Influence of Restitution Time in Treatment of Patellar Tendinopathy

The purpose of the present project is to investigate if the restitution time from loading in an exercise-based 12 weeks rehabilitation regime for patellar tendinopathy influences the clinical outcome, tendon structure and function.

The investigators hypothesize that greater restitution from loading (1 exercise day per week) will yield a greater positive clinical outcome, and tissue structure and function in patients with patellar tendinopathy compared to less restitution (3 exercise days per week), when impact activities are restricted in both groups.

This study is designed as a prospective, randomized, controlled, open label, superiority trial with a two-group parallel design and primary endpoint after 12 weeks. The study has two phases; The first phase includes the main trial in which a 12-week intervention period will be undertaken to test the hypotheses in patients with chronic patellar tendinopathy (symptoms \> 3 months).

At 12 weeks, a smaller group of patients (responding and not-responding to the 12-week intervention period) will be offered to participate in sub-study 1. In this explorative cross-sectional study, the feasibility of mapping brain structure, function and metabolism using Magnetic resonance imaging (MRI) with Blood Oxygenation Level Dependent (BOLD) imaging technique in chronic patellar tendinopathy patients will be assessed.

The second phase in the main study includes the follow-up from 12 week to the secondary endpoint at 52 weeks after baseline. During this period the participants will be monitored via questionnaires for treatment satisfaction and improvements at 4-week intervals. What treatment and the duration of treatment patients will receive in this phase is based on the concept of personalized medicine. We expect the majority of patient to continue in the group with loading-based intervention. A smaller group of the 52 patients from the main study is expected to be included in sub-study two.

Sub study two is designed as an observational cohort study. In this sub study, patients reporting no self-evaluated improvement after 12 weeks of loading-based treatment will be asked to be part of a group receiving corticosteroid injection treatment followed by continued exercise-based treatment and avoidance of impact loading. The cohort will further include patients that after week 20, 24, 28, 32, 36 and 40 respond that they have not achieved their Patient Acceptable Symptom State (PASS).

Eligibility Criteria:
Inclusion Criteria:

* Sports active men and women.
* Age (18-60) years old.
* BMI (18.5-30)
* Understand and read Danish
* Uni- or bilateral patellar tendinopathy
* Symptom onset \>90 days ago

Exclusion Criteria:

* Patellar tendinopathy longer than 24 months
* Smoking
* Previous surgery in the knee on the ipsilateral side.
* Corticosteroid injection in the patellar tendon on the ipsilateral side within the last 6 months.
* Any confounding diagnosis to the knee joint
* Known arthritis
* Known diabetes
* Inability to follow rehabilitation or complete follow-ups
* Enrolled in a resistance based-rehabilitation program for the affected patellar tendon within the previous three month
* Have a work were it is not feasible to avoid pain provoking tasks

Extra criteria sub-study one

Inclusion criteria:

• Five patients from the main study, rating "improved" and "not improved" respectively, will be invited to participate in sub-study one.

Exclusion criteria:

* Claustrophobia
* Pregnancy
* Breastfeeding

Extra criteria sub-study two:

Inclusion criteria:

* Patients from the main study, that rate themselves 'not improved' in symptoms after 12 week.
* Patients who have not achieved Patient Acceptable Symptom State (PASS) after week 20, 24, 28, 32, 36 and 40, will be invited to participate in sub- study two.

Exclusion criteria:

* Pregnancy
* Breastfeeding
* Previously had an allergic reaction for steroid (Depomedrol).
* Previously had an allergic reaction for local anesthesia treatment.