The purpose of this study is to measure the mechanical properties of the tendon after conservative treated Achilles tendon ruptures with or without early controlled loading. This is done in a randomized trial and the mechanical properties are measured using roentgen stereometric analysis (RSA).

The hypothesis is that early weightbearing improves mechanical properties of conservative treated Achilles tendon ruptures without causing elongation of the tendon.

Treatment of Achilles tendon ruptures includes surgical repair or immobilization in an orthosis, followed by prolonged rehabilitation. Improved rehabilitation regimens still display imperfect recovery, with deficits such as persistent end-range muscle weakness, tendon elongation and incomplete return to pre-injury activity level. The underlying mechanisms are unknown, but are likely to involve molecular and cellular aspects of the early healing processes. Animal experiments have shown that short episodes of vigorous loading during tendon healing create a stronger tendon, and lead to less elongation than continuous loading. Early controlled training has also been shown to improve the material properties of surgically repaired tendons. However, more and more clinics now turn away from surgery and towards conservative treatment, while studies on rehabilitation mainly concern sutured tendons. It is therefore also important to understand how to best rehabilitate conservatively treated patients. The aim is to investigate the effect of early controlled loading on conservatively treated Achilles tendon ruptures.

The patients (age 18-60 years of age) are treated conservatively by receiving a removable foam walker boot at the emergency department. The patients are thereafter called by the principal investigator and are asked if they want to participate in the study. Patients who are interested in participating in the study receive oral and in written information about the study of the principal investigator of the study (Pernilla Eliasson).

After 2 weeks, the rupture is localized by ultrasound and 4 tantalum beads are implanted percutaneously in the proximal and distal part of the tendon. These beads are used for measurements of the mechanical properties of the tendon by using RSA.

The patients are thereafter randomized to early controlled loading or control.

All patients wear the foam walker boot for 7 weeks. Full weight-bearing is allowed as tolerated from the beginning. Both groups perform motion exercises outside the boot with 20 repetitions, 3 times per day as of 14 days after rupture.

The patients in the early loading group are provided with a special training pedal where pedal resistance can be increased during the treatment period. The patients will use this pedal twice a day starting 2 weeks after rupture.

After the initial 7 weeks, the patients are referred to physical therapists uninvolved in this research, but with the instruction to follow the regional rehabilitation guidelines for Achilles tendon ruptures.

Mechanical properties of the tendon will be estimated by measuring tendon length, cross-sectional area (CSA) and stiffness at week 7, 19 and 52.

The elastic modulus of the tendon at 19 weeks it the primary variable of this study.

At week 7, both the elastic and plastic deformation will be measured. Tendon CSA will be evaluated using computer tomography (CT). Tendon elongation will be evaluated by RSA at week 2, 7, 19 and 52. Calf muscle circumference, passive and active range of motion in the ankle joint and a heel-raise test will be performed at week 19 and 52.

The overall function will be assessed by the Achilles Tendon Rupture Score at 19 and 52 weeks.

Complications and re-ruptures will be registered.

Inclusion Criteria:

• Complete Achilles tendon rupture placed in the mid-substance of the Achilles tendon
• Presented within 14 days from injury
• 18-60 years old

Exclusion Criteria:

• Inability to understand swedish
• previous injured tendon
• Diabetes mellitus
• History of Rheumatoid disease
• Treatment with steroids