Savoldi’s Theory on Navicular Disease
by Ann Ramsey BS, CERA, APF-I
Michael T Savoldi
At the 2019 EponaMind educational clinic in Paso Robles, Mike Savoldi, Hall of Fame farrier and author, gave an exceptionally interesting presentation on the development of navicular disease in horses. Now retired, Savoldi was Professor Emeritus of Farrier and Veterinary Sciences at California Polytechnical University in Pomona. He worked at the W.K. Kellogg Arabian Horse Center. Savoldi is famous for his extensive research into the functional anatomy of the horse’s foot.
There have been several theories offered about how navicular disease develops. Human error in husbandry and farrier work likely play a role in the disease. Dr Robert Bowker has explored the possibility that lack of caudal foot development in horses is a key factor. Dr James Rooney illuminated how a compensatory toe-first landing could exacerbate the disease. Savoldi’s research on limb mechanics, along with the hundreds of dissections he’s compiled, have led him to believe there’s a simpler and sadly more insidious explanation for navicular disease.
According to Savoldi, repeated normal limb loading can cause soft tissue damage through the midsection and caudal regions of the foot. This damage can build up and eventually the tissues begin to fail, with damage progressing to the navicular bone and deep digital flexor tendon. Normal horses, loading the limb as nature intended, can silently be accumulating micro injuries long before we are aware of any pain they may experience.
“Motion within the foot is what’s causing a lot of the problems…Run harder, play faster we’re going to have more stress on the tissues of the feet. Gravity always wins, and when the mid-section of the foot collapses, that’s pathology.”
-Mike Savoldi
His presentation was full of images of his dissections. He’s been generous enough to share some of them below.
Above we can see the sagittal ridge of the navicular bone acquiring wear, as if being sanded away in layers. Eventually exposing the soft spongy bone underneath the normal cortical bone. Normal cyclical loading of the foot can cause friction between the navicular bone and the Deep Digital Flexor Tendon (DDFT).
The above slide depicts the movement of the DDFT across the sagittal ridge of the navicular bone. Much like water flowing over a rock, friction between the tendon’s gliding action and the sagittal ridge of the navicular bone can cause wear. A simple “equation”:
Pressure + Time = Pathology.
The slide above shows where micro injuries can accumulate as the p3 bone, and navicular bone articulate with the surrounding soft tissues in normal locomotion. The circled areas above depict insults to the soft tissue, and ultimately bone changes to p3, note the “stress bump”.
Pressure + Time = Pathology.
Previous veterinary research supports this theory of micro injuries building under areas of repeated stress during loading. Studies of Osteoarthritis in the fetlock have shown that the distribution of the arthritis lesions within the joint is related primarily to where peak force travels. Essentially the damage occurs where the highest forces are loading through the tissues. (Colon et al. 2000; Kawack and McIlwraith 1994)
Other Scientists have described similar progressions for athletic injuries. Dr. Renate Weller Professor of Comparative Imaging and Biomechanics at the Royal Veterinary College said, “Cyclical overloading can cause an accumulation of micro damage. This results in progressive weakening and finally damage of bones or tendons.”
Dr. Weller described this phenomenon at a lecture given at the Beaufort College Educational Trust in 2019. Savoldi believes that the development of damage in the midsection and caudal aspects of the foot are occurring in the same way.
Why is this area taking abuse?
Weight and speed combine to create large forces moving through the horse’s limbs particularly at peak impact and deceleration of the foot. At the walk the horse’s forelimb is carrying about ½ its total body weight per step. For a 1000lbs horse that’s 500lbs loading and unloading through the tissues of the limb and foot.
At a trot the horses’ leg is absorbing about 1.5x bodyweight, roughly 1500lbs (over half a ton) per step. At a gallop, it is 2.5 times the weight of the horse according to Dr. Weller.
As Dr. Weller explains in her lecture at the Beaufort College Educational Trust,
“That’s impressive, that’s like a decent sized car smashing down on a horses’ leg every time it hits the ground. No other animal can cope with that…camels and ostriches come close. But I really think the horse is a miracle of bio engineering”.
The above photo illustrates the forces which are similar to a mid sized car crashing through the midsection and caudal foot at the gallop.
As spectacular as they are, horses like all athletes are not immune to problems. When we look at the forces that the horse is coping with in daily life, we can appreciate how vulnerable the horse is to overload of the limbs as Savoldi and others are describing.
What can we do about it?
Good footing that is firm yet soft enough to absorb some of the impact forces during loading and deceleration of the foot is important. How we manage the workload and training of the horse has an impact as well. But through shoeing, we can offer the horse even more orthopedic assistance.
According to Savoldi, using a carefully applied orthotic packing and a shoe that offers reinforcement of the sole, can help the foot avoid micro injuries. The packing when applied through the collateral grooves, can assist in stabilizing the decent of p3 onto the midsection and caudal areas of the foot.
The Importance of Orthotic Packing
Monique and John Craig documented the effects of packing on tissue movement within the foot at the Epona Institute, (EponaMind.com) in 2006. The images that follow are from that study. Using 80 radiographs per foot (160 radiographs in total), Craig and Craig measured the movement of the pedal bone from a standing posture to full compression of the limb. They compared the non-packed hoof, to one with an orthotic packing in place.
The higher red X markers shown denote where the sole body sits in the standing horse, before compression of the limb. The distance between the 1st and 2nd red X markers demonstrates the decent of P3 onto the sole body when no orthotic packing is applied. The distantce observed in the unpacked foot is significant, because there’s no stabilization of P3's decent onto the sole.
In this photo, the foot has an orthotic carefully applied. You can see a reduction in distance between the blue X markers as the horse's leg is moved from standing to full compression. The decent of P3 onto the sole body is stabilized by the orthotic packing in the fully compressed limb. Notice that some movement is still present and likely desireable for hoof mechanisim. This is why hoof packing is both a sceince and an art that must be approached with experience.
A note of caution, packing the foot correctly is crititcal. The correct amount of packing and where it is applied, can vary from horse to horse and at different periods of a horse's treatment. Over filling the foot can cause pain, and should be avoided. Additionally innapropriate material selections can lead to poor results. This topic will be explored further in another upcoming article.
Conclusion
Navicular disease has been described and defined by multiple theories, but Savoldi’s argument is refreshingly straightforward. Horses are having to cope with tremendous forces in the normal loading cycle of the limb. The damage that occurs to the midsection and caudal aspect of the foot for some horses is happening quietly, often without clinical symptoms until much later in the disease progression.
There’s an old saying, that 50% of solving any problem lies in defining it. If we don't acknowledge that navicular disease is likely caused by the same factors that initiate joint disease in other areas of the body, how will reduce the impact? We must also recognize that potentially any horse regardless of breed, age or discipline could be vulnerable to this kind of wear and tear in the foot. Even horses we believe are meticulously managed.
Prevention of the initial micro injuries to the soft tissues of the foot via whole horse management, is key. The concept of offering the foot stabilization of movement within the capsule via our farrier practices, is a good place to start.
About the Author:
Ann Ramsey holds a Bachelor of Science degree in Animal Science with a minor in Equine Science, from California Polytechnical University, San Luis Obispo. Ramsey is Certified in Equine Rehabilitation via the Animal Rehab Institute in Florida. She is a therapeutic farrier specializing in the rehabilitation of the hoof capsule and ultimately, the whole horse. She currently serves as Director of Farrier Education for Equitopia. www.EquitopiaCenter.com