[Biomechanical aspects in the treatment of periprosthetic humeral fractures]

Periprosthetic humeral fractures represent a relevant complication of shoulder arthroplasty and the incidence of 0.5-3% is expected to increase given current demographic trends. Biomechanical aspects are considered in therapeutic decision-making and planning, including fracture location and morphology as well as patient-specific factors. These include among others osteoporosis and age, but also other comorbidities of the patient, such as nicotine abuse or obesity. The fracture classification follows the internationally recognized system developed by Sanchez-Sotelo und Athwal. Conservative treatment is recommended for nondisplaced or minimally displaced fractures without loosening of the prosthesis. Displaced fractures with sufficient bone stock and no loosening of the prosthesis can be treated with plate osteosynthesis. In the case of loosening of the humeral component and displaced fractures with inadequate bone stock for stable fixation using plate osteosynthesis, revision arthroplasty is indicated. In revision arthroplasty, bone defects of the proximal humerus increase the bending forces and result in a substantial torsional load on the distal anchorage of the prosthesis shaft. Hence, for bone defects exceeding 5-6 cm, the additional use of an allograft has shown biomechanical superiority, however, this procedure should be reserved for specialists.