Distal soft tissue injuries

Question 1

Safety factor of equine soft tissues

Answer 1

the amount of stress that a structure can withstand before failure.

Many equine soft tissues have safety factors less than 1.5 and some are as low as 1.2

Question 2

Factors affecting structural properties of tendons

Answer 2

Crimp

Glycosaminoglycans (GAG)

Cartilage oligometric matrix peptide (COMP)

Collagen

Question 3

Crimp

Answer 3

Straightens out in the initial phase of tendon loading

Distributed differently over the cross section of the tendon in older horses

Question 4

Glycosaminoglycans (GAGs)

Answer 4

Important components of the extracellular matrix

Question 5

Cartilage Oligometric Matrix Peptide (COMP)

Answer 5

Correlates with elasticity of tendon

Increased COMP, more elastic

Question 6

Tendon change with age

Answer 6

COMP and crimp reduce with age– tendons become less elastic

Affects injury rates

Question 7

Blood supply of distal tendons

Answer 7

poor – particularly within sheaths and bursae

Poor recruitment of inflammatory cells

Question 8

Collagen deposition in DDFT

Answer 8

In the mid metacarpal region – lots of type 1 collagen with elastic properties

In the fetlock region – more type 2 collagen which is resistant to compression

Chondroid metaplasia

Question 9

Collagen deposition in the suspensory ligament

Answer 9

Evolutionarily the suspensory ligament should be called the interosseous muscle

The proximal end of the ligament still retains some muscle fibres and some fat – makes ultrasound challenging!

Question 10

Pathophysiology of SDFT injuries

Answer 10

The vast majority of SDFT injuries/pathology occur in the mid metacarpal region of the forelimb

(Occasionally hindlimb pathology is seen, and occasionally disease of the branches close to the insertion onto second phalanx)

Question 11

Pathophysiology of DDFT injuries

Answer 11

The vast majority of DDFT injuries/pathology occur within the digital flexor tendon sheath, pastern or within the hoof.

(Occasionally seen in the mid-metacarpal region in the forelimb alongside severe check ligament injury)

Question 12

Pathophysiology of suspensory ligament injuries

Answer 12

The majority of SL injuries/pathology occur at the proximal origin or at the branches of insertion onto the proximal sesamoid bones.

(Occasionally lesions in the suspensory body are seen but rarely as solitary lesions)

Question 13

Pathophysiology of check ligament injuries

Answer 13

Check ligament injuries are easily palpated in the proximal third of the forelimb metacarpus, usually larger on the lateral side.

(Hind limb injuries are VERY rare, and some horses don’t have a hindlimb check ligament at all!)

Question 14

Pathophysiology of stifle soft tissue injuries

Answer 14

Stifle soft tissues including the cruciate ligaments and medial meniscus are a common site of pathology, usually accompany effusion

(Patellar ligaments can also be injured, and very occasionally the lateral meniscus)

Question 15

Interference/overreach injuries:

Answer 15

Horses at speed can strike a loaded forelimb with a rapidly protracting hind limb leading to acute damage of a previously normal soft tissue

Often skin lacerations are seen alongside

Question 16

Causes of microdamage of distal soft tissues

Answer 16

Increasing age,

working in non-elastic region of loading curve,

repetitive loading,

poor reparative and adaptive processes in tendon tissue,

matrix degeneration,

reduction in crimp,

reduction in comp,

increases in type 2 and 3 collagen,

poor vascularity,

tendon heating…………….

Question 17

Prevention of microdamage in the distal soft issues

Answer 17

A competitive horse is going to be working above thresholds for microdamage and degeneration, so how can we adapt a training program

Solid boots reduce risk of direct trauma
BUT – consider the implications these might have for the physiological heating effect!!

Consider track surfaces

Question 18

SDFT damage

Answer 18

An easy diagnosis by palpation/visual inspection

Characteristic “palmar bow” seen to the profile of the tendon

Heat, pain, swelling, resentment of palpation

Question 19

Clinical signs of the inflammatory phase of SDFT injury

Answer 19

Lameness,

pain on palpation,

heat,

swelling

Question 20

Pathology of the inflammatory phase of SDFT injury

Answer 20

Haemorrhage,

inflammation,

neutrophils,

macrophages and monocytes,

increased blood flow,

oedema,

proteolytic enzymes

Question 21

Clinical signs of the reparative/proliferative phase (fibrosis) phase of SDFT injuries

Answer 21

Reduction or absence of lameness,

resolution of signs of inflammation,

tendon still palpably enlarged and soft,

signs of re-injury if exercised too early

Question 22

Pathology of the reparative/proliferative phase of SDFT injuries

Answer 22

Angiogenesis,

fibroplasia,

++ fibroblasts,

collagen III,

small collagen fibrils formed

Question 23

Clinical signs of the remodelling/maturation phase of SDFT injuries

Answer 23

Tendon size decreases,

tendon less pliable,

reduced fetlock extension,

contractures

Question 24

Pathology of the remodelling/maturation phase of SDFT injuries

Answer 24

Collagen transformation from III to I,

cross-linking,

thicker collagen fibrils

Question 25

How does scar tissue behave in tendons?

Answer 25

Core lesions -> fibrotic scar tissue -> non-compliant area in centre of tendon

Fibrotic lesion – less compliant than the tendon around it. Adds stress to surrounding tendon. Usually means that lesions propagate in a proximo-distal direction.

Question 26

The main structures in the digital flexor tendon sheath

Answer 26

Superficial digital flexor tendon
Deep digital flexor tendon
Manica flexoria
Palmar/Plantar annular ligament

Question 27

Manica Flexoria injuries

Answer 27

Often diagnosed with US but contrast tenography is more sensitive.

MRI struggles!

Definitive diagnostics and therapy:
- Tenoscopy and removal of the torn manica

Question 28

PAL Syndrome (Palmar/plantar annular ligament syndrome)

Answer 28

A compartment syndrome-like disease - inflammation of the sheath causes constriction of the ligament which causes further inflammation etc.