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Joint Medication: Part 3 - Commonly used joint medications



OK - Just putting this out there at the beginning of this post, this is a long read. I wanted to provide an all encompassing guide to the routinely available options for joint injections. Injections into joints are routinely called intra-articular injections. Although your choice might be driven by what is financially viable, insurance policy or availability of certain medications and services in your area, knowledge is power.


Scientific data is constantly evolving. Things change, and as a result, when new, additional or contradictory information is available, I will try to update the blog. Equally, if someone knows of a scientific study which would add to the blog, please send it my way.


A lot of the studies involved in this blog post are based on injection into a single type of joint. The medication may work better, or worse, in another joint. None of the studies involved provided the owners with regimented rehabilitation plans based on which area was being injected. This MUST have a huge influence on the success of the medication. This is why I call joint injections LIQUID PLASTERS. I truly believe that hard work before and after joint injections significantly improves the outcome.


This also influences the most frequently asked question associated with joint injections: ‘How long will the medication last for? Will I have to repeat it again?’

Nobody can ever give you an accurate time frame. It depends on the severity of the lesions, and again, the work which you are prepared to put in. Working with someone that truly understands the biomechanics of your horse’s joints can really help to get you on the right track.


Every case is specific, and my preferred treatment would be based on a multitude of factors discussed during consultations. This guide in mainly to help you understand how the treatment is supposed to help your horse.


 

The risk associated with every type of joint injection - flare and sepsis (joint infection)


Unfortunately, an occasional risk of joint injections involves reactions to the procedure and medication injected. This may be a:

  • Flare up - non infectious process and generally resolves with pain relief, more commonly after injection of hyaluronic acid (1).

  • Sepsis - infectious disease due to introduction of bacteria or fungi into the joint (1). May require surgery to remove the infection.

Can risk of sepsis be decreased?

A sterile scrub should be performed before any joint is injected. A 2021 study (2) showed that the frequency of sepsis is about 0.04%, with no difference between joint injections performed in the field or in hospital settings, or when antibiotics were combined with the medication.

The most commonly used antibiotic is amikacin, however, it has recently been found to cause joint damage as well (3).


 

Steroids

The body naturally produces corticosteroids. Corticosteroids are strong anti-inflammatories, decreasing inflammation both in the short and long term. Although the short term change is pretty obvious, long term change is achieved through gene regulation (4). This basically means that the increased load of steroids affects the body to subsequently produce more anti-inflammatories. Therefore, decreased inflammation is due to the steroids injected and their effect on the rest of the body.


The two main steroids used are called Triamcinolone (TA) and Methylprednisolone Acetate (MPA).

  • TA is detected within the joint for just 10 days after administration, and is almost undetectable in the blood after 48 hours (4).

  • MPA gets broken down to methylprednisolone (MP) within the joint, and remains detectable within the joint for 5-39 days. Although MPA is not detected in the blood, MP can be detected for 1-30 days (4).


What does this mean?

The FEI outlines the importance of anti-doping to promote a clean and fair sport. Because of how long TA and MP last in the blood for, the withdrawal period (time between injection and when a horse can compete) is 7 days for TA and 28 days for MPA.

A full list of detection times can be found here: https://inside.fei.org/system/files/FEI%20Detection%20Times%202018_0.pdf


Do they have any negative effects?

  1. In the joint, MPA has negative effects on articular cartilage (5). This does not appear to be the case with TA (6).

  2. Laminitis - scientific evidence shows that appropriate TA dosage administered into a joint does not increase the risk of laminitis in healthy horses (7). I have not been able to find a paper regarding MPA or use of intra-articular steroids in horses with hormonal diseases, such as Cushing’s or Equine Metabolic Syndrome (EMS).


Any other positive effects?

Intra-articular administration of TA (8) and MPA (9) also improve lung function in horses with severe asthma, and this lasts longer with TA. No vet would ever advocate using intra-articular steroids to treat asthma.


Which steroids are generally injected into which joints?

Due to the degenerative side effects of MPA, it is usually injected into smaller joints, like the tarsometatarsal joint, to promote ankylosis (fusion), therefore decreasing pain.


After the 2nd blog about joint communication, do we need to treat every joint compartment?

Every vet preference is based on their own personal experience and success rates. However, studies show that steroids always transfer between the tarsometatarsal and distal intertarsal joints (10) and between the coffin joint and navicular bursa (11).


 

Lack of joint lubrication plays a significant role in the pathogenesis of osteoarthritis (OA).


