BioPoly® RS Partial Resurfacing Patella Registry Study

Inclusion Criteria: * Age 21 years and older * Cartilage lesion(s) located in the facets of the patella that have failed prior therapy (conservative or surgical) * Symptomatic lesions classified as ICRS grade 2, 3, or 4 * Lesion size may not exceed 3.1 cm2 and must be circumscribed by a 15 mm or 20 mm circle of normal or nearly normal (ICRS Grade 0 or 1) cartilage, with an overall depth less than 4 mm from the articulating surface * Subchondral bone quality sufficient to support the implant * Understanding and willingness to comply with the post-operative rehabilitation instructions and follow-up visits. Exclusion Criteria: * Body mass index (BMI) ≥ 35 * Generalized degenerative or autoimmune arthritis * Gout * Uncorrected chronic malalignment of the patella (may be corrected at the same time as the implantation of the BioPoly device). * Uncorrected ligamentous instability (may be corrected at the same time as the implantation of the BioPoly device). * Kissing lesion on femur * More than one implant required to accommodate lesion * Allergy to ultra-high molecular weight polyethylene (UHMWPE), or hyaluronan/ hyaluronic acid (HA) * Use with opposing articulating femoral components * Any concomitant painful or disabling disease of the spine, hips, or lower limbs that would interfere with evaluation of the afflicted knee * Pregnant, prisoner, vulnerable population, or unable to provide informed consent.