Realignment of P3 - the basis for treating chronic laminitis

Reprinted with permission from Equine Veterinary Education (EVE).
Original published in Equine Veterinary Education Vol 8 August 2006.

1. Introduction

Chronic laminitis is a frustrating, and often disheartening, condition to manage. The biggest challenge to the veterinarian and the farrier is to improve function in a foot that has substantial and possibly permanent structural changes. Among these is displacement of the distal phalanx (P3), the underlying problem responsible for the clinical hallmarks of chronic laminitis: chronic lameness, recurrent foot abscesses and abnormal hoof wall growth (Hood 1999a; Morgan et al. 1999; Pollitt 1999).

Rotation of P3 is the most common form of displacement and has several clinically important consequences. With rotation, weight bearing is thought to be concentrated at the apex of the distal phalanx, which predisposes the foot to focal pressure on the solar corium in that area. Pain is the most obvious and most urgent consequence. Ischaemia of the solar corium (and probably of the tip of P3) is also an important sequela, as it retards sole growth (Redden 1997; Hood 1998).

In addition to causing further damage to the laminar attachments by the lever effect of the dorsal hoof wall on the lamellae, rotation of the distal phalanx is thought to lead to excessive pressure on the coronary corium by the extensor process. The resulting ischaemia alters the rate and, in severe cases, the direction of horn growth from the coronary papillae in this area (Pollitt 1995; Hood 1999b). These problems can be ameliorated only by restoring the alignment of the distal phalanx relative to the bearing surface of the foot (i.e. to the ground surface) and significantly reducing the forces of the DDFT.

2. Capsular vs. phalangeal rotation

When discussing rotation of the distal phalanx, it is important to make the distinction between capsular and phalangeal rotation. In horses with capsular rotation the hoof capsule diverges from the dorsal surface of the distal phalanx. The alignment of the distal phalanx in relation to the other phalanges may, or may not, be relatively normal in these feet. In horses with phalangeal rotation, the distal phalanx is displaced in relation to the long axis of the first and second phalanges - i.e. there is an abnormal degree of flexion in the DIP joint at rest (O'Grady 2002). Phalangeal rotation indicates functional shortening of the deep digital flexor musculotendinous unit.

In horses with capsular rotation and relatively normal longitudinal alignment of the distal phalanx, realignment of the distal phalanx relative to the ground is easily achieved with trimming and shoeing alone. Horses with significant phalangeal rotation may benefit from a surgical release procedure (deep digital flexor tenotomy or inferior check ligament desmotomy). A release procedure is generally necessary to facilitate alignment of the distal phalanx and improve patient comfort. Further indications for a tenotomy or desmotomy is severity of the pain, chronicity, severity of the rotation and how much sole depth is present. Trimming and shoeing alone is often inadequate in many of these horses.

The severity and chronicity of the phalangeal rotation dictates which procedure (tenotomy or desmotomy) should be performed. Typically, more marked change in the angle of the DIP joint is achieved with tenotomy than with desmotomy. When a surgical release has been considered necessary for laminitis cases, deep flexor tenotomy is the procedure used most often. This author prefers to perform surgery after applying the shoe.

3. Basis for treating chronic laminitis

Therapeutic trimming and shoeing has long been the mainstay of treatment for chronic laminitis, and will continue to be crucial for effective management. However, the principles must be thoroughly understood and skillfully applied. The objective is to restore the distal phalanx to its proper orientation in relation to the ground, and restore the normal phalangeal axis. Realigning the distal phalanx by reducing the horn heel height extends the weight bearing surface of the foot palmarly. However, realignment increases the forces within the DDFT, and therefore, it is necessary to elevate the heels to compensate for the loss of heel horn height.

Several different methods may be used to achieve this goal. However, the effectiveness of many conventional techniques is limited by inadequate sole depth and, even, prolapse of the sole in a foot with significant distal phalanx rotation, and by individual foot conformation (e.g. inadequate heel mass in horses with underrun heels).

If inadequate hoof wall is available to accomplish realignment, glue-on shoe technology is ideal for this purpose. Attaching the shoe using a polymethylmethacrylate has some important advantages over conventional shoeing techniques in horses with chronic laminitis. The procedure is atraumatic, as it eliminates the need for nails. But equally important, it allows the veterinarian or farrier to adjust the angle of the shoe in relation to the foot (and thus to the solar margin of the third phalanx) with precision, so the technique can easily be tailored to the specific conformation and requirements of a particular foot. This paper describes the technique used for restoring the alignment of the distal phalanx with glue-on shoes in horses with chronic laminitis.