Two important molecules produced by synovial lining cells (the inside of the joint) are called hyaluronic acid and lubricin. They help to protect and maintain the integrity of the articular cartilage surfaces in synovial joints by reducing friction. As part of the OA complex, the synovial fluid (fluid within the joint) does not remain as visco-elastic, meaning that it loses its ability to properly provide shock absorption.

Apart from injection of the substances which are generally naturally created by the joint, a synthetic alternative is also available.


Hyaluronic Acid (HA)

HA is present in the skin, connective tissue, eyes and synovial fluid, and its main responsibility is in pulling water into that space. It is a naturally occurring unbranched non-sulfated glycosaminoglycan (semi-important to remember for the 4th blog in the series).

HA functions in a number of ways (12), mainly in reducing friction, decreasing pain, cartilage damage and inflammatory markers. When injected, it is said to improve visco-elasticity, decrease inflammation and increase natural production of hyaluron.


But does this hold up scientifically?

The issue with this naturally occurring product is just that. Because it develops naturally, it is metabolized and broken down in a natural way.

Subsequently, when HA is administered intra-articularly (IA), it dissipates out of the joint within 14–18 hours before being rapidly eliminated from the body (13). This means that it has a very limited window to provide benefit.

A number of studies exist which show the effect on inflammation in joints when HA is used alone or in combination with TA (14) or MPA (15).


The big question: Does HA used intra-articularly in combination with steroids actually improve lameness?

Unfortunately, not many studies exist to show this. The study I found looked at only 80 horses which blocked to one particular joint (16). The horses then either received TA or a combination of TA and HA into that joint. They were reassessed after 3 weeks and 87.8% of horses which received only TA had improved by 2 lameness grades (out of 5), compared to 64.1% in the combination group. By 3 months, only half of the horses in the study, regardless of which group they were in, had returned to the same level of work.


What do these results actually mean though?

So many variables exist within the study - the age, breed, discipline, rehab routine, paraprofessional help after injection. However, the relative lack of initial lameness change and lack of improvement in the combination group compared to the TA group at the 3 month point shows that intra-articular HA may not be the best use of resources. Further studies are definitely needed to show that it should be a mainstay in joint treatment, however, a recent systemic review also highlighted its lack of long term effectiveness (17).


Can HA be used in another way?

Keep an eye out for the 4th part of this blog series to find out.


Lubricin

Lubricin also helps to maintain visco-elasticity, however, there are currently an insignificant number of studies into its intra-articular use and subsequent long term benefit.



Polyacrylamide - Arthramid

Arthramid is a synthetic polyacrylamide hydrogel (PAAG), consisting of 97.5% sterile water and 2.5% PAAG. It has a similar structure to HA, however, as it is non-degradable, has a significantly longer effect.


A 2021 study (18) of TB horses with middle carpal joint lameness showed that horses which received PAAG had an 83% chance of being lameness free at 6 weeks, as opposed to 27% that received TA and 40% that received HA. This is a great case study as all the horses were in flat race training and the lameness was localized to the same joint in every horse. I know what the next question is going to be - How is the HA group better than the TA group? - I will cover this in the 4th part of this blog series.




So how does it work? (19)

The PAAG incorporates into the joint lining (synovial membrane), reducing the exposure of the cells which produce joint fluid (synoviocytes) to the inflammatory markers within a diseased joint. Gradually, blood vessels start to develop around the attached PAAG, creating a supportive network. By day 14, synovial cells start to infiltrate this network, with a noticeable rejuvenation of the synovial membrane within 30 days. This has been shown to last for 2 years (20).


The study also showed that the gel was highly unlikely to cause any long term side effects, despite being present for an extended period of time.



Due to this mechanism of action, case selection is essential. PAAG should only be used in cases with a significantly positive intra-articular block. Owners should not expect an immediate improvement, rather one which begins at 4-6 weeks post injection. Some horses (about 15%) may need a second dose.


Due to its properties, I would only expect it to access different joint compartments if there was physical communication. As discussed in the second part of this blog series, it is very rare for owners to know about this communication. This could mean that the gel remains concentrated, and therefore, you would think, more effective in one horse, but more diluted, and therefore, possibly less effective in other horses. These horses may need the second dose. It is also why it may be less effective in larger joints, like the stifle, unless a larger volume was administered. Further studies are needed to help to determine whether this holds true.


 

Biological products


In a recent survey of over 400 vets, they found that the best responding joints to biological therapy were the stifle, followed by the fetlock and coffin joint (21). But what are biological products and how do they work?


A biological product implies that it is a product derived from animal origin, namely from a horse. This can fall into two categories:

  • Autogenous - product comes directly from the horse being treated.

  • Allogeneic - product is produced from a pool of horses and commercially sold.


The biological products are obtained from a few categories:

  • Blood

  • Autogenous