Bone Fracture

Recall: Three types of Stress: Three types of Stress: Tension Tension Compression Compression Shear Shear

Compression Shortens an object. Shortens an object. Load pushing molecules more tightly together Load pushing molecules more tightly together Bones are designed for compression. Bones are designed for compression. As you stand, your bones (Femur, tibia, etc.) are supporting your body weight. 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 body weight is a result of gravity acting on your mass. This causes compressive stress (load) on your bones. This causes compressive stress (load) on your bones. Can lead to bruising of soft tissues or crushing fractures of bones Can lead to bruising of soft tissues or crushing fractures of bones

Tension Pulling apart of molecules, resulting in elongation of material. Pulling apart of molecules, resulting in elongation of material. More likely to lead to bone fracture. More likely to lead to bone fracture

Types of Fractures Closed – skin not punctured. Closed – skin not punctured. Open or Compound – skin punctured and bone exposed. Open or Compound – skin punctured and bone exposed. Transverse – perpendicular to long axis of bone. Transverse – perpendicular to long axis of bone. Comminuted – 3 or more fractures in same 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 Bones have the ability to heal Key Players: Key Players: Osteoclasts – break down bone Osteoclasts – break down bone Osteoblasts – build new bone Osteoblasts – build new bone

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

Soft Callus Several days later, the fracture hematoma turns into a soft callus Several days later, the fracture hematoma turns into a soft callus Fibroblasts develop collagen & chondroblasts begin developing fibrocartilage Fibroblasts develop collagen & chondroblasts begin developing fibrocartilage Transforms from soft callus to fibrocartilage callus – bridges gap between bones (3 wks) Transforms from soft callus to fibrocartilage callus – bridges gap between bones (3 wks) Source:

Bone Callus (Hard Callus) Formation of the bone callus Formation of the bone callus Osteoblasts begin building new bone Osteoblasts begin building new bone 3-4 month process 3-4 month process Provides enough stability for the bone to finish healing Provides enough stability for the bone to finish healing Source:

Remodeling Not done yet… Not done yet… Osteoclasts and Osteoblasts spend months remodeling the bone by replacing bone callus with compact bone Osteoclasts and Osteoblasts spend months remodeling the bone by replacing bone callus with compact bone Overtime, remodeling reduces the bulge 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. Some fractures only require casting to aid healing. Casts provide stability and prevent the bones from misaligning during healing. Casts provide stability and prevent the bones from misaligning during healing.

Repairing Bones: Overview Some serious breaks need the aid of engineers because: Some serious breaks need the aid of engineers because: Need to restore function and position Need to restore function and position Likely not to heal correctly Likely not to heal correctly High risk of infection High risk of infection Very long healing time Very long healing time Biomedical engineers use internal and external fixation approaches Biomedical engineers use internal and external fixation approaches While beneficial, added challenges and possible complications exist 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 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,

External Fixation Installing temporary repair supports outside of the skin to stabilize and align bone while the body heals. 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. Examples: screws in bone, metal braces, casts, slings. Image source: US National Library of Medicine, National Institutes of Health, MedlinePlus,

Example: Rods, Plates and Screws Rods are used for alignment and support of long and large bones Rods are used for alignment and support of long and large bones Plates hold together loose pieces of bone and support smaller bones Plates hold together loose pieces of bone and support smaller bones Screws hold plates and rods in place Screws hold plates and rods in place Image source: US National Library of Medicine, National Institutes of Health, Medline Plus,

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. Used with permission.

Medical Implant Materials Bone is an amazing material: strong and flexible Bone is an amazing material: strong and flexible Most human-made materials that are strong are also brittle 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. 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: Engineers design materials especially for medical implants that are made of: Surgical stainless steels (blends of nickel, chrome and molybdenum) Surgical stainless steels (blends of nickel, chrome and molybdenum) Titanium alloys Titanium alloys Polymers Polymers

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

Your Design Challenge You will engineer a device to support the broken bone throughout healing. 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? Your device will be tested in the same way the bone was broken. Can you make it stronger? Things to consider: Things to consider: Strong? Strong? Minimally invasive? Minimally invasive? Compatible? Compatible? Inexpensive? Inexpensive? Ease of implementation? Ease of implementation?

Prediction How many lbs can a chicken bone hold? How many lbs can a chicken bone hold?

Breaking Bones Form a group of 3. Form a group of 3. Take turns breaking the bones. Take turns breaking the bones. Convert Kg to lbs. Convert Kg to lbs. 1 Kg = 2.20 lbs 1 Kg = 2.20 lbs **Multiply your Kg value by 2.20 to convert to lbs. **Multiply your Kg value by 2.20 to convert to lbs.