Cadaveric-biomechanical evaluation of bone-implant construct of proximal humerus fractures (Neer type 3).

Background A biomechanical cadaver study was performed to test the stability and strength of screw osteosynthesis of surgical neck fractures of the humerus. Methods After bone density measurement, 64 cadaver proximal humerus bones were bent to create a subcapital fracture. The fracture was then stabilized by means of screw osteosynthesis randomly assigned to subgroups of screw positioning, size of screw, and stress test (torsion/bending). Results Two screws applied laterally and parallel were 34.2% more stable than the normal arrangement. Bone density had a dominant role with regard to maximal bending and torsion force, but no significance was found with respect to additional screws through the major tuberculum or diameter of screws. Conclusion Two of the smaller 4.5-mm cannulated screws should be applied parallel from the lateral direction. Only range-of-motion exercises that produce a bending stress should be considered early after surgery, avoiding axial stress.