Patient Specific Talus Spacer Post Approval Study

Inclusion Criteria: 1. Subject plans to undergo implantation of the Patient Specific Talus Spacer for avascular necrosis of the ankle joint independent of this research protocol; 2. Avascular necrosis of the ankle joint; 3. Age 21 years old or older; 4. Subject has good general health; and 5. Subject signs a written informed consent form (ICF) prior to the surgical procedure. Exclusion Criteria: 1. Presence of any contraindication identified in the device Instructions for Use; 2. Surgeon determines that the patient is not appropriate for the Talus Spacer procedure based on the device IFU (including the enumerated Warnings and Precautions); 3. Based on the medical opinion of the surgeon, the patient is not appropriate for the Talus Spacer procedure; 4. For female subjects, pregnancy; 5. Active systemic disease, such as AIDS, HIV, or active infection; 6. Active infection or the skin is compromised at the surgical site; and 7. Systemic disease that would affect the subject's welfare; 8. Is a prisoner, incarcerated, or has been coerced to participate in the study that could impact the validity of results; 9. Is currently participating in an investigational therapy (device and/or pharmaceutical) within 30 days prior to entering the study or such treatment is planned during the time course of follow-up. 10. If the Sponsor has notified the site that 30 subjects have been enrolled in the study with a Cobalt Chromium Patient Specific Talus Spacer, and the surgeon believes that a Cobalt Chromium Patient Specific Talus Spacer is the best option for the patient. 11. If the Sponsor has notified the site that 30 subjects have been enrolled in the study with a Titanium (Ti6Al4V) with Titanium Nitride (TiN) coating Patient Specific Talus Spacer, and the surgeon believes that a Titanium (Ti6Al4V) with Titanium Nitride (TiN) coating Patient Specific Talus Spacer is the best option for the patient.