Hello and welcome to this Webinar on external skeletal fixes for fracture fixation. I'm Doctor James Guthrie, and I will be your host for the next hour. I'm a R, CV, S and EBVS specialist in small animal surgery and also a diplomat of the American European colleges of veterinary sports medicine and rehabilitation.
So I suppose start off simple. We're gonna use the acronym ES FA lot. So ESF stands for an external skeletal fixture.
So very, very basic. I'm sure you'll all be aware. Basically, what these are are external scaffolding frames that have metal pins that penetrate through the skin into the bone, various connecting bars on the outside, like a scaffold in order to stabilise the bone to allow a fracture to heal.
Now, there are different types of ESF, and we have various different classifications. So we have the most kind of simpler device, which is a linear ESF. So with the linear ESF, we essentially have straight bars on the side, and then pins going through the skin into the bone.
We can also have a circular ESF, and then this is whereby some of the external bars are in a circular shape travelling around the limb and allow pins to enter at various different trajectories. We could actually combine a linear and a circular together, and that would give us a hybrid ESF. So in this example, we can see proximately.
It looks like a linear ESF, but distally. There is a circular frame component, and another phrase sometimes used would be the transarticular ESF. And this is where the frame travels across a joint.
So it's going across an articular surface. It's across a joint, and these can either be rigid, like in in the example shown, or they can potentially have hinges involved to to allow them to move. Sometimes the transarticular frame can also be what's called flexible.
This is typically where there may be elastic bands that allow some movement, so it's not completely rigid, but it is not a sort of necessarily a hinge mechanism, but it's kind of an elastic band across not used very often. And as we are going to be covering more for fracture fixation, we won't go into too much detail with regards to hinged or flexible transarticular frames. So I suppose what's really important if we're starting off thinking about, an ESF, we need to know what we're using and everything has a name.
So everything within an ESF. Also has a name. So some of the key things are that we have a, fixation pins.
These are the pins that actually penetrate into the patient into the bone, and they have a connecting bar. The connecting bar is then on the outside, and then we have connecting clamps, and the connecting clamps basically connect the bar to the pins. And there are various different components, or various different, forms of these, which we'll come on to a little bit later on.
So when should we use an ESF? Well, an ESF is amenable to many types of fractures. However, they're mostly applicable for for sort of shaft fractures or fractures of the diaphysis, especially those of the tibia and the radius and the ulna.
So especially kind of, the more distal end of the limb. But with correct application, they can be used from everything from a a simple dhole fracture in a juvenile patient to a highly comminuted juxta articular fracture. And although more difficult.
They can be successfully applied to fractures of the femur and the humerus. There's also other uses of, ESF. And that can be if you have, for example, a luxated joint.
You may want to hold the joint in position whilst it's healing. And you could also use it to assist with ligament and tendon injuries. So in the examples on the right hand side, this was a cat that had a triceps muscle.
Tear had the triceps muscle primarily repaired. And then, in order to take tension off the triceps muscle, the limb was fixed with the elbow in an extended position, whilst the tissues of the tendon were starting to heal, and then the frame was removed once tissue healing had begun, and then the tendons could take the additional load with a greater degree of flexibility being applied to that muscular tenderness unit. So ESF does have advantages over internal fixation, so they can cause less damage to blood supply to the bone, and also minimal interference with soft tissues.
Because we're typically doing perhaps a kind of closed approach or a sort of minimally invasive open approach, sometimes kind of referred to as open but do not touch. So generally we can be less invasive, therefore causing less soft tissue damage and less likely to disrupt blood flow. They can be particularly useful when, stabilising sort of open fractures as well.
Because they can allow stabilisation of bones whilst simultaneously allowing you to access a large skin wound in order to manage that. And it also means that in cases where we are concerned about contamination of internal implants and subsequent infection, we know with an ESF we are going to remove it, and therefore, that can often mean removing a NUS where bacteria could stick to and therefore helping to resolve an infection. And also the one of the nice things is that because the framework is external, it means it's accessible.
And that means we can adjust it after it has been applied. And either you could make adjustments, to improve, perhaps, say the fracture fixation, and reduction. So it might be that you take some immediate post operative radiographs.
You think I'm not quite happy, and you can actually just make little adjustments to the frame rather than having to go kind of back into, say, surgery, open everything back up again. And also, the adjust ability of the ESF frame makes it uniquely suitable for dynamic adjustments in the correction of limb deformities or segmental bone defects, where perhaps you're gonna actually transport bone or use something like distraction osteogenesis. So in some situations, and these are quite complex uses.
But they do allow you to actually manoeuvre bone throughout the healing process, which can have advantages in very sort of complex cases. However, although everything has an advantage, everything usually also has a disadvantage. And there are some biological and mechanical disadvantages associated with ESF.
So the percutaneous nature of ESF does increase the risk for infection. Bacteria could potentially travel down the implants to the bone. We leave little areas that are open little holes in the skin.
Because these kind of pous implants are sort of breaching the natural barriers of defence. The body has so the the sort of skin as a barrier. And, the sort of external and eccentric placement of the fixation can result in large bending moments.
Acting on the fixation, pins and due to mechanical and, biological disadvantage associated with ESF. This type of fixation is generally not intended for long term use when delayed healing is anticipated. Now there is a risk for patient morbidity and and that can include sort of premature pin loosening.
You can get pin tract inflammation or, as you mentioned, infection, and the potential, for fixation. Failure increases with time. So generally an ESF will eventually always loosen.
And it's kind of a race between what happens first, the bone healing or the ESF becoming loose. So sometimes other considerations when selecting an ESF as a means of stabilisation can also include whether or not the patient will tolerate it, and also whether the owner will be compliant with its use. So whereas with internal fixation, generally everything is tucked out of the way.
