Musculoskeletal System, Nervous System & Bioelectricity: Overuse, Ageing, and Disease

50 practice flashcards covering bone biomechanics, mechanotransduction, ageing, osteoporosis, and various fracture types based on the lecture MNB.3.

What specific type of cells act as the mechanosensors distributed throughout bone?

Osteocytes

What is the name of the spaces within the bone that mature bone cells occupy?

Lacunae

What are the narrow, fluid-filled canals through which bone cell processes pass?

Canaliculi

How do osteocytes respond to changes in their physical and chemical surroundings?

They release chemicals that cause bone to be removed or formed.

By what percentage does an astronaut's weight-bearing bone density decrease for every month spent in space?

Approximately $1\%$

Why do astronauts' bones not undergo the stress of supporting their bodies against gravity while in space?

They experience microgravity.

What are the best types of activities to build bone mass on Earth?

Load-bearing activities, such as walking or running.

As bone ages, how do the rates of bone resorption and bone formation change?

The rate of bone resorption increases and bone formation decreases.

What changes occur in trabecular bone composition due to the imbalance of bone resorption and formation during ageing?

Reduction of trabecular number, decreased thickness, and increased spacing.

What change occurs to the bone marrow cavity as bone ages?

Expansion of the bone marrow cavity.

What happens to the Young’s modulus of bone over a lifetime?

It increases as we age.

A higher Young’s modulus in older bone is indicative of what mechanical property change?

The material becomes less elastic.

How is bone strength typically expressed and determined?

As bone mineral density ($BMD$), determined by dual-energy X-ray absorptiometry ($DXA$).

What factors constitute 'bone quality'?

Bone structural and material compositional properties.

What is the clinical definition of osteoporosis regarding its effect on bone?

A disease that compromises the matrix structure of bone, significantly reducing its mechanical strength.

What are the common symptoms of osteoporosis mentioned in the transcript?

Fracture from slight trauma, loss of height, stooped posture, and back pain.

At what age range does peak bone mass typically occur in adults?

Approximately $30$ years.

What is the definition of a T-score in the context of a $DXA$ scan?

The number of standard deviations the result is from the average $BMD$ of an adult of the same sex and race at peak bone mass.

What T-score value is required for an osteoporosis diagnosis?

A T-score of $< -2.5$

What is the classification for a T-score between $-1$ and $-2.5$?

Low Bone Mass (Osteopenia)

What percentage of people who suffer a hip fracture will experience permanent functional disability?

$$50\%$$

What is the mortality rate within six months for people who suffer a hip fracture?

$$20\%$$

Which specific bones show the greatest increase in fracture risk due to high trabecular bone content?

Spine, hip, wrist, humerus, and pelvis.

How many vertebrae make up the spine?

$$33$$

In vertebral biomechanics, what does the thin layer of cortical bone represent?

The tube

What is the function of the cylinder of trabecular bone within the vertebral body?

It acts as a shock absorber.

What is the mechanical function of the horizontal struts within healthy vertebrae?

They develop tension when loaded and keep the vertical struts from bowing.

What happens to the vertebral body in osteoporosis when horizontal struts are lost?

It cannot sustain the same loads and would collapse like an empty cardboard box once loaded.

What is the clinical term for 'Dowager’s hump' caused by compression fractures of thoracic vertebrae?

Progressive thoracic kyphosis

What are the physical consequences of thoracic kyphosis on the internal organs and ribs?

Lower ribs rest on iliac crests and downward pressure on viscera causes abdominal distention.

What are the primary causes of bone fractures?

Falls, trauma, direct impact, sudden excessive force, overuse, or diseases like osteoporosis.

What is a greenstick fracture?

An incomplete fracture where the bone bends and cracks on one side instead of breaking completely.

Why are greenstick fractures most common in children below $10$ years of age?

Their bones are softer (less mineralised) and more flexible than adult bones.

In a greenstick fracture, on which side does the cortex fail?

The tension side.

How long does it typically take for a greenstick fracture to heal?

Around six weeks.

What are stress fractures characterized as?

Tiny cracks in the bone arising from repetitive force or overuse.

In which part of the body do stress fractures usually occur in athletes?

Lower extremities.

How long does it typically take the body to generate new bone cells to repair stress fractures?

Six to eight weeks.

What is a transverse fracture?

A complete fracture where the break is perpendicular to the length of the bone.

What type of force typically causes a transverse fracture?

Shear force or side impact from trauma like a fall or car accident.

What mechanical action results in a spiral fracture?

Rotational action ($\text{torque}$) on the bone.

What is a common complication of spiral fractures involving surrounding tissues?

Sharp bone edges can penetrate muscle or other tissue resulting in soft tissue damage.

What is the typical healing duration for a spiral fracture?

Four to six months.

Why does a greenstick fracture originate on the side under tension?

Because bone is weakest under tension.

What is the maximum stress a child’s ulna can sustain in compression?

$$13 \times 10^{7}\,Nm^{-2}$$

What is the average cross-sectional cortical bone area of a child's ulna used in the problem?

$$50\,mm^2$$

Convert $50\,mm^2$ to square meters ($m^2$).

$$50 \times 10^{-6}\,m^2$$

What is the formula used to calculate the maximum force the ulna can sustain?

$$\text{Force} = \text{Stress} \times \text{Area}$$

What is the calculated maximum force a child's ulna can sustain in compression?

$$6500\,N$$

Why is bone density loss in space specific to 'weight-bearing' bones?

Because these bones normally support the body's weight against gravity, a function absent in microgravity.