Welcome to this edition of the webinar Vet. We're talking about approaching the suspected septic joint, and how to get a sample and how to make the most of it. I'm Doctor Matt Sinovich.
I work at the Lupok Eine Hospital, and, we'll get straight into it. Over here are our learning outcomes, as listed. And, while this is a very large topic, I will try and address many of the salient and important bits here, some in more depth than others.
There also will be some, bits of reading, etc. Recommended through, so please feel free to pause and take those down as you need. All right.
So approaching a synovial structure, also known as getting the needle in the joint. A couple of things we'll look at first, is there a wound? Very often these horses, are presented because they have a wound, and also knowing, is it safe to approach the joint through that wound?
Is there cellulitis over the joint? Are you likely to, introduce any infection into the joint by tapping it, and we'll see if there is another way to A, determine if it's septic, and B, if there's another way to get into said joint. So, some general points, .
Horses are often moving at speed. They also often are kept in groups, so they are prone to being kicked. And on top of it, once they're wounded, they are prey species, so they're often prone to panic.
The limbs particularly are poorly covered, distal to the hock and the carpus, and there are many vital structures, joints, tendons, sheaths, and they're very poorly protected, as we said. So it's very important to know your anatomy and you'll hear me harping on about that many times today. Whenever you're faced with an injured horse, the most important thing to remember is don't panic.
You've been called in to save the day, and you get to take charge of the situation. You also get to play the hero, and your arrival at the yard should restore some calm, in what is very often a very frightful situation. So, keep calm, make sure everyone knows what they're doing, don't let the horse hurt anyone in the first instance, particularly if it is panicking, where you can move to a safe area and then assess the injury and make a plan.
So you've now gained control of the situation. You can get to work on the horse, if sedating, sedate the horse if it's fractious and if it's necessary. Try to assess the degree of lameness first though, as this may change later and often you need the baseline to compare.
You can begin to get a history covering the injury occurred whilst you're assessing the horse. A little multitask and will speed this up. Find out if it was witnessed by anyone, how sore the horse was initially, if it was a kick, was the other horse shod, and secured in the, in the safe exam area.
Of course, it's important to assess the obvious injury, but vital to evaluate the horse completely, particularly to identify any concurrent injury or signs of cardiovascular collapse, if there's been any significant haemorrhage. So a general assessment should be made for any signs of concurrent or pre-existing disease or debilitation prior to kind of getting into the, the bits. This is a more detailed layout of the approach to wounds and we we'll go through kind of step by step.
There's a very useful book there, if you're interested in wound management in the field as well, very good reading and very practical. So, the patient restraint, some people have twitches and under some circumstances with certain horses, they provide invaluable, restraint. However, do be aware that not all horses tolerate twitches, and some horses can react quite explosively.
Be sure that you are wearing the correct PPE so if you're handling horses or anywhere that may be dangerous, do look after your heads and your hands. You'll see our handler there has gloves as well as head protection. Similarly, don't get lulled into a false sense of security when horses are, very heavily sedated.
Some of them will often strike out, or kick out quite violently and then fall straight back asleep. So do be aware all the time and don't just rely on. Station.
Local or regional anaesthesia will provide a much safer patient to work on, but never block a horse where you have any suspicion of a fracture, because then they will lose all self-preservation and that potentially non-displaced fracture may, develop a severe complication. Be aware of the potential for local hyperestesia when placing blocks, as the horse may be more resentful, particularly if there's a wound in that area, and, pain receptors may have been up-regulated. Hevicaine is generally a non-irritant, local anaesthetic and has a rapid onset of action, so that would generally be what we would recommend.
Control haemorrhage where it is, pouring out and that is, always the first part of, first aid once you have the patient restrained and sedated, check the wound, assess, and then, if there is uncontrollable haemorrhage, a tight bandage or a tourniquet, is very, very useful. And then where possible, if needed, you can also provide, surgical hemostasis, and that can be through things like a hemostat, a suture, and then you can get onto your nerve blocks thereafter. So your initial wound assessment, where needed, apply a water-soluble jelly such as KY to the actual wound surface to protect it prior to doing any clipping or removing any dirt or hair.
The jelly can then be lavaged away. Clipping is probably preferable to shaving as it causes less damage to the hair follicles and reduces the risk of local infection. Be generous with your clip, include the.
The distal limb if needed, or the entire area around the wound. It'll be much easier for you to then provide a thorough inspection and you could also unearth concurrent injuries. And then if you do need to perform any centesis of synovial structures, a large regional block is then more convenient and you've got a clean environment through which you can work.
