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Good evening. And uh welcome to you all to this uh webinar from mastering Orthopedic Implant series. This is delivered to you by Orthopedic Academy and myself are now the convenor of this course. Uh Today's session is a special, it's about shoulder and el elbow implants. Uh This should be very exciting. Um I'm very pleased that we have with us today, David Hughes. Um David Hughes is one of the senior tutors and mentors with also with the Academy. He is one of the founders. Um and we rely on him heavily for our teaching and he's always gets excellent feedback. So David today is gonna talk about shoulder elbow implant, a huge topic. But um David is, is a senior fellow um uh the Royal National Orthopedic Hospital in shoulder and specializing in shoulder and elbow primary and revision replacement. So he's the best person to talk to us today about this uh interesting topic. Uh As usual, we will have a presentation, this will be followed by um set of MC Qs to help enhance your learning. And obviously, there will be a chance for questions and answer at the end. So please, we encourage you all to ask questions. If any of you would like to speak directly with David, then please just let us know during the chat and we can un mute you and you can speak directly to if you want to ask your questions directly, otherwise you could write in the chat. Yeah, so uh welcome everyone. And without further ado I hand you over to Mister Hughes over to you David, right? Thank you very much for us. OK. So today I'm gonna talk to you about shoulder and elbow replacement. Um I it is a long sort of slide, lot of slides, but I promise her lots of pictures. Um We're gonna talk a bit about the different types, uh a little bit about indications and history and I also mentioned uh a bit about some of the um some of the one of the approaches, particularly the delta pectoral approach for the shoulder and the poster approach for the elbow. So moving on in terms of the history, um shoulders have actually been done for quite a long while. The first time a shoulder replacement was done was in 18 93 by French surgeon Pian who inserted the platinum rubber component into a proximal humerus for a joint that had been destroyed by tuberculosis. Those days to infection was probably the most common indication for any form of joint arthroplasty, whether it be fusion or um excision. OK. Um Then in the 19 fifties, we had Charles Neer, a very famous surgeon who sort of pushed elbow replacements forward with his vital um and hemiarthroplasty prosthesis, much like, er, Charlie is the father of hip replacements. Nearer is the father of shoulder replacements. Now, this is a picture of that very first shoulder arthroplasty designed by PN in E 18 93 for TB. And you can see there's a, how long it is and you can see that it's a, it was a linked one. It somehow survived, ok. I don't think the patient did though. Um, in terms of the shoulder joint, it is a bit of a mad one. It is a minimally constrained ball and socket joint with lots of mobility and some stability. Much. You can see it here the way how it sits on top of the glenoid, the humeral ha head and sometimes you get a bit of wear and tear. It's very similar to a golf ball. Ok. So if you think how you have a big humeral head, a very small socket and is a golf ball outside. So you can imagine we have lots of fun trying to keep it stable and part of it, you've got some static stabilizers, the joint surfaces, the capsule um complexes. You got some dynamic stabilizers, those include the rotator cuff muscles and some of the scapular stabilizer muscles around the back. We'll talk a bit more about those later. Ok. Now, I understand some of these sort of medical students. So just in terms of some basic anatomy, the key things are sort of the, the humeral b bone, um the clavicle, the acromion. So the scapula and the humerus form the glenohumeral joint and then above it, you have the subacromial space. Ok. The sternum we do get involved in, but we think of the ribs but in terms of the scapula, thoracic area as well, which contributes quite a bit of movement to the shoulder joint. Now again, just moving forward as, as we talked about the four main components, you've got the Galal joint here, your chromic clavicular joint, uh the sternoclavicular joint, which also acts in terms of the main linkage of the shoulder to the axial skeleton, the scapular thoracic joint around the back where the scapula rests on the chest and that acts as in terms of movement as well. So effectively, most of the, in terms of movement at the glenohumeral joint that is going to be um up to 90 degrees. So up to shoulder height, when you're moving your shoulder, up and up to the side, when you're going above shoulder height in a normal individual that starts to, that starts to involve the scape thoracic joint coming in display. So these are things what we have to consider when we're designing shoulder uh a replacements. Um So again, just talking a bit more about the stabilizing joints in terms of around that. So you got the sternoclavicular joint. So it, it is, as I said, the only bony attachment of the upper extremity to the actual skeleton. So that's a very, very important joint. So if that's unstable, it'll cause issues further along the line. Thankful, that's a very rare thing. But we do see it, it also allows for movement and depression of the