4. Principles of application

When managing chronic laminitis, it appears to make little difference which shoeing system is used, as long as the method achieves the following goals:

• Re-establish weight bearing along the entire solar surface of distal phalanx (rather than being concentrated at the apex)
• Reposition breakover by moving the functional breakover point palmarly
• Decrease tension in the deep digital flexor tendon (DDFT)
• Recruit additional ground surface for weight bearing using a silastic polymer material

In the method described below, these 3 goals are achieved by trimming the heels, applying a shoe that places the functional breakover point near the apex of the distal phalanx, glueing the shoe to the foot such that the shoe and solar margin of the distal phalanx are parallel relative to the ground with at least 15 mm of depth in-between, and raising the heels using wedge-shaped rails attached to the shoe.

Trimming the heels and applying the shoe as described below restores a more normal orientation of the distal phalanx relative to the ground, and hence more normal loading of the solar surface of the distal phalanx. Moving the breakover palmarly decreases the moment arm exerted on the distal interphalangeal joint (DIP), and therefore it is thought to decrease tension on the dorsal lamellae. Removing more wall at the heels than at the toe during realignment increases the forces within the DDFT. This increase in DDFT can be partially mitigated by moving breakover palmarly. Therefore, moving the functional breakover point more palmarly is an important element of this procedure.

Decreasing tension in the DDFT is achieved by subsequently raising the heels using rails or by using a shoe where the heels of the shoe are thickened relative to the toe. The height of the rails of heels of the shoe are determined by the amount of heel horn removed from the foot, sufficient height of the rails necessary to encourage heel first landing and how comfortably the horse moves. By diminishing the pull of the DDFT on the distal phalanx and associated tissues, this part of the procedure reduces tension on the dorsal laminae and focal pressure on the solar and coronary corium. It therefore reduces pain, limits further laminar damage, and makes way for more normal perfusion and horn growth.

Pain relief is important, not just from a humane perspective but because it interrupts the vicious cycle of pain and increased tension in the deep flexor unit which is one of the great challenges of managing these cases effectively. Raising the heels following realignment of the distal phalanx yields better results, in terms of comfort and hoof growth, than simply realigning the distal phalanx.

A commercially available rail shoe is a convenient and effective means of raising the heels in these horses. Alternatively, a rail shoe can be made from a standard aluminium shoe by welding or glueing a pair of wedge-shaped rails to the ground surface of the shoe (see below). As well as being necessary for realignment, trimming the heels maximises the weight-bearing capacity of the heels, since shorter heels are stronger and less likely to contract than long heels, and it helps to move the weight bearing surface of the foot more palmarly.

To further increase the bearing surface in the palmar portion of the foot, the area between the branches of the shoe is filled with an elastic, yet resilient, silastic polymer material. In this way, the entire ground surface in the palmar 50-60% of the foot (including sole, frog, and bars) is used to distribute the load.

These corrective procedures should not be implemented in the chronic laminitic case until the condition is stable, i.e. the coffin bone is stable but out of alignment vs. unstable where the bone is still actively displacing, the laminae are still tearing and the sole corium beneath is still being compressed. The horse should be relatively comfortable on minimal medication with no further radiographic evidence of further rotation for at least 10 days and supportive therapy commenced in the acute stage should be continued.

5. Materials and methods

The following materials are needed:

• Lateral radiograph of the foot (see below)
• Aluminium shoe and 2 wedge-shaped rails (see below)
• Denatured alcohol
• Equilox1 or similar composite material
• Two pieces of fibreglass mesh, 10 x 10 cm (4 x 4 in)
• Nonsterile gloves (e.g. latex examination gloves)
• Plastic wrap (sufficient to cover the foot)
• Silastic polymer (e.g. Equilox Pink)¹
• (Plastic) gutter guard (to hold the silastic polymer in place)

A high-quality lateral radiograph that shows both soft tissue and bone detail is critical to the success of this technique. The area of primary interest is the solar margin of the distal phalanx. The radiograph should therefore be taken with the x-ray beam directed horizontally at a point approximately 1 cm above the bearing surface of the wall, midway between heel and toe. A radiopaque marker on the upper surface of the wooden positioning block should be used to represent the ground surface in unshod feet. A thumb tack should be placed at the apex of the frog as a radiographic landmark. As the tack is removed, a notch is created in the frog with a the hook of a hoof knife, which can then be used as a reference point when fitting the shoe.

