Septic Arthritis & Osteomyelitis

Question 1

infectious (septic) arthritis - overview

Answer 1

*infection involving the diarthrodial joint space
*rheumatologic emergency!
*typically acute in onset & monoarticular in localization, with predominant involvement of large, weight-bearing joints
*usually arises secondary to hematogenous seeding of the joint from distant focus of infection
*synovial tissue with increased susceptibility to infection due to lack of basement membrane & high degree of vascularity

Question 2

causes of acute monoarthritis

Answer 2

*infectious arthritis
*osteomyelitis
*reactive arthritis
*crystal-induced synovitis
*trauma
*mechanical internal derangement
*rheumatoid arthritis and other connective tissue disorders
*pigmented villonodular synovitis
*metastatic tumors

Question 3

“big four” causes of acute monoarthritis

Answer 3

1. infectious arthritis
2. crystal-induced synovitis
3. trauma
4. RA / other connective tissue disorders

Question 4

infectious (septic) arthritis - clinical manifestations

Answer 4

*pain with BOTH passive & active motion
*erythema & heat overlying joint
*tenderness
*SWELLING
*limited range of motion

Question 5

infectious (septic) arthritis - consequences of delayed diagnosis and treatment

Answer 5

*enhanced intraarticular inflammation:
-release of cytokines & proteases from PMNs
-pressure necrosis secondary to large effusion
*damage to ground substance of articular surface
*erosion of cartilage
*joint space narrowing
*OUTCOME: chronic pain with impaired joint function & mobility, causing disability

Question 6

when to suspect diagnosis of infectious (septic) arthritis

Answer 6

*appropriate clinical setting: patient with defined risk factors for joint infection AND
*compatible clinical manifestations: joint pain, local inflammatory signs, fever

Question 7

infectious (septic) arthritis - pathogenesis

Answer 7

1. hematogenous seeding (most common)
2. joint aspiration/inoculation
3. animal or human bites
4. foreign body puncture wounds
5. spread from contiguous infection (osteomyelitis)
6. arthroscopic surgery
7. open surgical procedures

Question 8

infectious (septic) arthritis - predisposing factors

Answer 8

*recent joint surgery
*age > 80
*prosthetic joint
*skin/soft tissue infection
*diabetes
*rheumatoid arthritis
*skin infection

Question 9

infectious (septic) arthritis - historical features

Answer 9

*history of prior joint damage or disease (underlying non-infectious arthritis or previous joint surgery/trauma)
*presenting symptoms: pain, erythema, swelling, fever, acute in onset
*number of involved joints is important
*sites of involved joints (common = knee, ankle, wrist, shoulder, hip, elbow)
*age of affected patient

Question 10

infectious (septic) arthritis - physical exam findings

Answer 10

1. signs of joint inflammation: erythema, warmth, tenderness to palpation, joint effusion
2. decreased ROM of affected joint
3. tenosynovitis
4. skin rashes
5. concurrent extraarticular infections

Question 11

infectious (septic) arthritis - common sites of concurrent infection

Answer 11

*skin infections (cellulitis, abscesses)
*decubitus/pressure ulcers
*pneumonia
*UTI
*“primary” bacteriemia

Question 12

presence of polyarticular disease as a clue for bacterial etiology

Answer 12

polyarticular disease = Staph aureus or Neisseria gonorrheae

Question 13

presence of tenosynovitis as a clue for bacterial etiology

Answer 13

tenosynovitis = Neisseria gonorrheae

Question 14

presence of rashes as a clue for bacterial etiology

Answer 14

rashes = Neisseria gonorrheae

Question 15

presence of skin infection as a clue for bacterial etiology

Answer 15

skin infection = Staph aureus or Strep

Question 16

presence of pneumonia as a clue for bacterial etiology

Answer 16

pneumonia = Strep pneumoniae

Question 17

infectious (septic) arthritis - labs & other assessment

Answer 17

*joint fluid analysis (arthrocentesis)
*blood cultures
*cultures of other infected sites
*radiology (plain X-ray, radioisotope scans, CT or MRI)
*synovial biopsy (rare)

Question 18

infectious (septic) arthritis - joint fluid analysis (overview)

