MSK: Limbs Over Time

The Limbs Over Time

Sarcopaenia: Loss of muscle mass and strength as you age

With age:

• SA of muscles decreases
• Infiltration of non contractile tissue into muscles - increase in adipose tissue
• Muscle strength decreases
• Reduction in motor units 
• Change in type of motor neurones - deinnervation of fast motor neurones therefore increased innervation of slow motor neurones

Factors that contribute to Sarcopaenia

• Nutritional
• Hormonal
• Metabolic
• Immunological

This leads to 

• Reduced motor units
• Decreased muscle fibres
• Atrophy 
• Loss in muscle mass/strength
• Reduced physical activity = risk of falls

Osteopoenia 

• Bone loss
• Reduced bone mineral density
• Bones become more fragile
• Vertebrae, hip and wrist most at risk
• Previous fracture, increases risk of fracture

Cortical and trabecular bone are affected differently with age. 

• cortical bone strength ↓ by 2% per decade, from age 20 yrs

• toughness ↓ by 7% per decade (bone becomes more brittle)

• trabecular bone affected more than this due to thinning and loss of trabeculae

Sex Hormones

• Stimulate bone formation
• Hormones levels decrease with age 
• Menopause - bone loss twice as fast in women
• Hormones also affect bone via muscle - decreased muscle therefore reduced loading therefore reduced BMD

Aging and Fibrous Tissue

• Collagen cross-links increase and mature
• NEG - tissue is yellow and stiffer
• Microdamage accumulates + tissue becomes weaker 
• Tissues are avascularised therefore damage takes longer to heal

Cross links are proteins that stabilise the molecule. There are two different types. 

As you age, NEG increase as you age. This makes the tissue more brittle and stiffer. Reduces the ability to absorb shock. 

Tendons and Ligaments 

• Tendons become smaller + harder
• Ligaments are less able to absorb shock
• The more ligaments are stretched, the more likely it will not return to its original shape or will break

Cartilage and Age

• ↓ proteoglycan content

• ↓ aggregation of PG's

• ↑ collagen content and cross-linking

• ↑ levels of non-enzymatic glycation

• ↑ apoptosis

• ↑ stiffness

Disk Degeneration

Disk consists of nucleus pulposus and annulus fibrosis. With age, they become dehydrated, reduced proteoglycans and increased NEG (hence yellow appearance). 

With age, height of intervertebral disks decrease. 

Furthermore, disc degeneration leads to stress-shielding (loading on bone decreases therefore density decreases)  of the vertebral body. This accelerates osteoporotic changes and increases the risk of fracture. 

A fracture = kyphotic deformation. Forward curvature of the spine.