Tendon Pathology

Question 1

what are tendons made up of

Answer 1

collagen bundles arranged around a central elongated collection of tenocytes (tendon fibroblasts) and capillaries

Question 2

what are tendons composed of at birth

Answer 2

cellular and vascular

Question 3

what are tendons composed of in an adult

Answer 3

collagen fibrils form 80% of dry matter

Question 4

what is the structure of collgen fibrils in collagen type 1

Answer 4

form a zigzag waveform in longitudinal orientation

Question 5

what are tenocytes

Answer 5

elongated tendon fibrocyte/fibroblast

longitudinal rows alongside the collagen fibrils

Question 6

how do tenocytes communicate

Answer 6

via gap junctions and respond to mechanical signals

Question 7

what are the function of tenocytes

Answer 7

1. synthesize and degrade all of the collagenous and non-collagenous matrix
2. repair the tendon matrix when injured
3. slow turn-over in normal tendon

Question 8

what are the predisposing changes in the injury and repiar of tendon

Answer 8

cartilaginous metaplasia, ischemia, fibroblast proliferation

Question 9

what are the predisposed sites for injury and repair of a tendon

Answer 9

anatomic weakness or disproportionate stretch

Question 10

what are stretch lesions (3)

Answer 10

1. fibrils pulled out of kink register
2. ruptured collagen fibres
3. rupture of capillaries

Question 11

how are tendons repaired (3)

Answer 11

1. tenocytes and peritenon cells form myofibroblasts
2. collagen type III (immature collagen)
3. maturation over time (collagen type I)

Question 12

how are large lesions repaired

Answer 12

more necrosis, fibrin, malaligned, scar collagen, adhesions

Question 13

what occures in the acute phase of injury

Answer 13

inflammatory cells

pro-inflammatory mediators and cytokines

commonly asymptomatic horses

Question 14

what occurs in the subacute phase of injury

Answer 14

3-6 weeks post injury

inflammatory cells replaced by fibroblastic cells and small blood vessels (granulation tissue)

Question 15

what cells are responsible for repair of tendons

Answer 15

fibroblastic cells (tenocytes)

Question 16

what two sites do fibroblasts migrate into the tendon from

Answer 16

1. tendon sheath (extrinsic repair)
2. epitenon/endotenon (intrinsic repair)

Question 17

what are the chronic phase of injury and repair

Answer 17

more than 3 months post injury

scar tissue

disorganized collagen fibrils

increased numbers of fibroblasts

enlarged endotendon

Question 18

what occurs with maturation over time

Answer 18

decreased cellularity

alignment of collagen fibrils

Question 19

what problems occur in tendon healing

Answer 19

1. no regeneration: fascicles stuck together and destroyed by scar tissue
2. ruptures may occur at margins of normal and scar tissue
3. persistence of inflammatory cells (and blood vessels) in endotenon

Question 20

what are the tendon pathologies

Answer 20

1. vascular
2. inflammatory
3. traumatic
4. anomaly
5. metabolic/toxic
6. idiopathic/iatrogen
7. neoplastic
8. degenerative

Question 21

where are SDFT injuries most common

Answer 21

usually mid-metacarpal region

Question 22

what occurs after a SDFT injury

Answer 22

microdamage

microscopic level

subclinical changes to the tendon

naturally present in tendons of older horses

accelerated accumulations in tendons of horses <10 years due to high intensity exercise

Question 23

how does exercise accelerate the levels of microdamage

Answer 23

1. mechanical overload
2. hyperthermia
3. hypoxia
4. death or dysfunction of tenocytes –> poor tendon healing –> further presence/increase of microdamage

Question 24

what occurs during mechanical overload in SDFT

Answer 24

high levels of force break collagen fibrils and alter microscopic structure of the tendon –> microdamage

Question 25

how does the SDFT improve locomotion efficiency

Answer 25

SDFT converts both potential and kinetic energy into elastic energy

reduces muscle energy expenditure –> increases effeciency of locomotion

low mechanical safety marigin

Question 26

what is hyperthermia in the tendon core

Answer 26

not all elastic energy is returned during recoil of tendon

5-10% lost as heat

inefficient dissipiation of heat within the tendon core due to its poor vascular supply

high temp leads to tenocyte death

Question 27

what are the features of early microdamage in SDFT due to ageing

Answer 27

1. decrease crimp angle (core) > 10 years
2. decrease cellularity
3. decreased gap junction communication
4. increase in % type 1 tenocytes (and length)

Question 28

what are the features of early microdamage in the SDFT due to exercise

Answer 28

1. decreased crimp angle (core) < 10 years
2. decreased collagen fibril diameter (core)
3. decreased glycosaminoglycan content

Question 29

what are the features of advanced microdamage in the SDFT

Answer 29

red core lesion

no clinical signs, no swelling

more type III collagen = immature (smaller, weaker fibrils)

Question 30

what are parasitic diseases of tendons

Answer 30

horse and cattle

adult worms in tendon, tendon sheaths, connective tissue of brisket or abdominal walls

microfilariae migrate to skin, picked up by blood sucking parasite

low grade or no tissue reaction; asymptomatic

Question 31

what is suspensory desmitis

Answer 31

degenerative diseases of tendons

changes in proteoglycan decomposition –> abnormal decorin and aggrecan

Question 32

what occurs during suspensory desmitis

Answer 32

hyperextension of metacarpophalangeal/tarsophalangeal joint

Question 33

what are the histological features of the tendon

Answer 33

tenocytes

vessels

not very cellular

Question 34

what are these cells