The HYALEX Pivotal Study

Inclusion Criteria (Phase 1): 1. 22-70 years. 2. Body Mass Index (BMI) ≤ 40. 3. Up to two treatable joint surface lesion, ICRS Grade 3 or 4, located on the medial and/or lateral femoral condyle. 4. Up to 2 implants (one implant per condyle) to treat up to 2 individual symptomatic lesions with a total summative area up to 4.52cm2 / condyle. 5. Knee Injury and Osteoarthritis Outcome Score (KOOS) pain subscale score between 20 and 65. 6. Ligamentously stable knee. 7. Failure of non-operative treatment (e.g., physical therapy, physician-directed at home exercise program, intra-articular injections, bracing) for at least 4 months prior to consideration for participation in the study. Exclusion Criteria: HYALEX Implant, Surgical Technique, and Lesion Site Exclusions: 1. Known allergy to polyurethanes, bone cement, acrylic, or titanium. 2. Lack of 2mm of cartilage (ICRS Grade 0 to 2) and 2mm of vital bone wall on all sides of the implant site. 3. Osteochondral defect affecting subchondral bone more than 11mm in depth from adjacent non-defect articular surface. 4. Bipolar cartilage lesions involving patellar or tibial lesions ICRS Grade 3 - 4 opposite the lesion intended for treatment. 5. Insufficient bone stock or bone density determined intra-operatively preventing implant press fit. Patient Orthopaedic Health Exclusions: 1. Kellgren and Lawrence (KL) grade 3 or 4 on standing radiographs. 2. Hip-knee-ankle (HKA) angle of greater than +/- 8 degrees (varus or valgus malalignment \> 8 degrees) on standing X-ray. 3. Lack of normally functioning contralateral knee that restricts activity. 4. Recent Osteochondritis Dissecans within 1 year. 5. Diagnosis of a concomitant knee injury which the investigator believes may interfere with study participation or confound effectiveness assessment. 6. Untreated ACL and/or PCL deficiency or complex ligamentous instability of the study knee according to IKDC Grade C (abnormal) or D (severely abnormal). Previous Surgery and Intervention Exclusions: 1. Previous surgical cartilage treatment in the index knee within the last 6 months 2. Previous intra-articular injections, including HA and steroids, within the last 3 months prior to the date of surgery. Patient Overall Health and Health History Exclusions: 1. Any known history of inflammatory arthropathy or untreated or uncontrolled crystal-deposition arthropathy. 2. Current cigarette smoker or user of other nicotine products. 3. Known Type 1 or Type 2 insulin-dependent diabetes mellitus. 4. Currently undergoing immunosuppressive therapy or long-term steroid use (corticosteroid, excluding inhalers) or within 3 months prior to surgery.