Aluminium shoes are lighter than steel, easy to shape, and bond well to the composite. A wide web aluminium shoe can be squared off and either rounded or beveled at the toe to set the breakover point back as far as necessary. The shoe should be of sufficient size and when fitted the branches extend at least 1.5 cm beyond the heels. Sizing and fitting the shoe this way increases the weight-bearing surface of the foot and moves it more palmarly.

Unless a commercial rail shoe² or a shoe with a thickened heel is used, wedge-shaped strips of aluminium (rails) are glued to each shoe branch to elevate the heels. The rail is glued along the axial border of the shoe branch, on the ground surface of the shoe (Fig 1). Note: the rails are applied after the shoe is shaped to fit the trimmed foot.

Fig 1: An inexpensive wide web aluminum shoe with rails attached using composite.

Fig 2: Schematic drawing of measurements for realignment. Line 1 is drawn parallel and about 15 mm distal to the solar surface of P3. Line 2 is drawn parallel and approximately 15-18 mm dorsal to the parietal surface of the distal phalanx. Point A at the intersection of lines 1 and 2 is the point where the toe of the shoe should be set. Point B is approximately 6 mm dorsal to the dorsal margin of P3 and the point of breakover.

6. Preparation

The procedure essentially involves trimming the heels and attaching the shoe in such a way that the shoe is parallel with the solar margin of the distal phalanx. In a foot with significant phalangeal rotation, there will inevitably be some divergence of the shoe from the bearing surface of the hoof in the toe area. Before applying the shoe, it is necessary to determine what the relationship between the hoof and the shoe will be when the shoe is positioned parallel with the solar margin of the distal phalanx. The lateral radiograph is used to guide trimming of the hoof and alignment of the shoe (Fig 2; Parks 2003).

First, a line is drawn 20 mm distal to, and parallel with, the solar margin of the distal phalanx (line 1); this is the plane to which the ground surface of the foot should be trimmed. Any horn at the heels and quarters that extends below this line is removed before the shoe is applied. A distance of 20 mm is required to ensure an adequate distance between the solar margin of the distal phalanx and the ground surface.

Next, a line is drawn 15-18 mm dorsal to, and parallel with, the dorsal surface of the distal phalanx (line 2). Where lines 1 and 2 intersect (point A) is the dorsal-most point that the shoe should be positioned relative to the ground surface of the foot, although it may be positioned more palmarly.

Lastly, a short line is drawn from the tip of the third phalanx to meet line 1; this line should be perpendicular to line 1 (rather than vertical). A mark (point B) is made at the ground surface approximately 6 mm dorsal to where these lines intersect; this is the preferred location for breakover (Page 1999).

Alternatively, a vertical line can be drawn from the apex of the third phalanx and a mark made where that line meets the ground surface of the foot (Page 1999). In most cases, both methods place point B in approximately the same location. To guide shoe placement, a mark is then made on the sole of the foot to indicate the location of point B, using the notch in the apex of the frog as a reference point.

When there is significant phalangeal rotation, which for this paper is defined as 10° or greater, line 1 and the bearing surface of the hoof will diverge, creating a wedge-shaped gap at the toe. The distance between the bearing surface of the hoof and line 1 (which represents the inner surface of the shoe) indicates how much composite will be required to fill the gap between the shoe and the hoof. This space should be at least 15-20 mm.

When bonding the shoe to the foot, the composite will not extend further forward than the apex of the frog, so only the caudal part of the gap will be filled. It is useful to measure the distance between line 1 and the bearing surface of the foot at the apex of the frog (thumb tack) on the lateral radiograph. This measurement indicates how thick the composite should be at its widest point when bonding the shoe to the foot.

7. Procedure

Prepare the foot and apply the shoe as follows:

Fig 3: The shoe is pressed into the composite until the angle predetermined on the radiograph is achieved.

