Inclusion criteria:

1. Age 18-75 years.
2. Diagnosis CMPAT verified clinically by orthopedic surgeon. Symptoms must include mid-portion pain in the Achilles, swelling and reduced tolerance for weightbearing.
3. Verified diagnosis with MRI findings representing pathologic processes of tendon degeneration and repair (13). MRI no older than 12 months.
4. Duration of symptoms must be at least 12 months.
5. Isolated gastrocnemius tightness must be verified with the Silfverskiölds test before inclusion. The Silfverskiöld test is considered positive if ankle dorsiflexion is restricted to 5 degrees or less with the knee extended, and there is an increase of ankle dorsiflexion of at least 10 degrees when flexing the knee.
6. At least three months of conventional physical therapy with eccentric training must have been tried without providing relief of symptoms.

Exclusion criteria:

1. Previous history of complete Achilles tendon rupture.
2. Other combined pathologies in the Achilles tendon of calf (Sequela from trauma, infections, cancer etc.).
3. Insertional Achilles tendinopathy.
4. Previously undergone surgery in affected tendon.
5. Patients with severe talocrural pathology or serious malalignment of foot and ankle.
6. Severely reduced peripheral circulation.
7. History of alcoholism, drug abuse, psychological or other emotional problems likely to jeopardize informed consent.
8. Patients with a contraindication/non-compliance for MRI examination.
9. History of allergic reaction/anaphylactic reaction to local anesthetics.
10. Not able to read and/or speak a Scandinavian language or English adequately.
11. Other serious comorbidity that makes surgery unadvisable.