Ligament and Tendon

Question 1

Ligament

Answer 1

Attach bone to bone

Stabilise joint

Restrict movement

Question 2

Tendon

Answer 2

Attach muscle to bone

Transfer force from muscle to skeleton

Facilitate movement

Store and return elastic energy

Question 3

Made up of:

Answer 3

Cells - fibroblasts

Water - 66% of wet weight

Collagen - 70% of dry weight

Proteoglycans

Elastin

Uniform structure

Question 4

Mechanical Limits

Answer 4

Material properties governed by arrangement of collagen fibres

Strength of structure dependent on CSA - the more collagen fibres the greater resistance to stretch

Tensile stress = Force / CSA

Strain = Change in length / Initial length

Question 5

Material properties

Answer 5

Collagen fibres orientation between insertions to resist tensile forces

Stiffness varies non-linearly with force

Initial toe region - flattening of crimp

Linear relationship between force and deformation

Until tensile strength is exceeded and fibres begin to fail

Complete rupture occurs around 10-12% strain

Ligament operating range ~1.5-2.5% strain

Tendon operating range ~2.5-7% strain

Question 6

Failure of ligament

Answer 6

Difficult to measure force and strain in ligaments in vivo

Some implantable transducers but most estimates of stresses and strains come from computer modelling studies

Question 7

Common ligament injuries

Answer 7

Knee

• anterior cruciate ligament
• medial collateral ligament

Ankle

• anterior talo fibular ligament
• calconeal fibular ligament

Question 8

Lateral ankle sprain - injury mechanisms

Answer 8

Combination of ankle inversion and internal rotation places high strain on:

• AFTL
• CFL

Question 9

Lateral ankle sprain - risk factors

Answer 9

Previous ankle sprain

Poor ankle stability - proprioception

Poor ankle muscle strength

Nature of sport

Question 10

Lateral ankle sprain - targets for prevention

Answer 10

Ankle supports

Balance board exercises

Strapping and taping

Strengthening exercises

Mobility exercises

Question 11

Healing of ligament

Answer 11

Influx of blood cells to damaged area cause inflammation and pain

New collagen fibrils laid down but not as orderly arranged as ‘normal’ ligament

Scar tissue forms which has different stiffness properties

Scar tissue will very slowly remodel to become more ‘normal’

Question 12

Contact ACL injury mechanisms

Answer 12

When lateral force is applied to the knee when the foot is planted

Structures affected:

• ACL
• MCL
• Medial meniscus

Often also damage to lateral meniscus due to compression

Question 13

Non-contact ACL injury mechanisms

Answer 13

Classic non-contact ACL involves pivoting or landing movements

Pivot - fixed foot and rotation results in excessive rotation and valgus torque

Landing - insufficient knee flexion and weak hamstrings result in excessive anterior force

Question 14

Risk factors for non-contact ACL injuries

Answer 14

Sex

Previous injury

Poor neuromuscular control

• Imbalance in strength of quads and hamstrings
• Valgus collapse of the knee on jump landing tasks

Question 15

Prevention of non-contact ACL injuries

Answer 15

Neuromuscular training programmes

FIFA 11+

Usually in form of warm-up

Aim to improve strength in key muscles

Appropriate muscle activation

Focus on movement quality

Improving balance

Effective in controlled trials

Have to be viewed as performance enhancing as well to be implemented in practice