clavicle. Um And as I say, it's heavily involved with axial rotation of the shoulder, particularly above um shoulder height. Then you've got the acro clavicular joint. So that contributes to the total arm movement as well in terms of transmitting power forces between the clavicle and the acromial. So it's much like when you think of a crane, you've got the big arm of the crane and the small arm of the crane, you can't use the big arm of the crane without the small arm of the crane. And this is a small arm of the crane. And again, it is heavily involved in terms of movement with rela with regards to the scapula, it acts as a stabilizer there. OK. And again, uh in heavily involved in ro a rotation and elevation of the shoulder. And these are some very important little structures here. Co uh these are the c coracoclavicular ligaments, col trapez and trapezoid and they help add stability when you have a fracture here, you can lose stability around the Covic clavicle joint which can cause problems for function in uh in function in patients. Later on, I did mention we also have the scapular thoracic mus muscles at the back. They have no real bony attachment to the axial skeleton other than through the acro and the joint. But they, they're holding the shoulder blade onto the spinous processes. It's got your trapezius uh and then they help in terms of movement. So you've got Trapezius, serratus, ania, rhomboid major and minor levator scapula. These all are heavily involved in terms of improving the increase of range of movement of shoulders. So approximately one degree of fr fr elevation for every two degrees of glenohumeral joint elevation. So as I say, here we go and you can see Serentil helping in that, helping elevate that shoulder up. Ok. Oops, sorry. Well, jump to it further ahead. So with regards to the actual g humeral joint, it is a classic synovial ball and socket joint. Other than we talked about that large mismatch between the socket and the ball um has a sort of say shallow glenoid. So a a quarter to a third of the humeral head is in contact with the glenoid any one time. So it does rely on both the static and dynamic stab stabilizing forces to give it stability. Sorry, I'm just having a, there we go. And here are some of those static stabilizers. I won't go through all of them. But the key thing is the articular surface creates glenoid is slightly thicker at the periphery. So creating a little bit of a cup and then that is further deepened by the glenoid labrum, um which is, which is all dense fibrous tissue that's around it and creating a little C cup. The joint capsule is also very good and important as well. It adds approximately twice the surface area of the humeral head. So, giving a bit more stability and contact, you've also got these conflations, we call them ligaments within that. So you've got the coral humeral ligament, the capsular ligaments which are the um in superior, mid, superior, middle glenohumeral ligament and inferior glenohumeral ligament, which are sort of strong con conformations of capsule around the shoulder joint. And then we mentioned about the statics, the dynamic stabilizers. So these are the rotator cuff muscles which you will have heard of before. So, subscapularis um which is around the front. So sits on the anterior aspect of um the scapular fossa attaches to the lesser tuberosity around the front of the glenohumeral joint. OK. Infraspinatus, which sits on the poster aspect inferiorly in the infra fossa and sits there and that and attaches to the greater tuberosity also with it underneath is terrace minor. OK. So they sa they're sandwiched in between and a sandwich be in between is the is the actual scapa itself. And supraspinatus which sits on the top in the suprascapular fossa and comes over the top underneath the carvi to attach to the, the top of the grade tuberosity. So all the tendons of the rotator cuff muscles blend interarticular with a fibrous capsule. So um it's very, sometimes you, it's difficult to see the difference but they're there. Um And the contraction of rotator cuff rotator cuff muscles inr results in concavity compression, helping centralize the humeral head and adding a stabilizer. And this is sort of a key concept in terms of what we think now, what least arthritis is some form of instability, whether it be um as a damaged when people in disk, their shoulder or later on in life, when they tear the rotator cuff. So, shoulder pain is very common. Um if you go into general practice, you will see a lot of it. Uh osteoarthritis is what we always think of because we're orthopedic surgeons, rheumatoid arthritis is in there as well. In our older age group. They might not necessarily have osteoarthritis, but they'll have rotator cuff, tear arthropathy where there's been a loss of the rotator cuff. And that has led to instability which causes this um pain, very rare avascular necrosis. It does happen particularly people who are unlucky, had um steroids or um acute new tuber necrosis, some form of um vascular event. We do see a lot of posttraumatic arthritis and that can happen as a result of instability, whether they've dislocated their joint, whether it be from um mechanical dislocation or they have inherent instability. And very occasionally, we also see very severe proximal humeral fractures which result in destruction of the hue of the joint in terms of osteoarthritis. Um In addition to sort of the