Triathlon All-Polyethylene Tibia Outcomes Study

Inclusions: * Patient underwent primary TKA and is currently implanted with the Triathlon All-Polyethylene Tibia as well as compatible Stryker femoral and patellar components with no pending revision or removal. * Patient has signed an IRB-approved, study specific Informed Patient Consent Form. * Patient is a male or non-pregnant female and is 18 years of age or older at the time of study device implantation. * Patient is willing and able to comply with postoperative scheduled clinical and radiographic evaluations. Exclusions: * Patient had an active or suspected latent infection in or about the affected knee joint at time of study device implantation. * Patient had distant foci of infection which could have caused hematogenous spread to the implant site at time of study device implantation. * Patient was skeletally immature at time of study device implantation. * Patient has a mental or neuromuscular disorder which would create an unacceptable risk of prosthesis instability, prosthesis fixation failure, or complications in postoperative care. * Patient's bone stock was compromised by disease, infection, or prior implantation which cannot provide adequate support and/or fixation to the prosthesis. * Patient had severe instability of the knee joint secondary to the absence of collateral ligament integrity and function. * Patient was immunologically suppressed or receiving steroids in excess of normal physiological requirements at the time of surgery (e.g. \> 30 days duration of treatment). * Patient is a prisoner.