The effect of humeral implant thickness and canal fill on interface contact and bone stresses in the proximal humerus

Abstract

Background Stem size is an important element for successful time zero primary fixation of a press-fit humeral stem in shoulder arthroplasty. Little basic science research, however, has been conducted on the effects of implant thickness and canal fill on load transfer, contact, and stress shielding. The purpose of this finite element study was to determine the effects of varying stem thickness on bone contact, bone stresses, and bone resorption owing to stress shielding. Methods Three generic short-stem implant models were developed and varied based on cross-sectional thickness (thinner – 8 mm, medium – 12 mm, thicker – 16 mm). Using a finite element model, three outcome measures were determined (1) the amount of bone-to-implant contact, (2) changes in cortical and trabecular bone stresses from the intact state, and (3) changes in cortical and trabecular strain energy densities which can predict bone remodeling or stress shielding. Results Increasing the size of the humeral stem had no significant effects on bone-to-implant contact during loading ( P > .07). The thinner implant with the lowest canal fill ratio produced significantly lower changes in stress from the intact state in both cortical and trabecular bone ( P < .002). In addition, the thinner implant resulted in a substantially lower volume of bone predicted to stress shield and resorb when compared with the medium and thicker stems. Discussion The results demonstrate that thinner implants and lower canal fill may be beneficial over thicker sizes, provided equal initial fixation can be achieved. The thinner implant has a greater degree of load sharing and increases the mechanical load placed on surrounding bone, reducing the risk of stress shielding and bone resorption.

Recent Advances in the Design and Application of Shoulder Arthroplasty Implant Systems and Their Impact on Clinical Outcomes: A Comprehensive Review

“…However, this approach carries the risk of stress shielding and, in extreme cases, bone resorption. 33 , 40 , 42 , 43 Therefore, it is important to be mindful of canal fill ratio when designing short- stem implants to prevent stress shielding of the metaphysis.…”

Personalized Artificial Tibia Bone Structure Design and Processing Based on Laser Powder Bed Fusion

“…Compared with traditional dense materials, porous metal materials are closer to the strength and elastic modulus of human bones, which can alleviate the "stress shielding" phenomenon and increase the service life of bone implants [9,10]. In addition, the design of the porous structure is conducive to the adhesion, proliferation and differentiation of human bone cells, thereby promoting the formation of biological fixation between the bone implant and the human bone to improve the strength of osseointegration and can promote the transmission of body fluids and nutrients in the pores, thereby promoting the regeneration and reconstruction of human bone tissue [11,12].…”