Stryker Triathlon Total Knee System for Total Knee Arthroplasty Implanted Using Shapematch Cutting Guides:Sub-Study A

Inclusion Criteria: * The patient is a male or non-pregnant female between the ages of 50-90. * The patient requires a primary total knee replacement and is indicated for computer-assisted surgery. * The patient has a primary diagnosis of osteoarthritis (OA). * The patient has intact collateral ligaments. * The patient is able to undergo MRI scanning of the affected limb. * The patient has signed the study specific, HREC-approved, Informed Consent document. * The patient is willing and able to comply with the specified pre-operative and post-operative clinical and radiographic evaluations. Exclusion Criteria: * The patient has a history of total, unicompartmental reconstruction or fusion of the affected joint. * The patient has had a high tibial osteotomy or femoral osteotomy. * The patient is morbidly obese (BMI ≥ 40). * The patient has a deformity which will require the use of stems, wedges or augments in conjunction with the Triathlon Total Knee System. * The patient has a varus/valgus malalignment ≥ 15° (relative to mechanical axis). * The patient has a fixed flexion deformity ≥ 15°. * The patient has a neuromuscular or neurosensory deficiency, which would limit the ability to assess the performance of the device. * The patient has a systemic or metabolic disorder leading to progressive bone deterioration. * The patient is immunologically suppressed or receiving steroids in excess of normal physiological requirements. * The patient has a cognitive impairment, an intellectual disability or a mental illness. * The patient is pregnant. * The patient has metal hardware present in the region of the hip, knee or ankle (as this is known to create geometrical distortion in the region of the implant). * The patient has any known contraindications for undergoing assessment by MRI (e.g. ferrous implants, metallic clips, magnetically activated implanted devices such as cardiac pacemakers, etc).