The aim of this study is to evaluate the efficacy and safety of intra-tendon injection of allogeneic adipose-derived mesenchymal stem cells (Allo-ASC) in intractable common extensor tendinosis patients in comparison with a control treatment.

A phase II randomized placebo controlled trial will be done with following 3 groups. Each group will have 10 participants, so, the total patients will be 30 people.

1. High concentration of Allo-ASC group: stem cell 0.5cc (Total: 10 million cells) + Fibrin glue 0.5cc
2. Low concentration of Allo-ASC group: stem cell 0.5cc (Total: 1 million cells) + Fibrin glue 0.5cc
3. Placebo Comparator (Fibrin) group: Normal saline 0.5cc + Fibrin glue 0.5cc The investigators will compare the efficacy difference with visual analogue scale (VAS) during activity (primary outcome), VAS at rest, Mayo elbow performance index (MEPI), grip strength, ultrasonographic assessment at baseline, 6 weeks, 12 weeks, 6 months, 12 months and 24 months after injection. Shear wave elastography (SWE) and magnetic resonance image (MRI) will be done at baseline, 12 weeks, 12 months and 24 months after injection

Inclusion Criteria:

• clinically diagnosed as lateral epicondylosis (tennis elbow)
• symptom duration is over 12 months
• pain visual analogue scale (VAS) during activity ≥ 5
• recurrent pain in spite of conservative treatment such as physical therapy, medication, steroid injection
• common extensor tendon injury can be observed under ultrasound (hypoechoic lesion) and MRI (hyperintensity or discontinuity)
• patient that can understand the clinical trials

Exclusion Criteria:

• patient that underwent other injection such as steroid injection or prolotherapy within 6 weeks
• patients with following conditions (such as arthritis related to the target lesion, synovitis related to the target lesion, paralysis related to the target lesion, entrapment of related nerve to the target lesion, radiculopathy related to the target lesion, infectious disease, generalized pain syndrome, rheumatoid arthritis, impaired sensibility, dementia, history of allergic or hypersensitive reaction to bovine-derived proteins or Fibrin Glue, contraindication to MRI)
• patient that enrolled other clinical trials within 30 days
• current pregnancy or breast-feeding, planning for pregnancy
• history of drug/alcohol addiction, habitual smoker
• operation history of affected elbow
• previous clinical trial involving stem cell administration
• other severe medical illness or bleeding tendency
• size of intramural calcification over 2.0 mm under ultrasound evaluation