Dorsal Break-over; an Overview

II Break-over enhancement techniques :

A. Barefoot trimming: Feral horses are subject to “self trimming” phenomena, depending on ground conditions and amount of movement, which is usually correlated to food, sex and danger.
Domestic horses, like breeding stock, are often kept barefoot but rarely experience equilibrium between hoof-growth and -wear. When trimming barefoot, domestic horses, dorsal BO can be enhanced by rasping back the toe at a ± 45° angle with the sole. This rather steep angle, permits setting back the point of BO on the hoof, without diminishing sole depth excessively under the distal, dorsal, margin of PIII.
As the hoof wall’s slope at the heels is generally more oblique than the dorsal hoof wall’s slope, if the foot is to be left with a reasonable surface area, the heels should, when necessary, also be trimmed back, this may be done to the widest part of the frog, or to the heel-frog junction, which tends to make the trim correspond to uniform sole thickness[6]. Dorsal flares are also trimmed back.
Latero-medial BO is facilitated, and distal hoof wall splintering is prevented, by rounding off all sharp edges around the hoof at a ± 5mm radius.

On shod horses, BO enhancement can be aided by the shoe placement, shape and type:

B Shoe placement:
1. Setting the shoe back, relative to the, flatly trimmed, hoof, brings back the COP of the ground surface of the shoe, relative to the foot/limb. As the dorsal hoof wall has a limited thickness, this precludes the use of a toe clip.Clip-les shoes can be quite satisfactory on the front limbs, if no studs or pads are used. If either, or both, are called for, side clips should be considered, as they increase the stability of the shoeing and can save on the need of stronger and more numerous nails to fix the shoe to the hoof. As front feet tend to be more rounded than hind feet, front shoe patterns, with side clips in the quarter area (quarter clips), should be used for this purpose, when using factory made shoes; 2 clip, factory hind shoes do not offer enough length of bar between the clips to set the shoe back, and may lead, overtime, to a pointed-toe front hoof shape.
Hind feet have a different stance phase and more backward shearing forces on initial ground contact, therefore clip-less shoes are easier torn backwards on hinds than on fronts. On the other hand, the hinds can adapt more to forward growth between shoeing intervals and generally have a narrower toe area. In practice this means, that a normal side-clipped hind shoe pattern can be set back enough, if needed, on a hind hoof.
When placing a factory shoe further back, relative to the toe of the hoof, the nail stamps in the toe area can become too coarse, with the risk of hot nailing the horse. If this is the case, the first nail stamps should not be used, or two new, less coarse, nail holes should be stamped in the shoe.

 

2. Reverse, or open toe shoeing is of course also a form of dorsal BO enhancement, with the added feature that it increases caudal ground surface of the shoe in the way an egg-bar shoe would. Open toe shoes also wear quicker in the toe area than other shoes, which means that there can be less hoof angle loss between shoeing intervals. Open-toe or Napoleonic shoes (Napoleon is believed to have had a regiment shod in reverse fashion, so as to fool the enemy during the Russian campaign) can be forged from scratch, by swedging and stamping with nail holes the heels of a normal shoe, or by cutting a side clipped hind shoe just in front of both clips and welding the resulting piece of (toe) bar between the heels of the original branches; the resulting shoe will have the swedges, nail holes and clips in the correct place for a reverse shoe.

 

C Shoe shape and type:
Shoe shape can enhance all around BO by it’s intrinsic design; concave, and half round stock does this by bringing the outside, ground edge of the shoe, and thereby the COP, closer to the center of the hoof in all phases of the stance and in all directions of BO. Full rolling motion shoes, like Colleoni COBMD, and PG shoes, do this to much greater effect, as their ground base is much narrower than their hoof side. Other commercial shoes are available with a blunt toe, e.g. NBS shoes, sagittalshoes, speed toe racing plates etc. These mainly enhance dorsal BO. Dorsal BO can also be enhanced by the use of a rolled toe, a commercial example is the equilibriumshoe.
All these shoes derive their BO enhancement from the shape and design of their ground surface, while their foot side remains flat and therefore requires a flat trim.
Both rolled and blunt toes, can easily be made by hand or by modifying factory made shoes.
No factory shoes come out of the box with a rockered toe, where the dorsal part of the shoe is bent upwards, to bring BO back, or closer to the center of the hoof.Rockered toes can be easily forged, but usually require a hot fit, as the foot surface of the shoe and the trim of the foot are not flat anymore. A particular interesting type of rockering, is the French (and Swiss) type of “ajusture ”. With a rounding hammer, the upper surface of the toe area of the shoe is forged downwards in a concave, dish type shape. This rocker thereby includes not only the dorsal toe, but goes all the way to the quarters, enhancing BO over the outside or inside toe during turns. Added advantages of this type of rocker, which is standard practice in France on warm-bloods, is that it provides sole relieve, improves nail pitch and holds excessively flat, wide feet well together, due to it’s concave upper seat.

