Inclusion Criteria (Phase 1):
1. 21-70 years.
2. Body Mass Index (BMI) ≤ 38.
3. Singular treatable joint surface lesion, ICRS Grade 3 or 4, located on the medial or lateral femoral condyle.
4. One implant to treat a single symptomatic lesion with up to 3.8cm2 total lesion area.
5. Knee Injury and Osteoarthritis Outcome Score (KOOS) pain subscale score between 20 and 65.
6. 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 weeks prior to consideration for participation in the study.
Inclusion Criteria (Phase 2):
1. 21-70 years.
2. Body Mass Index (BMI) ≤ 38.
3. Up to three treatable joint surface lesion(s), ICRS Grade 3 or 4, located on the medial or lateral femoral condyle(s).
4. Up to 3 implants to treat up to 3 individual symptomatic lesions with a total summative area up to 10cm2.
5. Knee Injury and Osteoarthritis Outcome Score (KOOS) pain subscale score between 20 and 65.
6. 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 weeks 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 healthy 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. Insufficiency fracture of the femoral condyle or tibial plateau.
5. Recent Osteochondritis Dissecans within 1 year.
6. Diagnosis of a concomitant knee injury which the investigator believes may interfere with study participation or confound effectiveness assessment.
7. 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 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.
