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© James Rooney, D.V.M. This addendum should be read in connection with the section: The Egg Bar and Support in the article The Basic Mechanics of the Foot and the Horseshoe. Henry Heymering, always alert and thoughtful, called me to task for not giving the egg bar the respect and value that it deserves. As the result of Henry's doubts and a well-done demonstration, I have reevaluated the mechanics of the egg bar situation and wish to add to and correct my earlier statements. Henry, as well as others, have indicated that the egg bar shoe is of value in the treatment/rehabilitation of legs with tendon damage, i.e, bow, suspensory strains, deep flexor check ligament strains. My earlier evaluation suggested to me that could not be the case, and I herewith wish to correct that incorrect evaluation. Once again I must refer to the figure, Fig. A, which indicates the basic moment equilibrium equations and situation for the coffin and fetlock joints. DF, the tension in the deep flexor tendon operates around the moment arm b at the coffin joint while T represents the tension in the suspensory, deep flexor and superficial flexor operating around the moment arm c at the fetlock joint.
Pain arising from damaged tendons can be alleviated to some extent by decreasing the tension in those tendons. In this case either DF or T must decrease. The horse can do this by standing back, Fig. B. By doing so the line of action of F, the ground reaction force, is moved from 1 to 1', Fig.A. This movement clearly decreases the length of the moment arm, a and the moment arm, 1. That reduces the value of Fa and Fl, allowing a decrease in the tension of the deep flexor in the one case and all the tendons, T, in the case of the fetlock. This decrease in tension is, of course, mediated by shortening of the tendons. The same effect can be achieved, that is, reduction tension in the tendons and suspensory by applying the egg bar shoe. When that shoe is applied, as indicated by the dotted line in Fig. A., the line of action of F will be moved closer to the coffin and fetlock joints just as when the horse itself moves the leg to the standing back position. And, again, this allows shortening of the tendons which decreases tension and, so, pain. The four photographs, labeled Photos 1 through 4, are of the demonstration Henry Heymering provided which enforced my rethinking. In the Photo 1 the horse is standing back on the right fore with a regular shoe. Photo 2 is immediately after removal of the shoe. In Photo 3 an egg bar shoe has just been applied without any trimming of the foot. In Photo 4, 5 minutes after application of the bar shoe, the horse has moved the foot into normal relationship with the other foot. The cause for the standing back to begin with in this horse is moot. Henry feels it was suspensory pain; I did not examine this horse and do not know.
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