Structural analysis of hollow versus solid‐stemmed shoulder implants of proximal humeri with different bone qualities

Abstract

Stress shielding of the proximal humerus following total shoulder arthroplasty (TSA) can promote unfavorable bone remodeling, especially for osteoporotic patients. The objective of this finite element (FE) study was to determine if a hollow, rather than solid, titanium stem can mitigate this effect for healthy, osteopenic, and osteoporotic bone. Using a population-based model of the humerus, representative average healthy, osteopenic, and osteoporotic humerus FE models were created. For each model, changes in bone and implant stresses following TSA were evaluated for different loading scenarios and compared between solid versus hollow-stemmed implants. For cortical bone, using an implant decreased von Mises stress with respect to intact values up to 34.4%, with a more pronounced effect at more proximal slices. In the most proximal slice, based on changes in strain energy density, hollow-stemmed implants outperformed solid-stemmed ones through reducing cortical bone volume with resorption potential by 11.7% ± 2.1% (p = .01). For cortical bone in this slice, the percentage of bone with resorption potential for the osteoporotic bone was greater than the healthy bone by 8.0% ± 1.4% using the hollow-stemmed implant (p = .04). These results suggest a small improvement in boneimplant mechanics using hollow-stemmed humeral implants and indicate osteoporosis could exacerbate stress shielding to some extent. The hollow stems maintained adequate strength and using even thinner walls may further reduce stress shielding. After further developing these models, future studies could yield optimized implant designs tuned for varying bone qualities.

Design and validation of a novel 3D-printed glenohumeral fusion prosthesis for the reconstruction of proximal humerus bone defects: a biomechanical study

“…Soltanmohammadi et al performed the structural analysis of hollow versus solid-bearing shoulder implants of proximal humeri with different bone qualities. The result showed that the hollow stems maintained adequate strength and using even thinner walls may further reduce stress shielding ( Soltanmohammadi et al, 2022 ). Therefore, we can improve the biomechanical environment of implants through structural design.…”

Porous versus solid shoulder implants in humeri of different bone densities: A finite element analysis

“…The Young's moduli of the bones ( E bone ) were assigned on an element‐by‐element basis, with a minimum allowable E bone of 15 MPa. For the reconstructed humeral bone models, the humeral heads were virtually osteotomized and the medullary cavities in the proximal humerus were virtually size‐to‐size reamed for stem placement 22 . Each bone mesh comprised approximately 300,000 linear tetrahedral elements with an average edge length of 1.5 mm.…”

“…The resultant forces and frictional moments used in this study (Table 1) were calculated from the average weight (63.5 kg) of donors used in the statistical shape and density model. These four loading scenarios were also used in a similar study by Soltanmohammadi et al, 22 where they compared the use of solid versus hollow humeral stem implants.…”

“…37 A secondary goal of this study was to observe the mechanobiological impact of these porous stems in comparison with a solid respect to intact bone when compared with solid stems. 22 Razfar et al showed that shortening the length of the implant stem also results in the reconstructed bones experiencing stresses that better match intact bone. 19 The percentage of bone resorption/bone formation was also modeled to get a better understanding of the stress shielding impacts of the porous implants compared to a solid one.…”

“…Furthermore, it is also important to consider the potential mechanobiological impact that porous stems may have on surrounding bone. Previous studies of proximal humeral implants for the shoulder have used computational models, radiographic and clinical outcomes postoperatively to examine the effects of stem length (Razfar et al, 19 Aibinder et al, 20 Denard et al, 21 ) hollow stems (Soltanmohammadi et al, 22 ) cementing (Denard et al, 23 Kim et al 24 ) and coatings (Tan et al 25 ) Porous humeral stems, however, have not been investigated.…”