It is harder for the dog or cat to access and get to, and also it's kind of tucked out of the way for the client as well. It means usually there's less for them to monitor, less for them to to worry about. There's also then, nothing there for the dog to get it caught on.
So you do run the risk of the dog damaging other parts of its body from the ESF if it knocks against or scratches, potentially damaging part of the client's home and potentially the ESF getting caught in AAA crate or frame, a cage that the animal is being sort of penned in with during the post operative care period. So there are some some disadvantages. So in regards to ESF implants, let's have a little run through kind of some variations.
So again, sort of some terminology. So the ESF has kind of two basic elements, and this is kind of, regardless of the device or system being used, the kind of fundamental components are the fixation pins and then the connecting sort of column. The sort of fixation frame which is made up as we touched on earlier of the connecting clamps and the connecting bar.
Something that we also kind of cover is also, acrylic. And you can have acrylic frames whereby the acrylic is a form of connecting column and actually replaces the need for connecting clamps. So we we'll come on to those a little bit later.
So our fixation pins. These are usually made of stainless steel. They usually have a a tr car tip, and they can either be sort of smooth or threaded.
So smooth is essentially a a smooth pin like a K wire. Whereas a threaded pin has a thread running around it. Like the three examples shown here.
And there are different types of, threaded pins, you can either have what's called a a positive threaded pin. This would be the example in the middle, and this is where by the diameter of the inner part of the thread, so the inner part of the red section in that middle pin is equal to the diameter of the shaft. So the grey section further down, and in terms of the thread, you can either have them designed for cancerous bone or for cortical bone, and that will change the the pitch of the thread.
And then you can also have negative threaded pins, and this would be an example of the pin on the left. Now, in this pin, the diameter of the inner thread, of the diameter of the pin at the thread section. Which is the red area again at the top, is actually less than that of the shaft and what you'll perhaps then notice that there is potentially a stress riser at the thread shaft interface.
So that pin on the left hand side, you can imagine if you applied a bending force to that, try to snap it. It's most likely going to snap at the interface between the red and blue areas. Another sort of phrase to be aware of is full pins and half pins, so half pins are like the three examples shown here whereby the thread is at the end of the pin.
Therefore, these pins are designed to only go halfway into the leg. So just in one side of the leg itself, through both cortices of the bone, but just through one side of the leg. So through one skin incision, whereas a full pin is designed to go all the way through the leg and come out the other side, and therefore the thread section is actually in the middle or sort of centre of the pin.
So the threaded section is within the bone, and then you have a smooth section coming out either side of the skin and either side of the leg. So here's those examples again of a negative profile, positive profile. So the positive profile pins have a single diameter solid shaft with threads that are rolled onto the end or the centre of the shaft, such that the outside diameter of the threaded portion is larger than the diameter of the rest of the shaft.
The diameter of the shaft and the core of the threaded portion maintain a constant cross section, and positive profile pins have increased pin stiffness. Greater axial pull out strength and a greater fatigue life compared to smooth pins and positive profile pins can also be so classified according to their thread type, whether they're cortical or cancerous, similar to the thread type on bone screws. So whereas the negative profile pins have threads cut into the pin such that the outer diameter of the threaded portion is the same as that of the shaft, and the core of the threaded portion is of a similar diameter, the way in which transition between the threaded portion and a non threaded shaft is cut is important.
If the transition is abrupt, then we get this stress riser, which we mentioned earlier on. And that's the interface between the red and blue section, where it's likely to fail. So what has been developed is some negative profile pins that have a tapered transition in the shaft diameter between the threaded and non threaded portion to try to avoid that abrupt stress riser transition point.
So an example would be some of the dura face. Pins from Imex are an example, so you can see that the bottom pin, the dura phase profile, is actually a transition of the diameter as the blue section goes into the red section, so you have less of an abrupt stress riser. And as we touched on earlier, here are the examples of full pins and half pins.
So you can see that a bit more clearly in this illustration, where half pins just go through one side of the limb and full pins would go all the way fully through the limb. OK, let's move on to connecting bars so they come in different materials. The most kind of common would be stainless steel, but they also come in in aluminium and titanium metals.
These are lighter weight compared to stainless steel. You can also get them in carbon fibre, which are the black ones in the image. Again, these are extremely lightweight.
The other advantage of of carbon fibre pins is they don't show up on radiographs. Or don't show up that clearly. So you can radiograph through them and you can actually see then your fracture your bone through the pins.
So I do quite like the the carbon fibre pins for that. And also, we touched on very briefly acrylic. We again will come on to those in more detail.
So, by being able to have these more kind of lightweight, materials, it means we can actually then create rods of a larger diameter, which can then increase the the strength and stiffness of the frame construct. Now, we, have clamps, and the clamps rely on compression of components, resulting in friction for stabilisation of the construct and and therefore the bone segments. So generally, advances in clamp design over the years have eliminated many of the limitations and complications present with the kind of early, Kirchner Emma types of systems.
Some examples of more modern clamps include the i MA SK clamps, the securo Titan and also U clamps. So the fixation clamp design was kind of improved in order to sort of limit them slipping along the connecting bar and also limit slippage through the clamp of the transcription pins, as well as also to try to resist rotation of the pain about the clamp and generally just increase, stability. Every advantage of some of these modern clamps is they can be, dissembled taken apart.
And this allows you to perhaps add or remove clamps within the middle of the frame without taking the whole frame apart. So with the older KE clamps, you had to work out how many clamps you were going to use almost before you started and attach them all to the connecting bar. Whereas now you can actually add additional clamps or take clamps away once the the frame is already mostly in construction.
