Tendons

Question 1

Tissue composition of tendons and ligaments

Answer 1

Dense connective tissue

Question 2

Toe region relevant to tendons/ligaments

Answer 2

Means that they can be flexible first to allow movement but then stable

Question 3

Tendon function

Answer 3

• Store, absorb and release energy (save energy), Achilles and patella
• Power amplification (stretch to store then release)
• Protect the muscle from damage but acting as a shock absorber
• Transmit force from muscle to bone

Question 4

Energy storage tendons

Answer 4

Energy storage tendons have increased elasticity and fatigue resistance (most fail at 8%, Achilles strains at >12). Achilles is the best at this

Question 5

Energy buffering/amplifying

Answer 5

Buffer - Tendon lengths before muscle to precent eccentric damage (walking down hill or landing from jump)

Amplifying - Achilles slowly stores then quickly releases for more power

Question 6

Achilles’ tendon fascicle alignment

Answer 6

Fascicles spiral 90 degrees during decent

• LG and soleus insert onto calcaneus with strong torsion
• MG fairly parallel

Important for strain distribution

Question 7

Tendon stiffness calculation

Answer 7

Stiffness (k) can be calculated from tendon strain and ankle joint torque (strain gauge)

Question 8

ITB

Answer 8

Important in energy storage, particularly during running (7J). Common overuse injury for running.

Question 9

What is the electro-mechanical delay

Answer 9

A tendon that has increased compliance will require more muscle contraction before force can be generate around a joint. The tendon is taking the slack before force on bone.

This means there is a delay between muscle activation and production of force which is referred to as the electro-mechanical delay. ⬆️ compliance = greater electro-mechanical delay, less force transmitted for given change in length

Question 10

Aponeurosis

Answer 10

Broad sheet of dense regular connective tissue, attaches muscle to bone or muscle to muscles or muscle to fascia

Question 11

Enthesis

Answer 11

• Enthesis - insertion region for tendon/ligament onto bone
  
  • Aids in load transfer between the elastic tendon and the rigid bone (100x stiffer than tendon/ligament)
  • Fibrous - directly onto bone
  • Fibrocartilaginous - 4 zones with a gradual transition
  • Muscular - attachment of muscle without tendon

Question 12

Muscular tendon junction

Answer 12

• Abrupt rather than gradual transition
• Collagen fibers and muscle fibers interdigitate, this increases SA for force transmission and therefore decreases stress
• Less relevant for proximal muscle as they have fleshy attachments meaning their CSA will already be high

Question 13

Structures surrounding tendons

Answer 13

• Fibrous sheath/retinacula (hand), assist in joint stability
• Synovial sheath and peritendinous fluid, reduce friction
• Bursae, reduce compression on tendon

Question 14

Tendon vs ligament composition

Answer 14

Both have similar fibroblast to ECM ratio (10-20%:80-90%)

Ligament mainly collagen type 1 with some 3,4 and 5. Tendon mainly type 1 (stronger) less type 3.

Ligament has varying amounts of elastin while tendons have small amount

Ligaments have varied collagen arrangement (resist force in multiple direction) Tendons have collagen aligned along long axis (anisotropic, loading direct is important)

Tendons can have proteoglycans

Question 15

Difference in stress strain curves

Answer 15

• Failure mode differs with tendons failing abruptly and ligaments failing progressively, due to fiber orientation.
• Tendons have a smaller toe region, easier to uncrimp as all in one direction.
• Tendons have smaller elastic regions (higher gradient) because of lower elastin, results in increased stiffness

Question 16

Toe region

Answer 16

due to crimp of relaxed collagen fibrils, large strain for little stress.

Question 17

Rate and time dependent properties of tendons and ligaments

Answer 17

Because they are viscoelastic

• Creep
  
  • Fixed force length will gradually increases until unloading (recovery non linear. Bad posture
• Stress relaxation
  
  • Strain is constant the stress will decay over time. Change position of splints or boots
• Hysteresis
  
  • Tissue loading and unloading will cause some energy to be load through heat. More compliant over time
• Loading rate
  
  • Low loading rates - avulsion fracture more common
  • High loading rates - mid substance tear more common
• Temperature
  
  • High temperatures increases stress relaxation and creep (heat for more complience)

Question 18

Maturation vs ageing

Answer 18

Maturation - occurs quickly, dramatic increases in mechanical properties of tendons and ligaments (strength, stiffness). Stops at skeletal maturity. Altered mode of failure (avulsion in younger)

Ageing - more gradual decrease in mechanical properties

Question 19

Maturation

Answer 19

Patella tendon in adults is larger and stiffness than children, due to increased collagen fibril diameter and CSA