Naturally the several types of BO enhancement can be combined, up to a point. A full rolling motion shoe can be set back, a toe can be both rockered and rolled, a rolled toe shoe can be set back. One should be careful though when tempted to set a rockered toe back on a shortly trimmed foot, as the bent up, upper surface of the shoe might cause sole pressure in the toe area when placed too far backwards relative to the foot.

 

III Appropriate use of break-over.

A. On sound horses.
Dorsal BO enhancement reduces peak tensions on the podotroclear apparatus and limits the forward travel of the COP at the end of the stance phase, when the horse travels in a straight line. On turns, latero-medial BO enhancement reduces asymmetrical pressures on joint cartilages, and tensions on collateral ligaments, but also on other anatomical structures with a lateral and medial component, e.g. the lateral and medial lobes of the distal DDFT.
Type of work, ground surface encountered, conformation and hoof shape and quality, should all play a role in choosing the type of BO as a preventive measure in the sound horse.

1. Ground – conditions – type of work:
Horses working mostly in straight lines, on firm ground (NPG) are candidates for dorsal BO enhancement like blunt toes, set back shoes, or rockered toes, especially on the fronts. e.g. harness horses. (Caution: trotters which go close to pacing sometimes need some toe length.)
Horses which do a lot of turning (e.g. show jumpers) can benefit from a French rocker type shoe.
Endurance horses and trail horses often encounter uneven and compact ground, shoes with a reduced ground surface (e.g. St. Croix eventers, Kerckhaert classic rollers ), reduce latero-medial strain caused by uneven footing.
On the other hand, sound dressage horses, which invariable work on PG and need some hoof mass at the toe for expression and to keep from digging their toe into the soft arena, should not have to much dorsal BO enhancement, if they have regular feet, they also like wider webbed shoes.
Carriage horses need well pronounced rockered toes, as the surface they work on is both compact and non penetrable. If they need studs, a narrow, centrally placed toe caulkin, close to the inside rim of the shoe, together with heel studs, mimic the three point foot bearing surface, facilitating latero-medial BO.
On penetrable ground, the ground gives in all phases of the stance; not only during BO. In these conditions, modifying the ground surface area of the shoe, will unload certain structures at the expense of others. A reverse shoe, for example, will permit greater penetration of the toe than the heels in the mid-stance phase, when weight bearing and fetlock extension are greatest. By flexing the DIP joint, the DDFT is indeed unloaded, but the superficial digital flexor tendon and suspensory ligament have to take increased strain[7].

 

2. Conformation and hoof shape and quality.
Horses with a tendency to flare at the toes, with under-run heels and oblique pastern and hoof angles, will have more forward growth during shoeing intervals and benefit from setting the shoe back and/or rolling the toe, so that the COP remains further back, even at the end of the shoeing interval, which should in any case be kept as short as possible. Horses with thin soles and walls are usually easier to shoe with set-back or rolled toes; thicker soled warm-bloods can get away with hot fitted rocker toe shoes.