And the clamps are specific to a certain connecting bar diameter, and this kind of in turn dictates the frame size. So many current ESF clamps are designed to accommodate accommodate multiple pin sizes. And they have greater modularity and customization of the frame constructs.
Clamps are also available either in a sort of single clamp model, which is attended to secure a fixation pin to the connecting bar. Or you can also get a double clamp model, to secure two connecting bars to each other in order to form an articulated frame. So, the example that you can see here, labelled a at the top.
This is an IMXSK. Clamp. This is the one that I personally use.
Number, sorry. Letter B, is a securo titan clamp. And C is the securo U clamp.
So what the white arrow is pointing out is where the fixation pin goes in to that sort of smaller hole and the black arrows are pointing out the position with the connecting bar would go into the clamp. So if we just look at some of these a little bit closer. This is our Kirchner.
Emma, this is the kind of older, older design, IMXSK, probably what lots of veterinary surgeons would use. And then we also have this kros system as well. Clamp assembly.
So we can see how these can be taken apart and put together, which means they can be added and removed. Throughout the procedure. Now, in terms of clamps, as you can see in this picture, there's two different ways in which they could be attached A or B.
Now, clamps should be positioned on the connecting rod such that the fixation pin working length is kept as short as possible. So that would be example. A.
When the clamp is positioned such that the pin gripping, the bolt is between the connecting rod and the skin surface. This is referred to as the clamp in position. This is, say, the preferred position because it shortens the fixation pin working length.
But when the clamp is positioned such that the pin gripping bolt is towards the outer aspect of the connecting rod, this is referred to as the clamp out position. That's the example in B, which kind of unnecessarily increases fixation pin working length, and the shorter the working length of the pin, the stronger the construct will be. So the clamp out position should only be used when it provides a unique angle required to place the pin in a safe region of the bone that cannot be obtained with the clamp in position.
This is something that could be a really simple mistake when you're in the midst of surgeries but your clamps on the wrong way, so always pay attention to that and show. Do what's shown in image A. Now something that I've kind of referred to a little bit so far, and we'll kind of go into a bit more detail now.
This is the acrylic ESF, and they've been developed using various acrylic based components. These are frequently either kind of methyl metta or epoxy resins, and these replace the conventional connecting bar and fixation clamps. Now, because these constructs are custom moulded specifically for a particular application, they're frequently referred to as a free form ESF and the use of acrylic as a free form connecting column provides greater freedom in the placement of fixation pins while still providing appropriate mechanical strength for fracture stabilisation and with acrylic free form ESF.
The placement of fixation pins is not restricted by the clamp and the connecting bar. Therefore, unlike other ESF systems, the pins can be placed in any plane at any angle and in any configuration. So although the image here has shown the acrylic looking like a fairly standard ESF, you can actually completely change the shape and have it as a very free form design.
But a significant drawback of the acrylic ESF is the inability to adjust the apparatus once the acrylic has been applied and hardened. So the acrylic is applied as kind of like a a doughy liquid, and then it sets and hardens, and it cannot be changed once that happens. If you did need to make an adjustment, you have to remove all of the acrylic from the pins before it's replaced.
And this also then limits the possibility of a staged disassembly so here would be an example of what you may have. You'd have this kind of plastic tubing. You would then essentially position the tubing around all of the pins or effectively poke the pins through it, and then you could inject the acrylic down through the tube, and then it would set.
So it's, quite important that we get some of the the phrasing correct when referring to an ESF. And generally I suppose it provides two purposes. It evokes kind of a a mental picture of what a given configuration should look like.
Which is helpful in clinical practise, also helpful in teaching and also in in research. So lets people know, what you are doing, what you have done and also allows you to know what you're going to do and what the plan is. Additionally, it can also help them predict the mechanical performance of one construct relative to others.
And, you know, this is an advantage of external fixtures as their ability to assume a wide range of different and sometimes imaginative configurations. But the downside of this is that sometimes no classification system can encompass all possible assemblies. However, that being said, basic classifications are commonly used and generally kind of, you know, commonly accepted.
So, some general frame configurations can include unilateral constructs, and this is where the pins are located on one side of the limb using half pins. A bilateral construct is where pins are located on both sides of the limb, and this could perhaps be achieved using full pins. So the pins that go all the way through further to this frames can either be classified as uni planar constructs where all the pins are in one plane.
So this example here, maybe you'd say, is a kind of, meteor, lateral plane or horizontal plane. Or they can be consi considered bi, bi planar. Sorry, constructs.
And this is where pins are placed in two different planes. So we've kind of got maybe a horizontal plane and a vertical plane. Both you say at 90 degrees to each other?
They're perpendicular. They don't have to be perpendicular, but generally they are would have to be in two planes. And finally, there could also be what's called multiplanar.
And this is where you could have, perhaps again, essentially more than two planes coming in. So, let's have a look at some examples, then. This is, the most basic type of ESF.
This is a type one, a frame, so type, one frames are unilateral, and then they also have a subtype. Which designates the uni, uni planar frame. So it would be type one a so type one A means unilateral and, uni planar.
In type one frames, only half pins are used and they're connected to a single connecting bar and the type one a frame is the least rigid type of frame. And therefore, these are useful if they only need to be in place for a short period of time, such as in a juvenile patient where healing is going to be rapid. And the implant is not expected to suffer from, a large amount of cyclic loading over a long period of time.
Now similar to the type one A frame. This is a type one B frame, and these are also composed of half pins. So it's, similar to the so this is essentially a unilateral construct, and pins are only going through essentially one side of the the limb.
However, this construct have pins placed in two planes as shown in the illustration. We've got some pins coming in from the media lateral direction and some pins coming in from a craniocaudal direction. So it's a B, planar unilateral B, planar and unlike the type one A in the type one B.
