Relationship Between Insertion Torque and Compression Strength in the Reverse Total Shoulder Arthroplasty Baseplate

Abstract

Reverse shoulder arthroplasty is a well‐established procedure, however, there is limited data in the literature regarding adequate insertion torque and the resulting compression for glenoid baseplate fixation. In this biomechanical study, we evaluated the relationship between insertion torque and baseplate compression by simultaneously measuring the insertion torque and axial compressive forces generated by two reverse shoulder arthroplasty baseplates with central screw design. Three different bone surrogates were chosen to mimic clinical scenarios where differences in compression achieved during baseplate insertion may exist due to varying bone quality. Epoxy resin sheets were combined with the bone surrogates to simulate the glenoid vault. A digital torque gauge was used to measure insertion torque applied to the baseplate, while compression data were collected continuously from a load cell. A strong positive correlation was found between baseplate compression and insertion torque. Among the lower density bone surrogates, neither baseplate design reached maximum insertion torque (6.8 Nm) due to material strip‐out. This phenomenon did not occur in denser bone surrogates. Both baseplate designs experienced a significant increase in mean baseplate compression as insertion torque increased and were found to behave similar in the denser bone surrogates. The results presented here suggest that larger compressive forces can be achieved with an increase in insertion torque in denser bone surrogates, but caution must be used when trying to achieve fixation in poor‐quality bone. Clinically, this could be useful preoperatively to minimize baseplate failure, and in further studies regarding baseplate design for improved initial fixation and stability. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:871‐879, 2020

Avoiding Glenoid Baseplate Fixation Failure by Altering Surgical Technique for Varying Bone Densities

“…This is in stark contrast to the testing of our standard technique, in which 3 of the 4 implants broke mid-implantation at the midportion of the screw, and the fourth was unable to be fully seated prior to meeting the 60 in-lbf end point. These findings are similar to those of a study by Diaz et al that evaluated differing implant central screw designs in highand low-density bone 23 . In their high-density group, they observed lower compression forces during implantation.…”

“…The modulus of elasticity, density, and strength of the utilized foam blocks are similar to the material properties of cancellous glenoid bone 24 , 34 . Additionally, there exist numerous previously published RSA biomechanical studies utilizing similar bone substitutes 20 , 23 , 30 , 35 , 36 . Another limitation of the study is that these alternative techniques are only applicable to baseplates with a monoblock central screw and may not be generalizable to modular or central-peg implants.…”

“…The secondary objective was to identify whether glenoid sclerosis width on preoperative radiographs was associated with the implementation of these techniques. To determine the efficacy of these novel techniques, a previously described testing methodology for assessing the torque-compression relationship was utilized with a bone surrogate testing model including 3 densities to mimic low-, normal-, and high-density bone 23 . In addition, we sought to identify a cohort of patients among whom an alteration in the standard technique of bone preparation for baseplate insertion had occurred.…”

Compression generated by cortical screws in an artificial bone model of an equine medial femoral condylar cyst

“…30 polycarbonate foam (Young's modulus 445 MPa) and short fiber filled epoxy shell (Young's modulus 157 GPa, density 0.48 g/cm 3 ; Sawbones, Vashon, Washington). This foam analog is used in human orthopedic studies to represent normal bone quality 13 . The foam density was 0.48 g/cm 3 and the cortical shell thickness was estimated from a computed tomography (CT) of a yearling Thoroughbred 6 .…”

“…This foam analog is used in human orthopedic studies to represent normal bone quality. 13 The foam density was 0.48 g/cm 3 and the cortical shell thickness was estimated from a computed tomography (CT) of a yearling Thoroughbred. 6 A 3D printed polylactic (PLA) acid analog (Young's modulus 2004 ± 63 MPa) 14 was designed using Tinkercad by Autodesk (© 2020 Autodesk, Inc.) and exported to Ultimaker Cura (Ultimaker B.V., Utrecht, the Netherlands; Version 4.5) for printing.…”