Written and presented April 2012 by R.F. (Ric) Redden, DVM
To better understand the club foot syndrome, we must be familiar with the mechanical formula and how it greatly influences the various degrees of hoof capsule distortion and bone remodeling associated with this syndrome. There appears to be a direct relationship between the degree of tension increase or contributive force of the DDF muscle and these two very distinct alterations from the normal healthy foot. This paper will describe that relationship and the soft tissue and coffin bone alterations that are found in the four basic categories of club feet.1 These characteristics are unique for each grade, however several variables can influence the stereotype mechanical model.
The Healthy Foot
First let's briefly describe a healthy foot on a light boned breed such as a thoroughbred, quarter horse, Arabian and other similar breeds. A healthy foot will have a relatively constant growth pattern heel vs. toe, especially when left barefoot. This uniform toe to heel growth rate is clearly revealed by the relatively even spaces between the growth rings, which routinely occur approximately every 30 days. Shoeing styles, trim and reset timeframes can alter this natural pattern to some degree, but it remains well within a range that can quickly adjust back to its original pattern. The hoof wall has a relatively straight, linear appearance and the toe angle has a very large range depending on bone angle (BA) and palmar angle (PA), which can also vary considerably. The approximate angle found along the growth rings when the toe and heel grow at a different rate will closely mimic the PA on the foot that has not been trimmed for 30-45 days.
Figure 1A Left: This horse has very healthy, sound feet despite a grade 1 right front club. Figure 1B Right: The right front growth rings indicate a tendency for a negative PA in the right hind due to the club in front.
Figure 1C Left: Radiographs of same horse taken prior to 5 week reset. The left front has 25mm of sole, a 0 PA and a very healthy horn wall.
Figure 1D Right: The right front has approximately 22mm of sole, a positive PA and very healthy horn wall. Note difference in bone angles. Both feet are sound and healthy even though strikingly different.
Sole depth maintains around 15mm plus with a few millimeters of natural cup. This is the goal on trim day. Strong feet and healthy digital cushion go hand in hand - you won't find one without the other. Domestic horses with strong, intact heel tubules will have a positive PA that will fall into a range of 2 to 5°. Contrary to what we have thought in the past, hind feet of light breeds do not have a larger PA or hoof angle than front feet. Observing many foals as they mature, the large majority have a 0° PA behind, which may explain why their heels can quickly crush and a negative PA develops once put into training.
With this very basic description of a healthy foot we can start comparing one foot to another, from horse to horse as well as feet on the same horse. Observing the external characteristics and soft tissue parameters before and after trimming or shoeing helps us better understand the interconnectedness of each component as well as how we can enhance the natural healing mode with shoeing mechanics.
Club syndrome influence on the opposite foot
The foot opposite a club also appears to be greatly influenced by the club syndrome. The hoof capsule silhouette has several distinguishing characteristics that apparently occur due to a significant laxity of DDF muscle tension, which reduces suspension function. In these feet the pastern sits back well away from the face of the dorsal half of the wall but can remain parallel to the face of the body when digital alignment is present. Imagine pushing the pastern forward just above the heel on the club foot. The tension on the DDFT displaces the pastern on the club and the lack of tension on the opposite foot lets it sag, creating the distinct difference. The growth ring pattern on this low foot is often wider at the toe than the heel, indicating the toe is outgrowing the heel. This ratio steadily increases from one shoeing to the next, as blood flow is exceptionally good to the toe but impaired in the heel due to excessive heel load that results from lack of adequate suspension.
Figure 2A: Photo of a hind foot with a negative PA and crushed heel. Note the growth ring pattern, very low heel angle, bull nose and coronary band angle.