We have two connecting bars, and I suppose a way of thinking about the type one. B is essentially two type one A's at 90 degrees to each other. Kinda don't wanna kind of confuse you too much, but this is kind of a an interesting but, technically an alternative form of a one.
B. It does have a single connecting bar with connecting clamps orientated on alternating sides. And this actually then means that the pins are coming in in two separate planes.
So this is kind of a little bit of an interesting type one B. But in terms of, if we're trying to simplify everything, I think this maybe could be a little bit confusing, but it's an interesting one. So, let's now move on to type two frames and in type two frames, we introduce the use of full pins.
Therefore, these are a bilateral construct. They're coming out of both sides of the limb, and this allows for fixation on either side of the pin using two connecting bars, opposite each other at 100 and 80 degrees. But these are unip planar frames.
So bilateral uni planar. Now the type two a uses exclusively full pins so you can see all of the pins going through the bone are all full pins. Now, due to the requirement for bilateral connecting bars, type two frames are typically restricted to the distal limb.
Cos if you try to put something like this on a humerus, the connecting bar on the medial side would be impinging on the dog's chest. So generally, these can only really be used, distally. And then the type two B, share many similarities to the type two a frame.
However, the only difference is that you have a combination of four pins and half pins, so you can see the pins on. The most proximal and distal ends are full pins, and the pins lower down are half pins. Now, as I say, we can always get, complicated.
And we can always modify these ESF frames so we can also have a type 12 hybrid. And this has been introduced for certain anthem locations where the full pins can only be introduced in the distal fracture segment safely. So, example of this would be If you were using a frame on the humerus, you may have a, connecting bar that's on the lateral side and half pins but distally on the medial side.
You could have a full pin down close to the elbow, and these have the advantages of the mechanics, of a type one and type two. And they also allow the introduction of a diagonal bar, which can then increase the stiffness of the construct. So we've done type one we've done Type two.
Now, the most complex ESF configuration is the type three, and the Type three consists of a combination of type two and type one frames, with the latter the the sort of type one frame typically being placed 90 degrees to the type two frame. And these type three frames allow for the highest construct stiffness. Now to allow the surgeon to add further stiffness to a construct.
Several techniques have been introduced for this purpose, so we have articulations and diagonals. So on the picture on the left, you can see an articulation. So this is a type one B, whereby the two connecting bars have then been interconnected by proximal and distal linkages using double clamps and connecting rods.
Now note that the articulations do not cross the fracture gap. So for these articulations, they are connecting, bars that do not go through the bone. They are outside of the patient, but connecting the two, essentially the two type one be together.
Now the picture on the right illustrates an ESF with a diagonal. Now the same kind of construct, as an image on the left has been augmented by interconnecting the two connecting bars via double diagonal linkages using double clamps and connecting rods. Now, here's the difference between diagonals and articulations.
The diagonals do cross the fracture gap. Now, diagonals add more stability to the frame than articulations. And in the application of diagonals, the connecting bar often needs to be contoured around the limb.
So you often need to actually curve and bend these connecting rods so they travel around. Perhaps the cranial aspect of the limb and carbon fibre bars cannot be contoured, so you can only use diagonals in a curved way if you're using acrylic connecting bars, stainless steel or some titanium connecting bars, so that needs to be kept in mind. If you're using this technique, make sure you've got the correct bars to use.
Some systems also allow the placement of an augmentation plate. This can be attached to the outer surface of some modified clamps in order to stiffen a portion of the frame. Perhaps that spans directly over the fracture, and ESF can also be used in combination with an IM pin, and what you can also do is commonly tie in the IM pin.
So it's a configuration whereby the IM pin is actually incorporated into the fixative frame configuration, and this strategy can be employed in the femur, tibia and humerus to perhaps compensate for the relative weakness of half pins. The IM pin is connected or tied to the unilateral fixator. Now being in a mechanically favourable position on the inside of the bone, the iron pin can support the remainder of the unilateral type one fixator, greatly enhancing the stiffness, and these are called a tie in configuration.
So let's talk about how to apply some of these techniques in practical terms. So patient, positioning. Typically a patient is going to have an ESF placed below the elbow or the knee.
So generally the patient replaced in dorsal recumbency. And also, I suppose, you know, application for the humerus or femur. The patient is going to be in a lateral recumbency with the affected side Atmos, and we'll typically you want to do what's often called a hanging limb, and preparation with the limb is hung, allow you to drape all the way around it so that the limb can be free within the surgical field and can be manoeuvred.
Also, if you are hanging the limb like this, it does allow you to supply some axial traction in order to help with your reduction. And some surgeons may even actually have the limb hanging whilst they apply the frame. Now one of the beauties of ESF application is that the implants can be placed by percutaneous in, introduction.
And in certain cases, however, an open approach to the fracture can still be used if required. So normally, a stab incision is performed in the desired location of the pin placement and sometimes the skin incision might be extended a longer pin track in areas of motion to try to prevent soft tissues impinging, which can sometimes then decrease patient, impingement could decrease the patient's comfort and also decrease the mobility. So, again, we I might do a, closed fracture.
That can sometimes then mean it can be a very quick surgical procedure. We don't disrupt blood supply. We don't disrupt all of that.
Initial bone healing that begins straight away may use an open, but do not touch approach, or an open approach can be used. Probably going to do that if you have some real significant overlap. And you really need to try to manoeuvre these bones back into better position.
