The purpose of this study is to determine whether early mobilization after Achilles tendon rupture can speed up healing, prevent development of venous thromboembolism and improve patient outcome.

Patients with acute Achilles tendon rupture will be screened for eligibility at the Karolinska University Hospital and Södersjukhuset, Stockholm.

One hundred-fifty patients will be included and enrolled and assigned to the interventions either by a third party nurse or by a research nurse. Randomisation will be performed with use of computer-generated random numbers in permuted blocks of four, through an independent software specialist, and consecutively numbered, sealed, opaque envelopes opened after surgery and prior to treatment.

The patients will be randomized to undergo either treatment as usual using plaster cast treatment alone or direct post-operative functional mobilization with a weight-bearing orthosis with adjustable range of motion of the ankle.

The power calculation was based upon data from a recent study reporting a 50% rate of CDU-verified DVT after ATR surgery (Domeij-Arverud et a. 2015). We estimated early functional mobilization (EFM) to confer a 50% risk reduction. Sixty-three patients in each group were required to detect a difference of 25% in the incidence of DVT (two-sided type-I error rate = 5%; power = 80%). We decided to include 150 patients to counteract drop-outs. On recommendations from the ethical committee, a ratio of 2:1 was chosen, since our hypothesis was that the EFM group would perform better.

The endpoint of the first part of the study is tendon healing quantified at 2 weeks by microdialysis followed by quantification of markers for tendon repair. The sample size for the outcome in the microdialysis study was calculated on a difference of the glutamate metabolite of 12 µM between the two groups. For this power analysis, we used a glutamate standard difference of 15 µM resulting from a previous study. It was determined that a sample size of 25 patients per group would be necessary to detect the glutamate difference with 80% power when alpha was set equal to 5%. Anticipating that we would lose 10% of participants enrolled, we plan to enroll 27 patients in each group for microdialysis.

The primary aim of the short-term follow up of this randomized, controlled trial was to assess the efficacy of EFM to reduce the DVT incidence after ATR surgery, at two and six weeks post-operatively, compared to treatment-as-usual, i.e. two weeks of plaster cast followed by four weeks' orthosis immobilization. The secondary aim was to evaluate the effect of patient intrinsic factors (age, BMI, calf circumference, ankle range of motion, pain and fear of movement) and patient extrinsic factors (amount of weightbearing, number of daily steps) on the risk of sustaining a DVT.

The primary aim with the long-term follow up is to investigate the effect of early postoperative functional mobilization compared to immobilization on patient-reported function, health, fear of movement, physical activity level, and differences in functional capacity. The second aim is to explore if the occurrence of DVT postoperatively effects functional outcome in the long-term after surgical treatment of ATR.

Additional aims:

The primary aim of the second part of this study was to assess the number of steps and the amount of loading in a weight bearing orthosis during the first six weeks post-surgical ATR repair. A secondary purpose was to investigate if the amount of loading was correlated to fear of movement or/and pain.

The aim with this substudy is to describe differences between the two groups over time regarding tendon elongation, differences in muscle cross-sectional area and differences in tendon cross-sectional area (on the injured side) and to examine if the differences can predict functional outcome in the long-term and if any of the follow-up occasions are most important for long-term functional outcome.

Few studies have evaluated outcome more than one year after injury. The aim of this substudy is to investigate differences in outcome at 3 years after injury between the patients that sustained a DVT and those who did not sustain a DVT. Another aim is to compare the two intervention groups over 3-years time.

Inclusion Criteria:

• Acute unilateral ATR, operated on within 96 hours
• Age between 18 and 75 years

Exclusion Criteria:

• Inability to give informed consent
• Current anticoagulation treatment (including high dose acetylsalicylic acid)
• Planned follow-up at other hospital
• Inability to follow instructions
• Known kidney failure
• Heart failure with pitting oedema
• Thrombophlebitis
• Thromboembolic event during the previous three months
• Other surgery during the previous month
• Known malignancy
• Haemophilia; and pregnancy