The primary objective of this pilot study is to collect data on the safety and effectiveness of the Atlas Knee System in subjects with medial knee osteoarthritis through 24 months postoperative follow-up.

This study is designed as a prospective, multicenter, open-label, single arm, pilot study. Eligible subjects with symptomatic osteoarthritis of the medial compartment of the knee will be enrolled in the study and will receive the Atlas Knee Implant. The study population will consist of adult subjects age 25 to 80 years, with a diagnosis of medial knee osteoarthritis (Kellgen and Lawrence Grades 1-4, except those with bony erosions) and has pain in the study knee demonstrated as an overall WOMAC pain score of ≥ 40 (scale 0-100).

Inclusion Criteria:

1. Male or female subjects age 25 to 80 years at time of screening

2. Clinical symptoms (such as pain primarily localized to the medial aspect of the knee and generally exacerbated by weight bearing) and radiographic evidence of osteoarthritis in the medial compartment of the knee

   • Weight-bearing Fixed Flexion view is recommended to verify radiographic evidence of osteoarthritis
   • KL Grade 1-4, except those with bony erosion

3. Has pain in the study knee as demonstrated by a minimum score of 40 (scale 0-100) on the WOMAC pain questions in KOOS

4. Has failed at least six (6) months of non-operative treatment with continued osteoarthritis (OA) pain. Prior treatment is defined as treatment with at least one of the following interventions (listed on the AAOS Clinical Practice Guidelines on the Treatment of Osteoarthritis of the Knee Non-arthroplasty):

   • Lifestyle modification
   • Weight loss, if BMI ≥35
   • Pain relievers
   • Physical Therapy
   • Orthotics (Splints, Braces)
   • Intra-Articular (IA) corticosteroid injections.

5. Knee flexion ≥90⁰

6. Body Mass Index (BMI) of <35 or weight <300 lbs.

7. Subjects who are able to give voluntary written informed consent to participate in this clinical investigation

8. Subjects, who, in the opinion of the Clinical Investigator, are able to understand this clinical investigation, cooperate with the investigational procedures, and are willing to return for all the required post-treatment follow up visits.

Exclusion Criteria:

1. Clinical symptoms or radiographic evidence of osteoarthritis in the lateral compartment of the study knee defined as Kellgren & Lawrence (K&L) grade of > 1

2. Clinical symptoms or radiographic evidence of osteoarthritis in the patella-femoral compartment of the study knee defined as K&L grade ≥ 3

3. Clinical symptoms or radiographic evidence of osteoarthritis at the contralateral knee that would preclude activity of daily living, stair climbing, stair descending, or requires the use of an assist device

4. Tibial-femoral alignment of more than 10⁰ of varus, or more than 6⁰ of valgus, as measured using anatomical axis on a standing Hip-Knee-Ankle or long standing AP view X-ray OR Hip-Knee-Ankle alignment of more than 16⁰ of varus, or more than 0⁰ of valgus, as measured using mechanical axis on a standing Hip-Knee-Ankle AP view x-ray

5. 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

6. Arthroscopic surgeries for joint lavage, meniscectomy, chondral debridement, and loose body removal are excluded if within 3 months prior to planned surgery date;

7. Active infection, sepsis, osteomyelitis or history of septic arthritis in any joint;

8. Previous lateral meniscectomy >30% of the study knee

9. Previous patellar surgery in the study knee

10. Previous osteotomy or failed knee joint replacement in the study knee

11. Hyperextension >5⁰

12. Flexion contracture > 10⁰

13. Pathologic ligamentous or meniscal instability (Lachman > 1) as assessed by the Investigator;

14. Suspected or documented allergy or hypersensitivity to cobalt, chromium, iron, or nickel metals;

15. Rheumatoid arthritis, other forms of inflammatory joint disease or autoimmune disorder;

16. Paget's disease or metabolic disorders which may impair bone formation;

17. Known or suspected diagnosis of Osteomalacia;

18. Known or suspected diagnosis of Osteonecrosis;

19. Rapid joint destruction, marked bone loss or bone resorption apparent on x-ray;

20. Osteoporosis or radiolucency of the femoral or tibial cortex on x-ray suggestive of moderate to severe osteoporosis, pathologic fractures, or bone mineral density T score of > 2.5 Standard Deviation (SD) below young adult reference mean (all subjects will be screened for risk of osteoporosis using the validated Osteoporosis Self-Assessment Tool (OST) score, subjects with high risk will undergo a DEXA scan to determine eligibility;

21. Charcot's joint disease or other severe neurosensory deficits;

22. Vascular insufficiency, muscular atrophy, neuromuscular disease;

23. Immunologically suppressed or immunocompromised;

24. 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

25. Any significant medical condition including:

    • Diabetes mellitus requiring daily insulin therapy
    • Neuropathic pain or fibromyalgia, or any knee or other pain requiring chronic pain management
    • Advanced liver and kidney diseases
    • Congestive heart failure
    • Uncontrolled transient ischemic attack
    • Cancer
    • HIV (immunocompromised subject)
    • Radicular symptoms associated with lumbar spine pathology
    • Neurological disorders that result in gait disturbance
    • Restless leg syndrome
    • History of complex regional pain syndrome (Reflex Sympathetic Dystrophy (RSD); l. Significant psychiatric disorders (such as major depression, anxiety disorders, bipolar disorder, and schizophrenia); m. History or active substance and alcohol dependence and abuse (meeting standard diagnostic criteria described in the Diagnostic and Statistical Manual of Mental Disorders DSM-IV)

26. Other factors that the investigator feels would interfere with the participation and completion of the study:

    • Planned relocation
    • Litigation for or workers compensation for musculoskeletal injuries or disorders
    • Uncooperative subject
    • Or any other reason.

27. Pregnancy or planning to become pregnant

28. Subjects who are currently involved in any investigational drug or device trial or have been enrolled in such trials within the last 3 months

29. Prisoners or wards of the state.

Adverse Events collected from enrollment through 24 months.

Adverse Events related to treatment and unrelated to treatment as reported by the investigational site are included.