AIR (Artificial Implant for Medial Meniscus Replacement) Study

Inclusion Criteria: 1. Has medial compartment joint pain with \> 6 months ago a medial partial meniscectomy as confirmed by patient history and MRI 2. Has a KOOS Pain of ≤ 75 (100 being no pain and the highest attainable score) 3. Is between age 30 and 65 years (inclusive) at the time of screening 4. Has neutral alignment ± 5° of the mechanical axis, i.e., 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 to the center of the ankle joint, as confirmed by X-ray 5. Is willing to be implanted with the Trammpolin® meniscus prosthesis. 6. Is able to do the study required follow up visits, questionnaires, X-rays, CT-scans, and MRI's 7. Is able and willing to understand and sign the study Informed Consent Form 8. Is able to read and understand the national language of the country in which the relevant clinical site is located Exclusion Criteria: 1. Has a symptomatic knee because of a tear that could be addressed by a repeat partial meniscectomy 2. Has evidence of a modified Outerbridge Grade IV cartilage loss on the medial tibial plateau or femoral condyle that potentially could contact a Trammpolin® meniscus prosthesis (e.g., a focal lesion \> 0.5 cm2 correlating to a circular defect of \> 8 mm in diameter) 3. Has lateral compartment pain and Grade III or Grade IV modified Outerbridge cartilage score in the lateral compartment 4. Has a varus or valgus knee deformity of \> 5° requiring a tibial or femoral osteotomy 5. Has a varus alignment that is not passively correctable 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 modified 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 surgery 11. Has a BMI \> 32.5 at the time of screening 12. Received any type of prosthetic knee implant made of artificial non-resorbable plastic, metal or ceramic, not including the Trammpolin® meniscus prosthesis 13. Has a knee flexion contracture \> 10° 14. Has flexion \< 90° 15. Had a previous medial femoral condyle surgery (not including microfracture) or High Tibial Osteotomy (HTO) 16. Has insufficiency fractures or avascular necrosis of the medial compartment 17. Has an active infection or tumor (local or systemic) 18. Has any type of knee joint inflammatory disease including Sjogren's syndrome 19. Has neuropathic knee osteoarthropathy, also known as Charcot joint 20. Has any medical condition that does not allow possible arthroscopy of the knee 21. Has neurological deficit (sensory, motor, or reflex) 22. Is currently involved in another investigation of the lower extremity 23. Anticipates having another lower extremity surgery during the study period 24. Is contraindicated for corticosteroid injections (i.e., patients with allergy to any of the components or with idiopathic thrombocytopenic purpura) 25. Has received any corticosteroid knee injections ≤ 3 months prior to surgery 26. Has chondrocalcinosis 27. Has proven osteoporosis 28. Is on immunostimulating or immunosuppressing agents 29. 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) 30. Is a female who is lactating, expecting, or is intending to become pregnant during the study period 31. Is an active smoker 32. Is mentally incapacitated (incapable of appraising or controlling conduct) or have mental disability (e.g., dementia or Alzheimer's) 33. Is a prisoner 34. Has a condition or be in a situation that, in the Investigator's opinion, may confound the study results, or may interfere significantly with the subject's participation in the study