Septic arthritis/bone tumor Flashcards
Septic Arthritis
general
An infection of the joint due to direct inoculation, contiguous extension, or hematogenous spread of infectious organisms into the joint space
Surgical emergency: irreversible damage to tissue after 24 hours
septic arthritis
etiology
Etiology: majority of septicarthritisinfections are monomicrobial
Staphylococci:
Staphylococcus aureus(most common), S. epidermidis
Streptococci:
Streptococcuspyogenes, S. pneumoniae, S. agalactiae
Gram-negative bacteria:
Pseudomonas aeruginosa
Escherichia coli
Kingella kingae
Neisseria gonorrhoeae → Young, sexually active patient
Haemophilusinfluenzae
Salmonellaspecies → Sickle cell anemia
gonorrhea usualy multiple joints
septic arthritis
RF of infants and kids
Infants and children:
Prematurity
Hemophilia (due to hemarthroses)
Immunosuppression:
Chemotherapy
HIV
Sickle cell anemia
Diabetes
septic arthritis
Adult RF
Age > 80 years
Chronic disease/immunosuppression:
Diabetes
HIV
Joint disease:
Rheumatoid arthritis
Osteoarthritis
Gout
Joint procedures:
Surgery
Intra-articular injections
Joint prosthesis
Skininfectionsor ulcers
IV drug use
septic arthritis
Invasion of the joint occurs through:
Previously damaged joints
Hematogenous seeding(most common)
Direct inoculation of organisms into the joint
Extensionfrom an adjacent infection
Previously damaged joints are particularly susceptible to infection by way of:
Neovascularization
Dysfunctional cellular defenses
Absentbasement membraneon thesynovial membrane
know how you can end up w infection
septic rthritis
Progression of the disease:
Bacterial invasion → inflammation →release ofcytokines andproteases
This response, plus bacterial toxins → destruction of:
Articularcartilage
Synovium
Subchondralbone
If a large effusion develops → impairment of the blood supply → aseptic necrosis
septic arthitis
Clin man
Constitutional symptoms:
Fever
Fatigue
Tachycardia
Signs and symptoms:
Moderate-to-severejoint painand effusion
Erythema and warmth
Tenderness to palpation
Limited active and passiverange of movement
Usually monoarticular, but may be oligo- or polyarticular
septic arthritis
commonly affected joints
Knee (> 50% of cases)
Wrist
Ankle
Hip
Elbow
Axialjoints (in IV drug users):
Sacroiliac
Sternoclavicular joint
septic arthritis
Dx
Arthrocentesis
Diagnosisis made withsynovial fluid analysis
Should be attempted before antibiotics are given
A positiveGram stain and/or culture confirms the diagnosis
A purulent aspirate gives a presumptive diagnosis:
WBC count > 50,000 cells/μL
Neutrophil predominance
Nucleic acid amplification testing may be performed ifN. gonorrhoeaeis suspected
Include an analysis for crystals to rule outgout
septic arthritis
septic arthritis
lab tests (4)
Lab tests
Used to support the diagnosis:
↑Erythrocyte sedimentation rate (ESR)
↑ CRP
Can be used to monitor response to therapy
↑ WBC count
Bloodcultures
Cervical,urethra, rectal, or oropharyngeal swabs fornucleic acid amplification testifN. gonorrhoeaeis suspected
septic arthritis
imaging
Plain-film radiograph:
Joint-space narrowing or widening
Subchondral bony changes,osteopenia
Periarticularsoft tissueswelling
Normal studies do not rule out septicarthritis
Ultrasound:
Identificationof a joint effusion
Can assist with aspiration of the effusion
MRI:
Sensitive for earlyidentificationof joint effusion
Evaluates the extent ofboneand soft-tissue abnormalities
Assesses for associated osteomyelitis
septic arthritis
Abx
Antibiotic therapy
Antibioticselectionis based on the initialGram stainand tailored based on culture data
Empiric regimen ifGram stainis negative:
Vancomycin plus 3rd- or 4th-generation cephalosporin
Duration of therapy depends on additional factors:
With negative bloodcultures:
2 weeks of parenteral antibiotics