So, harping on again about the subject, from your dim and distant past, anatomy, but it is important in your initial appraisal of the wound to compile a mental list of all the structures which are potentially involved in this wound. And then from there you can work out what what structures you need to sample and how you can get to them. Also important to keep in mind that it's not just joints that can be damaged and that tendons and ligaments as well as bony structures live underneath where you're lurking.
So, what is the difference between sepsis and contamination? Bacterial contamination of a synovial structure often leads to sepsis, which is life-threatening to all horses. Synovial sepsis occurs when bacteria enter a synovial cavity either via direct penetration, hematogenous spread, or iatrogenic contamination.
And that's one of the things we want to try to prevent, in sampling joints is iatrogenic contamination. And that is how you get your, infections in just following routine joint injections. Positive culture of a synovial fluid and synovial membrane samples is considered the gold standard technique to diagnose septic synovitis.
However, bacterial culture usually takes a minimum of 24 to 48 hours and tend to have a very low sensitivity. It's been reported in the literature that only about a third of septic synovial fluid samples have positive bacterial culture. And we'll see later through the talk that this can be improved.
When your nucleated cell count and protein are high, septic arthritis is relatively easy to diagnose, whereas early infection or contamination is often very difficult to determine. So through this talk, I'll try to give you the best current advice to determine if the synovial structure you're looking at is contaminated, i.e.
Open to the outside world, and to get as much synovial fluid as you can and then make a useful lab submission and diagnostic decisions following on from that. So, essentially for the purpose of this, we're not going to try to distinguish between contamination and sepsis, because essentially it's really academic. When you have a horse standing in front of you, a goal-orientated approach is far more useful.
So what are you trying to achieve? As we said, if there is a wound, you're trying to determine if it communicates with the synovial structure that you're worried about, that you've determined through your examination, and if there is no wound, is the synovial structure septic. So through this talks, .
We'll get to how to get that sample and what you will do with it at that point. This graphic here is an attempt to simplify a very complex thought process. So what we will do is focus on this section here.
Essentially, very briefly, we've gone through, is there a wound? Is it over a joint, and can you get a normal approach to it? And then, once you've got the synoviocentesis, what are we going to do with the sample that we get?
So, the old adage goes that there are many ways to skin a cat, and the standard approaches to synovial structures are very well reported and taught as a standard. But looking at Surgical texts, oh sorry, looking at surgical texts, you will often find many different approaches to synovial structures, and these are well established and described, but not always well known in first opinion practise. So these are some of the better descriptions of approaches to the caudal and lateral pouches of joints.
Where often we will do surgery to try to get to them. So, in the next couple of slides, we'll just go through a couple of those approaches very, very briefly, but what I would say is if you do have interest in this, is to turn to these texts, and see if you can, broaden your knowledge in those. So the calf and joints, we all know that there's a very standard dorsal approach and that can be kind of horizontal to the ground or sort of vertical or either side of the extensor tendon, 1 to 2 centimetres off the coronary band and off midline.
But as you can see there, there also is a lateral approach where you. Palpate the proximal edge of the collateral cartilage halfway between the dorsal and palma or plantar aspect of P2, and then you angle medial and downwards towards the joint. And that's particularly useful where horses have struck forward, and there's a suspected wound over the coronary band where you would normally place your block.
Fetlock joint, traditionally you would go in either dorsally or, plantally or palmally. The important thing I'm going to say here is that remember that a horse's leg essentially has two sides, and that sounds very obvious, but you can approach this joint from medial and lateral, as well as, dorsal and palma or plantar. So don't be afraid to go under the horse once it's sedated and pop in a dorsal block if there is a a a wound on the lateral aspect, and that's just something to just get into your head that there are different options and as you're going through your evaluation, think in the back of your head, how am I going to approach this joint.
Your carpus, everyone, as I said, is taught the traditional dorsal approaches, but you can also do a lateral approach, and laterally you can palpate the notch created by the ulnais lateralis tendon and the lateral digital extensor tendon, just in front of the accessory carpal bone and insert the needle into the small depression immediately distal to this notch, and essentially you can isolate the radiocarpal and intercarpal joint through those two descriptions as you can see there as well. DIT and TMT, so the TMT is relatively commonly injected, and most people know how to do this. DIT, can be injected on the medial or the lateral aspect.
