A single-arm, multi-center study to verify that knee joint function at 52 weeks after injection of FF-31501 is better than at screening in patients with meniscus tear who are eligible for meniscectomy .

Inclusion Criteria:

1. Patients with suspected meniscal flap tear

2. Patients with knee pain

3. Patients with one or more of the following symptoms

   • Feeling stuck in the knee・Instability of the knee
   • Knee range of motion impairment
   • Knee joint edema

4. Other

Exclusion Criteria:

1. Patients with poor knee alignment

2. Patients who underwent meniscus surgery or platelet rich plasma therapy

3. Patients with or history of knee ligament injury

4. Diabetic patients with poor glycemic control

5. Patients with the following complications and poor general condition

   • Severe cardiovascular disease
   • Severe liver disease
   • Severe renal dysfunction
   • Severe anemia・uncontrolled mental illness
   • Other diseases for which sudden change or worsening of symptoms can be expected during study participation

6. Patients who are pregnant or possibly pregnant and/or breast-feeding, or patients planning to become pregnant during the study period

7. Other