Patients are randomized to either surgery or non-operative treatment. Surgery will be performed by open technique or by using a mini-invasive approach. Open surgery remains widespread and arguably the best documented treatment, however mini-invasive surgery is also included because of its potential to lessen the risk of wound complications. Michael Amlang and Hans Zwipp at the University of Dresden represent some of the leading foot- and ankle surgeons in Europe. They and their co-workers have developed a protocol for mini-invasive surgery using specially adapted proprietary instruments. Michael Amlang visited Ahus in 2012 teaching the general principles of the Dresden mini-invasive treatment. To ensure optimal and reproducible results, surgeons participating in the study must master both techniques.

All patients included in the study will be immobilized in equinus position for the first two weeks using a below-the-knee cast. Following the first two weeks the cast is replaced with a brace maintaining ∼12° plantar flexion (three heel lifts). We have chosen to use standardized heel lifts because it eases weightbearing compared to a hinged brace. After two weeks (four weeks from injury) the ankle position is adjusted to ∼8° plantar flexion (two heel lifts) and following additional two weeks the ankle position is adjusted to ∼4° plantar flexion (one heel lift). The last week of the orthosis treatment the heel lift is completely removed. Hence, the brace is retained for a total of six weeks, and patients are allowed full weight bearing as tolerated during the entire time period. The brace is worn day and night for the first two weeks, but is removed during nighttime for the last four weeks. Importantly, the immobilization regimen is identical for all three-treatment groups. To ensure identical rehabilitation following immobilization, physical therapy has to adhere to a standardized protocol supervised by an experienced physiotherapist at the Norwegian Sport Medicine Clinic (NIMI).

The defined endpoint is treatment results evaluated by the Achilles tendon Total Rupture Score (ATRS). This is a patient-centered self-reporting instrument with good reliability, validity and sensitivity. Furthermore, ATRS will be combined with SF36, another commonly used self-reporting instrument. Pain is evaluated by a visual analogue scale (VAS). Functional results are evaluated by The MuscleLab measurement system (Ergotest Innovation, Porsgrunn, Norway). The system consists of two different jump tests (drop counter-movement jump and hopping), two different strength tests (concentric heel rise and eccentric-concentric heel rise) and one muscular endurance test (standing heel rise) and the system has been shown to be both valid and reliable assessing lower leg function in patients with Achilles tendinopathy. We will also measure dorsiflexion and plantarflexion range of movement (ROM) as well as the circumference of the calf, all widely used endpoints in similar studies. Secondly, we want to compare the risk of complications such as infections and reruptures. The patients are examined at baseline and after 6 and 12 months. Since there are only minor functional improvements after 12 months, we do not plan any later follow-up as part of the main project. The 6 and 12 months examinations will be completed at the Norwegian Sport Medicine Clinic (NIMI), these examinations are blinded and performed by two physiotherapists who have not been taking part in the study prior to final follow-up. Patients will be wearing knee socks to hide potential scar tissue.

Although the minimum clinically important difference in ATRS score has yet to be determined, Carmont and coworkers have shown that 7 points represent the smallest detectable change. Moreover, a study by Metz et al. found that patients with reruptures of the achilles tendon presented on average 18 points lower scores whereas patients with injuries of the sural nerve or superficial wound infections presented scores 10 and 9 points lower than average, respectively. In order to detect a difference of 7 points in ATRS score with 80% power there must be 160 patients in each group. Power calculations are based on one-way ANOVA analyses assuming a common standard deviation of 20. This concomitantly allows us to detect differences as low as 8 % with respect to complications. This is of pivotal importance since assessing the risk of reruptures is essential when establishing treatment recommendations. We therefore plan to include a total of 530 patients allowing for expected loss during follow-up. Ahus, The Emergency Department of Oslo University Hospital, Drammen and Fredrikstad Hospitals have a catchment area of nearly 1.3 million people and treats in excess of 300 achilles tendon ruptures annually. This allows for completion of the inclusion period within three years. In our view, this is the first study to include a sufficient number of patients to detect lesser, but yet important differences, and the results will be published in a suitable international peer-reviewed journal.

The prospective randomized trial embodies many different disciplines and will spur off follow-up studies. As part of the main project we will conduct a treatment-cost analysis in relation to individual results. We will also perform an investigation based on ultrasound grading of Achilles tendon ruptures according to a classification system established by Michael Amlang and colleagues. Previous studies have provided evidence suggesting that treatment results may depend on the extension of the injury, and that treatment recommendations should be based on type of rupture sustained. This is of particular interest as it may facilitate individualized treatment. Together with the prospective randomized trial and the treatment-cost analysis, the ultrasound investigation will constitute the core of the Doctor of Philosophy (PhD) project.