MSK 17 Ageing of the Musculoskeletal System Flashcards
Sarcopaenia Definition
Inevitable loss of muscle mass and strength that occurs in-ageing muscle, even in the healthy elderly
Sarcopaenia Determinants of muscle strength
Muscle cross sectional area (decreases with age)
Sarcopaenia Muscle fibre atrophy leads an opening for
Invasion of space with connective tissue
Sarcopaenia Age related muscle changes
- Marked hypertrophy (type II fibres)
- Marked reduces strength
- Marked reduced muscle area
- Dynamic forces decline with age (stading up etc.)
- Los of force
- Selective loss of type II fibres (the stronger fibres)
Sarcopaenia Systemic Factors that contribute to age-related sarcopaenia
- Nutritional
- Hormonal (IGF-1 and GH)
- Metabolic (enzyme loss)
- Immunologic
Sarcopaenia Peripheral factors that contribute to age-related sarcopaenia
- Reduced Motor units
- Reduced Muscle Fibres
- Muscle Fib Atrophy
Sarcopaenia Factors peripheral and systemic lead to
Loss of muscle mass and strength
Weakness
Decreased mobility and so
Disability and loss of independence
Sarcopaenia Consequences of Sarcopaenia
- Force and speed of contraction are reduced, leading to slower and weaker muscles
- Loss of alpha motor neurons leads to fewer motor units with increased no. of muscle fibres, causing loss of fine control**
- These age-related changes may contribute to loss of co-ordination, slower muscle reflexes and increased risk of falls
- Reduced loading of skeleton due to sarcopaenia may also contribute to osteopaenia
*Muscle quality →
type II fibres has a higher specific force
**Muscle fibre atrophy →
- Loss of alpha motor neurons is selective for alpha IIb lost most with ageing
a. Necrosis of fibres that aren’t innervated and therefore die rapidly
b. Can get re-innervation of these fibres by axons close
i. More muscle fibres per motor unit = loss of skill and coordination - Type II fibre atrophy more common
Wolff’s law →
bone adapts its mass and architecture to mechanical demands.
Osteopaenia: Definition
Age related bone loss (can be seen with corticosteroid use)
Osteopaenia: Characterised by
- Sever bone loss
- Reduced boen mineral density
- Micro-architecture deterioration
Osteopaenia: Ageing
Due to imbalance between bone formation and bone resorption
Osteopaenia: Consequence
Bones become more fragile
Osteopaenia: Affects
50% women and 30% men
Osteopaenia: Bones most effected
Vertebrae → large volume of trabecular bone – more susceptible to osteoprotic changes due to large LA.
Hip
Wrist
Osteopaenia: Augmenting risk
Previous fracture increases the risk of future fracture
Osteopaenia: Cortical vs trabecular bone:
• Cortical bone strength decreases by 2% per decade, from age 20 yrs
• Toughness reduces by 7% per decade (bone becomes more brittle)
o Toughness is energy absorbed at failure
• Trabecular bone affect more than this due to thinning and loss of trabeculae
Osteopaenia: Causes
- Reduced physical activity
- Reduced muscle mass
- Altered hormones/Growth factors (IGF-1)
- Poor nutrition
- Genes
Osteopaenia: Oestrogen and progesterone and their effects
➢ Stimulate bone formation
➢ Hormones decrease with age (men too)
➢ Menopause → bone loss becomes twice as fast in women
➢ Effect is systemic (so other factors operate)
➢ HRT reverses some of effects of menopause
➢ Hormones also affect bone via muscle (testosterone in men for muscle)
Osteopaenia: Diet and bones
o Inadequate dietary calcium is a problem
o Vitamin D, and sunlight hel
o Alcohol and smoking can reduce bone mass but caffeine has little effects
o Low body weight increased risk of low BMD
o Diet has less effect than genes, hormones and exercise
Ageing of fibrous Tissues Age changes in Fibrous tissues
- Cell number and morphology
- Collagen cross-links increase and mature (become non-reducible)
- Non-enzymic glycation (NEG) makes tissue yellow and stiffer
- Microdamage accumulates and makes tissue weaker
- Cells become less responsive to mechanical stimuli?
Ageing of fibrous Tissues Tendon cells normally
Elongated cells: long processes (cell signalling and mechanotransduction) → involved in cellular response associated with mechanical laoding.
Ageing of fibrous Tissues Immature tissue
Fat fibroblasts –>
Ageing of fibrous Tissues Mature tissues
Thin “tenocytes “ or “ fibrocytes
Reduction in cell density → the tissues are less metabolically active (cells for proteoglycan matrix and collagen) = hypertrophy
Ageing of fibrous Tissues Collagen Cross-linking
- Reducible (young tissue) and non-reducible (older). Cross links increase tissue strength and stiffness and size of collagen fibres.
- Non-enzymatic glycation (NEG)-sugars → makes tissues brittle and yellow
- NEG uncontrolled by cells : problem in tissues with low turnover
Ageing of fibrous Tissues Ligaments with age
Stiffer
Ageing of fibrous Tissues Collagenous tissues in muscle changes
Epimysium (connective tissue that surrounds tissues) increases in stiffness with age.
Age-related changes in cartilage
- Reduce proteoglycan content
- Reduced aggregation of PG’s
- Increased collagen content and cross-linking
- Increased levels of non-enzymatic glycation
- Increased stiffness
- Increased apoptosis
Cartilage cell density
Decreases with age (chondrocytes stop dividing at skeletal maturity and less responsive to loading
Nucleus pulposus
Loss of Proteoglycans → Reduce Hydration
Increased collagen → collagen type II changes to collagen type II
Endplate defects → depressurise nucleus and allows annulus to collapse inwards
Annulus fibrosis
Made up of lamellae of type I collagen fibres
Stress-shielding but the neural arch
o Disc narrowing causes the neural arch to resist compression (see image) in erect posture
o This unloads the vertebral body and disc
o And reduces BMD in the vertebral body
Greatest loss seen in anterior vertebral body
