Septic arthritis/bone tumor

Question 1

Septic Arthritis

general

Answer 1

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

Question 2

septic arthritis

etiology

Answer 2

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

Question 3

septic arthritis

RF of infants and kids

Answer 3

Infants and children:
Prematurity
Hemophilia (due to hemarthroses)

Immunosuppression:
Chemotherapy
HIV
Sickle cell anemia
Diabetes

Question 4

septic arthritis

Adult RF

Answer 4

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

Question 5

septic arthritis

Invasion of the joint occurs through:

Previously damaged joints

Answer 5

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

Question 6

septic rthritis

Progression of the disease:

Answer 6

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

Question 7

septic arthitis

Clin man

Answer 7

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

Question 8

septic arthritis

commonly affected joints

Answer 8

Knee (> 50% of cases)
Wrist
Ankle
Hip
Elbow
Axialjoints (in IV drug users):
Sacroiliac
Sternoclavicular joint

Question 9

septic arthritis

Dx

Answer 9

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

Question 10

septic arthritis

Question 11

septic arthritis

lab tests (4)

Answer 11

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

Question 12

septic arthritis

imaging

Answer 12

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

Question 13

septic arthritis

Abx

Answer 13

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

Question 14

septic arthritis

P. aeruginosa infection length of Tx

Answer 14

4–6 weeks

Question 15

septic arthritis

Surgical interventions

Answer 15

Joint drainage – open or arthoscopic drainage; needle aspiration
Surgical debridement in patients with prosthesis

Question 16

Question 17

Bone Tumors

General

children vs adults

Answer 17

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

Question 18

bone tumor

Answer 18

Question 19

bone tumor

Proto-oncogenes

Answer 19

Genes that promote normal cell growth
With mutations, proto-oncogenes become oncogenes → overstimulate the cell growth

Question 20

bone tumor

Tumor suppressor genes

Answer 20

Help to balance cell growth by promoting apoptosis of mutated cells

Question 21

bone tumor

Oncogenes and/or mutated tumor suppressor genes

Answer 21

allow cells to keep growing uncontrollably resulting in tumors

Question 22

Bone Cancer

S/Sx

Answer 22

Symptoms
Pain
Unexplained, progressive
Occurs without weight bearing
Particularly painful at night
Increased pain with mechanical stress
Swelling
Fatigue

Signs 
Tenderness over the involved bone
Palpable painful bone mass
Limping (children)

Question 23

bone tumor

Dx/imaging

Answer 23

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

Question 24

Question 25

# Osteosarcoma general Arise from what cell

Answer 25

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 femur or proximal 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

Question 26

# osteosarcoma RF

Answer 26

Risk factors Prior treatment with **radiation therapy** Other bone disorders: Paget’s disease Hereditary **retinoblastoma** (mutation of the pRB protein – seen in both cancers)

Question 27

# osteosarcoma Dx & labs

Answer 27

**↑ 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**

Question 28

# osteosarcoma Tx

Answer 28

Combination of chemotherapy and surgery Chemotherapy initiated prior to resection Surgery: limb-sparing or amputation

Question 29

# Ewing sarcoma General Mutation

Answer 29

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

Question 30

# ewing sarcoma Dx

Answer 30

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**

Question 31

# ewing sarcoma Tx

Answer 31

Combination of surgery, chemotherapy and radiation therapy

Question 32

# Multiple Myeloma general Originate from what cells? That produce?

Answer 32

Most common primary malignancy of the skeleton Malignancy derived from antibody producing **plasma cells** Arises in the bone marrow with production of large amounts of **monoclonal immunoglobulin (IgG or IgA)**

Question 33

# multiple myeloma Clin man

Answer 33

Lytic lesions Sharply circumscribed (punched-out lesions) on x-ray Diffuse demineralization Occurs mostly in older adults Median age at diagnosis is 65 years

Question 34

# multiple myeloma Destruction of Bone Affects on electrolytes?

Answer 34

**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

Question 35

# multiple myeloma Tx

Answer 35

**Bisphosphonates** Stimulates osteoclast apoptosis Prevent pathologic bone fractures and helps to lower serum calcium levels

Question 36

Answer 36

Question 37

# Chondrosarcoma general Arise from what cell

Answer 37

Malignant tumor of **cartilage** Arises from **chondrocytes** Occurs most commonly in people aged 40-75 years Tends to grow slowly Can have a soft tissue component involving surrounding soft tissues

Question 38

# Chondrosarcoma Most common site of involvement

Answer 38

Flat bones (pelvis and scapula) Long bones (proximal femur, proximal humerus)

Question 39

# Chondrosarcoma Dx What will you see?

Answer 39

Plain film x-rays followed by CT scan or MRI **Punctate or ring and arc calcifications Cortical bone destruction** **Biopsy** Required for definitive diagnosis Determine the tumor grade Low-grade: indolent, slow growing High-grade: excruciating pain, fast growing

Question 40

# Chondrosarcoma Tx

Answer 40

Wide surgical resection for nonmetastatic disease Chemotherapy (advanced disease)

Question 41

# Osteochondroma general

Answer 41

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

Question 42

# osteochondroma Most commonly arise from the appendicular skeleton in the metaphysis of long bones

Answer 42

Femur Proximal tibia Proximal humerus

Question 43

# Osteochondroma Imaging

Answer 43

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

Question 44

# Osteochondroma Tx

Answer 44

**Observation if asymptomatic** **Excision if** the tumor is causing **pain, compressing a large nerve or vessel, disturbs growth, or has a destructive appearance** (transformation into malignant chondrosarcoma)

Question 45

# Osteoma general Where are they found? What do they produce? Describe it

Answer 45

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**

Question 46

# Bone Tumors Key Points

Answer 46

In children, most bone tumors are benign In adults, especially those age > 40, metastatic tumors (breast, lung, prostate, or renal cancer) are about 100x more common than primary malignant tumors Have a **high suspicion** for bone tumors in patients who have **unexplained bone pain, particular pain at night or at rest** Assessment begins with plain film x-rays, but typically requires MRI and biopsy for definitive diagnosis Treatment of malignant tumors often involves a combination of surgery, chemotherapy, and radiation therapy