Kevin Famer, MD
Read complete study: Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss
In the article “Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss” by Martin et al, the authors looked to quantify glenoid baseplate stability with worsening superior glenoid bone loss. The authors utilized a polyurethane bone model, and created superior glenoid bone loss defects such that the attached baseplates had 100% support, 90% support, 75% support, and 50% support. The authors found the 50% support group had significantly greater micromotion than the other defects and the native state. The majority of micromotion occurred at the beginning of testing, indicating that some settling may occur with time. Interestingly, micromotion in the 50% support group exceeded 150 µm, which has been shown in animal models to be the maximum amount of micromotion that allows bony ingrowth.
The authors spend a lot of time describing their testing methods, compared to other published manuscripts. The authors applied cyclic loading at a fixed 60º glenohumeral angle, which mimics the superiorly directed force during the initiation of abduction, as opposed to other studies that apply force to the baseplate that mimics the force during the range of abduction. The benefits of the study design of this current study is that it allows real time assessment of micromotion during the course of the analysis, as well as pre and post testing, potentially allowing a better assessment of micromotion early in the loading process.
The information presented in this study is valuable in the sense that using real time of assessment of micromotion, the authors find that increasing superior glenoid wear leads to increasing superior micromotion early in the loading process. There also appears to be some settling over time, but the issue failure of early bony integration, and its association to loosening over time, is a concern. Surgeons should be aware of results of this study, and the potential risk of glenoid loosening with uncorrected superior glenoid wear.
When approaching superior glenoid wear, surgeons have three main options.
Curtis Noel, MD
Read complete study: Total shoulder arthroplasty for glenohumeral arthritis associated with posterior glenoid bone loss: results of an all-polyethylene, posteriorly augmented glenoid component
The authors reported on 19 patients with 20 total shoulders with minimum two-year follow-up using an augmented glenoid component. They hypothesized the need for augmented glenoids as a way to save bone and prevent medializing the joint line. The average follow-up was 36 months, and the average pre-op retroversion to be corrected was 23.5⁰. The study showed significant improvements in forward elevation and external rotation, while also showing improvements in the SF36 physical form. The implant used in this study was an all-polyethylene, step-cut glenoid with an “anchor peg” for bone growth, in which 12 of the 19 patients showed osseus integration. The conclusion of the authors was that the short-term results are promising for these augmented glenoids, but further research needs to be completed.
I agree with these authors, and others, on the need to address retroversion in total shoulder arthroplasty. Treating the retroverted glenoid is challenging. For these B2 and B3 glenoids, surgeons have limited options. We know that implanting the glenoid in retroversion is not a good option as it increases the edge loading and leads to early loosening and failure. Reaming down the high side and placing a ‘standard’ glenoid can medialize the joint line and places the implant on subcortical bone, which is also not ideal. Using an anatomic total shoulder with an augmented glenoid implant is an attractive option, as it allows the placement of the implant on more solid bone and maintains the joint line. A final option is placing a reverse total shoulder, which may be the best option for some patients.
I currently prefer a wedge augmented glenoid component, instead of a step-cut implant. In my hands, the wedge glenoid is easier to implant and is more bone preserving.
Joseph Zuckerman, MD
These authors studied the ability to implant a custom glenoid component in 10 cadaver glenoids with glenoid defects using patient-specific guides and traditional non-guided techniques. The use of the patient-specific guide reduced angular deviations from the plan and significantly improved the position and length of the screw placements when used to implant the custom made glenoid components.
The authors have focused on a well-known challenge in shoulder arthroplasty – treatment of the deformed glenoid during anatomic or reverse shoulder arthroplasty. There is no doubt that two approaches canbe developed to address this issue. The first is the use of patient-specific guides (or intraoperative positioning devices) to improve the accuracy of component placement. We all recognize that a properly placed glenoid component will have longer-term survival than a malpositioned component. The second approach is to have non-standard glenoid components available to address the deformity. These can be either custom-made implants specific for the patient being treated or augmented “off the shelf” implants that address the common deformities encountered.
I have found that using non-custom or “off the shelf” augmented glenoid components have addressed many of the bone-loss issues I have encountered.
The authors actually combine both approaches – they use a custom implant with a specimen-specific guide. This could be perceived as the “best of both” but in actuality it is quite impractical from a cost perspective. The incremental cost of a custom implant combined with a CT-generated, patient-specific guide would add significant incremental cost. In 2016, regardless of where the surgery is being performed in the world, it is a surgeon’s responsibility to consider cost, especially in the context of cost vs. potential benefit. In addition, the FDA has been very strict on the use of custom implant components, which leaves us surgeons limited options for this approach. Continue reading