Overuse injury of the Achilles tendon is a common entity in athletes. Currently, the usual treatment for chronic midportion Achilles tendinopathy is an eccentric exercise program. In most cases this gives satisfactory results, however there is a significant group of patients in which the exercise program is not sufficient. Prior to our study, three United Kingdom based studies have investigated the efficacy of High-Volume Image-Guided Injections (HVIGI's) in chronic midportion Achilles tendinopathy. They all showed promising results. However none of these studies had an adequate control group. This double-blind, placebo-controlled, randomized clinical trial will investigate the value of a High-Volume Image-Guided Injection in chronic midportion Achilles tendinopathy.

Background of the study - Overuse injury of the Achilles tendon is a common entity in athletes. Especially middle aged athletes are at risk. Elite running athletes have a lifetime risk of sustaining an Achilles tendon injury of 52%. At the moment the usual treatment for chronic midportion Achilles tendinopathy is an excentric exercise program. In most cases this gives great results, however there is a significant group of patients in which the exercise program is not sufficient. Three United Kingdom-based case series evaluated the efficacy of High-Volume Image-Guided Injections (HVIGI's) in chronic midportion Achilles tendinopathy. They all showed promising results. However none of these studies used a comparative group. There is consequently a lack of high-quality studies in this field and therefore the investigators cannot recommend this treatment yet for this indication.

Objective of the study - To investigate the efficacy of a high-volume image guided injection (HVIGI) in chronic midportion Achilles tendinopathy.

Hypothesis - The average VISA-A score is higher in the patient group treated with a progressive exercise program in combination with a high volume image guided injection in comparison with the group treated with low volume injection as a control group in combination with a progressive exercise program.

Study design - A double-blind, randomized, placebo-controlled clinical trial. Randomization and stratification (based on activity level using the Ankle Activity Score) will be performed using a computer-generated model. Measurements will be performed at baseline, 2, 6, 12 and 24 weeks post injection. At every time point both the primary and secondary outcome measurements will be collected. The painDETECT and the Pain Coping Inventory questionnaires will be derived at baseline and 24 week post injection.

Study population - In total, 80 patients with clinically diagnosed chronic midportion Achilles tendinopathy will be included in this study.

Inclusion Criteria:

1. Age 18-70 years.
2. Clinical diagnosis of chronic midportion Achilles tendinopathy: Painful swelling of the Achilles tendon, 2-7 cm proximal to it's calcaneal insertion.
3. Non-response to exercise program for 6 weeks.
4. Painful Achilles tendon for more than 2 months.
5. Neovascularisation is present on Power Doppler Ultrasonography examination

Exclusion Criteria:

1. Clinical suspicion of insertional disorders (pain at the site of the insertion of the Achilles tendon on the calcaneum)
2. Clinical suspicion of an Achilles tendon rupture (Thompson test abnormal and palpable "gap")
3. Clinical suspicion of plantar flexor tenosynovitis (posteromedial pain when the toes are plantar flexed against resistance)
4. Clinical suspicion of n.suralis pathology (sensitive disorder in the area of the sural nerve)
5. Clinical suspicion of peroneal subluxation (visible luxation of the mm. Peronea spot in combination with localized pain)
6. Suspicion of internal disorders: spondylarthropathy, gout, hyperlipidemia, Rheumatoid Arthritis and sarcoidosis.
7. Condition that prevents the patients from executing an active exercise program
8. Recently prescribed drugs (within 2 years) with a putative effect on symptoms and tendon healing (quinolone antibiotics, corticosteroids).
9. Previous Achilles tendon rupture.
10. Patient has received surgical intervention for his injury.
11. Patient does not wish, for whatever reason, to undergo one of the two treatments
12. A medical condition that would affect safety of injection (e.g. peripheral vascular disease, use of anticoagulant medication)
13. Known presence of a pregnancy
14. Condition of the Achilles tendon caused by medications (arising in relation to moment of intake), such as quinolones and statins
15. Inability to give informed consent.
16. Participation in other concomitant treatment programs.
17. Patient has already one side included in this study.
18. Allergy for lidocain.