Answer 18

*provides diagnostic and therapeutic value
*should be performed in virtually all cases of suspected inflammatory arthritis
*studies should include: color, clarity, viscosity, RBC & WBC counts, glucose, gram stain, cultures, crystal examination
*can be classified based on: normal, non-inflammatory, inflammatory, and septic

Question 19

joint fluid findings consistent of a diagnosis of infectious (septic) arthritis

Answer 19

*WBC > 100K with >75% PMNs
*gram stain may be positive

Question 20

common pathogens that cause infectious (septic) arthritis

Answer 20

*bacteria most common:
1. Staph aureus (majority of cases)
2. Neisseria gonorrhoeae
3. Strep spp
*mycobacteria, fungi, and viruses can cause some

Question 21

top 3 pathogens that cause infectious (septic) arthritis

Answer 21

1. Staph aureus
2. Streptococcus
3. Neisseria gonorrhoeae (mostly in females and MSM)

Question 22

infectious (septic) arthritis - management

Answer 22

*NEED BOTH:
1. adequate drainage (open or closed)
2. appropriate antibiotic therapy

*indications for open (surgical) drainage:
-hip/shoulder infections
-incomplete drainage with closed needle aspiration
-clinical failure of closed aspiration

Question 23

infectious (septic) arthritis - principles of antibiotic therapy

Answer 23

*select an empiric Rx
*parenteral Rx is the traditional norm
*duration depends on organism:
-Staph aureus, GNRs = 4+ weeks
-Strep, H flu, gonorrhea = 2+ weeks

Question 24

infectious (septic) arthritis - poor prognostic factors

Answer 24

*delay in initiation of therapy
*GNRs
*age > 60
*pre-existing RA
*infection of hip or shoulder
*polyarticular infections (>4 joints involved)

Question 25

osteomyelitis - overview

Answer 25

*chronic or acute infection of the bone
*inflammatory process of bone, leading to bone destruction
*usually secondary to pyogenic bacteria
*facilitated by relative lack of local host defenses in bone

Question 26

osteomyelitis - pathogenesis & predisposing factors

Answer 26

development of area of “damaged” bone (trauma, impaired blood supply, metabolic abnormalities)
*introduction of microbes (contiguous spread, direct inoculation, hematogenous seeding) with subsequent growth in a “protected” environment
*generation of local inflammation with production of toxins and cytokines that enhance osteoclastic & inhibit osteoblastic activity & PMN function
*bone necrosis and death cause formation of sequestra

Question 27

osteomyelitis due to hematogenous seeding

Answer 27

*age of onset: 1-20yo & > 50
*bones involved: long bones, vertebrae
*precipitating factors: bacteremia
*microbiology: monomicrobial, Staph aureus or GNRs most common
*clinical findings: acute onset of fever, local tenderness, limited ROM
*usually curable with antibiotics alone

Question 28

osteomyelitis due to contiguous spread

Answer 28

*age of onset: 40+ yo
*bones involved: femur, tibia
*precipitating factors: surgery, trauma, ST infection
*microbiology: mixed flora, usually includes Staph aureus or GNRs
*clinical findings: indolent onset of fever, erythema, swelling, heat
*requires aggressive debridement and long term IV antibiotics

Question 29

osteomyelitis associated with peripheral vascular disease

Answer 29

*age of onset: 50+ yo
*bones involved: feet
*precipitating factors: diabetes, PVD
*microbiology: mixed flora, Staph/Strep, GNRs/anaerobes
*clinical findings: pain, swelling, erythema, drainage, ulcer
*requires surgery for treatment; relapse rates high without amputation

Question 30

acute vs. chronic osteomyelitis

Answer 30

*acute: first presentation with short duration of preceding symptoms/signs
*chronic: clinical or X-ray evidence of infection or 6+ weeks
-XR evidence of sequestrum formation or sclerosis in addition to bone destruction
-relapse or persistence after Rx
-bone infection associated with a foreign body

Question 31

osteomyelitis - potential complications

Answer 31

*sinus tract formation
*contiguous soft tissue infection
*abscess
*septic arthritis
*systemic infection
*bony deformity
*fracture
*malignancy