Name: Glenoid Treatment Options: Managing Complex Morphology With Augmented Implants
Uploaded: 2021-10-25T00:00:00Z
Channel: Arthrex
Description: Patrick J. Denard, MD (Medford, OR), discusses implant selection, preoperative planning, and relevant literature regarding glenoid bone loss in shoulder arthroplasty.

<p>Patrick J. Denard, MD (Medford, OR), discusses implant selection, preoperative planning, and relevant literature regarding glenoid bone loss in shoulder arthroplasty.</p>

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VID1-002712-en-US | A | Glenoid Treatment Options: Managing Complex Morphology With Augmented Implants

Patrick J. Denard

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Glenoid Treatment Options: Managing Complex Morphology With Augmented Implants

I'm Patrick Denard from Medford, Oregon, and I want to share with you my algorithms for complex glenoid treatment. We have a lot of options available at our disposal. So I want to walk through my approach of how I choose each of these implants. On the anatomic side, when I'm addressing primary glenohumeral arthritis, the first two things I ask myself are, are there a stability problem and is there sufficient bone stock in particular, when we're talking about stability, when we're dealing with B1, B2 and B3 glenoid, we're dealing with an imbalance or stability issue because we know the natural history is that once that head sublux is posteriorly in a B1 type glenoid, it then wants to become a B2 and subsequently a B3 glenoid. This has been elegantly shown by Walker in a previous study, where they looked at type A glenoid and took CT scans 24 months later, and found that the A glenoid is 39 to 41, remained the same, but the B1 glenoid is 17 and 19 progressed, so 90% progressed on to B2 or B3 glenoid. So once you start down this path, it's hard to reverse. And this is why we know we have a high failure rate with B2. As Joe Walsh has shown us in 2012, where he had a 16% rate of revision and 21% rate of glenoid loosening at five years, in particular, when Retroversion was greater than 27 degrees and posterior subluxation was greater than 80%. So important numbers for us to remember. Conversely, when he looked at the same types of patients and treated those patients with B2 glenoid with a reverse, they had no loosening or posterior instability at five years post-operative. So a big change. What about the bone stock? We want to think about what are the limits of deformity correction, both from a Peg perforation standpoint and from a standpoint of violation of the subchondral bone. And then also, I think it's important to look at the results of bone grafting and augmented implants or the limits to correction. In general, there's several studies that have looked at this, but in general, they have concluded that it's about 15 degrees is the amount that you can correct without penetration of the of the glenoid vault. How about the subchondral bone? How deep is that? This study here suggests that depth is about 3.5mm in the setting of an eccentric glenoid. So you want to limit your reaming to less than that because we know that that's important for long term support. Augmented glenoid Ionadi has looked at his results and at 2.4 year follow up. Overall, many patients did well, but 6.9mm of bone loss predicted Radiolucency. And what does that mean? Well, that equates to about 25 degrees of retroversion, which happens to be similar to what we found in the other study reported by Walsh, where they had patients with 27 degrees of glenoid retroversion. Lastly, if we consider a convertible glenoid, we need to think about the thickness that is afforded by this implant, in particular with the universal base plate. We have about 4.5mm of offset that is provided by the metal implant alone. So you want to think about how much bone loss you're correcting with the use of this implant. Bottom line, what this all adds up to is that you really need to use 3-D planning to properly assess these patients, because we're talking about very small numbers in millimeters and very small degrees that have big implications for implants. So this is what my general primary osteoarthritis algorithm looks like in a patient with 15 degrees of retroversion or less. They are very amenable to anatomic glenoid placement with correction aversion. And this is based on the subchondral bone violation being minimal and the correction being affordable being less than 15 degrees. The studies I showed you earlier in a patient with greater than 25 degrees of retroversion, we know we're going to go to reverse shoulder arthroplasty almost regardless of age, because the risk of failure long term is so high with an anatomic implant, given that natural history of the glenoid. And then we have our in-between ranges that are 16 to 25 degrees that we can choose between AugMend, convertible and RSA based on age and activity level. And particularly that middle zone is what's going to perform well with an augmented implant. So here's some case examples. Kind of looking at this. This is a patient with an A-1 or concentric glenoid. We plan this in VIP and we have version of ten degrees with no evidence of eccentric wear. This is a patient that's very amenable to a VaultLock glenoid or a standard polyethylene glenoid. Here you can see post-operative x rays with a stemless implant centering of the head postoperatively. Let's move on to another case here. This is a mild B2 glenoid deformity. You can see a little bit of posterior wear on the axial view. We put this in the CT scanner in VIP. And we see there's 18 degrees of retroversion. Again falling into that middle range that I think is idealized for an augmented implant that between that 25 and 15 degrees of range. So this is an excellent one in my opinion for a augmented posterior glenoid. Now about options for addressing deformity with reverse shoulder arthroplasty. We really have three approaches we can use. We can collectively ream and lateralize the metal. We can use bone graft and we can augment. At our disposal is the MGS implant, which has offset options from 0 to 8mm in two millimeter increments. The nice thing about