This study will be conducted as a prospective single-blinded randomized clinical trial in a level one trauma center serving the southeast of Ireland. In this study, 4 weeks of plaster immobilization will be compared with 6 weeks of plaster immobilization. The methods of this study protocol are comparable to a previously published article comparing 3 weeks of cast immobilization to 5 weeks of cast immobilization in adult patients with non-displaced distal radius fractures. Patients will be treated in a lower arm cast in a neutral position. Following immobilization, treatment will be the same for both groups, in which additional physiotherapy after removal of the cast is advised, and exercises to train wrist function will be given. As extra structured advice programs may cause no extra benefit for the patient, this was not generally prescribed. However, during follow-up visits, patients will be asked if they were treated by a physiotherapist. If this is the case, details on the number of sessions per week and the total number of weeks the patient received physiotherapy, will be collected.

Patients will only be able to participate if closed reduction of the DRF is adequate. The indication for reduction will be set, using the Lidström criteria for misalignment. Patients will only be able to participate in this study if reduction is performed successfully. Successful reduction will be classified as radial shortening \<3 mm, dorsal tilt \<10° or intra-articular step-off \<2 mm, according to the guidelines of the American Academy of Orthopaedic Surgeons.

After providing informed consent, eligible patients will be randomised after 2 weeks when the fracture has proven to be stable. An independent research assistant will perform concealed permuted block randomisation using a computer-generated randomisation schedule after stratification for fracture type, gender, and age. Allocation will be at random in four blocks. To prevent bias, stratification by age (younger and older than 60 years) and gender will be performed . Randomisation between another 2 or 4 weeks cast immobilisation will be performed to complete a total of 4 and 6 weeks of cast immobilisation, respectively. Randomisation will occur after informed consent.

cast removal, number of re-interventions, delayed and non-unions and Complex regional Pain Syndrome (CRPS).

At each FU visit, the research coordinator or research assistant will ascertain patient status (ie, secondary interventions, adverse events/complications, deaths) and will verify the information within medical records. All adverse events will be addressed to the principal investigator. At each FU visit, the patients will be asked to indicate the actual pain level on a VAS. Patients will also be asked if they have any complaints of their treatment and will be asked if they are currently treated by a physical therapist. At each visit from 8 weeks onwards, the range of motion of the wrist will be measured using a goniometer, according to the reference values for joint range of motion published by the American Academy of Orthopaedic Surgeons. In addition, patients will be asked to complete the questionnaires relating to disability. Plain X-rays of the wrist will be made at the time of presentation in the hospital (ED), after 1 and 2 weeks, 4 or 6 weeks, and at the follow-up visit after 8 weeks, 3 months, 6 months, and one year. The X-ray at 6 months will be taken in order to determine the grade of degenerative joint changes. The time to define the presence of a delayed- or non-union will be at 3 or 6 months. The sample size of 44 patients per treatment group is calculated with a power (1-β) of 80% and a type I error (α) of 5%, allowing for 10% dropout. In this study, we decided to include 50 patients per treatment group. To allow a 10% dropout in this study, in total 100 patients will be included.