This study will be conducted to assess the survivorship of a particular prosthesis used in unicompartmental knee arthroplasties. Patients undergoing this procedure have been diagnosed with isolated medial or lateral compartmental arthritis and have failed conservative treatment. The patients received a unicompartmental knee replacement using the Sigma® HP Partial Knee System.

This study is an epidemiological Level IV-Case Series clinical study that will study the survivorship of the Sigma® HP Partial Knee System in a consecutive series of patients. All patients who received the Sigma® HP Partial Knee System between August 21, 2008 and October 31, 2009 will be available to include in the study. Data will be collected preoperatively, intra-operatively, and post-operatively at intervals of 6 weeks, 6 months, 1 year, 2 years, and 5 years. Data will be analyzed for survivorship status at the 2- and 5-year follow-up visits. Other data, including functional outcomes, radiographic outcomes, and wear will be analyzed at the 5-year follow-up visit. Subjects will participate in the study for five years after their surgery.

Inclusion Criteria:

• Adult patient over the age of 18
• Diagnosis of isolated medial or lateral compartmental osteoarthritis of the knee joint
• Must have failed conservative treatment and received a unicompartmental knee arthroplasty between August 21, 2008 and October 31, 2009.
• Must have received the Sigma® HP Partial Knee System.
• Must have received the surgery from Dr. Almand, Dr. Johnson, or Dr. Pickering at Mississippi Sports Medicine and Orthopaedic Center.
• Must be willing to provide written consent to participate in the study.
• Subjects who do not have the legal capacity to consent may be enrolled in the study by a Legally Authorized Representative (LAR). The LAR must provide verification that they have the legal authority to represent the subject.

Exclusion Criteria:

• Did not receive a unicompartmental knee arthroplasty between August 21, 2008 and October 31, 2009.
• Did not receive a unicompartmental knee arthroplasty using the Sigma® HP Partial Knee.
• Did not receive their unicompartmental knee replacement from Dr. Almand, Dr. Johnson, or Dr. Pickering at Mississippi Sports Medicine and Orthopaedic Center.
• Subjects lost to follow-up for any reason including, but not limited to: refusal to consent, death, or geographic isolation will also be excluded from the study.

Since the first Sigma® HP Partial Knee System was introduced at MSMOC, over 1,000 have been implanted in patients by the investigators of this study. The population used for this study was the first patients of our clinic to receive this particular prosthesis. The first replacement was implanted on August 21, 2008. By October 31, 2009, 300 patients had received the Sigma® HP replacement. These 300 patients will be the subject population whose data will be analyzed for the study upon their consent.