Aging = Change in the properties of a material over time, especially as oxygen bonds with free radicals (oxidation).
Amorphous = Lacking distinct crystalline structure.
Aseptic = Not caused by infection.
CIAN = Cold-Irradiated Non-Melt. Crosslinked polyethylene irradiated at room temperature. Annealed below melt to remove some free radicals.
CISM = Cold Irradiated Subsequent Melt. Crosslinked polyethylene irradiated at room temperature. Annealed above melt to remove all free radicals.
Crosslink = Molecular bond between adjacent polyethylene chains.
Crosslink density = a measure of the extent of crosslinking.
Crystalline = In UHMWPE, area where polyethylene chains fold into an orderly, laminar structure.
Dislocation = removal of the femoral head from the acetabular socket.
Embrittlement = Reduction or loss of ductility or toughness.
Current highly crosslinked polyethylenes = UHMWPE’s first introduced to the US orthopedic market around 1999. Generically, these materials undergo irradiation for crosslinking and a subsequent thermal treatment to remove/reduce free radicals.
Free radicals = Open or “free” molecular bonding sites created during irradiation when the material is energized and hydrogen atoms are released.
Jump distance = The distance the head must displace from the cup before dislocation.
kGy = kilo-Grey. Unit of measure for radiation dose (1 kGy = 0.1 Mrad).
Lever-out testing = Test designed to simulate an extreme case of the stem impinging on the liner edge, causing the liner to be peeled from the cup.
Molecular weight (MW) = Mass of one molecule of a substance.
Monomer = One “mer”, the building block of polymers.
Mrad = Mega-Radiation-Absorbed-Dose. Unit of measure for radiation dose (1 Mrad = 10 kGy).
Osteolysis = Latin: “bone death”.
Oxidation = Bonding of oxygen molecules to free radicals.
Polymer = Substance comprised of chains of repeating units or “mers”.
Radiation dose = Measure of energy deposited in a medium by radiation.
Resorption = Breakdown of the mineral matrix of bone.
ROM = Range of motion. The arc of motion that the stem can make within the acetabular cup before impingement.
Future highly crosslinked polyethylenes = Materials that deviate from the irradiate-and-anneal model of the current highly crosslinked polyetheylenes.
Semi-crystalline = A material consisting of crystalline and amorphous regions.
Tribology = The study of wear, friction, and lubrication.
UHMWPE = Ultra-high molecular weight polyethylene. Polymer consisting of long chains of carbon and hydrogen atoms.
Wear = Of UHMWPE acetabular liners. Removal of sub-micron particles from the surface of the liner as the CoCr head rubs against it.
WIAM = Warm Irradiated Anneal Melt. Crosslinked polyethylene that are warmed during irradiation to promote increased crosslinking. Annealed above melt to remove all free radicals.