Tendons and ligaments

Question 1

Describe tendons

Answer 1

transmit force from muscle to bone

Question 2

Describe ligaments

Answer 2

span a joint and attach bone to bone. They passively stabilise the joint

and then guide it in its normal range of movement during loading

Question 3

What are known as entheses?

Answer 3

osteotendinous and osteoligamentous junctions

Question 4

What are tendons composed of?

Answer 4

Tenocytes

Water

Collagen

Type I > II

Proteoglycans

Decorin – forms cross links between fibrils

Aggrecan – areas of tendon compression

Other components

COMP

Elastin

Fibronectin

Question 5

What is the hierarchy arrangement of the fibrils?

Answer 5

Microfibril > fibril > fibre > primary bundle > secondary bundle > tertiary bundle > tendon

Question 6

What do microfibrils consist of?

Answer 6

multiple triple helices of collagen

Question 7

What does the stress-strain curve in tendons demonstrate?

Answer 7

the non-linear relationship between strain the tendon and increasing stress

Question 8

Describe the different sections of the stress strain curve in tendons

Answer 8

Toe – this is the uncrimping of the tendon fibres

Linear – this is where the tendon starts to stretch causing it to deform in a linear fashion

Failure – where the tendon is unable to stretch any further and the cross links are broken.

Question 9

Describe a weight bearing tendon

Answer 9

These are exposed to large weight bearing loads and have an energy storing function. e.g. DDFT and suspensory ligament in horses

Question 10

Describe a positional tendon

Answer 10

These aid in the positioning of the limb without large amounts of weight being loaded. E.g. common digital extensor tendons

Question 11

Describe paratenon-covered tendons

Answer 11

These are tendons that are surrounded by a thickening of the surrounding soft tissue called a peritenon. They are in areas of less friction where they tend to move in straight lines. They have a rich blood supply

Question 12

Describe sheathed tendons

Answer 12

These are tendons held within a sheath and are in areas of high friction and where they have to bend sharply e.g. the digital flexor tendons. They are less vascular so healing is more challenging.

The same tendon can have portions that are sheathed and paratenon covered e.g. the SDFT and DDFT of the horse

Question 13

What can injury in tendons be caused by?

Answer 13

Direct / extrinsic trauma – laceration, contusions etc

Indirect / intrinsic trauma – due to overloading of the ligament leading to excess strain

Question 14

Describe indirect trauma in tendons

Answer 14

Indirect trauma is often preceded by some form of tendon degeneration whether that be due to age, exercise or underlying pathology (ischaemia, cysts etc)

It can range from individual fibre tears to generalised defects and, worst case scenario, full thickness rupture.

Question 15

Describe a strain injury in tendons

Answer 15

Stretching or tearing of the musculotendinous unit

Question 16

Define tendonitis

Answer 16

Inflammation of the tendon

Question 17

Describe Paratenon-covered tendons

Answer 17

Due to the rich blood supply, healing is often successful in these tendons but can still take several months.

Question 18

What are the three stages of paratenon-covered tendon healing?

Answer 18

1. Wound fills with blood (haematoma) and inflammatory products.

(further damage can occur at this point due to release of proteolytic enzymes)

Capillary buds and fibroblasts enter

2. Granulation tissue bridges the gap

Collagen type III formed in a haphazard manner

Fibrous bridge forms

3. Granulation tissue bridges the gap

Collagen type III formed in a haphazard manner

Fibrous bridge forms

Question 19

Describe sheathed tendons

Answer 19

Healing more limited due to lack of blood supply and severed ends retract into the sheath

Require surgery to repair and immobilisation

Allows ingrowth of connective tissue and adhesion’s to form between tendon and sheath

Question 20

What are the functions of ligaments?

Answer 20

Stabilise the joint

Help joint glide through the normal range of movement

Prevent excessive movement of joints

Joint proprioception

Question 21

Describe a peri-articular ligament

Answer 21

These are ligaments that are not involved with the joint surface e.g. collateral ligaments

Question 22

Describe intra-articular ligaments

Answer 22

These are ligaments within the joint e.g. round ligament of the femoral head, cruciate ligaments etc.

Question 23

The composition of ligaments is similar to tendons except ligaments tend to have:

Answer 23

Slightly less collagen

Slightly more water and proteoglycans

Less organised collagen fibres

Question 24

Describe a sprain injury in a ligament

Answer 24

The most common type of ligament injury is a ‘sprain’. This should NOT be confused with a strain and this relates to the musculotendinous unit.

Injury can be graded depending on severity:

Grade 1 - Mild sprain

Grade 2 - Moderate sprain or partial tear

Grade 3 - Complete tear, often leading to subluxation of the associated joint

Question 25

Define desmitis

Answer 25

This is a term given to the inflammation of the ligament. It is seen most commonly in the horse affecting the suspensory ligament and the check ligament of the deep digital flexor tendon.

Question 26

Name common clinical conditions of tendons and ligaments in horses

Answer 26

Superficial digital flexor tendon injury

Suspensory ligament desmitis

Check ligament desmitis

Deep digital flexor tendon injury

Collateral ligament injury

Question 27

Name common clinical conditions of tendons and ligaments in canines

Answer 27

Supraspinatus tendinopathy

Biceps brachii tendinopathy

Medial shoulder syndrome (rotator cuff injuries)

Cranial cruciate ligament disease

Achilles tendon damage (gastrocnemius avulsion / lacerations / rupture)