Perhaps if the bones are really markedly displaced out of place. If there's perhaps sort of any angulation, Or perhaps if the bone fragments have kind of rotated into the wrong position, then you may consider doing an open approach in order to try to place them into a more, anatomically appropriate position. Now, the introduction of percutaneous pins should ideally be placed through safe corridors in order to reduce morbidity of the, the ESF could cause, and now such areas have been described by Martin and Miller back in 1994 and these are administrations taken from their text and the safe corridors basically avoid significant muscle mass, gliding muscle groups and also neurovascular structures.
And these corridors therefore help to find options for ESF design. For a particular anatomical locations and corridors can be categorised as safe, hazardous, and are often then associated with kind of low, mild and high morbidity, respectively. So the red areas would be, kind of unsafe yellow would be hazardous, green would be safe.
And now the goal of the surgeon is to place all the pins through safe zones. However, pin penetration into hazardous zones may occasionally be unavoidable based on fracture, location and morphology. Safe zones for the mandible has also been, investigated.
So generally you want to go ventral in the mandible, in order to avoid two routes and publication by prao back in 22. Also described sort of safe corridors for ESF placement in feline long bones. So these papers are very useful to use.
It's really important to know your anatomy when applying in ESF now, external fixators should provide enough stability to maintain reduction and the surgeon has to understand the biomechanical principles in order to correctly apply the device to achieve adequate stability. Now, at least two pins have to be inserted into each main fragment through safe zones for each segment and for the construct to be stable. One pin should be placed close to the proximal and one pin close to the distal end of the bone.
Whilst other pins are placed near to the fracture and this is referred to as a far near near far placement. So in the image on the left, you can see we have a pin place far away, the most proximal one. We have a pin that's placed close to the fracture gap, proximately so close to the pink area.
We then have one that's near the fracture gap distally so just below the pink area. And then we have another pin far away, very distally, and in that example, we also have some extra pins in between. Now the image on the right hand side is incorrect because we do not have pins in the near position, and that would weaken the construct.
Now the stiffness of the frame can depend upon several factors. The distance. The pins are from the fracture line.
That's that distance X, so the closer the pins are placed at the fracture site, then the stiffer the construct will be. However, pins should not be placed closer than five millimetres, so you generally want to keep your pins at least half a centimetre away from the fracture site. But to go as as close to that as you can now, something else that affects these frames.
Stiffness is the distance between the pins inserted in each main fragment, and that's the distance. Why the further apart? These pins are the stiffer the construct will be, and you do not want to place one pin closer than 10 millimetres to another pin.
So always keep your pins a centimetre away from each other. If not more. And finally, the third thing that can, impact frame stiffness is the distance of the longitudinal connecting bar from the bone.
That's the distant Z, so the closer the connecting bar is to the bone, the stiffer the construct is so you generally want that bar as close as you can. However, you do not want the bar to impinge on the soft tissues, so you generally don't want it any closer than five millimetres to the skin edge. Remember that the skin, and the soft tissues are likely to swell after the the trauma of surgery, so you want to leave enough space for that swelling, and also important is to manoeuvre the leg through a range of movement.
Because sometimes as muscles can contract and change, shape and shorten, they can essentially widen and and bulge out. So you want to put the leg through a range of motion as well. To check there's no impingement, and for more, the number of pins in each segment can play a role.
So the more pins the stiffer the construct is. But the stiffness does not increase after four pins per segment, so there's no point putting more than four pins into each segment of bone. And the number of connecting bars can also affect the stiffness.
So two connecting bars are stiffer than one frame configuration. Plays a role, as we discussed earlier. So depending from a one a one B a two a three stiffness increases, and also the implant type.
So some clamps and bars are stiffer than others. Say the more kind of modern IME and secure implants have less reported complications than the original KE system. I use a little illustrations showing that as you increase the number of pins, stiffness increases.
But once you go beyond four, you can then get very further advantage. And here, as we show as we increase from, different types of frames and the stiffness also increases. So the most common source of weakness or failure of an ES frame is the pin bone interface.
A failure of the pin bone interface and subsequent pin loosening can jeopardise stable frac fracture fixations as well as result in soft tissue irritation, pin drainage and or pin tract infection. And this may result in fixation, failure and patient morbidity. Worst case leading to requirement of further stabilisation or premature removal of the frame prior to achieving bone union.
Therefore, it's important to understand and adhere to the principles that preserve the strength and longevity of the pin bone interface. And this, loosening is prevented with diligent adherence to proper pin insertion techniques, including selection of an appropriate pin, pre drilling and low speed insertion. So pin size selection is dictated by the diameter of the bone.
Now the stiffness of the pin increases exponentially with an increase in shaft amateur of the pin increasing the area moments of inertia. So the the bigger the pin, the stronger it will be. However, the hole in the bone is a limiting factor, and pinholes greater than 30% of the bone diameter will weaken the bone and predispose the cortical fractures through the pinhole.
Therefore, an ideal pin diameter should be around 20 to 25% of the bone diameter. Positive profile pins are generally recommended over negative profile pins, and this illustration shows the difference between smooth pins, negative profile pins and positive profile pins. Note again that the abrupt change in the size of the shaft to the threads in a negative profile pin can cause a stress rise or effect.
However, Ellis pins have been designed with a short length of negative thread designed to only engage one cortex. Therefore, the weak point of the pin will be located within the bone, therefore protecting it from bending forces. So if we compare pins B and C number, C is, so letter C is the Ellis pin, and you can see that the interface between the thread and smooth sections is located within the bone so it's protected, whereas in B you could see how that pin would break at the weak point.
Now, smooth pins rely solely on friction to hold them in place. And generally these are not commonly used, anymore. Now the fixation pin should be placed in the centre of the bone for maximum stability and pull out resistance from the bone.
