Postmarketing Study to Determine Performance of the SIGMA HP® PARTIAL KNEE SYSTEM

Inclusion Criteria: * Male or female subjects, aged at least 21 years. * Subjects who are able to give voluntary, written informed consent to participate in this clinical investigation and from whom consent has been obtained. * Subjects, who, in the opinion of the Clinical Investigator, are able to understand this clinical investigation, co-operate with the investigational procedures and are willing to return to the hospital for all the required post-operative follow-ups. * Subject has non-inflammatory degenerative joint disease (NIDJD), including: osteoarthritis, posttraumatic arthritis, avascular necrosis and chondrocalcinosis. * Subject has a functional stable knee. * Subject, in the opinion of the Investigator, is suitable for either a single or bicompartmental knee replacement. * Subject meets the following selected radiographic parameters: * X-ray evaluation confirms the presence of NIDJD * Disease location: 1 to 2 compartments, maximum. Disease can be present in the patellofemoral compartment, the medial tibiofemoral compartment, lateral tibiofemoral compartments alone or in any two compartments. * Disease severity: Kellgren and Lawrence44 Grade II or greater for all compartments replaced. Exclusion Criteria: * Subjects who, in the opinion of the Clinical Investigator, have an existing condition that would compromise their participation and follow-up in this clinical investigation. * Women who are pregnant. * Subjects who are known drug or alcohol abusers or …