Impact of Modeling Assumptions on Stability Predictions in Reverse Shoulder Arthroplasty

Transcription

1 Impact of Modeling Assumptions on Stability Predictions in Reverse Shoulder Arthroplasty Mehul A Dharia*, Jeff Bischoff* *Zimmer Biomet, Warsaw, IN May 17, 2017

2 Total Shoulder Arthroplasty Shoulder Joint Replacement Greater range of motion than any other joint in the body Shoulder Arthritis Types: Anatomical Shoulder Arthroplasty (TSA) Reverse Shoulder Arthroplasty (RSA) Humerus Head Clavicle (Collar Bone) Scapula Glenoid Cavity 2

3 Total Shoulder Arthroplasty (TSA) Humeral Component Glenoid Component American Academy of Orthopaedic Surgeons 3

4 Reverse Shoulder Arthroplasty (RSA) Glenoid Component American Academy of Orthopaedic Surgeons Humeral Component Bhosali et al, J Bone Joint Surg Am. 2017;99:

5 RSA Complications Instability 5% (78 studies , 4,124 shoulders) Glenoid failure 7.2% Baseplate failure Glenosphere Disassociation Bhosali et al, J Bone Joint Surg Am. 2017;99: Ackland et al. Journal of Orthopaedic Surgery and Research (2015) 10:101 Micromotion Between Baseplate and Bone Use Simulation to Identify Worst Case for testing per ASTM F

6 Superior Inferior Micromotion Test & Simulation ASTM F N 756 N Micromotion Virani et al, J Shoulder Elbow Surg 2008:17(3): Harman et al, J Shoulder Elbow Surg 2005;14(1S):162S-167S Hopkins wt al, Proc. IMechE Vol. 223 Part H: J. Engineering in Medicine,

7 Impact of Modeling Assumptions Study the impact of modeling assumptions (Screw- Bone interface) on stability predictions in RSA Head SI Offset (1.5mm & 3.5mm) Peripheral Screws 2 or 4 Screws Central Screw Baseplate Sizes based on diameters (28mm & 25mm) Zimmer Biomet Comprehensive Reverse Shoulder System 7

8 Simulation Stability/Micromotion Test Screw-Bone Interface De-featured Screws (No Threads) Bonded Screw-Bone Interactions Hopkins et al, Proc. IMechE Vol. 223 Part H: J. Engineering in Medicine, 2009 Hopkins et al, J Shoulder Elbow Surg 17, 2008 Denard et al, J Ortho. Research 2016 Geraldes et al, J Ortho Res 35, 2017 Hypothesis: Models can be used for one-to-one comparisons, as long as same assumptions are used across the models. 8

9 Configurations Questions of Interest 3 Screw-Bone Interface Conditions Bonded + No Threads (b-nt) Bonded + Threads (b-t) Frictional (Fc = 0.3) + Threads (f-t) 2 Peripheral Screw Configurations 2 Screws (2S) 4 Screws (4S) Is 4S better than 2S? 24 Combinations 2 SI Offsets 1.5mm, 3.5mm Is 3.5mm Offset better than 1.5? 2 Baseplate Sizes 25mm, 28mm Is 28mm better than 25mm? 9

10 FEA Model 2 Step Analysis 756N Axial Compression Load 756N Shear Load (Inferior to Superior) b-nt Bonded & No Threads b-t - Bonded & Threads f-t Frictional & Threads b-nt b-t f-t 10

11 Superior Inferior Superior Inferior Results Micromotion at Baseplate-Bone Interface f-t > b-t, b-nt Modeling Assumptions matter, if the goal was to measure Absolute Micromotion Load Lift-off Subsidence Normalized Micromotion 11

12 Normalized Micromotion Normalized Micromotion Results Micromotion at Baseplate-Bone Interface 4S < 2S b-nt Bonded & No Threads b-t - Bonded & Threads f-t Frictional & Threads Is 4S better than 2S? Yes 28mm Baseplate 25mm Baseplate mm b-nt b-t f-t 3.5mm 1.6 b-nt b-t f-t 1.5mm 3.5mm S 2S 4S 2S 0.0 4S 2S 4S 2S James et al, J Shoulder Elbow Surg, 2013 Hoenig et al, J Shoulder Elbow Surg,

13 Normalized Micromotion Normalized Micromotion Results Micromotion at Baseplate-Bone Interface < mm Is 3.5mm Offset better than 1.5mm? Yes for 28mm baseplate No for b-nt assumption in 25mm baseplate b-nt b-t f-t 25mm mm b-nt Bonded & No Threads b-t - Bonded & Threads f-t Frictional & Threads 4 Peripheral Screws 2 Peripheral Screws b-nt b-t f-t 25mm mmSI 3.5mmSI 1.5mmSI 3.5mmSI mmSI 3.5mmSI 1.5mmSI 3.5mmSI 13

14 Normalized Micromotion Normalized Micromotion Results Micromotion at Baseplate-Bone Interface 28 Baseplate < 25 Baseplate b-nt Bonded & No Threads b-t - Bonded & Threads f-t Frictional & Threads Is 28mm Baseplate better than 25mm? Yes for 3.5mm Offset 4S Offset 2S Offset b-nt b-t f-t b-nt b-t f-t mm 25mm mm 25mm Baseplate Size Baseplate Size 14

15 Normalized Micromotion Normalized Micromotion Results Micromotion at Baseplate-Bone Interface 28 Baseplate < 25 Baseplate b-nt Bonded & No Threads b-t - Bonded & Threads f-t Frictional & Threads Is 28mm Baseplate better than 25mm? No 4S, 1.5mm Offset for b-nt, b-t No 2S, 1.5mm Offset for b-nt 4S Offset 2S Offset b-nt b-t f-t b-nt b-t f-t mm 25mm mm 25mm Baseplate Size Baseplate Size 15

16 Summary 3 Levels of Model Fidelity were used (Screw-Bone Interface) Bonded & no threads (b-nt) Bonded & threads (b-t) Frictional & threads (f-t) Three specific questions pertaining to comparative analysis within a single baseplate system: Impact of number of peripheral screws (2 or 4) on baseplate stability? Impact of superior-inferior offset (1.5mm or 3.5mm) on baseplate stability? Impact of baseplate diameter (25mm or 28mm) on baseplate stability? Modeling Assumptions Matter! 16

17 Conclusions Importance of FEA model fidelity Level of rigor in modeling screw-bone interface To evaluate differential performance Increased sensitivities on modeling assumptions When comparing different designs or fixation mechanisms Model validation is important Even for comparative analyses 17

18 Thank You!