Mechanics of Human Movement Final part 2

What makes up the axial and appendicular skeleton?

• axial: skull, vertebrae, ribs 74 bones

• appendicular: extremities, shoulder girdle, pelvis 126 bones

• Adult skeleton = 206 bones (6 auditory)

What is the function of the skeletal system?

• biomechanical: levers, supports

• physiological: protection, storage of fat and minerals, blood cell formation

What is human bone composed of?

• water

• minerals (resist compression), what bone mostly made of

• protein (collagen, resist tension)

label

1. articular cartilage

2. cancellous bone

3. cortical bone

Cortical bone

• compact

• low porosity

• shaft of long bones

Trabecular (cancellous) bone

• less compact

• high porosity (spongy)

• ends of long bones, vertebrae

What does isotropic mean?

• materials have the same mechanical properties in every direction of loading

• synthetic materials are isotropic

What does anisotropic mean?

• different mechanical properties depending on the direction of load

• connective tissue and biological tissue are anisotropic

When is bone the strongest and weakest?

• bone is strongest in compression

• bone is weakest in shear

Are tension forces between compression and shear?

• yes

What is Wolff’s law?

• bone strength increases and decreases as the functional forces on the bone increase and decrease

• bone in a healthy person will adapt to the loads under which it is placed

Describe the structure of Trabecular (cancellous) bone

• system of columns of bone

• the main columns are based on the direction of loading. Support the main loading (compression or tension)

• main columns are tied together with smaller transverse trabecular

How does age affect bone?

• decrease bone mineral density

• trabeculae lose thickness

• some transverse trabeculae disappear

Who does osteoporosis affect?

• type 1 (post-menopausal): 40% of women > 50 years

• type 2 (age associated): most women and men after age 70

How is trabecular (calcaneus) bone affected by osteoporosis?

• less porosity (spongy)

• hollow

• air pockets

Do bones need be under stress to develop?

• yes

How do bones respond to weight bearing exercise?

• larger the forces acting on the skeletal system, greater bone development

What does the national institute of osteoporosis and related bone disease recommend people do?

• walk

• hike

• jog

• climb stairs

• dance

What does the SCSM recommend?

• weights-bearing endurance activities, activities that involve jumping, resistance exercise

• moderate to high intensity for bone-loading forces. weight bearing endurance activities 3-5 times per week; resistance exercise 2-3 times per week

• 30-60 minutes

what is joint stability?

• resistance to movement in planes other than those defined by specific joint

• movement of articulating surfaces away from each other through sliding and pulling apart

Characteristics of tendons

1. attach muscle to bone

2. transmit tensile load from muscle to bone to produce joint stability or motion

3. provide mechanical pulleys

4. motor control

characteristics of ligaments

1. connect bones to bones

2. mechanical joint stability

3. guide joint motion

4. contribute to proprioception/position sense

composition of ligaments

• type 1 collagen fibers that are not completely parallel

• bear tensile loads in long direction

• can bear smaller tensile loads in other directions

• more elastin than tendons

Ligaments

• prevent dislocation when force trying to pull bones apart

• necessary when bone configuration not stable

• not good with shear forces

Characteristic for healing

• poor blood supply = bad healing

• bone have better blood supply than ligaments

grades of tears

• grade 1: very mild and can potentially heal on its own

• grade 2: more damage and this will take much longer to repair itself. therapy advised

• grade 3: complete tear. surgical intervention typical

factors affecting biomechanical properties

• age: decreased stiffness, strength, and ability to withstand deformation

• Pregnancy and postpartum period: increased laxity of tendons and ligaments in the pubic area during later stages of pregnancy

• Mobilization/Immobilization: increased strength/stiffness with mobility, decrease with immobility

composition of tendons

• parallel fibered collagenous network

• type 1 collagen sustains large tensile loads

• elastin: 2% of the dry weight

muscles

• contraction typically pulls bones closer together

• help make joint stable (good) but may increase joint compression to unsafe levels (bad)