European Post-Market Study for Medial Knee Osteoarthritis Treated With the Atlas Knee System for Load Reduction

Inclusion Criteria: 1. Male or female, older than 25 years of age; 2. Have clinical symptoms in the study knee such as pain primarily localized to the medial aspect of the knee and generally exacerbated by weight bearing; 3. Radiographic confirmation of osteoarthritis of the medial knee compartment without bony erosion and best assessed using a Rosenberg view X-ray; 4. Have failed at least 6 months of conservative therapy prior to surgery with continued OA pain. Prior conservative therapy is defined as treatment including at least one of the following (OARSI Recommendations)9: 1. Lifestyle modification; 2. Weight loss, if BMI \>35; 3. Pain relievers; 4. Physical therapy; 5. Assist devices (Canes, Orthotics, Braces, etc.); 6. Intra-articular (IA) injections. 5. Have active knee flexion ≥ 90⁰; 6. Are able to give voluntary, written informed consent to participate in this clinical investigation. 7. Are, in the opinion of the Clinical Investigator, able to understand this clinical investigation, cooperate with the investigational procedures, and are willing to return for all required post-treatment follow up visits. Exclusion Criteria: 1. Clinical symptoms and radiographic evidence of OA in the lateral compartment of the study knee; 2. Clinical symptoms and radiographic evidence of OA in the patella-femoral compartment of the study knee; 3. Tibio-femoral alignment of \> 10⁰ of varus, or \> 6° of valgus, as measured using anatomical axis on a long standing (Hip-Knee-Ankle) antero-posterior (AP) view X-ray, or tibio-femoral alignment of \> 16⁰ of varus, or \> 0⁰ of valgus as measured using mechanical axis on a long standing (Hip-Knee-Ankle) AP view X-ray; 4. Previous joint modifying surgery in the study knee within 12 months prior to planned surgery date such as ligament reconstruction, meniscus repair, cartilage transplantation, and microfracture; 5. Arthroscopic surgeries for joint lavage, medial meniscectomy, chondral debridement, and loose body removal if within 3 months prior to planned surgery date; Note: concomitant diagnostic arthroscopy including debridement during Atlas procedure is permitted. 6. Active infection, sepsis, osteomyelitis or history of septic arthritis in any joint; 7. Rheumatoid arthritis, other forms of inflammatory joint disease or autoimmune disorder; 8. Excessive scarring of soft tissue structures of the medial knee; 9. Hyperextension \> 10⁰; 10. Pathologic ligamentous instability (\> 1 Medial collateral ligament injury or Lachman \> 1 without hard stop) as assessed by the Investigator on physical examination; 11. Severe deformities leading to impaired fixation or improper positioning of the implant; 12. Paget's disease or metabolic disorders which may affect bone formation; 13. Known or suspected diagnosis of Osteomalacia; 14. Known or suspected diagnosis of Osteonecrosis; 15. Known or suspected diagnosis of Osteoporosis; 16. Rapid joint destruction, marked bone loss or bone resorption apparent on X-ray; 17. Charcot's joint disease or other severe neurosensory deficits; 18. Vascular insufficiency, muscular atrophy, neuromuscular disease; 19. Immunologically suppressed or immunocompromised; 20. History of systemic steroid treatment, medication use that affects bone metabolism (such as chemotherapy) within the previous 6 months, or radiotherapy within the previous 6 months; 21. Any significant medical condition and other factors that the investigator feels would interfere with the participation and completion of the study; 22. Pregnancy; 23. Subjects who are currently enrolled in another clinical investigation that could affect the results of this investigation.