Written November 2018 by R.F. (Ric) Redden, DVM
Toe extensions with a slightly rolled toe work mechanically in two basic ways. The most beneficial is to prevent the horse from dragging the foot when unable to extend the coffin joint due to a traumatically severed extensor tendon. The toe simply cannot be extended in absence of the function of the extensor tendon. This is a very common injury as this tendon lies along the face of the cannon bone and just under the skin leaving it vulnerable to serious injury. The other function is to use it as a lever to force the heel down via the weight of the horse when there is an air space under the heel when fully loaded. This can be a useful tool but demands great respect and a thorough understanding of the circumstances that can prevent the heel from touching the ground in absence of a painful response. Injury to the muscle belly and or deep flexor tendon that can cause temporary shortening of the flexor apparatus. Easy stretching in small increments can offer beneficial results as healing occurs.The club foot is often thought of as a candidate for a toe extension but it can be contraindicated with grades 2 through 4 Redden categorized club feet. (4 basic grades of 1 to 4)
Click image to enlarge (Image courtesy of Sebastian Duran) This diagram reveals the fragile and vulnerable nature of the blood supply in the toe area. Extending and or lowering the heel on club feet greatly increases the mechanical load on the soft tissue and apex of the coffin bone and that can be counterproductive.
Grade 1 being only 5 degrees and a naturally steeper toe angle than the opposite foot. A small toe extension can produce favorable results with a grade 1 provided the sole depth remains adequate, growth rings uniform, and the heel rests on the ground when the foot is placed slightly behind the opposite foot.
Grade 2 has more heel growth than toe. Note the wider heel growth rings. The palmar angle (PA) will be larger and the bone angle may also be larger than the other foot. When the excess heel is trimmed off, the heel can no longer touch the ground therefore this age-old concept becomes contraindicated as it is increasing the very force that caused the club.
We know with great certainty that the seat of the contraction syndrome lies in the synapsis of the muscle fibers, creating continuous firing of the signal shortening the muscle length and subsequently the muscle tendon unit. Attempting to counter this force with a toe extension could offer favorable results provided that the hoof capsule, laminae, and solar corium are durable enough to absorb the remarkable increased tension. Unfortunately, this is not the case as the foot inside and out remodels very quickly due to the increased force applied by the toe extension lever. The sole gets thinner, the hoof develops a dish simply bending due to the pull of the DDFT, the apex rapidly develops a lip appearance and then starts to resorb as the tension remains constant.
Grade 3 has a dish and all the above ill effects and is most often the product of trying to stretch the tendon at the cost of the foot. Removing the dish with a rasp along with the excessive heel adds fuel to the fire and soon the potential for athletic soundness is in jeopardy.
Grade 4 the heel is almost as high as the coronary band at the toe, most proximal dorsal wall is 80 to 90 degrees and the PA can be as high as 30 to 40 degrees. This is the upper range of the club syndrome. The mismatched syndrome is apparently a manifestation of the club syndrome ranging from grades 1-4. Points of interest There are common alterations that occur respective of each grade that can be routinely identified in the high foot, the opposite, and the hind foot that follows the steeper foot in front. The rocker concept is an option that can accelerate sole grow, increase the dorsal horn grow rate and suppress heel growth especially when employed the first few weeks of life.
For those wanting to use toe extensions for foals, think about the forces at play that are responsible for the club foot. Would it not be better to reduce the tension on the DDFT and bypass the ill effects of thinning the sole, slowing the growth, creating a dish and increasing heel growth? One can reduce the tension responsible for the club foot by using the properly applied rocker concept to accelerates sole and toe growth, reduce heel growth and prevent the dish from forming. The mature horse with a Grade 2 or 3 can respond very nicely with the same concept that is used to manage it in the young horse and remain competitive in the rocker shoe.