joint pathology

Question 1

Define synovial joint.

Answer 1

A diarthroidial joint that adjoins two bones. It is freely moveable and contains a joint cavity filled with synovial fluid.

Question 2

Describe the anatomy of a synovial joint.

Answer 2

Each surface of the adjoining bones is covered in articular cartilage made of hyaline cartilage. This articular cartilage is protected by the joint capsule, which is lined with a synovial membrane (synovium). The synovium is filled with synoviocytes, cells that produce synovial fluid.

Question 3

What is synovial fluid of and what are its functions?

Answer 3

A highly viscous fluid that is composed of hyaluronic acid; acts as a lubricant and reduces friction between layers of articular cartilage.

Question 4

What is articular cartilage composed of and what are its functions?

Answer 4

Composition: a dense extracellular matrix filled with chondrocytes that produce collagen and proteoglycans, which maintain and sustain the hyaline articular cartilage.

Function: to distribute weight-bearing forces and to minimize friction between adjoining bones during locomotion.

Question 5

What is subchondral bone and what is its function?

Answer 5

The bone that sits immediately underneath the calcified cartilage (a thin interlayer b/w unmineralized hyaline cartilage and mineralized subchondral bone) in joints, and it helps attenuate forces generated during locomotion.

Question 6

Where are synovial bursae located, what are they composed of and what are their functions in joints?

Answer 6

Location: near large joints/bony prominences

Composition: a soft-tissue structure lined with a synovium containing synovialcytes

Function: help attenuate forces generated during locomotion

Question 7

What are tendon sheaths?

Answer 7

Thin layers of tissue lined with synoviocytes and wrap around tendons. They help reduce friction between tendons during locomotion.

Question 8

Where is fibrocartilage found?

Answer 8

In the discs between spinal vertebrae (IVD) and in the meniscus of the stifle (cartilage that cushions and stabilizes the joint)

Question 9

Define arthrogryposis.

Answer 9

A congenital and hereditary CNS disease that affects cattle, manifesting as joint contractures in which the calf is unable to stand or nurse. Calfs are infected intrauterine.

Question 10

What are ways that cows can become infected with arthrogryposis?

Answer 10

Pregnant cows ingesting toxic plants, or becoming infected with viruses that target the CNS (Akbane, Bluetongue, Schmallenberg viruses).

Question 11

What happens in degenerative joint disease (DJD)?

Answer 11

Articular cartilage gradually becomes deteriorated by damage to chondrocytes because of proteoglycan depletion.

Question 12

What are not the inciting causes of DJD?

Answer 12

Inflammatory and infectious agents

Question 13

What are some examples of inciting causes of DJD?

Answer 13

aging, hip dysplasia, patellar luxation, excessive wear (athletes), repetitive motions that lead to inflammation like arthritis

Question 14

What are the 5 steps in the pathogenesis of DJD?

Answer 14

1. proteoglycan depletion
2. loss of normal hyaline AC viscosity
3. progressive loss of hyaline AC due to normal locomotion via fibrillation
4. release of inflammatory cytokines
5. degradation of the AC ECM exceeds repair –> eburnation to the SC bone

Question 15

What are the pathologic changes from A to B?

Answer 15

A. Articular cartilage with a fissure present (the crack in the cartilage). Normal chondrocytes in lacunae.
B. Articular cartilage that underwent fibrillation (erosion, degradation) due to the fissure. Chondrocyte degradation has lead to decreased hyaline AC viscosity.

Question 16

What does subchondral bone look like in patients with DJD, and why?

Answer 16

Eburnation- “polished” and ivory-like surface due to the degenerative erosion as the articular cartilage disintegrated with fibrillation progression.

Question 17

What is the etiology of this lesion?

Answer 17

Hypertrophied joint capsule of the acetabulum caused by a compensatory response to joint instability caused by chronic DJD.

Question 18

What region of a horse’s body does navicular syndrome typically affect? What is a predisposing factor?

Answer 18

Forelimb of horses who have an abnormal foot-angle conformation.

Question 19

What occurs in ankylosing spondylosis? When may this occur as an attempt to stabilize a joint?

Answer 19

The fusion of vertebral bodies in the spinal column due to conditions like DJD- can occur secondary to IVDD as an attempt to stabilize the ruptured nucleus pulposus.

Question 20

What cause of polyarthritis is most common in young animals?

Answer 20

A hematogenous infection- infectious agent got to the joint via the bloodstream, sequela to septicemia, etc.

Question 21

What is a cause of monoarthritis?

Answer 21

A direct extension injury, i.e. a penetrating wound, an adjacent soft tissue infection.

Question 22

What is the pattern regarding outcome and degree of cartilage damage?

Answer 22

An increase in cartilage damage = an increase in the severity of arthritis = an increase in risk of secondary DJD.

Question 23

What is the cardinal feature of infectious-causing arthritis in a joint?

Answer 23

The presence of fibrin.

Question 24

What is a sequela of erosive arthritis?

Answer 24

Pannus formation: when a membrane of fibroblasts and and inflammatory cells migrates and “pans” across the surface of articular cartilage of a joint.

Question 25

Where can lesions from systemic lupus, a cause of non-erosive arthritis, be found?

Answer 25

In the kidneys, skin and lungs due to reactions against anti-nuclear antibodies.

Question 26

What are two causes of primary joint neoplasia?

Answer 26

1. Synovial cell sarcoma (SCC)
2. Peri-articular histiocytic sarcoma (PAHS)

Question 27

What do SCC and PAHS arise from? How do these tumors differ in spread?

Answer 27

SCC: synoviocytes –> moderate-to-low chance of distant metastasis

PAHS: histiocytes –> higher chances of distant metastasis