Gulshan B. Sharma

Effect of glenoid prosthesis design on glenoid bone remodeling: Adaptive finite element based simulation

Glenoid prosthesis loosening is the most common cause for revision total shoulder arthroplasty. Improved glenoid prosthesis design requires looking beyond initial post-implantation static stress analyses. Adaptive bone remodeling simulations based on Wolffs law are needed for predicting long-term glenoid prosthesis results. This study demonstrates the capability of predicting glenoid bone remodeling produced by changing prosthesis design features. Twelve glenoid prostheses were designed to fit each of six donor human glenoids, using combinations of three peg types and four backing-peg material combinations (polyethylene and or metal). The twelve FE prosthesis models were individually combined, simulating surgical implantation, with the glenoid models. Remodeling simulations, using a validated adaptive bone remodeling simulation, commenced with homogeneous glenoid bone density. To produce bone remodeling, center, posterior-offset, and anterior-offset physiologic loads were consecutively applied to the bone-prosthesis FE models for 300 iterations. Upon completion, region-specific mean predicted bone apparent densities were compared between bone-prosthesis and intact glenoid FE models. Metal fixations significantly increased proximal-center bone density. Polyethylene fixations resulted in bone density approximately equal to intact. Two angled polyethylene peg designs with longer-anterior and shorter-posterior pegs, reflecting natural glenoid shape, best maintained mid and distal glenoid bone density. While these initial results were not validated, they demonstrate the capability and potential of adaptive glenoid bone remodeling simulation. We expect FE glenoid bone remodeling simulations to become powerful and robust tools in the design and evaluation of glenoid prostheses.

Adaptive scapula bone remodeling computational simulation: Relevance to regenerative medicine

Shoulder arthroplasty success has been attributed to many factors including, bone quality, soft tissue balancing, surgeon experience, and implant design. Improved long-term success is primarily limited by glenoid implant loosening. Prosthesis design examines materials and shape and determines whether the design should withstand a lifetime of use. Finite element (FE) analyses have been extensively used to study stresses and strains produced in implants and bone. However, these static analyses only measure a moment in time and not the adaptive response to the altered environment produced by the therapeutic intervention. Computational analyses that integrate remodeling rules predict how bone will respond over time. Recent work has shown that subject-specific two- and three dimensional adaptive bone remodeling models are feasible and valid. Feasibility and validation were achieved computationally, simulating bone remodeling using an intact human scapula, initially resetting the scapular bone material properties to be uniform, numerically simulating sequential loading, and comparing the bone remodeling simulation results to the actual scapulas material properties. Three-dimensional scapula FE bone model was created using volumetric computed tomography images. Muscle and joint load and boundary conditions were applied based on values reported in the literature. Internal bone remodeling was based on element strain-energy density. Initially, all bone elements were assigned a homogeneous density. All loads were applied for 10 iterations. After every iteration, each bone elements remodeling stimulus was compared to its corresponding reference stimulus and its material properties modified. The simulation achieved convergence. At the end of the simulation the predicted and actual specimen bone apparent density were plotted and compared. Location of high and low predicted bone density was comparable to the actual specimen. High predicted bone density was greater than actual specimen. Low predicted bone density was lower than actual specimen. Differences were probably due to applied muscle and joint reaction loads, boundary conditions, and values of constants used. Work is underway to study this. Nonetheless, the results demonstrate three dimensional bone remodeling simulation validity and potential. Such adaptive predictions take physiological bone remodeling simulations one step closer to reality. Computational analyses are needed that integrate biological remodeling rules and predict how bone will respond over time. We expect the combination of computational static stress analyses together with adaptive bone remodeling simulations to become effective tools for regenerative medicine research.

Using Mathematical Modeling to Design Effective Regenerative Medicine Strategies for Orthopaedics.

The acceleration of scientific discovery in orthopaedic regenerative medicine and its transformation into bedside application require a paradigm shift in computational methods and strategies. Computational modeling must move from static simulations to adaptive methods that predict integrative physiology and physics from the molecular scale to human body scale. Computational methods have been extensively used tostudymusculoskeletalsystemsand go hand in hand with experimental studies. However, computational methods have primarily modeled a moment in time and not the adaptive response to altered environments produced by mechanical or biologic intervention. Computational strategies must be developed that integrate biologicremodelingrulesandpredict how musculoskeletal systems will respond over time. As we better understand musculoskeletal systems,

Natural Form Modeling

Most engineering software has been designed and optimized for parametric shapes. Sophisticated modeling of natural objects is free-form based, reflecting their inherent design. The merging of natural with parametric-based forms presents additional challenges. While work is needed, there are solutions that enable natural form modeling and analysis. Our focus is to use medical imaging and 3D modeling to analyze the natural form of human joint structure with specific application to joint replacement. The need for natural form modeling is also present in such other fields as varied as art, archeology and paleontology. In this chapter we illustrate examples of the breadth and power of natural form modeling.

Frontiers in Medical Device Design: An Approach for Making Arthroplasty Affordable Globally.

The global structure of health care and its service provision are in a state of flux and affect national budgets worldwide. 1 To meet the added healthcare burden associated with the expected increase in the number of arthroplasties, 2 there must be an active effort to design devices and instrumentation that are usable and affordable in the global market. We believe that to succeed in larger but more financially restricted emerging markets, device manufacturers must think globally but act locally. Consideration of economies of scale and “keeping it simple” may help promote affordability while novel approaches can help maintain access to and provide personalization of

Effects of Glenoid Prosthesis Design Variables on Glenoid Bone Remodeling: A Finite Element Based Simulation and Validation Study

Finite element (FE) analysis has been used to improve glenoid prosthesis design. One of the major complications of shoulder arthroplasty has been glenoid prosthesis loosening. Design improvements are needed to increase their longevity [1]. Current FE analyses have used static or non-linear solutions to compare design variations with respect to stresses in the glenoid bone and prosthesis [2, 3]. Previous numerical models have not incorporated Wolff’s Law of adaptive bone remodeling to simulate normal glenoid bone remodeling or remodeling in response to implanted glenoid prostheses. Of the numerous remodeling simulation theories available in the literature, this study controlled internal structure remodeling using bone strain-energy. In order to design longer lasting glenoid prosthesis bone remodeling behavior due to various prosthesis fixation geometries and materials needs to be considered.© 2008 ASME