un universal features, we, we talk about such as loss of joint space, osteophytes, sclerotic changes. We also got to think of in the shoulder, the shoulder can have what we call posterior glenoid erosions, flattening of the humeral head, which you can also see in hip arthritis, enlargement of the humeral head with osteophytes, large inferior osteophytes, which we sometimes call the goat's beard. And obviously rotator cuff tears can also uh rotator cuff, tears tend to be uncommon in osteoarthritis, but they can feature on later. You can have in um incompetence of a rotator cuff due to lack of use if it, if your osteoarthritis is severe. Now, Walla was a um a very senior surgeon who de first described the glenoid wear. He called it. He did put into subgroups of A B and C. So A humeral head is still scented. I'm in the Gle I fossa with minimal erosions B. There is major central erosion. So we've got more of a cup B poster subluxation of the humor head. Again, we talked about with people who have had some form of instability but minimal posterior loss. And B one B two, there's a significant postural loss and you have this sort of dip. Ok. Um Then in uh well, like classification C, this is more of a dysplastic um uh glenoid with retroversion of more than 25 degrees, which can cause some issues as such. Ok. Now again, we talk as well, not just the glenoid, but also the humeral head can have problems. You've got stage one with a little bit of wear and tear stage, uh uh uh uh stage two, some superior migration. Stage three, you've got abutment onto the acromion. Um Stage four, you can see the osteophytes forming with a but, and again, superiorly, again, it's no longer centered as it was in stage one. And then the E in stage four B, you can see it's almost looking to look a bit more like what we call ace. And then stage five, you can have flattening of that glen of that glenoid uh humeral head. Sorry. Now, in terms of treatment for this, obviously, we talk about the there's not just conservative treatments, but today we're gonna talk, focus more on the surgical treatment. So we're first off, the off the bat is gonna talk about anatomical total shoulder arthroplasty. So I mentioned about um 90 about Neer. So this is a copy of 19 of n uh first uh implant in 1951. Um This is the one he came up with later in 1973. These were more hemiarthroplasty particularly used in complex fractures. Hence the reason why you can see there's frustrations there which allowed surgeons to stitch bits of bo bits of the bone back onto the, onto it in 1974. The near two prosthesis came out. It was modified near to conform to a glenoid component. So this is the, this is a new concept. So he's made a glenoid to replace it for an osteoarthritic picture. Uh This event evolved, we went as with hips, we've gone, we now have modular components. So we've got a humeral head component. We've got a stem glenoid component. Um and that stem, a glenoid can also have a keel or pegs. And you can also have different types of stems in terms of Trabecula metal hydroxyapatite coating um and different methods of to get the humeral head on. So you can have a round one to dial in a certain, a certain sort of uh uh conversion or you can have a sort of a, a more rou routine one where you're gonna have the humor head sitting in the same place all the time. No, with total shoulder arthroplasty, some very important things need to be aware, need to have a good rotator cuff, good Glen uh Glenoid bone stock and a normal version preferably. Um if you don't have a, so the key aim is to get everything centered. So it's stable that allow good balance of the humeral head. If these are deficient, you'll end up with a bit of rocking much like a rocking horse effect, which therefore will lead to imbalance and wear and tear and eventual failure of that implant. So that those are very important that when you're putting those shoulder replacement in, you pick your winners. OK? Cause the aim of a shoulder replacement is reproduction of a normal bone morphology. This is an anatomical one with optimum restoration of capsular tension, which is very key and resto RAA and restoration of the stabilizing and motor function of the, of the muscle. This is not always possible because if the person's had arthritis for a long period of time, they may have dysfunctioning muscles already. When we're putting our implants in, we have to be very careful, we don't overstuff. So it's really important that we get it in the right position because you can see here, this is what happens when it's overstuffed, that's putting a lot of tension on supraspinatus. Um not too low. If it's too low. Again, you may have a re uh I increased tension because it's now unstable. OK. And you can see the poly here. OK. So here is a, a more a classic sort of uh um stem that's been put in, that would be used. Um But delta extend with fest ras where you could sort of stitch capsule back on top of capsule, sorry, bone back on and also greater uro give you or bits of um caps uh bits of rotator cuff and this is the glenoid component that is a keel one. But we'll talk a bit about those and different ones. Um obviously like with shoulder, like with hips, shoulder surgeons are also like to experiment. So we looked at metal black glenoid. So this is a metal back glenoid where we screw in a metal uh component to fit into the glenoid and then put a plastic cup on, on your uh uh uh this