Overview of Arthridities: Patterns, Synovial Fluid Analysis, and Septic Arthritis

Question 1

What is meant by mono vs oligo vs polyarthritis?

Answer 1

Mono - one joint
Oligo - 2-4 joints
Poly - 5+ joints

Question 2

What type of arthritis are septic arthritis, gout, pseudogout, and reactive arthritis typically?

Answer 2

Typically they are classed as acute, inflammatory monoarthritis

Question 3

What is meant by the intima and subintima of the synovium? What does this membrane lack versus other tissue types?

Answer 3

Intima - specialized macrophages and fibroblasts which line the synovium. The intimal fibroblasts secrete the hyaluronic acid.

Subintima - blood and lymphatics in a collagenous extracelllular matrix

Lacks a basement membrane -> keeps the chemical environment of the joint relatively homogenous with the surrounding tissues

Question 4

How will the color of the synovial fluid appear in hemarthroses vs inflammatory arthropathies vs septic arthritis?

Answer 4

Hemarthroses - red or orange
Inflammatory arthropathies - cream or white
Septic arthritis - purulent and often discolored by bacterial chromogens

Question 5

What is the normal nucleated cell count in synovial fluid and what is the minimum threshold for inflammatory joint disease? What conditions can cause extremely elevated counts?

Answer 5

Normal: <200 cells/uL
Inflammatory: >2,000 cells / uL

Extremely inflammatory: >50,000 cells /uL
4 conditions:
1. Acute rheumatoid flares
2. Septic arthritis
3. Acute crystal arthritis
4. Reactive arthritis

These are mostly PMNs

Question 6

What cell types are present in non-inflammatory arthropathies? What color is this fluid? Give an example condition.

Answer 6

This is the 200-2000 cell range. Typically they are lymphocytes, macrophages, and synoviocytes (fibroblast-like cells)

Fluid is clear and yellow, as in osteoarthritis

Question 7

How does the viscosity of the synovial fluid change with inflammation?

Answer 7

It decreases markedly. Think about inflammation causing massive edema, which makes the synovial fluid runny. Normal synovial fluid is clear, colorless, and very viscous.

Question 8

What is the definition of septic arthritis and who is it most common in?

Answer 8

Infection of a joint space, most often caused by hematogenous spread of organisms from a distant infection site.

Most common in CHILDREN (2-5 years old), despite the fact that it is rarely caused by osteomyelitis.

Question 9

What is the most common cause of septic arthritis overall and in young adults?

Answer 9

Overall - Staph aureus

Young adults - if sexually active, Neisseria gonorrhea

Question 10

What accounts for the major of septic arthritis in prosthetic hips and knees? What other bacteria does first aid list as a prime cause of septic arthritis?

Answer 10

S. aureus and coagulase-negative staphylococcal species account for >50% of septic arthritis in these patients

Streptococcus species (i.e. Group A strept) are another major cause

Question 11

What is a common cause of septic arthritis in neonates? Do viral infections ever cause septic arthritis?

Answer 11

Neonates - Group B streptococcus (agalactiae)

Viral - primary joint infections are rare, but immune-mediated arthritis accompanies many viral syndromes (i.e. Parvovirus B19, Rubella)

Question 12

Why does bacteria spread so easily to the joints and why is septic arthritis so dangerous?

Answer 12

Because the synovial membrane lacks a basement membrane.

Bacterial products in the joint space induce TNFalpha and IL-1 production -> neutrophilic chemotaxis, release of elastases and protelytic enzymes.

Pressure rises in the joint space, compromising vascular supply, inducing necrosis of cartilage, and enzymatically destroying cartilage.

Question 13

How many joints and what joints are typically involved in septic arthritis?

Answer 13

Usually one joint, and usually the knee

But in infants / young children, the hip is more commonly infected

Question 14

What is gonococcal dermatitis-arthritis syndrome? Who is at greatest risk?

Answer 14

Triad of pustules, migratory polyarthritis, and tenosynovitis

Greatest risk are sexuually active women, especially those with terminal complement deficiencies (C5-C9)

Question 15

How do you typically diagnose septic arthritis of the hip vs a typical knee arthritis?

Answer 15

Knee arthritis - typically swollen, red, and painful

Hip arthritis - more difficult to palpate because the joint is deep
-> limited range of motion and refusal to walk is highly suggestive of the diagnosis

Patient often has fever as well

Question 16

What joints and tendon sheaths are affected in gonococcal dermatitis-arthritis syndrome?

Answer 16

Joints - typically few small joints or monoarticular infection of a large joint (knee)

Tenosynovitis - multiple tendons of wrist, fingers, ankles, and toes can be affected

Question 17

Are blood cultures positive in gonococcal dermatitis-arthritis syndrome?

Answer 17

Not always -> often gonorrhea must be cultured from extraarticular sites such as genitals, rectal area, or pharyngeal sites

Question 18

What are the characteristics of the pustules in gonococcal dermatitis-arthritis syndrome?

Answer 18

They are few in number, and usually located on the extremities.

Typically painless vesicles or pustules.

Question 19

How is diagnosis of the etiologic organism of septic arthritis made and how is treatment monitored?

Answer 19

Diagnosis made via blood culture, culture of synovial fluid, or nucleic acid amplification tests / extraarticular sampling if gonococcus is suspected.

Treatment is monitored via ESR / C-reactive protein levels to see if inflammation is falling following antibiotic treatment.

Question 20

What are the complications of too slowly treating septic arthritis?

Answer 20

Extensive joint destruction with possible osteoarthritis in the future.

Epiphyseal destruction in infants

Growth plate damage in children can lead to deformity / shortening.

Can spread and cause osteomyelitis

Question 21

What is the treatment for septic arthritis?

Answer 21

IV antibiotics

Closed aspiration of dead cell contents, following response with serial WBCs / cultures

If no resolution with above two: open debridgement and lavage by orthopedics.