Newsletter: November - December 1996

HOOF CAPSULE IMBALANCE

by J.H. Young, D.V.M.

The hoof capsule reflects 9 months of growth history, effected by hydrostatic and mechanical forces on the hoof capsule which include vertical, horizontal, torsional, weight-bearing and acceleration forces. The hoof capsule deformation during flight due to blood profusion adds to the stresses on the hoof capsule. In addition, there is the stress of an artificial application of a steel plate nailed on to a balance that is predetermined. These variables affect the growth rate and are reflected in abnormal hoof capsule distortion, tight rings in a localized area or lack of horn growth as well as pathology such as sheared heels and some quarter cracks. The parallel relationship of the horizontal rings and the vertical horn tubules will reflect these stresses in the resultant growth. These same observations will give clues on how to relieve the stress and improve the problem.

Ideal medial/lateral balance will result in parallel horizontal rings of normal horn. Imbalance of the hoof capsule will result in uneven loading of the wall and will result in distorted hoof wall growth. Tight rings on the side of excessive loading will indicate slower growth. Unloading of the wall, such as occurs with a toe resection, will free the coronet from weightbearing and result in faster growth of new horn in that region of the coronary band.

Differential wall length can lead to sheared heels. A quarter crack can also be caused by imbalance and can be considered a sheared quarter. Measurement of wall length will confirm that the longest wall length is in the area of the crack. Quarter cracks may be acute or chronic with other causes including heavy concussion, hard surfaces, thin hoof walls, coronary band lacerations and hoof wall avulsions. The acute crack can be very painful and may bleed with movement or palpation of the coronary band. Blind quarter cracks may not be evident from the outward appearance of the foot, but internal hoof wall capsule splitting may cause lameness from pinching of the sensitive laminae with movement. Cracks usually travel in a dorsopalmar/ lateromedial direction and overriding horn wall must be debrided. Chronic cracking or abscessation warrant further investigation to rule out the presence of a foreign body or bone sequestrum. Trauma to the coronary band may result in permanent disfigurement of future horn growth, due to scarring of the coronary corium or a resultant step-lesion at the coronary band. Many types of repair have been utilized, but all are aimed at the stabilization and immobilization of the crack. Bar shoes with clips, stapling, wiring, brass plates and acrylic patches have all been described, as well as aggressive wall removal and coronary band avulsion. Most attempts are directed at repairing the crack, whereas more focus should be on correcting what is causing the crack and dealing with that primary problem. Differential wall length is a major cause of quarter cracks. Simple removal of the shoe will resolve 50% of the quarter cracks due to imbalance. The hoof wall will typically break out in the area of the quarters and make that part of the wall non- weightbearing. Quarters are not weightbearing in the natural foot of the Mustang. Quarter cracks are very rare in the unshod foot. The coronary band will "settle" to its normal position being parallel to the ground. The local shear stress is removed and the quarter crack resolves and grows out uneventfully. If shoeing is required, a heartbar shoe is indicated. The quarter and heel of the affected side are unloaded by trimming the foot so that it does not contact the shoe.

Coronary band lameness can result from chronic imbalance of the hoof capsule. Constant jamming of the coronary band with presumed bending of the coronary cerium papillae, can lead to areas of bruising that may go undetected in the pigmented foot. Although the lameness is real and can be localized by diagnostic nerve blocks, radiographs may not indicate the cause of this soft tissue problem. Removal of the shoes and allowing the foot to restore its normal shape and wear pattern will alleviate some lamenesses do to imbalance. Protecting the wall with duct tape will help to prevent breakage of the hoof wall. Soaking of the foot in warm water for 15 minutes per day for 3-10 days will help to speed the process. If a bounding digital pulse develops the horse may not be able to go without shoes and will need to be reshod or have frog supports applied to prevent a laminitic episode.

Rebalancing of the foot will be reflected in the new wall growth at the coronary band. Previously non-concentric rings will become parallel. Coronary band constriction will respond with an increase in coronary band diameter. Concentric rings in the goof wall growth may indicate signs of laminitis. Laminitic rings may only be evident in one foot, the front feet only, the hind feet only, of all four feet. Selenium toxicosis can also cause horizontal ringing in all four feet, but is usually associated with mane and tail hair loss and lameness and will present as a regional problem in that practice area.

Anterior/posterior balance will be dictated by the horse's conformation of that particular limb. The long too/low heels typical of the Thoroughbred racehorse, will break the hoof/pastern axis back and cause excessive loading of the heels, slower heel growth and long, distorted toes. The whole hoof capsule collapses with the horse bearing weight on the heel wall, the frog dropping with the sole and the whole foot size increasing. The white line is enlarged and yellowed or contains flecks of old hemorrhage. The heel bulbs are usually sore to palpation, and growth rings are tighter at the heel.

A broken forward hoof/pastern axis, will slow the growth at the toe and can result in long heels and toe cracks originating at the coronet, as commonly seen in the club foot syndrome.

Since graduating with honors at Colorado State University in 1980, Dr. Young has become a certified farrier, receiving the 1992 American Farriers Association Humanitarian Award.

She is a current member of the major veterinary and farrier's associations, and serves on numerous committees including Acting President of the Equine Trust Foundation, chairperson of the A.A.E.P. Farrier Liaison Committee, the A.F.A. Veterinary Liaison Committee and the A.F.A. Research Review Board.

Dr. Young is involved in lameness research and has published many journal articles. She has also been active in the teaching field, serving at C.S.U. in both veterinary and farrier topics, and Scottsdale Community College in Arizona in their Equine Science Department.

She has presented seminars on various topics in therapeutic shoeing and veterinary lameness problems in the United States, Australia and Switzerland.

Dr. Young currently has a lameness and therapeutic shoeing referral practice in Arizona.

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