is the SMR one. And then we have these sort of modular components. We got a stem um a metaphyseal component and then a humoral head. Um This is very good in terms of revision pro procedures or someone who has slightly more complex anatomy. Um There are other different methods in terms of we got other ones. Again, Trabecula metal, again, around the metaphysis around the metaphysis with a, a simple stem and again, different form of metal black glenoid where you have these little cups that sort of go in. These are the the traditional um sort of poly glenoid we used to have, which are cemented into the glenoid. This is the keel cut. So you make a small groove inside the glenoid and then you put a little bit of cement in and press fit into that. Again, you can have a similar component this time round with a again, a little bit of cement and then press fit into it. You obviously have to decorticate the glenoid and take off the labrum to allow that to happen or else you'll have it sitting off and it will cause unequal wear um un cause imbalance. OK. And this is hopefully what you'll end up with that little line there is um a little metal pin inside the glenoid. So that on the x-ray, you know where it is because you don't, you don't want to make sure it's up here or up here. And again, you can see you a different, a different picture there as well. Um These are slightly different stems. So they're both uncemented, both trabecula sort of metal and hydroxyapatite coated. Uh This is a slightly longer one and this is a short of a short stubby one. And then again, we do have difference in stems that have evolved over time. We can have stemless ones where we have little fenestrations or um cru uh cuts. Uh We can have a short stubby stem which you may have seen on in, in hip replacements as well. And this is a typical standard stem which is about 10 centimeters in length. So 100 millimeters again, generally proximally coated with hydroxy appetite coating. Um We're trying our best to minimize the use of cement because it in order to minimize bone loss. Ok. Now, even though the glenoid is pear shaped, there's been lots of different um sort of studies into it. There's now a lot of a lot of glenoid that we use now are more oval shaped. Whilst previously, everyone tried to recreate anatomy, but that created more problems. So most of the shape, most of the components now on the market are going to be oval shaped, the gleno component tends to be polyethylene, which can be as little as 2.5 millimeters thick. Um This has greatly come on in the last sort of 10 years with the advancement in polyethylene with highly crosslinked poly. And the if it's been rich in rich ones, they tend to be either convex or fat or flat back. Um Again, it does depend on the shape of the humeral head. Um So the one of the biggest controversies has been with regards to whether you use cemented or metal back glenoid, lots of different randomized control studies, unfortunately, seems to suggest that sadly, um polyethylene uh sorry, the polyethylene cemented ones are probably better than the long run than the metal back component. It may also be that surgeons decide to put the metal back theno in the younger patients. So they're going to have slightly more demand than say the older patient. So they're more like to have wear and tear. Um But certainly the most recent sort of multi um uh multi, multi randomized controlled trial from not 2020. That is unfortunately did say that metal back Benoy seem to have more loosening and revision surgery compared to with the conventional cemented poly glenoid. Ok. Now, in the past, we were very keen to do hemiarthroplasty, particularly in trauma. Um So we still have indication for doing those nowadays when the glenoid is intact. So there is in a fracture situation. People will definitely consider it when the Glenn component cannot be inserted. I glenoid dysplasia when there's a risk of glenoid where or loosening is high in the young. So that's something that we, we do consider a lot. Nowadays. Um If you look at the joint registry and the NJR, uh when they first started doing it, hemiarthroplasty were the most common implants put in. But certainly now with the advancement of um glenoid poly polys and reverse shoulder replacements, it's gone further down the list. So we're doing fewer hemiarthroplasty mainly in the trauma situation, all the very young. So this is the Copeland Global Cap, which is the, which was one of the first and most commonly used sort of hemiarthroplasty. It literally sort of you put your reamer over the top of the humeral head, get rid of the decorticate and then place this into the center of the humeral head and hopefully hit it. It will fit properly concern with this one was if you don't get your angle right, it's very easy to overstuff and then cause unequal wear and tear and damage to the su uh supraspinatus. Um This is another unique um implant called the Inspire from Tonier. Um This is basically a big ball bearing. Um I made a pyro carbon and um you basically hollow out the humeral head and you place this big um ball bearing in there and it creates an articulation because it will spin even within the humoral head sort of space and with the glenoid. So when you put an arthroscopic uh study in and you, you can actually touch and you can spin it quite easily. However, in for it caused some issues with regards to wear and tear on the glenoid. Um Despite