Navicular disease in the horse is a common lameness condition impacting equine athletes of all disciplines, but with varying degrees. The condition results in ongoing heel pain associated with soft tissue damage and navicular bone remodeling, which occurs progressively over time. The horses impacted by navicular disease suffer variable degrees of pain and have a shorted forward phase of their stride, which inevitably impacts performance and comfort. Current therapies are limited and most of those therapies are directed towards alleviation of clinical signs, more so than altering the condition itself. Could an herb like Curcumin, or Turmeric, impact navicular disease in the horse and potentially improve bone health alone or with bisphosphonates?
Navicular disease (podotrochleosis) in the horse is a lameness condition that has been around for many years and in some practices, appears to be increasing in frequency in horses of all categories. Heel pain in the horse is a common source of lameness, often resulting in a reduced forward or anterior stride during various gaits. These horses also tend to shuffle as they step from one side to the other in a circle, trying not to move their front feet too far forward. The reduced forward stride is due to the lack of wanting to fully extend the front limbs, which would then require more loading of weight onto the heel region, which is already painful. By keeping the stride shortened, this helps to reduce the amount of weight distributed to the heels.
What is Navicular Disease in the Horse?
Navicular disease is a condition in which there is a deterioration of the navicular bone in the horse, which creates pain and discomfort. The navicular bone is located in the heel region, on the backside of the coffin bone, between the heel bulbs. Like any other bone in the body, the navicular bone is living tissue and goes through remodeling over time, which is the process of bone loss (resorption) and new bone formation. Bone is resorbed by cells called osteoclasts and is created by cells called osteoblasts.
In cases of navicular disease, the balance between the two cell types is upset, and in most situations, there is an increased rate of bone loss in comparison to new bone formation. This is not too different from osteoporosis in people, but in reality, the pathophysiology is different. In osteoporosis, the condition is attributed to the aging process, chronic inflammation, dietary and lifestyle influences, hormones, medications, and genetic factors. But, like navicular disease, in osteoporosis, there is an upset balance between bone loss and new bone formation, leaning towards more bone loss and bone density reduction. However, unlike osteoporosis, navicular disease is not generally associated with increased aging or hormonal influence, but there are distinct connections with diet, lifestyle factors, exercise, and chronic inflammation.
This increased bone loss or resorption is evident on radiographs or x-rays in the horse with navicular disease. When evaluating the navicular bone, it is common to see bone thinning, increased vascular channels, and overall reduced bone density. In some other cases, due to increased wear or stress upon the navicular bone, there is a localized increase in bone density due to sclerosis, along with bone loss in other areas. This bone remodeling creates ongoing pain for the horse and over time, the navicular bone can become altered in shape and be predisposed to fractures.
The thing to keep in mind with navicular disease is that by the time evidence is present on radiographs, in regards to bone remodeling, the condition is often well advanced. Most cases of navicular disease start off with pure heel pain and no major bone damage on radiographs. In the early phase or stage, the damage is being done in the soft tissue structures around the navicular bone, which includes the joint capsule and ligaments associated with the bone. We don’t often see these early soft tissue changes unless and ultrasound or MRI is performed.
The take-home point here is that due to the progressive nature of navicular disease in the horse, ideally, you want to intervene much earlier in the course of the condition.
Navicular Disease Causes in the Horse
The exact cause of navicular disease is not known, as likely there is no ‘one’ cause in every case. More so, navicular disease is actually a syndrome or complex of events that lead up to a progressive and debilitating condition in the horse. The bottom line problem is increased stress being placed upon the heel region in the horse, which equates to stress upon the soft tissue structures in the region which eventually impact the bone over time. This increased stress creates an internal inflammatory response within those tissues and bone structures, attempting to adapt to the stressful situation. This inflammatory response is what then creates and sets the wheels in motion for altered soft tissue and bone changes, along with production of pain.
Contributing factors to increased heel stress and navicular disease in the horse include:
- Dietary and nutritional factors
- Genetic influences
- Increased body mass
- Heel contraction
- Improper foot loading
- Concurrent foot condition (thrush, white line disease, abscess)
- Concurrent health condition
Navicular Disease Therapies and Bisphosphonates in the Horse
There are many approaches that are used to help ease the discomfort in the navicular horse, but most are targeting symptoms such as pain and comfort more so than directly impacting the disease process. This is important to remember, as most cases of navicular disease continue to deteriorate over time for this very reason. They may improve in the short-term to get through a competition or otherwise, but long-term many demonstrate no real improvement in soundness or quality of life.
