The NUsurface® Meniscus Implant SUN Clinical Trial is a multi-center, single-arm, prospective, open label, non-randomized, observational clinical trial to gather safety and probable clinical benefit data on the NUsurface® Meniscus Implant in treated the target population.

Inclusion Criteria:

1. Had > 6 months ago a medial partial meniscectomy as confirmed by patient history and MRI
2. Has a KOOS Pain of ≤ 75 (100 being the highest attainable and no pain)
3. Is between age 30 and 75 years (inclusive) at the time of study treatment
4. Has neutral alignment ±5º of the mechanical axis, as measured from the angle formed by a line drawn from the center of the femoral head to the medial tibial spine and a line drawn from the medial tibial spine and the center of the ankle joint
5. Has ≥ 2 mm intact medial meniscal rim capable of being fitted with a NUsurface® device
6. Is able to do the study required follow-up visits, questionnaires, X-rays and MRI's
7. Is able to read and understand the English language if treated at a U.S. site or read and understand one of the official country languages if treated at a site Outside the U.S.
8. Is able and willing to understand and sign the Informed Consent Form

Exclusion Criteria:

1. Has a symptomatic knee because of a tear that could be addressed by a repeat partial meniscectomy leaving > 4 mm of medial meniscus rim
2. Has evidence of a Outerbridge Grade IV cartilage loss on the medial tibial plateau or femoral condyle that potentially could contact a NUsurface implant (e.g., a focal lesion > 0.5 cm2 correlating to a circular defect of > 8 mm in diameter)
3. Has complete disruption of the posterior root attachment of the meniscus
4. Has lateral compartment pain and Grade III or Grade IV Outerbridge cartilage score in the lateral compartment
5. Has a varus or valgus knee deformity > 5º requiring a tibial or femoral osteotomy
6. Has a laxity level of more than Grade II (IKDC), primary or secondary to an injury of the anterior cruciate ligament (ACL) and/or posterior cruciate ligament (PCL) and/or lateral collateral ligament (LCL) and/or medial collateral ligament (MCL)
7. Has significant trochlear dysplasia, patellar instability or symptomatic patellar misalignment
8. Has patellar compartment pain and Grade III or Grade IV Outerbridge cartilage score in the patellar compartment.
9. Compared to a normal knee, has obvious radiological evidence of medial femoral squaring, anatomical variance in the medial tibial plateau, or irregularly shaped cartilage surface
10. Had an ACL reconstruction performed < 9 months prior to study treatment
11. Has a BMI > 32.5 at the start of study treatment
12. Decides to receive (if eligible and an option) allograft medial meniscus transplantation
13. Received any type of prosthetic knee implant made of artificial non-resorbable plastic, metal or ceramic, not including the NUsurface® Meniscus Implant
14. Has a knee flexion contracture > 10º
15. Has flexion < 90º
16. Had a previous medial femoral condyle surgery (not including microfracture) or High Tibial Osteotomy (HTO)
17. Has insufficiency fractures or avascular necrosis of the medial compartment
18. Has an active infection or tumor (local or systemic)
19. Has any type of knee joint inflammatory disease including Sjogren's syndrome
20. Has neuropathic knee osteoarthropathy, also known as Charcot joint
21. Has any medical condition that does not allow possible arthroscopy of the knee
22. Has neurological deficit (sensory, motor, or reflex)
23. Is currently involved in another investigation of the lower extremity
24. Anticipates having another lower extremity surgery during the study period
25. Is contraindicated for hyaluronic acid injections (i.e., patients with known hypersensitivity [allergy] to hyaluronan [sodium hyaluoronate] preparations); patients having knee joint infections or skin diseases or infections in the site of possible injections
26. Is contraindicated for corticosteroid injections (i.e., patients with allergy to any of the components or with idiopathic thrombocytopenic purpura)
27. Has received any corticosteroid knee injections ≤ 3 months prior to study treatment
28. Has chondrocalcinosis
29. Is on immunostimulating or immunosuppressing agents
30. Has ipsilateral or contralateral lower limb joint conditions that may affect ambulation or KOOS (e.g. have a leg length discrepancy > 2.5 cm [1 inch], causing a noticeable limp)
31. Is a female who is lactating, expecting, or is intending to become pregnant during the study period
32. Is an active smoker
33. Is mentally incapacitated (incapable of appraising or controlling conduct) or have mental disability (e.g., dementia or Alzheimer's)
34. Is a prisoner
35. Is a patient who has economic incentive not to improve
36. Certain patient populations that are at high risk for poor healing or outcomes such as patients who have a co-morbidity that reduces life expectancy to less than 36 months
37. Patients who are contraindicated for MRI (i.e., pacemaker, defibrillator, cochlear implants, etc.)