the fact that pyro carbon is supposed to be closest to bone in than the usual metals, this is Culbert chrome. Um and there's some concern with regards to the placement in the, in the, in the in the superior humeral humerus. So it's now evolved to a stemmed sort of implant or a short stubby stem with hydro hepatite coating. And now this black shiny thing isn't Cobalt chrome but pyro carbon coating. So it seems to be more gentler on the glenoid in the younger patients. So it certainly is an option when you don't want to do more and have less destructive damage there. However, when you do hemiarthroplasty versus total shoulder replacements, we still find that total shoulder replacement does give better result in the mid to long term. Ok. So these are a few of the um sort of things that have shown it. Um And the key thing for the trial nut did not find any statistical er with uh with regards to rheumatoid arthritis. However, in the short term, but in the long term, it did cause issues a lot as well. Now, with everything, there are always complications. So the most common complication we find with total shoulder replacements is the glenoid loosening, whether it be metal backed or cemented, uh, it's very difficult to predict. Um, but it certainly is, most common hub stems can also become loose, particularly now with the further use of, um, trabecular metal ones, it's less of an issue, but certainly in the old cemented ones, you could quite cause a problem because it's quite easy to overfill this with cement. Um When we're doing our approach to the shoulder, we will do a tenotomy of subscapularis, but that can sometimes fail. And if it fails, that can cause problems with, again, with stability. Um If there's a fracture, greater tuberosity may come off, sometimes it can come off when you're doing AAA uh elective case. And if it doesn't heal nonunion can cause problems because again, you're damaging, the supraspinal malposition is really important. So it's quite easy to get the cut wrong. So you, you think you've, you actually the cut is quite shallow. Um In terms of this, you're not following the anatomical neck line, but you're following a different neck line. Um Iatrogenic cut rotator cuff tear is unfortunately also very common. It's really important that when you're dislocating the shoulder to expose the humeral head, you protect the supraspinatus and Intrasinus subscapularis should be off if you've done a tenotomy properly. Event infection. Unfortunately, P acnes is a very common one because this is a very dirty area. Ok. Nerve injury is another common injury and, and it's axillary nerve and that runs if you think about it. So your deltoid comes here, inserts there. So if you put your tractors in the wrong place, you can damage the auxiliary nerve as it supplies deltoid and then it runs around there and comes around the inferior aspect. So this is the glenoid where that LD, the top of the tis Dorsa insertion is, that's where um the uh so auxiliary nerve will also be as well. So you've got to be very careful when you're doing your clearance of the glenoid. Otherwise you could damage that and with any sort of shoulder replacement, when you're putting them in, you have to be careful with regards to fracture. Now, we talked about rotator cuff arthropathy previous in terms of po potential co um re reason for doing a shoulder replacement. It's really important because when the rotator cuff muscles are gone, it does mean you can't do a normal shoulder replacement because the, you've lost some of that ST some of those dynamic stabilizers which create stability. It was first described by Neer properly and Craig Andra in 8, 1983. And it does fo form a distinctive form of osteoarthritis, which is associated with a mass massive chronic rotator cuff tear and generally rotator cuff tears do come do occur less than 10% shoulder by way, but they can be there. Now, why is rotator cuff arthropathy important because the function of rotator cuff is to depress the humeral head and keep it scented on the glenoid. When it's not there, it right, it, it migrates proximally and superiorly causes unequal wear and tear on the glenoid. So instead of having you to have more erosion superiorly. And also, um there is a contraindication in terms of glenoid resurfacing as due to the EENT glenoid loading with regards to the humeral placement, surgical options. So we can look at a hemiarthroplasty of a large head is one option. Um The problem with this though, with this large head is if you've got a youngish patient, you will cause a lot of unequal wear and tear. It certainly is a bailout option when you can't do AAA. Um A a get a good um uh So the uh glenoid inserted, if it's not too bad, you can consider repairing the rotator cuff. In that situation, you have to have good evidence that the tiss, the muscle, the muscle is repairable and then you can think of a reverse shoulder replacement. This is a Clayton spacer very rarely done, but it's effectively just trying to offload. Um So take offload the superior migration of the humeral head. So in terms of hemiarthroplasty Rockwood did suggest 86% of results after four years, Zuckerman. So, again, adequate pain function relief, 90% had improved function. Um Sanchez and 75% modest improvements in range of movement strength and ad AD ls. So it, it is a good option in terms of pain relief. But certainly when these were done, these studies were done, um