Large, wide feet, with sloping side walls, are good candidates for wide webbed shoes (more sole protection) with pronounced French type rockered shoes, the concave seat going all the way to the quarters, leaving only the heels of the shoe flat.
Steep, narrow feet, with large palmar/plantar angles of PIII, benefit from a pronounced dorsal rocker toe, as their DDFT is not very lax. The rocker should leave plenty of sole depth in the toe area, as in this area the sole is often crushed by the dorsal edge of PIII.[6] The quarters of the shoe should not be seated in here, as these hooves are already narrow, with less hoof expansion.
Upper limb conformation should also influence our choice, horses with hyper extended carpi (back at the “knee”) and which do fast work, like racehorses, can use blunt or set back toes as a preventive measure against slab fractures of the dorsal aspects of the carpal bones, as the carpus gets over-extended just before BO.
Inward rotations of the limb (pigeon toes), cause more lateral BO and shoe wear, which should be favored in forging and applying the new shoe.

 

B. On lame horses:
Shoeing, including BO enhancement, is an essential part of lameness therapy in many pathologies of the (lower) limb.
Recent strides in diagnostics ( digital X-rays, ultrasound, MRI, CAT) have greatly increased our understanding of many pathologies, specifically those which used to be lumped together under the common denominator of “palmar hoof pain”. Better diagnostics however, also leads to more detection of lesions, with many horses showing more than one lesion, often in different, though adjacent, anatomical structures, which theoretically require opposite biomechanical solutions from the therapeutic shoeing. Besides the best instrumental diagnosis obtainable, clinical evaluation remains of paramount importance in choosing the appropriate shoeing. Classical observations like: lameness gets better/worse on hard/soft ground, after warm up, uphill, down-hill, on the right/left turn etc., still play an important role. In the author’s practice, the most useful clinical instrument after hoof testers, has proven to be the digital extension device (DED); reduced dorsal extension, lateral or medial elevation, by themselves or in combination, on one or more limbs, are relatively easy to measure, give repeatable results and together with information on the ground surface conditions the horse works or is rehabilitated on, offer a lot of the elements to choose the most appropriate therapeutic shoeing.

 

On PG surfaces, therapeutic shoeing can usefully modify ground bearing surfaces, examples include:
Wide toe-web shoes: rehabilitation for SL desmitis, SDFT tendonitis (intolerance to heel elevation)
Bar-shoes, reverse shoes: DDFT lesions, check ligament desmitis, (intolerance to dorsal extension).
Wide lateral branch: lateral collateral desmitis, medial subcondral bone lesions of the digital joints (intolerance to medial elevation), bone-spavin with typical dorso-medial location.
Wide medial branch: medial collateral desmitis, lateral subcondral bone lesions (intolerance to lateral elevation).
Wide lateral branch + egg-bar or reverse shoe: distal DDFT lesion in the lateral lobe (intolerance to dorsal and medial elevation) etc.

 

On NPG surfaces, BO enhancement becomes more important then ground bearing surface modification, examples include:
Dorsal BO enhancement: DDFT lesions, check ligament desmitis, laminitis (intolerance to dorsal extension).
Lateral BO enhancement: medial collateral desmitis, lateral bone lesions (intolerance to lateral elevation).
Medial BO enhancement: lateral collateral desmitis, medial bone lesions (including most forms of spavin).
All around break-over enhancement: some forms of DIP-PIP artrosis (intolerance to dorsal, lateral and medial elevation).

 

BO enhancement will of course also work on PG, but wide web and bar shoeing will do little on NPG.
Club feet and chronic laminitis feet, with secondary contraction of the DDFT and large palmar/plantar angles of PIII, need pronounced rockered toe shoes, which spare the dorsal sole areas and which diminish the strain and pain in the caudal, break-over phase of the stride. The tall, long heels these hooves often present, make the first, heel-landing phase of the stance phase very traumatic, these feet can therefore benefit from an additional rocker at the heels. The resulting shoe has been called all sorts of names, including “Rock n’ Roll”, banana, self adjusting palmar angle, air-heel, etc., but independent of its name, can be quite functional in horses which present hypo extension of the DIP joint(s).[8]

 

IV Conclusion:

Like many shoeing techniques, break-over enhancement is often useful, but cannot be blindly applied to all horse’s feet in all circumstances, as unloading one anatomical structure will increase the load of others. Type and amount of BO should always take into account the individual horse and its conformation, use and most important of all, the type of surface the horse is called to work upon.
When choosing therapeutic shoes for lameness, valuable information, for the appropriate ground surface pattern and BO enhancement features of the shoes, can be gleaned from the results of a digital extension test.

 

References: