In the first half of 2014, FDA approved a new equine drug – OSPHOS distributed by Dechra, Ltd. – intended to control the clinical signs of navicular syndrome, a common cause of forelimb lameness in horses.
I attended another great Lunch & Learn about the use of Osphos during week 10. We have used Osphos a couple of times, so I knew the general idea pertaining to the use of the drug, but I was really pleased to get a more in depth look at it and what it does. In addition to that, I learned what goes on in the bone naturally that creates the issues that Osphos can help to address. The presentation was given by Victoria Maxwell, DVM MBA. She works with Dechra Veterinary Products, the makers of Osphos. I thought she had the ideal perspective from which to educate us. She has worked with many performance and lameness issues throughout her career. She was a great speaker, in general. She started by thanking the horse because she said that they have allowed her a better than average life. I loved that. So true. Imagine your life without horses…no thanks!!
After introducing herself she moved on to sharing a video of a lame horse to assist in educating us about different ways to identify lameness and the origin. Part of this was to express that early detection will be much more treatable and a lot less expensive.
Video assessment: Ways to visually pinpoint lameness.
The classic head bob. As the saying goes, down on the sound, meaning the horses head drops on the sound step and raises on the lame step. This may or may not be accurate depending on how obvious the lameness.
Next she talked about the 3 phases of the horses’ stride. A)Posterior B)Stance, and C)Anterior. When looking at lameness, you want to observe how far forward the anterior phase goes. The lame limb will not have good reach.
Another indicator to watch is the withers height. She feels this is more accurate than watching the head bob. On the lame limb, the withers will be higher and rigid on that step. It drops and rotates as intended when they take a step on the sound limb.
Her final suggestion and one she thinks is most effective is fetlock drop. In a lame limb, the horse will stab the ground and the fetlock will stay locked. On the sound limbs, the fetlock will drop.
You should be able to see most of this at the walk. She also suggested taking a video and watching it back in slow motion.
You might be asking – what does Osphos have to do with this? What is it? Osphos is a drug that belongs to the class of drugs called Bisphosphonates. These drugs have been used in humans for the past 30 years for osteoporosis, bone loss, and similar problems. In 2014, the U.S Food and Drug Administration (FDA) approved the use of the bisphosphonates tiludronate (Tildren) and clodronate (Osphos) for controlling clinical signs of navicular disease in horses.
So what does a Bisphosphonate do?
First of all, bones have some natural engineering going on that are important to understand. Osteoclasts (Bone-eroding cells) make a pit in the bad part of the bone. This takes roughly 7-10 days to happen.
Osteoblasts then come along and lay new bone in that pit. This takes about 30 days to complete its process.
Osteoclasts and osteoblasts are meant to be coupled. In bone disease, they don’t work together. The osteoclasts are digging down bone faster than the osteoblasts can keep up with.
Bisphosphonates bind to the surfaces of the bones and slow down the bone resorbing action of the osteoclasts (bone-eroding cells). This allows the osteoblasts (bone-building cells) to work more effectively
This is immensely important since the bones are what perform functions of support, protection, movement, mineral storage, and blood cell formation.
The continuous breakdown and repair of bone tissue, remodeling, allows bone to adapt to stresses, allowing for increased strength and repairing damage.
If a young racehorse has an oval cannon bone and then goes into heavy training for 6-9 months, it would not be unusual for that bone to look like a triangle after that period of time. Bone structure adapts to the horses type of work and the surfaces it works on. Warmbloods would be different because they are subjected to different training. The skeleton changes over time and remodels throughout life essentially creating a whole new structure over time.
Bone growth or modeling continues until adulthood as the horse increases in size. Remodeling happens in response to stress and repair.
If you are not familiar with what Navicular Syndrome is in the horse, it is defined as chronic, intermittent forelimb lameness associated with pain arising from the navicular bone and other surrounding soft tissue structures.
The best way to diagnose it is with the use of a Scintigraphy camera – a technique in which a scintillation counter or similar detector is used with a radioactive tracer to obtain an image of a bodily organ or a record of its functioning. The first option that is likely to happen is the radiograph, but it can lag. Radiograph can’t see how much issue there really is going on.
The horses Navicular bone acts as a fulcrum. When there is an issue, it will get little channels in it that weaken the bone.
By using Osphos, osteoclasts can be slowed or paralyzed while the osteoblasts catch up. It can take 30 days to see results and then lasts around 6 months. The dosage depends on where the issue is at in the process.
Something important to keep in mind, according to Dr. Maxwell, is that Osphos does is not spackle – while it does provide strengthening of the bone and in turn soundness, Radiographic lesions can still appear.
Osphos is given via intramuscular injection in 3 different sites. When it is administered, it is recommended that no anti inflammatory be used within 72 hours.
If after the 30 days there is not an imrovement, it would be likely that there is a soft tissue component involved. Another reason for possible poor result would be if the bone pathology is already too far gone.
In summary, Bisphosphonates inhibit osteoclasts (does not influence osteoblasts). It minimizes ongoing bone resorption seen in navicular disease and in turn decreases lameness.
One of the questions that came up afterward was if it is recommended to use in a prophylactic manner? Dr. Maxwell explained that aged and/or high mileage horses may benefit. It just won’t do anything if there is no bone pathology. She left that up to determining with your own vet depending on your specific case.
It was informative and interesting. Again, I thought she did a great job giving the presentation. I hope you have enjoyed my takeaways!