Stiffness did not different between gender

Asynchronous maturation of mid substance and bone-tendon/bone-ligament junction

Before skeletal maturity tendon/ligament substance has greater strength than bone-ligament junction which causes avulsion. After mature than failure in substance

Question 20

Severes disease

Answer 20

Also referred to as calcaneal apophysitis

Inflammation of growth plate of calcaneus (tendon attachment)

Children 8-11

Overuse problem (running, jump)

Question 21

Osgood Schlatter disease

Answer 21

Tibial tuberosity apophysitis

Overuse (jumping running)

More common in boys (could be because of sport participation)

Boys 13-14, girls 11-12

Question 22

Tendon and muscle imbalance for adaptation

Answer 22

Non uniform adaptation of muscle and tendon in young athletes leads to increase tendon stress (less CSA tendon, increasing muscle strength) during late adolescence

Muscles get stronger and tendon doesn’t get thicker

Strength training can help to limit this imbalance by increasing tendon stiffness

Question 23

Ageing in tendon

Answer 23

Very limited self renewal potential in tendons when compared to muscle

Tendons become less stiff (more compliant) with age. Muscle tend to become more stiff to counter this.

Found that increased exercise for patella tendon increased stiffness in older adults. Cannot stop ageing but can markedly reduce negatives.

Question 24

Exercise effects on tendon

Answer 24

Can induce hypertrophy and therefore increased tendon stiffness. Effects vary based on intensity and type of exercise.

Need high magnitude loading (high tendon strain) for increase stiffness, elastic modulus and size

Isometric → Concentric → eccentric

Perform consistently for at least 8 weeks

Type of exercise and specific tendon matter

Counter movement jumps to max height with increasing mass found:

• Achilles tendon increases strain with mass
• Patellar tendon decrease strain with mass

Question 25

Detraining

Answer 25

Sudden discontinuation of physical activity Detrain groups have unhealthier tendon than untrained groups.

Question 26

Ligament healing stages

Answer 26

Continuous process with 3 overlapping phases: - Inflammation (some haemorrhaging) - Proliferation - adding new (scar tissue) - Remodelling - turning over of scar tissue

Question 27

Ligament healing process

Answer 27

10 days - defect filled with vascular inflammatory tissue 3 wks - inflammatory cells subside and active fibroblasts dominated (new tissue generation) 6 wks - decrease in number and size of fibroblast, evidence of longitudinal alignment of nuclei (long axis of ligament) 14 wks - remodelling, increased realignment and decreased cell numbers 14-40 wks - few changes noted, cells re aligned larger and more numerous Increased CSA throughout to counter weakness (decreased from 3-14), however laxity is actually increased (less effective)

Question 28

Mechanical properties of healed ligament

Answer 28

Decreased stiffness, decreased load at failure, altered site of failure (entire ligament is weaken so mid substance failures become more common, not just insertional) Healed ligaments are more bulky (CSA) but not as strong

Question 29

Tendon injury MOI

Answer 29

- Excessive force (acute) - Repeated overload (hysteresis, loading curves change over time) - Normal force applied to weaker tendon (after detraining) - Stress shielding - Even if normal forces applied, some fibres in tendon may be underloaded (stress shielded) while others are overloaded - Walking in repetitive supination = more load on lateral fibers - Force applied in alternative direction - Compression often contributes to tendinopathy (Achilles or glute Medius)

Question 30

Other factors effecting tendon pathology

Answer 30

Other factors include ageing, obesity, physical activity levels, disease, medication, alcohol (inhibits fibroblast proliferation)

Question 31

Tendon pathology

Answer 31

- Overuse tendinopathy **-** Can occur in mid substance, insertion or musculotendon junction - Disorganised collagen, more vascularised, more cells, increased proteoglycans and water content - Reduced stiffness in Achilles but increased stiffness in patella - Paratendinitis - tendon rubs over bony protuberance - Inflammatory response (not in tendon), can cause crepitus - Tendon rupture - mostly occurs in tendon weakened by pre existing degenerative change (diabetes, alcohol) but can occur in normal tendon in load sufficient - Common in rotator cuff and Achilles Assess pathology through composition, structure (CSA) and function

Question 32

Rehab and immobilisation for tendons

Answer 32

**Rehab for tendinopathy** Exercise is critical, controlled loading (isometric). Progressive loading to remodel tendon. Avoid compressive loading (especially if insertional) Healing is slow (hypocellular ect) Insertion sites more resistant to recovery **Immobilisation** Few weeks can lead to decreased structural properties (weaker, disorganised collagen)