Generally it is done on the medial aspect. The needle inserted into the T-shaped gap formed by the junction of the fuse 1st and 2nd tarsal bones, just above the 3rd tarsal bone and central tarsal bone. T-shaped gap is immediately distal to the C and tendon, so that's something you can often palpate.
The TMT, as we said, is a relatively commonly injected, Structure and what I would say is that remember these joints essentially can be injected medially and laterally, and we'll get onto how to approach these in a slightly different way using some specialised imaging later. So, your tendon sheath or faecal centesis, and there are 4 standard approaches to your superficial digital flexor tendon sheath. As you can see on the left there, proximal into the pouch, your palma axial sesamoid on the 2nd, and then the base of the proximal sesamoid on the 3rd, and then distal kind of in the distal palma pastor.
What I would say is that most of the wounds that we see in our hospital tend to be in and around the, Palma pastan, so we tend to use that palma axial sesamoidian approach much more often, traditionally the tenoscopy technique goes through the base of the sesamoid portal, so we try and stay away from that one. And generally if you do have a wound, the proximal approach there is often not rewarding cos most of the fluid has disappeared down. Now if you're talking about sheaths, what you may be able to do is to use a vet wrap almost as an S marks.
So start at the hoof, once you've started to do some prep, wind the bandage up the way, and that may push some of the fluid from the distal part up further into that more proximal approach or around your prima axial sesamoid approach, and that often gives you a a better yield. So this was taken from a very good paper about evaluating 4 different techniques for the injection of the proximal interphalangeal joint. And I thought this was a, a very useful approach, particularly if you have a regional block in the horse for assessment, you can do a dorsal midline approach like that, or once flexed, you can do sort of a lamedial approach.
The, plantar or palmer approaches are very well described, and I'm not going to repeat those here. For the stifle, again, the normal approaches are very well described, but there is a technique out of Colorado for a single needle redirection, craniolateral site, in which you can get into all three compartments. The book which we spoke about earlier, the Schumacher, guide to injecting, Synovial Structures has a new edition out and this is very well described in that, so I won't get into it too much, but just to put it on your radar that there is a different approach and you can often get into all three compartments from one single needle stick.
Then there are some weird structures that will very occur very briefly, so don't forget that in and around the tarsus, there is the tarsal sheath, and over here you can see the anatomy of that sheath. Here, you can see how we can enter that sheath. So, generally labelled there 1 to 5 are the approaches.
1 is the most common, then 234, and 5. And this is how we would approach that sheath arthroscopically. But all of these can sometimes be palpated, and when in doubt, as I said, you can use advanced imaging for these sort of complex things, ultrasound being my favourite.
Your gastricnemius and intendinous bursa. As you can see there, distension of the calcaneon bursa is the, or the principal is tendinous bursa, dorsal to the super digital flexor tendon, and the deep bursa dorsal to the gastrocnemius tendon on the second arrow. So those can be approached through a number of ways, but again, referring to surgical tests, one of the most reliable ways of getting in and getting fluid is to distract the SDFT and then direct your needle proximately and actively beneath the SDFT fibrocartilage at the cap where it joins onto the calcaneus.
Then your carpal sheath, you would approach between the tendon of the digital extensor and . Your flexor tendons at the back and that forms a nice little gap above the accessory carpal bone. You don't want to go too distal, so you want to kind of feel the distal radial physis and approach it through the port there.
Again, when in doubt, use synoviocentesis under controlled circumstances. So as you can see there, there are some needles in. A TMT and DIT.
This was a horse under anaesthetic that had a wound laterally, so we couldn't approach those on the lateral aspect. And basically, for flushing, we had to put some needles in through the medial aspect there under radiographic control. I'm a very big proponent of using ultrasound guided injection, especially if you're not confident with alternate approaches.
There are many good studies looking at clinician confidence with synoviocentesis with a high confidence but poor actual accuracy. And most of us should have access to at least one of these imaging modalities, so either X-ray or, ultrasound, and they're often underutilised when you're trying to get into a joint. So make a habit of getting used to scanning things and making the most of the kit that you have, because A, it'll improve your scanning skills, but B, it'll also improve your clinical outcomes because you'll get accurate results and get good samples.
So we've kind of gone through, the general considerations, make sure it's sedated, restrained, safety, and again, traditionally, preparation of the site is done through clipping the hair prior to the needle insertion. This may not be necessary if the area's properly glove, properly scrubbed. Make sure you wear surgical gloves, use a new unopened bottle of drug, Amicain if you're gonna put that in, and then we've kind of gone through the, the restraint already.