Current therapies for navicular disease in the horse include:
- Non-steroidal pain medications (NSAIDs)
- Corrective trimming/shoeing
- Corticosteroid injections (joint or bursal)
- Stem cell therapy
- Medications to alter circulation
- Bisphosphonates (Tiludronate or Clodronate)
Bisphosphonate medications have become increasingly popular for management of navicular disease in the horse, going based off of research in women with osteoporosis. However, their benefits in the horse may not be what we would like to believe. This class of medications has the ability to alter the bone remodeling process, slowing down bone loss while increasing bone formation. Essentially, the goal of bisphosphonate medications is to restore balance in the bone regeneration process. While this is all well and good in theory, it does not always work out so well in research.
In human medicine, bisphosphonates have lost favor in therapy of osteopororis mainly due to side effects created, not just at a bone level but also in various organs in the body including the kidney and liver. Specifically looking at bone health, in human research, bisphosphonates increase bone formation while reducing bone resorption or loss. This can create bone density problems, bone pain, and increase risk of fracture in some instances.
In the horse, bisphosphonates have shown promise in some cases, but more recent research indicates that long term usage of this class of medications demonstrates no impact on bone health or remodeling over a 60-day period of time. (Richbourg, 2018) This study was conducted in a group of young and healthy horses, so there could be room for debate that a true navicular horse would be different.
In another study of true navicular disease horses, a bisphosphonate (tiludronate) was administered by two methods for comparison of effect; intravenously or local regional limb perfusion. Throughout the 120-day trial, there was a noted improvement in the amount of ground force applied with the limb, but overall there was little to no change in the lameness score. The regional limb perfusion approach did provide more improvement in the lameness score, but only at the end of the 120-day trial. This study only evaluated lameness and ground force, not the impact of the medication on the bone pathology. (Whitfield, 2016)
Ultimately, when it comes to bisphosphonates and usage in the horse, there is not much evidence that they impact the bone condition that is present nor improve bone health overall. The research that has been conducted is assessing improvement in lameness score, which generally indicates improvement in a period of time spanning 2-6 months, while using high dose therapy.
So, the question remains as to whether there are benefits to navicular bone health with usage of bisphosphonates, or is it possible that they are just impacting the pain cycle on a different level than traditional medications?? If that is the case, are they worth the potential risks and high cost?
Curcumin, Bisphosphonates, and Navicular Disease in the Horse
Taking into consideration that navicular disease in the horse is tightly connected with ongoing chronic inflammation, one has to question whether there are better options for management? This chronic inflammatory process is directly linked in with the pain, increased bone loss, and soft tissue damage associated with the navicular condition. Chronic inflammation, through cellular signaling, alters the osteoblast and osteoclast function and balance, leading to the increased bone loss and remodeling. This is the bottom line problem in the horse with navicular disease.
What is interesting is that in human research with osteoporosis, patients are encouraged to take proactive measures to either prevent or better manage the condition. Dietary changes are indicated and recommended, not just to increase mineral intake such as calcium, but through whole-food provisions, the patients can take advantage of the anti-inflammatory properties of those foods.
Curcumin, or Turmeric, is one such whole-food or herb that has been researched in women with osteoporosis. Curcumin has been heavily researched for its known antioxidant and anti-inflammatory capabilities. Considering that both osteoporosis and navicular syndrome are connected with chronic inflammation, it just makes sense that curcumin could provide benefits.
In one human trial, curcumin when combined with a bisphosphonate, provided increased benefits to patients with osteoporosis when compared to the bisphosophonate alone. The combination group demonstrated a higher level of increased bone density and bone turnover markers. (Khanizadeh, 2018)
In another trial, human patients with low bone mineral density responded very well to curcumin therapy alone, with no medications, alongside of a healthy diet and improved lifestyle. At the end of the trial, the patients demonstrated an improved bone density in all areas with no noted side effects. (Riva, 2017)
Although Curcumin or Turmeric has not been extensively studied in the horse, let alone a horse with navicular disease, this herb has been used successfully by many to manage such conditions. This is one herb that is used heavily by our own rehabilitation practice to aid in management of many inflammatory conditions in the horse, including navicular disease. Of course, no therapy is a stand-alone therapy. The best or most optimal results are achieved when other factors are addressed additionally, which helps to not only reduce the stress upon the heel structures, but improve overall health.
Curcumin can be very beneficial to any horse with navicular disease conditions, but the dosage or therapy regimen chosen can vary significantly based on my personal experience. Nonetheless, Curcumin can provide significant improvement in comfort and over time, there are indications that bone health can be improved upon serial radiographs. Again, this is best achieved with all contributors addressed.
Curcumin based formulas that I utilize in the management of equine navicular cases include:
Author: Tom Schell, D.V.M., CVCH, CHN