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

Abstract

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.