain and limited motion, narrowing of disc space
What is the most common cause of diskitis?
staph aureus
What is the most important symptom of an infected joint replacement following surgery.
Pain may be the only symptom
May also show increased range of motion, drainage, history of recent dental procedure
What type of diagnostic testing can be done for diagnosis of an infected joint replacement?
Bone Scan (triple phase or indium) Arthrogram (aspirate joint) Xray
Discuss the course of treatment for an infected total joint replacement?
Systemic antibiotics for 4-6 weeks
Debridement of joint and retention of prosthesis
One stage revision - exchange arthroplasty
Two stage revision - insert antibiotic spacer then re-do arthroplasty
Suppressive antibiotics
Describe the 3 stages of lyme disease
1 - early localized skin lesion (erythema migrans)
2 - early disseminated disease (neurological and cardiac) meningoencephalitis
3 - late stage (MSK symptoms) - monoarthritis usually in knee, arthralgia
May be an autoimmune response
Describe the management of human bites..
C&S, Debride, C&S, Leave wound open (unless on face or neck), Tetanus Booster,
Rx - Augmentin 875mg PO, Doxycyclin if allergic to penicillin
IV Rocephin if admitted to hospital
Describe the symptoms and treatment of a brown recluse spider bite…
Causes necrotising arachnoidism
Inflammation, eschar, tissue necrosis, sloughing
Syringomyelin D2 responsible for erythrocyte lysis