3D full-field biomechanical testing of a glenoid before and after implant placement

doi:10.1016/j.eml.2019.100614

Extreme Mechanics Letters

Volume 35, February 2020, 100614

https://doi.org/10.1016/j.eml.2019.100614 Get rights and content

Highlights

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Mechanical testing coupled with micro X-ray computed tomography.
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3D full-field deformation and strain inside native and implanted glenoid.
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Wider range of strain in the implanted glenoid than that in the native glenoid.
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Similar effective moduli for the native and the implanted glenoid.
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Increased bending moment inside implanted glenoid due to implant placement.

Abstract

Loosening of the glenoid component is the most common cause of failure of total shoulder arthroplasty. While the underlying mechanisms are not fully understood, mechanical factors are widely reported to play a key role in glenoid component loosening. In this study, mechanical testing coupled with micro X-ray computed tomography (micro-CT) is performed to apply various physiologically realistic loads on a native and implanted glenoid. Digital volume correlation of micro-CT images is used to compute the 3D full-field deformation and strain inside the glenoid. The measured strain distributions are in good agreement with the analytical solutions of beam bending models, especially for anteriorly and posteriorly eccentric loadings. The effective moduli of the overall native and implanted glenoid were similar. However, under the same eccentric loading conditions, implanted glenoid exhibited a wider range of strain, because the placement of glenoid component increases the bending moment inside the glenoid. This proof-of-concept study provides a feasible and powerful method for the study of 3D full-field biomechanics in native and implanted glenoids.

Graphical abstract

Introduction

Total shoulder arthroplasty (TSA) is a common orthopaedic procedure to treat glenohumeral osteoarthritis [1], [2]. Loosening of the glenoid component is the most common cause of failure of this procedure [3], [4]. While the mechanisms underpinning glenoid loosening are not fully understood, mechanical factors are widely reported to play a key role [5], [6], [7], [8]. There is a need to study the biomechanics of glenoid bone and the glenoid components in shoulder implants.

Numerical methods, such as finite element analysis, have often been used to compute the biomechanics of glenoid bone and glenoid implants [8], [9]. The validity of the results from these models has been questioned, because these models may oversimplify the complex geometry, material properties and interface interactions in these structures. The results from these numerical models need to be validated by experimental measurements.

However, the conventional experimental methods for mechanical strain measurement in the research of biomechanics for glenoid and glenoid components have various disadvantages. Most importantly, they are inherently limited to measuring external surface strains, instead of full-field internal strains. Conventional strain gauges [10], [11], [12], [13], [14] can only measure strain at single locations and need to be glued to a surface on the specimens. The photoelasticity method [15], [16], [17] needs to be performed on replica models made with photoelastic materials or on photoelastic sheets that are glued to bone specimens. To obtain Moiré fringe pattern [18], [19], a grid of lines needs to be overlaid on the specimens.

Mechanical testing coupled with micro X-ray computed tomography (micro-CT) and digital volume correlation is a non-contact method that can measure the internal structures and mechanics concurrently. It has been used to measure strain in engineering materials [18], [19], trabecular bone blocks [20], [21], [22], [23] and glenoid specimens with the absence of implants [24]. In our prior work, we have extended this method to study the biomechanics of dental implants in mandibles and to build corresponding numerical models of the micro-structures [25], [26].

In this study, mechanical testing coupled with micro-CT is carried out to apply various physiologically realistic loading conditions on a native and implanted glenoid. Digital volume correlation is performed to calculate the 3D full-field deformation and strain inside the glenoid. Analytical models, which incorporate the morphology measurements from the experiments, are developed to predict strain within the glenoid.

Section snippets

Mechanical testing coupled with micro-CT imaging

A fresh-frozen scapulae of upper extremity was obtained. The glenoid was isolated with the osteotomy being 44-mm medial to the glenoid face. All soft tissues were stripped off. The bottom half of the specimen was embedded in polymethylmethacrylate (PMMA, Ortho-Jet BCA, Lang Dental, Wheeling, IL) with the glenoid face surface parallel to the floor. The specimen was kept frozen at −23 °C until 12-h prior to the test, when it was thawed. After completing the mechanical testing on native glenoid

Load–displacement relationships and stiffness

The load–displacement relationships obtained from the mechanical testing of native and implanted glenoid were nonlinear (Supplemental Fig. S1). The slopes of the load–displacement curves, i.e. stiffness of the specimen, increased with increasing displacement until the load reached 750 N. Then the load was held constant and the displacement kept increasing, reflecting the viscoelastic creep behaviors. For each loading condition, the native specimen was generally stiffer than the implanted

Discussion

The results of this study show that the mechanical testing coupled with micro-CT is a feasible and powerful method to characterize 3D full-field deformation and strain inside native and implanted glenoids. The noise in the results (no-load in Fig. 2 and Fig. S2) was much smaller than the range of deformation or strain inside glenoid under glenohumeral joint contact loading. The measured strain distributions on a typical virtual section of the specimen were in good agreement with the results

Conclusions

This paper presents the results of 3D full-field biomechanical testing of a glenoid before and after implant placement. The deformation and strain inside a native and implanted glenoid under several physiologically realistic loading conditions were obtained by digital volume correlation of micro-CT images taken at no-load and loaded conditions. Under glenohumeral contact loading, especially eccentric contact loading, part of the specimen was under compression while part was under tension. The

Declaration of Competing Interest

Dr. A. Armstrong is a paid consultant for Zimmer Biomet and Globus, and we acknowledge that all other authors do not have any conflict of interest. Authors were fully involved in the study and preparation of the manuscript.

Acknowledgments

The authors are grateful to Dr. Timothy Ryan and Mr. Timothy Stecko at the Center for Quantitative Imaging (CQI) at Penn State University, United States of America for technical support on micro-CT scans. Appreciation is also extended to Mr. Richard Prevost at LaVision for useful technical discussions.

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3D full-field biomechanical testing of a glenoid before and after implant placement

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Mechanical testing coupled with micro-CT imaging

Load–displacement relationships and stiffness

Discussion

Conclusions

Declaration of Competing Interest

Acknowledgments

J. Shoulder Elb. Surg.

J. Biomech.

J. Biomech.

J. Shoulder Elb. Surg.

Compos. Sci. Technol.

Exp. Mech.

J. Mech. Behav. Biomed. Mater.

J. Biomech.

J. Mech. Behav. Biomed. Mater.

J. Shoulder Elb. Surg.

J. Shoulder Elb. Surg.

J. Shoulder Elb. Surg.

J. Biomech.

J. Biomech.

J. Shoulder Elb. Surg.

Total shoulder arthroplasty demographics, incidence, and complications-a nationwide inpatient sample database study

Surg. Technol. Int.

What can be learned from an analysis of 215 glenoid component failures?

J. Shoulder Elb. Surg.

Complications of total shoulder arthroplasty

J. Bone Joint Surg. Am.

Glenohumeral contact kinematics in patients after total shoulder arthroplasty

J. Bone Joint Surg. Am.