Little technique is to maybe place two hyperemic needles, or to to palpate the bone. If you're doing closed application of fixation pins to try to ensure that you get central placement of your transfix pin and the pins should exit around about two millimetres from the trans cortex and pre drilling the hole, something that is strongly recommended prior to pin insertion. The diameter of the drill bit should be about one millimetre smaller than the pin core diameter, and pre drilling significantly decreases mechanical and thermal injury during pin insertion, and these can negatively affect the pin bone interface.
So if we compare pin insertion with and without pre drilling pre drilling has been shown to increase the pin end insertional torque, basically a measure of how tight the pin is by 25% and increase the pull out strength by 13.5%. And pre drilling has also been shown to reduce micros structural damage, which is a leading cause of excessive bone resorption and therefore premature pain loosening.
We generally want to, insert pins at a slow speed. This avoids kind of bone necrosis from generating high temperatures and thermal necrosis. And that can occur if you insert at a speed greater than 700 revolutions per minute.
Also want to be careful not to wobble, and therefore, because you want to insert pins slowly, some surgeons advocate inserting them by hand rather than using a power tool. However, you need to be careful if inserting by hand as you are rotating. The Jacobs Chuck, that you are not sort of wobbling, need to have a very good technique.
Or you can, use, a power tool, in which case you are less likely to get a wobble. But you need to be very careful that again. You're using a slow speed.
Now we are ready to insert pins into the bone. We do need to take, some considerations and some guidelines into which pins we insert first. So the linear ESF generally do the most proximal, most distal first, then attach the connecting bars.
Place the pins closest to the fracture site and then some pins in the central portion where the kind of free form acrylic you would place all the pins and then connect all the pins with the acrylic. So, here's an example. We just want to put the pins furthest away from the fracture in first, then attach our connecting bars.
This is generally be parallel with the long axis of the bone, and then we can align the limb. And then we can insert all of the remaining pins. And again remember to use the near far, far near principle.
The clamps connecting bars should be placed. You know, approximately, I would generally say about a centimetre away from the skin kind of mentioned, you know, five millimetres is a real minimum, but generally about a centimetre. So a little tip is sometimes, if you can maybe fit your finger in between.
I know if we're using a sort of a tie in technique, let's have a little run through how we achieve that. So, this is quite a good alternative for bone plating in small dogs and cats. It's generally less rigid than with a a bone plate.
But it can be sometimes easier to apply and does have some advantages. So we're generally going to insert the iron pin, and it is going to protrude from, perhaps, say, the the proximal region say the gluteal region on the pelvic limb of a you using in a femur. Pin can counteract a lot of the bending forces.
The iron pin diameter should be around about 75 to 80%. At the isthmus of the Mari Canal. The isthmus is the narrowest point.
However, if we are gonna be inserting ESF pins and they're gonna go bicortical, they need space to get past. Therefore, the optimal exact iron pin diameter is unknown. But often people would aim for a pin diameter that's about 30 to 50% of the isthmus, so that you have space to put your transfix pins of the ESF past the IM pin, so you're probably gonna need to use a smaller IM pin if you're doing a tie in ESF than you would use if you were just placing an IM pin into the fracture.
So, you generally have the patient in lateral recumbency do a little small stub incision, over the tranter region. Insert the pin against the medial aspect of the greater tranter, into the fossa and sometimes recommend starting at a 20 degree angle. And then once you have entered the medulla and just kind of redirect and align with the long axis of the bone, you then align the fracture by kind of moving the distal bone segment, into the correct position and then drive the pin across, and then you want to see to the tip of the pin in the distal metaphyseal area.
You do not want to penetrate into the joint below. With the proximal part there IM pin protruding, you connect it to the connecting bar of the ESF frame. So here's a nice little example.
Type one ESF frame secured to the F MA two ESF pins in each major segment and the IM pin tie in Now, the acrylic or sort of free form. Nice use of this would be for bilateral comminuted mid body mandibular fractures. Quite specific.
But actually can be quite common. Type of mandibular fracture. So you can insert your ES your ESF pins, again aiming for safe zones.
And then we can have this silicon tube placed over the K wires. The tube should only be penetrated on one side, to try to avoid some of the acrylic material, escaping out. And then we can say, for example, use dental acrylic and place into a catheter, syringe and, inject into the tube whilst it's in its liquid phase, and then it can be allowed to set and solidify.
So we've applied our ESF. There are some particular things that we need to be careful about with the patients following surgery that can differ from internal fixation. So some things that are, reported are the application of topical antiseptics or antibiotics to the pin tracks to try to reduce bacterial contamination.
However, it is questionable whether this is really required. The pin tracks and interior portion of the frame can be loosely packed with some, foam. So what I would often do is keep the surgical scrub brushes that you used to scrub your hands cut off the foam from the back, and then you could actually sort of sterilise those, And then you can actually place those in between the connecting bars and the skin, and that will limit some of the, soft tissue swelling under the skin in that area.
Therefore, reducing contact and pressure on the the clamps and bars. Also, you might get some increased drainage from the pins and that can then be absorbed by the sponge. Some surgeons will perhaps advocate wrapping a padded bandage around the ESF frame.
That would be to try to protect the patient and also protect the home environment from the the The sharper aspects of the frame. Alternatively, sort of pin covers can be placed over some of the sharp cut ends of the the pin for protection. It's also really important to, kind of educate the clients.
And, a little tip for you is if the clients are having to keep the patient in, a crate that is like a cage sort of construct. You run the risk of the ESF getting caught, within the holes in the metal cage. A little tip, perhaps, would be for them to be inspired by their in a sort of blue Peter personality and to get creative at home.
And if you get some cardboard and kind of line the inside of the crate, then that would act as a smooth internal surface and therefore the frame. If it does contact, the sides of the crate will just rub on the smooth cardboard rather than getting caught. And they could do that just high enough to mean that the ESF is covered.