Fluid for cytological examination is generally collected in EDTA tubes, but into a plain, serum tube will also work. And then fluid for bacterial culture can be collected in a capped air-free syringe for immediate delivery to the lab, or if there's a delay, what our lab recommends is that you collect into plain tubes or into preferably a blood culture bottle, as this may increase your yield and you'll see that again later in the talk. OK.
At least 2 sterile disposable needles. 20 gauge needles will be appropriate. Most commonly, there's a trend among practitioners to use smaller gauge needles for centesis of some joints.
This is a personal preference, and while some smaller gauge needles may facilitate synovial centesis in some horses. It may cause less synovial haemorrhage. These needles are also more likely to break.
So, weigh up how confident you are getting into the structure and how much fluid you think there is there and use the largest needle that you feel comfortable with. Aspiration under pressure may cause the synovium to collapse over the end of the needle, or depending on the joint and the position, synovial villi may block the end of the needle, and this is why it's usually easier to collect fluid by a free flow method. As we've said before, we recommend using the small EDTA tube first, followed by the red top tube, and I'll comment more on that later as we go through.
When free flow does not occur, sometimes putting a small 25 gauge needle attached to the syringe, and then aspirating the sample from the hub, is very, very useful, as you see in the picture there. The air can then be removed from the syringe and the process repeated until you have enough sample obtained. If only a drop is collected, then this can be sprayed through the fine needle onto a glass slide and air dried, and that can be submitted to the lab for cytology.
This is a very interesting technique and a good reference by Schumacher, where a, Blood collection needle is inserted into the joint, and then the vacuum of the tube is used to allow to apply the the suction on and may be quite useful, particularly where you don't have two hands to get, hold the hub and place the needle, particularly in joints like the stifle or if you're working under the horse like that. So once you've got the needle in, it's very easy to get excited that you've achieved your goal, pull the need out with a triumphant flourish, as this talk is about maximising the benefits of synovia centesis, and that you've now that you've struggled to get that needle in the right place, let's see if there's more we can get out of this. So, culture is considered the gold standard for detecting sepsis, however, it's far from perfect for synovial fluid.
Culturing from a swab of fluid produces a positive result in only about 23.3% to a third of the time, depending on the results you read, of infected synovial cases. This can be increased up to 1.7 times in some papers or even up to a reported 80% when samples are placed in paediatric blood culture bottle on collection.
In the real world, this level of culture is not often obtained, but in order to maximise your chances, the use of a blood culture system has to be advised. If you do only obtain a small sample, you can distend the joint with sterile water for injection and then aspirate the diluted sample, and place that in a blood culture bottle and submit that to the lab for culture as well, so that is often a very useful test and, The other thing is by increasing the fluid in the joint, you can create a pressure test. So this procedure is a 2 in 1 because while you're getting the potential culture sample, you can also use the sterile water in a large volume to act as a pressure test, and that may allow you to determine whether you have communication of a puncture or a wound.
Do be mindful though not to overdistend a joint as this can make a sound horse painful and cause them to fidget even when they're sedated, less so if they are regionally blocked, but is something to keep in mind. Once distended and your test is complete, again, leave the needle in to drain some of the fluid, or if you're collecting some of the distention fluid as a culture sample. Now, I would not advocate the use of antimicrobials in routine synoviocentesis, particularly if you're prepping and using a good technique, and it is not something that we as a hospital do routinely, but when there is a strong suspicion of sepsis or contamination and you have a needle in a synovial structure, this is a good place to maximise the use of your needle placement and to start your therapy.
And very often amicasin is the first line of antimicrobials that are injected into synovial structures. OK, so now it is safe to remove the needle and obviously dispose of it responsibly. So we're gonna get back onto the concept of is bigger better.
So your sample size. In an ideal world, we'd get enough sample, a large enough sample that it can be divided up into an EDT tube, a normal red top, and stick some in a blood culture bottle. In the real world, this seldom happens.
So I've done most of the legwork. And asked my local friendly laboratory about their preference for samples and how they would like these presented in order to get the most out of your submissions so you get a useful result once you've sent these things to the lab. And that means we can extend our thought process a little further from section one into the laboratory analysis over there.
And let's focus on that here. So basically you can see we've divided that into a small sample or a large sample and what will be the most useful things for us to get. Use a small tube EDTA for a small sample.
In larger tubes, the concentration of EDTA has been shown to elevate protein, particularly on a refractometer, and skew the results. So try, that's why we advocate using the small tube first. If you only get one drop of fluid out, so if you've, for example, like we said earlier, aspirated something out of the hub, make a smear, air dry that and submit it to the lab.