this technique is we can really regain a lot of offset through the actual metal itself. Bone grafting is described by Pascal Boileau is a well described solution for bone loss in the setting of reverse shoulder arthroplasty. We know this is associated with high rates of osseous integration on CT scans. Postoperatively. However, when we compare metal to bone in finite element analysis, we find that metal performs better. In particular, the further lateral you go, the more subject bone is to displacement under stress compared to metal implants. So the ideal scenario probably is metal. All things being equal. Now with reverse augment system with the Emgs, we have a couple of options available for us. We have full wedges with ten degrees of retroversion and 20 degrees of retroversion. And then we have half wedges in 15, 25 or 35 degrees. So how much gaps do the augments restore? I think this is something that's important to consider when you do your planning. If you look at these implant pictures here, you see that with the ten degree implant you're having four millimeters additional posterior. Whereas with the 20 degree implant you have eight millimeters additional posterior. With the half wedges you have three five and eight millimeters respectively. So you can use these numbers and consider when you're planning in VIP and really decide which one is going to fit most appropriately. So first we need to consider some questions to think about what position we're going to accept at the implant. And this is going to vary based on your interpretation of literature. But how much retroversion can I accept? In my view, that's about ten degrees. How much inclination can I accept based on the study here, if we do not have glenoid erosion, we can typically accept the normal superior inclination that is there. And then a very important one is how much base plate contact is required. And this varies between 50 and 75% in the literature. I think that also varies by the implant. This study in particular here looked at contact area of a base plate with a central screw, which is similar to the MGS, and in this study as little as 50% of contact was acceptable. You see really an increase in displacement once the contact only went down to 25%. So in my view, with a threaded implant, 50% is acceptable in most cases. So this is what my deformity algorithm looks like with reverse shoulder arthroplasty. And I've established my parameters here that at 50% contact. And based on my assessment of the glenoid data I showed you earlier, on the anatomic side, I like to limit reaming to only 2 or 3mm. So if I have 50% contact in VIP with the version inclination parameters I suggested, I will first try to get metallic lateralization. If I can get 50% contact with only reaming 2 to 3mm. If I set those parameters and I have less than 50% contact based on the VIP plan, then I'm going to move up the chain. If I have a four millimeter gap posteriorly, I'm going to use a ten degree augmented base plate in most cases, because that's going to match up really nicely with my GAP. If I have a 4 to 8 millimeter gap, then I'm going to go up to a 20 degree AugMend because as I showed you earlier, you have about eight millimeters of additional area posteriorly. And then as you can see with an 8 to 15 millimeter gap, this is probably where I need to use bone graft, although it doesn't perform as well. Biomechanically that's the limit of what our augmented implants can go to. And I know that CT scans show a high rate of integration. And then finally, if that graft gets over 15mm, I want to think about a custom glenoid, because I'm really reaching the limits of what I can actually obtain with a bone graft. Now, if your parameters are different, say you want to you want to shoot for 75% contact. You can do the exact same thing using these same approaches. Your selection or threshold for augmented implants is just going to change appropriately, but the decision tree ends up being the same. So we'll look at some cases here. This is an individual with a B2 glenoid posterior subluxation, as you can see on the CT scan here. Pretty significant B2 glenoid. We plan this in VIP and we first look at what can we do with an anatomic glenoid. And you can see to get contact we have to ream over four millimeters of bone. So we violated the subchondral bone based on those rules I showed you earlier. In addition we have a lot of posterior subluxation. So we need to remove to reverse shoulder arthroplasty. And you can see here with just two millimeters of reaming, I can get complete contact with a little bit of acceptance of retroversion. So this is a patient where I'm going to accept metallic lateralization. Here's another case though. This is an example of a half wedge case. We look at our CT scan here. We have a really significant B2 glenoid occupying about 70% of the glenoid. And you can see in the scan here we have 26 degrees of glenoid retroversion. So we of course are going to have a higher rate of failure with an anatomic arthroplasty. So we select an augmented implant. In this case the half wedge lines up very nicely. And we're able to get correction of this deformity. And yet another example here of a full wedge case. This is a patient with a more symmetric deformity. You can see on the CT scan here we have posterior subluxation with retroversion of the glenoid. And you can see this one has become essentially a B3 type of glenoid where we have that posterior erosion. I plan to correct with ten degrees of retroversion excepting ten degrees of retroversion, but this resulted in a gap of 8.5mm posteriorly with only 8% contact. So this one is going to line up perfectly for a 20 degree augmented implant. Posteriorly is that you can see as I'm selecting here in my VIP plan, once I select that implant, I'm able to get good contact and therefore restore the joint line. And there's the final post-operative radiographs. So thank you for your attention. I hope this approach to treatment of the glenoid helps you in your practice.

Glenoid Treatment Options: Managing Complex Morphology With Augmented Implants

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