But when the dog or cat is standing or sitting, they can still see out above the cardboard, see what's happening. And clients can also still see their pet as well. Now, the kind of timing of radiographic evaluations is determined by biological and mechanical factors of the patient, the fracture type.
But generally, evaluations are perhaps done around about sort of 3 to 4 weeks, 6 to 8 weeks and sort of 10 to 12 weeks generally, for most adult patients, the kind of 6 to 8 weeks is the more kind of golden time frame. That's when most people would tend to to take radiographs. And that's also then, when most frames might be removed.
But, for young patients that you're going to heal more rapidly, you might be able to do that sooner. For older patients, Or perhaps, if there's any factors that mean that there's going to be more delayed healing, then you might want to leave it longer. And some surgeons might elect to kind of monitor and see what's happening and take sequential radiographs throughout the healing process.
And the radiographic assessment can include monitoring for evidence of progression of fracture callous formation. Also allow us to check maintenance of fracture apposition alignment of the fracture. Also, pay close attention to the integrity of the pin bone interface to see if there's any development of lucency around around any of the pin tracks that could indicate that the stability of the frame is reducing.
I would also typically tend to recommend that you do see patients back fairly regularly, and that would be to actually check the frame. Check that none of the pieces are coming loose. I mainly often suggest trying to see patients back on a weekly basis.
When they come in, I'll check the skin pin interface. Give things a little clean if needed, and just give all of the clamps an extra little titan with a spanner. Just to make sure everything is nice and tight and secure.
And, again, you may want to have a a bandage initially to try and reduce some swelling to the limb. And you're going to want to take the patient out for little lead walks? Going to want to do that, whilst the frame is in place.
But then also for a period of time afterwards, because often the bone, you will still be getting stronger. And you also want to avoid fracture through any of the open the holes in the bone where the pins were. So if you are going to kind of remove the frame, take off all the clamps, take off the connecting bars.
If you have any full pins, I'd suggest kind of trimming them short and then cleaning and disinfecting the end, it's gonna have to go back through the patient. So once you, start to twist that pin, some of it's gonna have to go back through because they have to come out through one side. So cut the other end short and give it a really good clean.
Can we remove them with a Jacobs Chuck? And then the little pin holes in the skin can be left to heal by secondary intention. And you might want to give things again.
Another little cleaner with a topical antiseptic. Some people might put a bandage on if there is a lot of discharge coming from the pinholes, maybe just a little sort of Primapore dressing just to cover it just whilst the pinholes start to dry and seal over within the first few days. Now, an excessively rigid fixation could cause a delay to fracture healing.
And if you see little evidence of fracture, healing activity and kind of minimal to no colour formation, then, you might want to consider trying to destabilise the frame. Or if you have really a highly commuted fracture, you might want to make it very rigid and stiff to begin with. But then taper and stay and, kind of dage it throughout the healing process so you could do some partial disassembly of the construct to decrease the rig rigidity and destabilise it try to optimise bone healing.
So, as a general rule, timing for destabilisation is around about 4 to 6 weeks in kind of young dogs. Yeah, sort of six weeks adult dogs, maybe 8 to 10 weeks for for older dogs and cats. And when a surgeon is considering stage disassembly, there must be sufficient stability present at the fracture site.
Otherwise, downgrading the fixation may result in an unstable construct and the potential for further delayed union or even a catastrophic failure and stage destabilisation can proceed if there is radiographic evidence of fracture healing. And you think there is an adequate stability of the fracture site on palpation. So what you could actually do is if the patient is sedated, you could actually loosen, all of the the clamps and actually palpate and see, does the fracture feel like it is stable?
Just be careful, though, that you don't loosen everything and suddenly everything falls apart. So, by destabilising, we're sometimes trying to increase micro motion. And by micro motion, we typically mean motion that often we can't really perceive.
So if you can actually see things moving, that's not micro motion. That's things are loose now, in terms of deciding, what do you remove? I generally say if there is any loose pins, then you may as well remove those.
If you did have sort of an iron pin tied in or an iron pin in as well, take that out. Pins that are closest to the fracture site. They're often good ones to remove.
First of all, if you put any augmentation in, then take that out. So if you remember those diagonals for it as an example, articulations, plates. You could take those out.
You could perhaps actually replace some of the component materials. Probably not done very frequently, but you could actually change some of the materials. You could downsize some of the components, and you can get some dynamization clamps, but, they're not that readily available.
I wouldn't worry too much about those and and also what you could do is. If you had something like a type three frame, you could downstage it to a type two or even then, say downstage, a type two to a type one A. Now, with any procedures, there are, unfortunately complications that can occur, and it's really important that the surgeon is aware of those so that they can try to avoid them.
And complications associated with the ESF can often be categorised as sort of soft tissue injuries or mechanical complications. So soft tissue injuries are kind of common seli from percutaneous pin placements. You can get skin irritation from pins being placed near joints, as these are often areas of higher motion.
And this can cause the skin to pull during a range of motion, which can result in, drainage at the pin site, maybe tearing of the skin around the pin. So putting the pin through a range of motion once the frame is applied and, if required, create a larger skin snub incision to minimise that complication of the skin dragging on the pin. Soft tissue injuries can also include impaled soft tissues such as muscles or neurovascular structures, so make sure you know your anatomy that will minimise the chances of this pin tract infection, probably the most common significant complication associated with the application of ESF.
And these can often be categorised as minor or major. Now, minor pin tract infections are almost inevitable. Major pin tract infections, invariably result in premature pain loosening, so fixative complications include sort of pin loosening and and pin breakage.