rotator cu or reverse shoulder replacements were very much in the infancy, but we're now a bit more robust and we're happy with them. Um However, they did all suggest there was going to be impaired deltoid function. Um and previous subacromial decompression, the loss of the coral ligaments, which associated with clinical shoulder instability, post hemiarthroplasty. So, this is quite important because it meant that you're saving up problems for later in the later in the day. So here is near um outcomes of shoulder arthroplasty were poorer when the rotator rotator cuff was not functional. This is a very important concept because even though the rotator cuff might not be torn if it's intact. If he's got very severe arthritis, it may not be, it may not be a functioning rotator cuff. So you have to be also careful about that. So as we showed earlier, when you don't have a good rotator cuff, you can get a rocking horse effect and that can lead to unequal wear and tear on the Glenna component and eventually lead to failure. And here's an example. So it's not come off very well where you've got superior migration of a large hemiarthroplasty, um a butting onto the chromium. And again, that's because there's no sort of super spinous tendon there to depress it. So what are our options. So we've got some rotator. So these are reverse shoulder replacements. This actually is near the near two. No, near free, sorry, which is a reverse shoulder replacement that he came up with. Um, it didn't do very well. So he said reverse shoulder replacements were rubbish. And, er, despite the fact, there are quite a few other ones on the market. Um, but unfortunately they got be because because of his power, he got, we all got lumped with the same problem. He didn't quite design this properly. This is more designed around a hip R a reverse hip replacement than the reverse shoulder replacement. This is the most, this is a delta er extend. And so this is one of the most commonly used hip rep um shoulder replacements in this country. Um And so you got the metal G glenoid um sort of base plate glenosphere, um a poly cup to hold it. And then you've got the socket part, very similar looking shape to a anatomical shoulder replacement in terms of a stem modular component. So there are some indications. So cuff tear, arthropathy, pseudoparalysis, anterior superior escape. So this is again with the shoulders, migrating superiorly and anteriorly. And it's very and from recent studies, it's very important that consideration in the four free part proximal humeral fracture in the elderly, it does seem to show that it has good results in terms of long term, if you can't get away with treating those patients non operatively. Now, this is probably a little bit old, but in terms of the prerequisites, we should talk about low functional demand patients, physiological patients, more than 70. However, I would say from my experience here at sta we certainly, we certainly can put them in the younger patients. We hope there's sufficient glenoid bone stock uh in order to get um a good base for the glenoid base plate to go on. However, you can also consider putting bone graft in as well, very important working deltoid muscle. That's key key qui if you don't have a working deltoid muscle, whatever you put in is gonna fail. So this is so in the nine, early 19 eighties, despite near dis um dismissiveness of reverse shoulder replacements, he put forward a few proposals. So in terms of his principles, the center rotation must be fixed, distal and medialized to the level of the glenoid surface. These are the first key things he talked about. The prosthesis must be inherently stable. The lever arm of the deltoid must be effective from the start of the movement. The glenosphere must be large and the hub cup small. So these are sort of comments that er comments that cremont um came up with in terms of coming up with his reverse shoulder replacement. So this is what we were talking about. So normally you've got the hu supers here, keeping everything intact, pushing things down and keeping it medialized Now, unfortunately, when it's gone, deltoid takes over, pushes the super pushes the humoral head up, um pushing it also more medial as well. So you can see the button there. So the center of rotation is no longer where it should be. So the mon wanted to get the center of rotation a little bit more medial. So, so that's the Glennis fit. It would probably be sorry. This is the a dia a diagrammatic what version of it? That would probably be a lot bigger and this would be probably a bit smaller in reality. And so this is one of the classic ones in terms of delta extend free reverse shoulder replacement. So very similar as the Vermont initial designs. So glenosphere hemispherical shape base plate including a central peg press fit peg about and a small cup with a neck shaft angle of 155 degrees and a nine mil nine millimeter offset. OK. So you can see you've got this sort of large humeral head hemisphere pushing into that. So a sense of rotation there. Now you can see there's a problem here can cause some issues with regards to abutment and then notching. So we got me but this is again, this concept of medialization. Now, in this situation, the classic mont one where you got medialization center rotation. Um because of this, this concern about coming into neck, going into the the scapular neck and causing notching. People talked