Inclusion Criteria - Phase 1
1. 21-65 years.
2. Body Mass Index (BMI) ≤ 35.
3. Singular treatable joint surface lesion, ICRS Grade 3 or 4, located on the medial or lateral femoral condyle.
4. Symptomatic, single treatable area 1 - 3.8cm2.
5. Knee Injury and Osteoarthritis Outcome Score (KOOS) pain subscale score between 20 and 65.
6. Stable knee.
7. Non-responsive to a minimum of 3 weeks of conservative treatment, consisting of non-steroidal anti-inflammatory drugs and/or physical therapy.
Inclusion Criteria - Phase 2
1. 21-65 years.
2. Body Mass Index (BMI) ≤ 35.
3. Up to three treatable joint surface lesion(s), ICRS Grade 3 or 4, located on the medial or lateral femoral condyle(s).
4. Symptomatic total treatable area 1 - 10cm2.
5. Knee Injury and Osteoarthritis Outcome Score (KOOS) pain subscale score between 20 and 65.
6. Stable knee.
7. Non-responsive to a minimum of 3 weeks of conservative treatment, consisting of non-steroidal anti-inflammatory drugs and/or physical therapy.
Exclusion Criteria - Phase 1 \& 2
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 or 1) 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 as defined:
2. Hip-knee-ankle (HKA) angle of greater than +/- 5 degrees (varus or valgus malalignment \> 5 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. Any known systemic cartilage and/or bone disorder, such as but not limited to osteoporosis, chondrodysplasia or osteogenesis imperfecta.
8. A symptomatic musculoskeletal condition in the lower limbs that could impede effectiveness measurements in the target knee.
9. Any known tumor of the treatment knee.
10. Prior radiation therapy to the knee joint.
11. Clinically significant or symptomatic vascular or neurological disorder of the lower extremities affecting gait or function.
12. 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 surgery in the past 6 months on the index knee except for:
1. Diagnostic knee arthroscopy and/or debridement / chondroplasty, and
2. Meniscectomy
2. Previous intra-articular injections, including HA and steroids, within the last 3 months prior to the date of surgery.