Catastrophic mechanical failure. It's generally an uncommon occurrence and is, to be honest, a result of a technical failure of the surgeon and generally a disparity either between the stiffness and strength of a construct or the durability and expected longevity of a construct necessary for the healing of a given fracture. So, in summary, cross sectional anatomy is crucial.
If you are placing these pins via a kind of closed approach, you need to know your anatomy. You need to know the application principles, so the far near near far. For example, knowing the different frame configurations is important.
So you can then know what cases you can use. These in what cases are best to use these in, and also how to construct the ideal frame configuration for that particular patient and its particular fracture. I really like them for juvenile patients, so that's my shout out.
If you have a a very young dog, pop a frame on, it only needs to be on for a very short period of time, and then you can take it off again. And they can live the rest of their life without having any implants in place. A really nice thing is you can make post-operative adjustments either immediately following surgery if you're not completely happy or later on in the healing process.
To destabilise or potentially even increase the stability of a frame if you think you haven't made it strong enough, does allow for the complete removal of implants, which again can be an advantage in the fact that then you don't have to worry about them interfering with Perhaps, future surgery don't have to worry about implants interfering with things like MRI in the future and don't have to worry about those implants causing long term complications such as a long term surgical site infection. What is really important, though, with ESF is client education and client compliance. So you do need to spend a bit more time educating clients how to look after the frame, what to expect?
Because sometimes it can be a bit of a shock to them. You you bring their beloved dog or cat back out to them, and they see this frame on the outside. If they're a bit squeamish, they can yeah, perhaps get a bit, upset.
Or perhaps even, you know, faint if it's really not what they were expecting. So what I would recommend, Perhaps, if you are going to put on an ESA. I do spend a bit of time trying to describe the client what it is.
Maybe even show them some images beforehand of a previous example. So they have an idea of what to expect. So as we approach the end, just finish off with a few little, examples.
Here's an example of a type one, a linear ESF frame used in a juvenile patient. This was a very young boxer dog. We've got three proximal three millimetre Ellis pins and then two distal pins.
You'll notice then in the middle images that you can't see the connecting bar. That's because it's a carbon fibre, so it's radiolucent, so it means on that media lateral radiograph. We can still see the the bone and the fracture site, which is very useful.
And then the image on the right hand side. You can see that the ESF has been removed. We have nicely healed complete healing of the fracture.
And you'll then notice the open holes in the bone. We then need those to go and fill in, so we'll still want to keep the patient rested for a little while afterwards. Now, for example, again, young patient, this was a really kind of minimally displaced fracture.
And, you know, we we could have got lucky. We maybe could have just rested this patient, and it might have gone and healed, but we just didn't want them to disrupt it. Very young dog.
Very lively, quick, simple little frame. You can actually even pop these on sometimes, you know, in the prep area, not even in in surgery. Still paying particularly close attention to obviously, being as aseptic as possible.
But this frame application super rapid means that the patient doesn't need to be under anaesthetic for very long. Get them back awake quickly, safely recovered third example, a little bit different than in this this application. So here we can see this big, large, open wound.
Gillo Anderson, Grade three. And the fracture is actually, you might miss it if you don't pay close attention. It's actually through the fs of the distal tibia.
So you can see there is that slight lateral cordial displacement. And what I've done in this case is I've actually placed the frame across the joint because that distal phys segment is so small. Be extremely challenging to get a pin just through the epiphyseal portion and not impinge the phys and not impinge the articular surface.
So I've actually placed this across the joint. Now, again, this is a young patient who are expecting this fracture to heal quite quickly so I can remove the frame quite quickly, not have the joint immobilised for too long. And then the other nice advantage of this frame, is that it means that there are going to be no permanent internal implants that very likely get contaminated and subsequently infected.
And by having a frame in place rather than something like AAA bandage or a cast, it means we can still access and tend to the soft tissue wounds. And I've been able to kind of close one area of skin, over the bone, reattaching it to some of the tendons underneath. And then we can allow this to heal with secondary intention, healing and to granulate, another example of where I personally tend to use ESF, perhaps, is for metacarpal fractures or metatarsal fractures and can apply this particular frame.
So we be inspired by Wolverine and have these intra medullary pins through the metacarpal bones. Realigning the fractures, we then have a pin going transversing through the radiocarpal bone, and then we can bend all of the pins around and secure them within some putty. And this is sometimes called a spider frame.
So a a secured pin. Intra Medill, epoxy resin frame. And it also looks a bit like a spider as well.
And here's a little tip we mentioned about using epidemic needles to outline areas of bone. So I've put these pins in to outline the most proximal and distal ends of the radiocarpal bone to allow me to place that transverse pin through the bone without using anything like fluoroscopy to to see it. So a little tip for you to finish.
I recommend keeping a case log. Now, some of you watching this might be doing perhaps qualifications that require you to keep a case log, maybe a certificate or a diploma. But even if you're not keeping a close case log can be really useful because it can allow you to refer back, other cases you've done in the past and you can see what worked and what didn't work.
So if you have a case come in, you could look back through your case log to perhaps find a similar fracture or a similar patient of size and weight. Perhaps pull up the radiographs and use that as an example to copy so you could copy the frame that was used in that case and make some comments on maybe what worked? Well, what didn't work?
Well, what you learned what you would do differently in future. So a great way to reflect on cases. And also you can perhaps sit down, have a cup of coffee or a beer with a colleague, and run through some of your cases and reflect as well and get some of their opinions.
So little tip there for you. So I hope you have enjoyed this Webinar. If you do have any questions, feel free to reach out and get in touch.
I'll be more than happy to discuss, anything that I've gone through. Cover any points in more detail, or just have a good chat about orthopaedics. So thank you very much.
Take care of yourselves. And if you can, someone else too.