A Post-Market Domestic (US) and International Data Collection to Assess the Truliant Knee System

Inclusion Criteria: Cohort 1. Prospective / Subjects- Enrolled in the study pre-surgery 1. Subjects who agree to participate in the study that have not had surgery prior to being enrolled in the study. 2. Skeletally mature (18 years of age or older). 3. Subject is willing and able to provide written informed consent for participation in the study. 4. Subject is to receive a Truliant® total knee replacement for Osteoarthritis, Avascular Necrosis, Rheumatoid Arthritis, Post-Traumatic Arthritis, Polyarthritis, Primary Implantation Failure, or as a Conversion of Uni-Compartmental Knee. 5. The knee replacement will be performed by the investigator or a surgeon sub-investigator. 6. The devices will be used according to the approved indications. Cohort 2. Retrospective to Prospective / Subjects enrolled in the study post- surgery then continue to participate in the study prospectively. 1. Subjects who agree to participate in the study that have undergone surgery prior to enrollment in the study. Data for these subjects will collected from the subject's medical record for the time period prior to enrollment in the study containing data pertaining to the index surgery (retrospective data) and from the patient after they are enrolled in the study during the post-operative time period (prospectively). 2. Skeletally mature (18 years of age or older). 3. Subject is willing and able to provide written informed consent for participation in the study. 4. Subject received a Truliant® total knee replacement for Osteoarthritis, Avascular Necrosis, Rheumatoid Arthritis, Post-Traumatic Arthritis, Polyarthritis, Primary Implantation Failure, or as a Conversion of Uni-Compartmental Knee. 5. The knee replacement was performed by the investigator or a surgeon sub-investigator. 6. The devices are/were used according to the approved indications. * Special consideration should be taken to ensure that these subjects meet all inclusion criteria, none of the exclusion criteria, and have a minimum of the following pre-operative, operative, and applicable postoperative data available in the subject's medical records, related to the Truliant® knee prosthesis manufactured or distributed by Exactech Inc (Gainesville, Florida, USA). Prior to inclusion in the study, the following details must be available for data submission: Pre-Operative: o Demographic Data 1. Gender 2. Age at surgery 3. Height/Weight 4. Indication for surgery 5. Prior Injuries/Surgeries on index knee 6. Comorbidities * Operative: * Date of Surgery * Type of Surgery (Primary / Revision) * All component product information, including catalogue reference numbers * Adverse Event Information, if applicable Cohort 3. Retrospective Only Subjects enrolled in the study post-study surgery with no intent to continue as prospective subjects. Note: No prospective data may be collected from a subject if they are enrolled under this cohort unless the subject is willing and able to provide written informed consent for participation in the study. 1. Skeletally mature at the time of the surgery (18 years of age or older). 2. The patient's clinical record includes a signed HIPAA waiver allowing for the use of clinical record data for the purpose of clinical research outside of the operating institution. 3. The patients clinical record includes a documented procedure that includes, or is related to, TKA with a Truliant® Knee system device. 4. The knee replacement was performed by the investigator or a surgeon sub-investigator. 5. The devices are/were used according to the approved indications. 6. Special consideration should be taken to ensure that these subjects meet all inclusion criteria, none of the exclusion criteria and have a minimum of the following pre-operative, operative, and applicable postoperative data available in the subject's medical records, related to the Truliant® knee prosthesis manufactured or distributed by Exactech Inc (Gainesville, Florida, USA). Prior to inclusion in the study, the following details must be available for submission: * Pre-Operative: * Demographic Data * Gender * Age at surgery * Height/Weight * Indication for surgery * Prior Injuries/Surgeries on index knee * Comorbidities * Operative: * Date of Surgery * Type of Surgery (Primary / Revision) * All component product information, including catalogue reference numbers Adverse Event Information, if applicable Exclusion Criteria: * Patient was \<18 years of age at time of surgery * Patient does not meet indicated population for use criteria for this device * Patient is pregnant * Patient is a prisoner * Patient has a physical or mental condition that would invalidate the results * Patient is contraindicated for the surgery (e.g., metal allergy)