Bone Fracture

Recall:

Three types of Stress: Tension Compression Shear

Compression

Shortens an object.

Load pushing molecules more tightly together

Bones are designed for compression. As you stand, your bones (Femur, tibia, etc.) are

supporting your body weight. This body weight is a result of gravity acting on your

mass. This causes compressive stress (load) on your bones.

Can lead to bruising of soft tissues or crushing fractures of bones

Tension

Pulling apart of molecules, resulting in elongation of material.

More likely to lead to bone fracture.

https://www.youtube.com/watch?v=FT8Xg98uw1o

Types of Fractures

Closed – skin not punctured. Open or Compound – skin

punctured and bone exposed.

Transverse – perpendicular to long axis of bone.

Comminuted – 3 or more fractures in same bone.

Undisplaced – broken pieces aligned.

Displaced – broken pieces not aligned.

Greenstick – fracture on 1 side of bone causing other side to bend.

Healing Nature of Bones

Bones have the ability to heal

Key Players: Osteoclasts – break down bone Osteoblasts – build new bone

http://www.exogen.com/physicians/how-it-works/

Inflammation

1) Fracture Hematoma forms – helps keep the bones aligned & cuts off oxygen from the fractured bone (killing it)

Source: http://science.howstuffworks.com/life/human-biology/heal-broken-bones.htm

Soft Callus

Several days later, the fracture hematoma turns into a soft callus Fibroblasts develop collagen & chondroblasts

begin developing fibrocartilage Transforms from soft callus to fibrocartilage

callus – bridges gap between bones (3 wks)

Source: http://science.howstuffworks.com/life/human-biology/heal-broken-bones.htm

Bone Callus (Hard Callus)

Formation of the bone callus Osteoblasts begin building new bone 3-4 month process Provides enough stability for the bone to

finish healing

Source: http://science.howstuffworks.com/life/human-biology/heal-broken-bones.htm

Remodeling

Not done yet… Osteoclasts and Osteoblasts spend months

remodeling the bone by replacing bone callus with compact bone

Overtime, remodeling reduces the bulge

Weight-lifting

Weight-lifting causes small fractures to occur in our bones, but DON’T panic!

These fractures signal osteoclasts to come remove the damaged bone and osteoblasts to build new bone.

Overtime, you end up with stronger, healthier bones!

Also, remember, the more muscles your have, the more bone you need at your joints to hold those muscles, further strengthening your bones.

Bone Repair and Biomedical Engineering

Casting

Some fractures only require casting to aid healing.

Casts provide stability and prevent the bones from misaligning during healing.

Repairing Bones: Overview

Some serious breaks need the aid of engineers because: Need to restore function and position Likely not to heal correctly High risk of infection Very long healing time

Biomedical engineers use internal and external fixation approaches

While beneficial, added challenges and possible complications exist

Internal vs. External Fixation

Internal fixation: Temporary or

permanent fixtures directly attached to the bone under the skin, for alignment and support pins rods or nails plates screws wires grafting

External fixation:

Temporary repair supports outside of the skin that stabilize and align bone while the body heals screws in bone to hold

in place metal braces or casts can be externally

adjusted

Internal Fixation

To determine the best repair technique, the break type and location are considered

Image source: US National Library of Health, National Institutes of Health, Medline Plus, http://www.nlm.nih.gov/medlineplus/ency/presentations/100077_3.htm

External Fixation

Installing temporary repair supports outside of the skin to stabilize and align bone while the body heals.

Examples: screws in bone, metal braces, casts, slings.

Image source: US National Library of Medicine, National Institutes of Health, MedlinePlus, http://www.nlm.nih.gov/medlineplus/ency/imagepages/18021.htm

Example: Rods, Plates and Screws

Rods are used for alignment and support of long and large bones

Plates hold together loose pieces of bone and support smaller bones

Screws hold plates and rods in place

Image source: US National Library of Medicine, National Institutes of Health, Medline Plus, http://www.nlm.nih.gov/medlineplus/ency/imagepages/18023.htm

More Plates and Screws

X-ray example of shattered dog femur that was repaired with a plate and seven screws

Image source: David M. Nunamker, University of Pennsylvania School of Veterinary Medicine. http://cal.vet.upenn.edu/projects/saortho/chapter_39/39mast.htm Used with permission.

Medical Implant Materials

Bone is an amazing material: strong and flexible

Most human-made materials that are strong are also brittle

To be accepted by the body and not cause other problems, the materials for rods, pins, screws and plates must also be biocompatible.

Engineers design materials especially for medical implants that are made of: Surgical stainless steels

(blends of nickel, chrome and molybdenum) Titanium alloys Polymers

Results

After a few months, patients should be back on their feet, ready to participate in everyday activities

Image source: US National Library of Medicine, National Institutes of Health, MedlinePlus, http://www.nlm.nih.gov/medlineplus/ency/presentations/100077_4.htm

Your Design Challenge

You will engineer a device to support the broken bone throughout healing.

Your device will be tested in the same way the bone was broken. Can you make it stronger?

Things to consider: Strong? Minimally invasive? Compatible? Inexpensive? Ease of implementation?

Prediction

How many lbs can a chicken bone hold?

Breaking Bones

Form a group of 3.

Take turns breaking the bones.

Convert Kg to lbs. 1 Kg = 2.20 lbs **Multiply your Kg value by 2.20 to convert to

lbs.