Fractures of the shoulder, the so-called proximal humeral fractures, can be treated with locking plates that have shown good results in clinical practice, but complications can occur. In order to further improve the treatment of proximal humerus fractures and decrease the rate of fixation failures, further research is necessary. As a first step, the reasons for potential implant failures need to be understood.

This study has been initiated by scientists at the AO Research Institute Davos (ARI), Switzerland, which is the research center of the AO Foundation (www.aofoundation.org), an international non-profit organization led by surgeons specialized in fractures such as these. Researchers at the ARI have been developing a computational simulation tool to predict fixation failure and demonstrated its efficiency in laboratory conditions. This clinical study has been organised to validate this tool using patient data, by comparing the risk of mechanical failure predicted by the computer simulated model with the clinically observed fixation failure. In future, this computer simulation tool is expected to help surgeons to select the best fixation for a given patient and to develop improved implants.

Older adult patients with complex, displaced and/or unstable proximal humerus fractures treated with the PHILOS plate (DePuy Synthes Inc.) will be recruited. Detailed patient background information will be assessed. Surgical details will be acquired. Pre-, intra- and post-OP imaging data will be collected in frame of the standard treatment protocol. A post-OP CT scan, which is performed only occasionally as standard of care, will be acquired for all patients participating in this study. The de-identified medical images will be transferred via secure file transfer protocol (FTP) to the sponsor. Patient activity will be recorded in the first 6 post-OP weeks by means of two wearable activity trackers attached on the skin of the treated upper arm and the chest. The tracker containing the encoded data will be shipped back to the sponsor.

According to the standard post-OP protocols, follow-up (FU) examinations will be performed at 6 weeks, 3 months and 6 months after treatment. Additionally, another FU visit will be required at 3 weeks after surgery, where the activity trackers will be exchanged. FU radiographs during the standard of care visits will be compared with post-OP radiographs to determine if any mechanical failure has occurred.

Mechanical failure or no failure status of the fixation will be determined at 6 months following fracture treatment.

The patient-specific fixation failure risk will be prospectively predicted by means of computer simulations created from the pre-OP and post-OP CT images and surgical details. The prediction accuracy of the simulations will be evaluated by comparing the predicted failure risk with the clinically observed failure / no failure outcome. As a second approach, patient-specific shoulder activity (estimated based on patient pre-injury activity or measured directly post-operatively) will be incorporated into the simulations sequentially and its effect on the prediction accuracy will be evaluated.

The interventions in this study, i.e. the examinations that are beyond the current standard of care, will be i) the extra acquisition of the post-OP CT image in the cases that the treating surgeon is not requesting them, ii) the questionnaires on comorbidities and pre-injury activity, and grip strength measurements to estimate activity of the patient and iii) the post-OP activity measurement by means of wearable sensors.

Inclusion Criteria:

• Age≥ 50 years
• Radiologically confirmed closed fracture of the proximal humerus and treatment within 10 days after injury
• Any displaced or unstable 3- or 4-part fracture of the proximal humerus except isolated displaced fractures of the greater or lesser tuberosity
• Completed primary fracture treatment with a PHILOS plate with or without cement augmentation of the screws
• Ability to understand the content of the patient information / informed consent form
• Willingness and ability to participate in the clinical investigation including imaging, activity tracking and other FU procedures
• Signed informed consent

Exclusion Criteria:

• Previous proximal humerus fracture on the ipsilateral side
• Splitting fracture of the humeral head or humeral head impression fracture
• Fibula grafting, bone block or any other non-cement augmentation of the PHILOS plate fixation
• Any serious fracture fixation issue (serious malreduction, too long screw or screw perforating through the humeral head, broken screw or implant) that are recognized on the immediate post-OP x-rays, independently of being re-operated or not
• Associated nerve or vessel injury
• Any severe systemic disease: class 4 - 5 of the American Society of Anesthesiologists (ASA) physical status classification
• Recent history of substance abuse (i.e., recreational drugs, alcohol) that would preclude reliable assessment
• Prisoner
• Participation in any other medical device or medicinal product study within the previous month that could influence the results of the present study
• Pregnancy
• Pacemaker