Open reduction and locking plate osteosynthesis is a commonly used and well-accepted treatment for displaced fractures of the proximal humerus. The shoulders tend to end stiff despite intensive rehabilitation, limiting the function of the upper extremity and decreasing the quality of life. The accepted postoperative mobilisation protocol includes passive exercises until six weeks postoperatively and active range of motion exercises after that. There is good evidence that conservatively treated fractures of the same site heal better and faster if mobilised immediately. The study compares "standard mobilisation" versus "immmediate mobilisation" in a prospective, randomized, controlled trial in order to find the optimal time-frame for physiotherapy to produce best possible results. Outcome measures are assessed at specific time points after the operation and comparisons between groups are made to follow the rate of recovery and end results.