The goal of this clinical trial is to learn whether a one-time injection of a person's own processed fat tissue (autologous lipoaspirate), a procedure called Adipose Stem/Stromal Cells for Enthesis/Tendon Therapy (ASSET), can reduce pain and improve function in adults (ages 18-80) with chronic tendinopathy- tendon pain lasting more than 3 months (for example, in the shoulder, elbow, hip, knee, or Achilles) - that has not improved with usual treatments such as physical therapy, cortisone shots, or platelet-rich plasma.
The main questions it aims to answer are:
* Does injecting a person's own concentrated fat into a painful tendon reduce tendon pain?
* Does it improve how well the tendon works, how long does any improvement last, and is the procedure safe?
This is a single-group study, so there is no separate comparison group; each participant's pain, function, and ultrasound results after treatment are compared with their own measurements taken before treatment.
Participants will:
* Have a one-time procedure in which a small amount of fat is removed from the abdomen by liposuction (under local numbing), concentrated, and injected into the painful tendon using ultrasound guidance.
* Complete short pain and function questionnaires and have ultrasound imaging of the tendon at study visits.
* Be followed for about 12 months, with a phone or video check-in 3-7 days after the procedure, a 2-week skin check of the fat-removal site, and visits at 6 weeks, 3 months, 6 months, and 12 months.