Additional 1–2 weeks of oral antibiotics
With positive bloodcultures:
4 weeks of parenteral antibiotics
P. aeruginosa infection: 4–6 weeks
septic arthritis
P. aeruginosa infection length of Tx
4–6 weeks
septic arthritis
Surgical interventions
Joint drainage – open or arthoscopic drainage; needle aspiration
Surgical debridement in patients with prosthesis
Bone Tumors
General
children vs adults
Develops when bone cells divide uncontrollably
Benign or malignant
Malignant can be primary or metastatic
Primary arise from bone cells
Metastatic spread to bone from other tissues
In children…
Most are benign
Malignant tumors – osteosarcoma, Ewing sarcoma
In adults…
Metastatic tumors are 100x more common than primary malignant tumors
Metastasis from breast, lung, thyroid, prostate, or renal cancer
bone tumor
bone tumor
Dx/imaging
Plain film x-rays
MRI with contrast
Whole body bone scan if multicentric or metastatic tumors are suspected
Biopsy
Exceptions
Imaging studies clearly show benign characteristics
Multiple bone lesions in a patient with a confirmed primary cancer
Osteosarcoma
general
Arise from what cell
Also referred to as osteogenic sarcoma
Most common malignant bone tumor in children and young adults (10-25 years)
Highly malignant
Arise from osteoblasts
Approximately 90% of osteosarcomas occur in the extremities
Most common site of involvement
Metaphyseal sites of the most rapidly growing bones are more commonly involved
Around the knee (distal femurorproximal tibia) - ~50% of cases
Proximal humerus
Most cases are sporadic and have no identified cause
Osteosarcoma produces malignant osteoid (immature bone) from tumor bone cells
osteosarcoma
Dx & labs
↑ alkaline phosphatase…Why?
Plain film x-rays followed by CT scan or MRI
“Hair on end” or “sunburst appearance” due to tumor spicules of calcified bone on plain films
Codman’s triangle due to lifting of the periosteum
Definitive diagnosis requires biopsy
Ewing sarcoma
General
Mutation
Round-cell bone tumor resulting from a translocation between chromosomes 11 and 22
Second most common malignant bone tumor in children (10-25 years)
Most common site of involvement
Diaphyseal region of long bones
Femur
Sacrum
Tibia
Fibula
ewing sarcoma
Dx
Plain film x-rays followed by CT scan or MRI
Moth-eaten destruction in a permeative pattern without clear borders
Multiple layers of subperiosteal reactive new bone formation in an onion-skin appearance
Definitive diagnosis requires biopsy
multiple myeloma
Destruction of Bone
Affects on electrolytes?
Plasma cells activate osteoclasts, which promote bone destruction → lytic lesions
Bone destruction is accompanied by an increase of serum calcium → hypercalcemia
Back, hips, and ribs are the most common areas for pain
Chondrosarcoma
Most common site of involvement
Flat bones (pelvis and scapula)
Long bones (proximal femur, proximal humerus)
Osteochondroma
general
Cartilage-capped bony overgrowth arising on the external surface of a bone
Most common benign bone tumor
Often occur in people < 25 years
May be single or multiple
Single tumors will develop into a secondary malignant chondrosarcoma in 1% of patients
Multiple tumors tend to run in families
Osteochondroma
Imaging
Imaging studies
Bony prominence with a cartilage cap (usually <2 cm) off the surface of the bone
MRI will reveal that the medullary canal is in continuity with the base of the exostosis
Osteoma
general
Where are they found? What do they produce? Describe it
Benign
Also known as osteoid osteomas
Areas of uniformly dense bone that produces high levels of prostaglandins
Most common in the skull, mandible, femur, spine
Painful most often at night
Pain relief within 30-60 minutes of administration of NSAIDs…why?
Diagnosed incidentally on imaging studies
Do not require biopsy and can be followed periodically with plain films