They'll be able to do a relatively accurate discount off that. If you get 2 drops, make a smear and get a protein off a refractometer. If you have 3 drops, you can do the 1st 2 and also add a stable side SAA analyzer to the mix, which is gonna be very helpful.
And if you have more than that, then submit this in a small EDTA tube for a nucleated cell count, which is essentially what you're looking for. If you've collected a sample and put it in a red tube, have a look at it. And if it clots, then you know that synovial fluid is not normal, and that in itself may give you the answer.
Normal synovial fluid will not clot, so if it is clotting, it's a strong indication that it has been contaminated. Synovial fluid is generally clear, pale yellow and viscous, you know, the classic straw colour or Sauvignon Blanc that everyone talks about, and it doesn't clot as we've said, but it may exhibit thixotropism, so that on standing, it becomes gelatinous, returning to normal with a gentle agitation. So it is yo your fluid is essentially a distillate of plasma and is variably reported as having a total protein of about 25% of peripheral blood concentration, so about less than 15 to 25 grammes per litre, depending on the reference.
Blood contamination can increase that. However, blood must make up more than 50% of a normal synovial fluid sample before the TP exceeds 25 grammes per litre. So don't worry if you do have a very little bit of blood contamination in your sample.
So a number of studies have looked at acute phase proteins, or SAA, both from synovial fluid as well as systemically in blood, and this may assist the, decision making process. What I would say is be very careful of using SAA on stable side devices, particularly if that device has not been calibrated recently, it can over or underread and give you a false positive. And the other thing to remember is that if there is a wound and or a large trauma associated with your suspected septic joint, the SAA is going to be systemically increased due to the trauma and the wound.
So do bear that in mind and don't use SAA as a standalone. It is there as an adjunct to the rest of your analysis. Normal synovial fluid contains mononuclear cells with neutrophils making up less than 10% of the nucleated cell count.
Inflammation increases the neutrophil percentage and sepsis often shows concentrations of more than 90%. So that's kind of the cut-off that we're looking for for neutrophils. Blood contamination increases cell count, but even so, the nucleated cell count over 20 times 109 per litre with a TP over 40 grammes suggests a septic process.
In septic synovitis, neutrophils may be non-degenerate in morphology and bacteria are often not seen. Lavage increases total protein, nucleated cell counts, and neutrophil percentage to levels that mimic early infection. So 24 hours after through and through lavage of healthy joints, your total protein may rise to 39 grammes per litre and your nucleated cell count to 20 times 109 grammes per litre, and your neutrophil percentage up to sort of 60 or 70%.
These parameters do return towards baseline over the ensuing days, but may still be mildly elevated at day 5. In those horses, serum and synovial fluid, serum amyloid A are not expected to increase above the baseline, and that was worked by Sanchez et al. Installation of antibiotics and glucocorticoids and hyaluronic acid into a joint may all temporarily increase nucleated cell count to to levels consistent with infection, so do be aware if you are sampling joints, particularly post medication, that you suspect to have a flare, that sometimes the medication may actually be elevating the levels, and giving you a false idea of where you're actually at with your synovial fluid values.
Generally, the rise in cells usually lasts less than 3 days for that though, except where pentazan and glucosamine may increase that further with protein concentrations up to 79 grammes per litre and cell counts up to 50 x 109, reported up to 3 to 4 days after administration. These parameters then do decrease, but they can remain elevated even up to a week post. So remember, post sampling is often a very .
What process and if you have any doubt, please refer to your local lab or a local friendly specialist to give you some advice on what the values may be. And don't forget to look at the horse clinically because that ultimately is where most of your decision making is going to be made. So in conclusion, plan your approach, maximise the use of the needles, particularly while it is in the synovial structure, and that can be through the use of pressure tests.
One thing that we didn't put there, but I've put here is when the needle is in the joint, you may put some contrast in, just to check. If it communicates with the wound and that gets back to our ultrasound and radiographs and make use of your advanced imaging. While you have a needle in the joint, if you have a strong suspicion of it being septic or contaminated, do put some medication in.
Choose the correct tubes, particularly for your sample size, and use your sample size to dictate what test you, you have. And when in doubt and you only have a small sample, just submit a slide, and often that will give you enough of a result in conjunction with your clinical exam. Thank you very much for your time.
I hope that was er useful and informative, and we'll see you soon.
