Biomechanical comparison of 2 augmented glenoid designs: an integrated kinematic finite element analysis.

Augmented glenoid implants are available to help restore the biomechanics of the glenohumeral joint with excessive retroversion. It is imperative to understand their behavior to make a knowledgeable preoperative decision. Therefore, our goal was to identify an optimal augmented glenoid design based on finite element analysis (FEA) under maximum physiological loading. FEA models of 2 augmented glenoid designs-wedge and step-were created per the manufacturers' specifications and virtually implanted in a scapula model to correct 20° of retroversion. Simulation of shoulder abduction was performed using the FEA shoulder model. The glenohumeral force ratio, relative micromotion, and stress levels on the cement mantle, glenoid vault, and backside of the implants were compared between the 2 designs. The force ratio was 0.56 for the wedge design and 0.87 for the step design. Micromotion (combination of distraction, translation, and compression) was greater for the step design than the wedge design. Distraction measured 0.05 mm for the wedge design and 0.14 mm for the step component. Both implants showed a similar pattern for translation; however, compression was almost 3 times greater for the step component. Both implants showed high stress levels on the cement mantle. At the glenoid vault and on the implants, the stress levels were 1.65 MPa and 6.62 MPa, respectively, for the wedge design and 3.78 MPa and 13.25 MPa, respectively, for the step design. Implant design slightly affects joint stability; however, it plays a major role regarding long-term survival. Overall, the augmented wedge design provides better implant fixation and stress profiles with less micromotion.

Sabesan VJ ，Lima DJL ，Whaley JD ，Pathak V ，Zhang L ... -  《-》

The effect of glenohumeral radial mismatch on different augmented total shoulder arthroplasty glenoid designs: a finite element analysis.

Augmented glenoid implants to correct bone loss can possibly reconcile current prosthetic failures and improve long-term performance for total shoulder arthroplasty. Biomechanical implant studies have suggested benefits from augmented glenoid components, but limited evidence exists on optimal design. An integrated kinematic finite element analysis (FEA) model was used to evaluate optimal augmented glenoid design based on biomechanical performance in translation in the anteroposterior plane similar to clinical loading and failure mechanisms with osteoarthritis. Computer-aided design software models of 2 different commercially available augmented glenoid designs-wedge (Equinox; Exactech, Inc., Gainesville, FL, USA) and step (STEPTECH; DePuy Synthes, Warsaw, IN, USA) were created according to precise manufacturer's dimensions of the implants. Using FEA, they were virtually implanted to correct 20° of retroversion. Two glenohumeral radial mismatches, 3.5/4 mm and 10 mm, were evaluated for joint stability and implant fixation simulating high-risk conditions for failure. The wedged and step designs showed similar glenohumeral joint stability under both radial mismatches. Surrogate for micromotion was a combination of distraction, translation, and compression. With similar behavior and measurements for distraction and translation, compression dictated micromotion (wedge: 3.5 mm = 0.18 mm and 10 mm = 0.10 mm; step: 3.5 mm = 0.19 mm and 10 mm = 0.25 mm). Stress levels on the backside of the implant and on the cement mantle were higher using a step design. Greater radial mismatch has the advantage of providing higher glenohumeral stability with tradeoffs, such as higher implant and cement mantle stress levels, and micromotion worse when using a step design.

Sabesan VJ ，Lima DJL ，Whaley JD ，Pathak V ，Zhang L ... -  《-》

Posterior augmented glenoid implants require less bone removal and generate lower stresses: a finite element analysis.

Glenoid retroversion can be corrected with standard glenoid implants after anterior-side asymmetric reaming or by using posterior augmented glenoid implants with built-in corrections. The purpose of this study was to compare 2 augmented glenoid designs with a standard glenoid design, measure the amount of bone removed, and compute the stresses generated in the cement and bone. Finite element models of 3 arthritic scapulae with varying severities of posterior glenoid wear were each implanted with 4 different implant configurations: standard glenoid implant in neutral alignment with asymmetric reaming, standard glenoid implant in retroversion, glenoid implant augmented with a posterior wedge in neutral alignment, and glenoid implant augmented with a posterior step in neutral alignment. The volume of cortical and cancellous bone removed and the percentage of implant back surface supported by cortical bone were measured. Stresses and strains in the implant, cement, and glenoid bone were computed. Asymmetric reaming for the standard implant in neutral version required the most bone removal, resulted in the lowest percentage of back surface supported by cortical bone, and generated strain levels that risked damage to the most bone volume. The wedged implant removed less bone, had a significantly greater percentage of the back surface supported by cortical bone, and generated strain levels that risked damage to significantly less bone volume. The wedged glenoid implants appear to have various advantages over the standard implant for the correction of retroversion. Basic Science Study; Computer Modeling.

Allred JJ ，Flores-Hernandez C ，Hoenecke HR Jr ，D'Lima DD ... -  《-》

Augmented glenoid implants in anatomic total shoulder arthroplasty: review of available implants and current literature.

Glenoid bone loss and retroversion increase the complexity of primary shoulder arthroplasty and affect the outcome. Although eccentric reaming, augmented glenoid implants, bone grafting, and reverse arthroplasty have been used to manage bone loss and retroversion, there is no consensus on treatment. Posteriorly augmented glenoid components can correct retroversion and avoid joint line medialization, which occurs with corrective reaming techniques. Full-wedged, half-wedged, and stepped polyethylene posteriorly augmented designs are currently available for use in the United States. The results of biomechanical and computer model studies support the use of augmented implants for the management of glenoid retroversion of greater than 15°. Currently, most clinical studies are retrospective case series. The short-term results of posteriorly augmented glenoid components are successful, with no clear evidence of the superiority of one design over another and unknown long-term survival rates.

Ghoraishian M ，Abboud JA ，Romeo AA ，Williams GR ，Namdari S ... -  《-》

Augmented wedge-shaped glenoid component for the correction of glenoid retroversion: a finite element analysis.

This study undertook a computational analysis of a wedged glenoid component for correction of retroverted glenoid arthritic deformity to determine whether a wedge-shaped glenoid component design with a built-in correction for version reduces excessive stresses in the implant, cement, and glenoid bone. Recommendations for correcting retroversion deformity are asymmetric reaming of the anterior glenoid, bone grafting of the posterior glenoid, or a glenoid component with posterior augmentation. Eccentric reaming has the disadvantages of removing normal bone, reducing structural support for the glenoid component, and increasing the risk of bone perforation by the fixation pegs. Bone grafting to correct retroverted deformity does not consistently generate successful results. Finite element models of 2 scapulae models representing a normal and an arthritic retroverted glenoid were implanted with a standard glenoid component (in retroversion or neutral alignment) or a wedged component. Glenohumeral forces representing in vivo loading were applied and stresses and strains computed in the bone, cement, and glenoid component. The retroverted glenoid components generated the highest compressive stresses and decreased cyclic fatigue life predictions for trabecular bone. Correction of retroversion by the wedged glenoid component significantly decreased stresses and predicted greater bone fatigue life. The cement volume estimated to survive 10 million cycles was the lowest for the retroverted components and the highest for neutrally implanted glenoid components and for wedged components. A wedged glenoid implant is a viable option to correct severe arthritic retroversion, reducing the need for eccentric reaming and the risk for implant failure.

Hermida JC ，Flores-Hernandez C ，Hoenecke HR ，D'Lima DD ... -  《-》