Eligibility Criteria:
Inclusion Criteria:
* Patients with a pre-operative Knee Society Assessment Score of \<70
* Patients undergoing primary partial knee arthroplasty as unilateral arthroplasty or bilateral arthroplasty, simultaneously or otherwise
* Patients diagnosed with osteoarthritis (Kellgren Lawrence Grade IV) or avascular necrosis limited to the medial compartment of the operative knee joint
* Male or female patients who are at least 21 years of age at the time of surgery
* Patients with full thickness cartilage loss, with or without bone loss in the medial compartment
* Patients with functionally intact ACL and PCL
* Patients who need to obtain relief of pain and/or improved function in their knee
* Patients with fixed flexion deformity \< 15°
* Patients who are able to follow post operative care instructions
* Patients who are willing and able to return for scheduled follow-up evaluations
* Patients in which natural alignment can be restored
* Patients with BMI \< 40
* Patients who have completed a valid, IRB approved Informed Consent Form
Exclusion Criteria:
* Patients with a pre-operative Knee Society Assessment Score of ≥ 70
* Patients in which the device would be used to revise a failed prosthesis
* Patients who are less than 21 years of age at the time of surgery
* Disease or damage to the lateral part of the knee that in the investigator's opinion contraindicates a partial knee replacement
* Patients diagnosed with rheumatoid arthritis or other forms of inflammatory joint disease
* Patients diagnosed with a failed upper tibial osteotomy in the operative knee
* Patients diagnosed with post-traumatic arthritis after tibial plateau fracture
* Patients who have had a patellectomy
* Patients with a flexion deformity \> 15°
* Patients with a fixed varus deformity \> 15°
* Patients who have rapid joint destruction, marked bone loss or bone resorption apparent on roentgenogram
* Patients with a fused knee on operative side
* Patients who have active or suspected infection, local or systemic that, in the opinion of the investigator, may put patients at undue risk.
* Patient with pre-existing condition(s) that may interfere with the survival of the implant or their outcomes, including: Sickle Cell Anemia, Lower extremity muscular atrophy, Neuromuscular disease, Vascular insufficiency, Metabolic Disorders which impair bone formation, Paget's Disease, Charcot's Disease, Osteomalacia, Osteoporosis, Osteopenia.
* Patients with clinical conditions that may limit follow-up (in the opinion of the investigator) including: Immuno-compromised conditions (i.e. HIV), Hepatitis, Tuberculosis, Neoplastic disease such as cancer of the prostate, lung, stomach, cervix, etc.
* Chronic renal failure
* Organ transplant (i.e., heart, liver, lung, etc.) recipients
* Known disease process that in the opinion of the investigator may limit long term (4 year) follow up (i.e., multiple sclerosis, leukemia, lymphoma, etc.)
* Patients diagnosed with Parkinson's or Alzheimer's Disease
* Patients who have had an above-knee amputation in the contralateral leg Instability or deformity of the ligaments and/or surrounding soft tissue, which would preclude stability of the prostheses
* Patients with a known metal allergy
* Prisoners or, individuals who are known to be abusing drugs or alcohol or are mentally incompetent
* Patients who have received systemic steroids within the past 6 months or steroid injection into the affected knee within the previous 6 weeks prior to enrollment
* Patients taking immunosuppressives
* Patients who are pregnant and/or breast-feeding females or females who intend to become pregnant during the time of the study
* Patients with severe valgus or varus knees (valgus or varus angulation of more than 20°) where collateral ligament, iliotibial band, or popliteal release is required
* Patients who refuse to sign the IRB approved Informed Consent Form
* Participation in an interventional clinical research study procedure, other than a bilateral knee arthroplasty in this study, within the past 12 months
* Patients with a history of osteomyelitis or sepsis of the index knee
* Patients who require patellar resurfacing
* Patients who are not skeletally mature
* Patients who have had a total hip replacement procedure \<18 months prior to entering the study
* Patients who have had a contralateral non-study knee replacement procedure \<18 months prior to entering the study
* Patients who are found intraoperatively to have inadequate bone stock or other conditions that contraindicate a partial knee replacement
* Patients who have a higher risk of falling
* Patients who are smokers or a history of smoking in the past 12 months
* Patients with alcoholism or drug addiction
* Tumors of the supporting bone structures
* Patients who have a permanent valgus or varus deformity including tibia vara deformity
* Patients with BMI ≥ 40
* Patients 80 years of age or older
* Patients who have undergone same-day or staged bi-lateral partial knee replacement
* Patients who may have an allergic reaction to the device materials or bone cement