Displaced four-part fractures are among the most severe injuries of the proximal humerus. The optimal treatment is disputed and published data are inadequate for evidence-based decision making.

The investigators aim to: 1) compare the effect of angle-stable plate osteosynthesis and non-surgical management, 2) compare the effect of primary hemiarthroplasty with both osteosynthesis and non-surgical management, 3) study prognostic differences between 'valgus impacted' and 'classical' four-part fracture patterns.

The investigators will conduct a randomised, multi-centre, clinical trial including patients from ten national shoulder units within a two year period. Patients will be randomised to non-surgical treatment, hemiarthroplasty or angle-stable plate osteosynthesis. All patients will receive a standardised three-month rehabilitation program of supervised physiotherapy. Patients will be followed at least one year and will be assessed blindly according to a standardised evaluation protocol including Constant Disability Scale, Oxford Shoulder Score, and Short Form-36.

Inclusion Criteria:

• Displaced four-part fracture of the proximal humerus
• Mentally alert
• Physically fit for surgery and rehabilitation (ASA-group 1-3)
• Informed written consent
• Operation can be conducted within 2 weeks of injury

Exclusion Criteria:

• Fracture-dislocations
• Head-splitting fractures
• Previous shoulder surgery on injured side
• Chronic shoulder pain
• Abuse problems
• Patients unable to understand instructions in Danish