about media sort of later it and there you can get see that there. So more, more later. So the sense of rotation is no longer there, but more, more later. And so that could be the and that's the difference there. So this is a less hemispherical shape. OK. So, and this is a, as I say, this was an initial issue that we had with um the first reverse shoulder replacement that came out in the eighties, this medialization of the center of rotation called sca and notching coming into that coming into that one. And it didn't really give enough of a lever arm to the del deltoid muscles because you were medial them. And so you get this pro as I say, you got this issue with scrap and notching which causes instability, wear and tear. So not you losing that good bone stock that was protecting the screws and the central peg. And this is described by Niro who gave four different um sort of examples of how it can happen. How can we avoid SCA and notching? So we can talk about inferior glenosphere position, inferior inclination of the glenoid component, increased lateral offset, decreased inclination of the neck shaft angle of the humeral hide component. OK. Now, it's interesting, those concepts had all been fought off before by the pre by some very earlier designs. So this is the Liverpool be do, which is basically a reverse hip replacement, but it severely lateralized the component. This one tried to, again naturalize component but had this protective bar going down the inferior angle. Um I, I think this is another, the key one. Again, you can see you've got quite a lateralized humeral head, um central rotation um and you had a constrained liner to give a bit more stability. This is the, the one I've seen most, most commonly. Um er because I'm working at Stanmore, this is the Bailey Walker one made by Stanmore instruments and it worked on a different concept. So it lateralized the humeral head, but also it's an inlay system. So you're taking away a little bit more bone. So, so it gives you that better sort of comp that better sort of definition with regards to the, the glenoid. So here we can look at them uh in terms of different ones. So um this is the new adaption. So very old Vermont one where you have the the tray on top, you've got a hemisphere and, but you got notching. This is a non hemisphere, slightly domed shape um with the center rotation lateralized, but you've got an inlay system. So the tray isn't sitting on top of the um cut of the of your humeral head. They're sitting just a ju on the inside and gives a bit of a cup dish. OK? So you have more lateralization, you get a better sort of curve to the shape of the shoulder and here's a novel version, OK? Um which is the, the most more commonly used one. Now, in terms of uh evolution of this model where you have a onlay tray, you have still have that hemisphere of a uh of a glenosphere. Um You have sort of this curve sort of wedge shape to the, the insert. So it gives you a little bit more co a little bit more uh sort of naturalization and a media and allows you but still has a medial center of rotation. And this is just to show the difference in terms of how you would have it look on top of that. But you can see this is the onlay and this is the inlay where it sits in there. So it does have it, they both have the advantages. So more the inlay is more anatomic, less humeral lengthening, better recreation of the shoulder contours and an easier subscap repair. Um The onlay preserves proximal humeral bone because you, you're, you're not hollowing this bit out, easier to convert. So if um if this was a anatomical shoulder replacement, you just swap it out in terms of the module systems, swap out this component sort of the anatomical component and put a tray on top. And you, you do talk about the deltoid wrap, but I feel you get the deltoid wrap better in this version because of the way I have held the curse round. However, reverse shoulder replacements do have more inherent stability than the anatomical one because they give a maximum angle to the net forces around. Ok. So reverse shoulder replacement tends to be 5 to 4 times more stable than the normal joint and two and 2 to 3 times more stable than a total shoulder joint, an anatomical shoulder joint replacement. So those are sort of key things. So you can get away with a lot more with reverse shoulder replacements than you can with a an anatomical one. Now, deltoid function is very important. So we do find with reverse shoulders, they do have some benefit um medialized and dis center of rotation increase increases deltoids moment on because now you don't have any rotator cuff muscles. So it does give it more movement and it gives it more protection because you have a lever arm that slightly longer. Um and all three subgroups of the deltoid muscle. So you got the an posterior, middle and anterior um demonstrate a primary abduct abductive force after reverse um shoulder replacement. So this does I I important because it does give some active internal rotation, exel ro rotation remain unchanged or reduced. So, very rare um decreased rotational movements of the arm of subscap and Tero sp after reverse shoulder replacement. And it's not less of an issue. Super rotational capability after lateralized, reverse shoulder replacements are tend to be better than with non lateralized. Uh reverse shoulder replacements again, because of this increasing the moment arm of deltoid