1. Internal fixation devices like plates and screws are used to stabilize fractures and add stability. They allow early motion to prevent stiffness and complications compared to casts. 2. Dynamic compression plates work by using offset screws that exert compressive forces to stabilize fractures. 3. Implant materials must have suitable mechanical properties to function like bone, including elastic modulus and strength. Common biomaterials are metals, ceramics, polymers, and bone cement.

1. Principle of Screw and Plate Fixation & Mechanical Behavior of Implant Materials

19. Materials http:// www.me.udel.edu/~advani/research_interest/implants.htm http://www.orthopedictechreview.com/issues/sep00/case15.htm Composite Ceramic http://www.centerpulseorthopedics.com/us/patients/hip/hip_issues/index Metal: Rough & Polished http://www.centerpulseorthopedics.com/us/products/hip/allofit/index Polymer

22. http://www.engr.sjsu.edu/WofMatE/projects/srproject/srproj3.html#overview 190 GPa (used with cement) 200 GPa 110 GPa Young’s Modulus Excessively corrosive in some cases Susceptible to fatigue cracking Very high modulus PMMA cement may cause fracture or tissue reaction Co, Cr, Mo known to be toxic in ionic form; High modulus *varies with smooth or porous surface Poor wear characteristics *varies with smooth or porous surface Problems Rarely used in new designs in joint replacement; Fracture fixation devices Total joint arthroplasty (usually fixed with cement); Need to be inserted with a lower modulus polymer cement for fixation to prevent stress shielding of surrounding bone Cementless joint replacements (total knee arthroplasty); Fracture fixation devices Uses Strong, cheap, relatively biocompatible; annealed, cold worked or cold forged; relatively ductile-contouring of plates and wires Stronger and more corrosion resistant than stainless steel; Excellent resistance to fatigue, cracking, and stress Yield strength; Ti > Stainless Steel Benefits Cr, Ni, Mo Cr: oxide layer when dipped in Nitric acid (reduced corrosion) 30-60% Co 20-30% Cr 7-10% Mo Ti 6 Al 4 V Chemical Make-up Stainless Steel Cobalt-chromium-molybdenum Titanium Metals

36. The End