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Biomechanical Comparison Of Stemless Humeral Components In Total Shoulder Arthroplasty

Biomechanical Comparison Of Stemless Humeral Components In Total Shoulder Arthroplasty

Raymond Chen, MD, UNITED STATES Emma Knapp, BS, UNITED STATES Anthony Miniaci, MD, FRCSC, UNITED STATES Hani Awad, PhD, UNITED STATES Ilya Voloshin, MD, UNITED STATES

University of Rochester, Rochester, New York, UNITED STATES


2021 Congress   Abstract Presentation   5 minutes   Not yet rated

 

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Summary: The purpose of this study was to compare initial fixation strength between various stemless and stemmed humeral components and to correlate component fixation strength of each implant with bone mineral density (BMD).


Background

The ideal design for stemless humeral components in total shoulder arthroplasty is currently unknown. Comparison of primary stability between different designs is lacking. The purpose of this study was to compare initial fixation strength between various stemless and stemmed humeral components and to correlate component fixation strength of each implant with bone mineral density (BMD).

Methods

Five humeral stem designs were included in this study: three stemless (Sidus, Simpliciti, OVOMotion), one short stem (50 mm) and one standard stem (130 mm). 50 cadaveric human humerii were obtained and divided into five groups. BMD within the humeral head was determined for all samples via DEXA scan. The 25 samples with the lowest and highest BMDs were categorized as “Low” and “High”, respectively, with a BMD threshold of 0.35 g/cm2, creating BMD subgroups. Mean BMD was similar between groups. After implantation, each sample underwent a standardized biomechanical testing protocol, with axial loading followed by torsional loading. Sensors attached to the specimen recorded micromotion throughout testing. Axial loading consisted of cyclic loading for 100 cycles at 3 peak forces (220, 520 and 820 N). Torsional loading consisted of 100 cycles of internal/external rotation at 0.1 Hz at 6 peak torques, or until failure (+/- 2.5, 5, 7.5, 10, 12.5 and 15 Nm). Failure was defined as the torque at which any bone fracture, implant detachment from anchor/stem or an excess of 50? internal/external rotation occurred. Statistical analysis was performed to compare findings between groups and subgroups using one-way ANOVAs.

Results

At maximal axial loading, Simpliciti demonstrated greater micromotion (540 µm) than OVOMotion (192 µm), p=0.003. Simpliciti and Sidus (387 µm) also had greater micromotion than Short stem (118 µm, p<0.001, p=0.03) and Standard stem (85 µm, p<0.001, p=0.01). When comparing low BMD samples at maximal axial loading, these differences were accentuated, but comparison of high BMD samples showed no significant differences between groups. Torsional testing demonstrated that Standard stem failed at greater torque (7.2 Nm) than Simpliciti (2.3 Nm, p<0.001), Sidus (1.9 Nm, p<0.001) and OVOMotion (3.9 Nm, p=0.01). When comparing torsional testing results of low BMD samples, both Standard stem and Short stem failed at greater torque than Simpliciti (p=0.02, p=0.003) and Sidus (p=0.03, p=0.004) but failed at a similar torque to OVOMotion. Torsional testing of high BMD samples showed that Standard stem failed at a greater torque than all stemless designs.

Conclusions

Primary fixation of stemless and stemmed humeral implants depends on implant design and proximal humeral bone quality. OVOMotion demonstrated less micromotion than Simpliciti during axial loading testing. Stemmed implants (short and standard length) outperformed Simpliciti and Sidus in low BMD specimen (<0.35 g/cm2) during both maximal axial loading and torsional testing. Of the tested stemless designs, OVOMotion (central screw and peripheral rim-fit design), demonstrated greater primary stability at low BMD when compared to Simpliciti and Sidus, while all stemless designs performed similarly at high BMD.


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