Overview
Biomaterials are materials used to replace, augment, or support biological structures of the musculoskeletal system. In orthopaedics, biomaterials are used in implants, prostheses, fixation devices, bone substitutes and joint replacements.
An ideal orthopaedic biomaterial must possess appropriate mechanical strength, corrosion resistance, biocompatibility and long-term durability. Because orthopaedic implants often bear significant mechanical loads, the material properties must match the mechanical demands of the skeleton while also remaining biologically compatible with surrounding tissues.
Classification of Biomaterials
Orthopaedic biomaterials are commonly classified based on their chemical composition and mechanical properties.
| Category | Examples | Common Uses |
|---|---|---|
| Metals | Stainless steel, titanium alloys, cobalt-chrome | Plates, screws, nails |
| Ceramics | Hydroxyapatite, alumina | Bone substitutes, joint bearings |
| Polymers | Polyethylene, PMMA | Joint prostheses, bone cement |
| Composites | Carbon fiber reinforced materials | Advanced implants |
Metallic Biomaterials
Metals are the most commonly used biomaterials in orthopaedic surgery because of their high mechanical strength and durability. They are widely used in fracture fixation devices such as plates, screws and intramedullary nails.
Common Metallic Materials
| Material | Properties | Applications |
|---|---|---|
| Stainless Steel | Strong, inexpensive | Plates, screws |
| Titanium Alloy | Biocompatible, corrosion resistant | Joint prostheses |
| Cobalt Chrome | High wear resistance | Joint replacement components |
Ceramic Biomaterials
Ceramics are brittle materials but have excellent biocompatibility and wear resistance. They are often used in joint replacement bearings and bone graft substitutes.
- Hydroxyapatite
- Alumina
- Zirconia
Hydroxyapatite closely resembles the mineral component of bone and promotes osteointegration.
Polymeric Biomaterials
Polymers are lightweight materials commonly used in joint replacement and bone cement.
| Polymer | Use |
|---|---|
| Ultra-high molecular weight polyethylene | Joint prosthesis bearings |
| PMMA | Bone cement |
Biocompatibility
Biocompatibility refers to the ability of a biomaterial to perform its intended function without producing harmful effects on surrounding tissues.
- Minimal inflammatory response
- No toxicity
- No carcinogenicity
- No allergic reaction
Corrosion of Implants
Corrosion refers to the degradation of metallic implants due to chemical reactions within the body.
| Type | Description |
|---|---|
| Galvanic corrosion | Occurs between different metals |
| Crevice corrosion | Occurs in small spaces |
| Pitting corrosion | Localized damage |
Stress Shielding
Stress shielding occurs when a rigid implant carries most of the mechanical load, resulting in reduced stress on the surrounding bone. According to Wolff law, reduced mechanical stress leads to bone resorption.
- Occurs with rigid implants
- Leads to bone loss
- May cause implant loosening
Key Exam Points
- Most common biomaterials are metals
- Titanium has excellent biocompatibility
- Hydroxyapatite promotes osteointegration
- PMMA is used as bone cement
- Stress shielding leads to bone resorption