1. Trim the bearing surface of the foot to match line 1 (i.e. remove the horn that extends below line 1 on the radiograph). If possible, trim down to solid horn; explore any tracts or areas of hoof wall separation before applying the composite. With severe phalangeal rotation and no appreciable sole depth, trimming the heels to realign P3 with the ground surface will result in an unlevel bearing surface (i.e. bearing surface at the heels and quarters on a different plane from the bearing surface at the toe). This is not a problem, as the shoe does not need to contact the bearing surface at the toe, and the composite will fill in and negate the change of angle.
2. Shape and fit the shoe to the foot.
3. Cut a piece of (plastic) gutter guard to match the size of the shoe.
4. Prepare the composite (85-115 g, depending on the size of the foot) according to the manufacturer's directions. Wear gloves when working with the composite.
5. Attach the rails to the shoe using approximately 28 g of composite.
6. Take each square of fibreglass mesh, cut the two borders and tease it apart to separate the fibres; keep the two piles of fibres separate. Mix an equal amount of composite with each pile of fibreglass; roll each pile of composite fibreglass mix into a solid cylindrical or tubular structure.
7. Clean the trimmed area of hoof and matching surface of the shoe with denatured alcohol; allow to dry completely.
8. Apply a thin layer of plain composite to the bearing surface of the wall, from frog apex to heel; work it into the hoof surface.
9. Place a composite-fibreglass roll along the bearing surface of the hoof wall on each side of the foot, beginning at the apex of the frog and extending back beyond the heels.
10. Place the shoe with gutter guard over the composite rolls, using the mark made on the sole to guide shoe placement. Note: the gutter guard is placed between the hoof and the shoe.
11. Press the shoe into the composite until the angle between hoof and shoe determined on the radiograph is achieved (Fig 3). In most cases, the shoe will be separated from the hoof by only a thin layer of composite at the heels but by several millimetres of composite at the level of the frog apex. Take care to ensure good lateral-medial balance when setting the shoe into the composite. Divergence of the shoe from the hoof results in a space between shoe and hoof at the toe. This configuration is to be expected in a foot with significant phalangeal rotation, as the shoe is positioned to be parallel with the solar margin of the third phalanx, rather than with the hoof. In addition to restoring the third phalanx alignment, it unloads the laminar and solar corium at the toe, and it prevents contact between the shoe and the sole in this area. Having premeasured the distance between line 1 and the bearing surface of the hoof at the frog apex on the radiograph is very helpful during this step.
12. Cover the foot with plastic wrap and continue to hold the foot off the ground until the composite cures, which usually takes 2-3 mins. Then remove the plastic and set the foot down.
13. Mix the silastic polymer and apply it to the solar surface of the foot (from dorsal to the frog apex to the heels) to fill the space under the toe and the shoe branches. Press it into the gutter guard to hold it in place.

In horses with bilateral laminitis, the same procedure is performed on the opposite foot. As mentioned above, if a surgical release procedure is deemed necessary, it is performed after the shoe is applied.

8. Aftercare

The horse should be confined to a stall for the first 3 weeks. Short periods of hand walking can begin after this time. Nonsteroidal anti-inflammatory drugs are administered as needed. In most cases the shoes are reset every 4-5 weeks. The shoe is easily removed using hoof nippers, beginning with one or two 'bites' through the composite at the heels.

The rails are lowered at each reset; typically rail shoes are needed for only 2 or 3 shoeings. This glue-on system is continued until there is sufficient hoof wall growth for alignment of P3 to be maintained just with trimming and conventional shoeing.

9. Results

Records were reviewed for 47 horses with chronic laminitis in which this technique was used. In all cases, the condition had been present for >3 months, there was >10° of P3 rotation, the hoof tester response was positive, and lameness severity at least Obel Grade II on a scale from I (mild) to IV (severe). All horses underwent the above procedure for realignment of the third phalanx. In addition, deep flexor tenotomy was performed on 14 horses and inferior check desmotomy on 2 horses that had significant phalangeal rotation.

At the first reset (5 weeks after the shoes were first applied), lameness was decreased at least one grade, hoof tester pain was absent, and there was a notable increase in sole thickness and hoof wall growth at the toe in all 47 horses. The average increase in sole thickness was 3-5 mm. By the third reset, hoof wall and sole growth were sufficient for continued realignment of P3 to be accomplished simply by trimming the hoof capsule. At this and subsequent resets, the shoes were attached in a conventional manner using nails.

No adverse effects of the procedure have been noted to date. In all cases the lameness was sufficiently improved that controlled turnout could be tolerated. Of the total, 30 horses (63.8%) returned to some level of usefulness, although below their former level of athletic ability. The 2 cases that underwent inferior check desmotomy were in this group. The remaining 17 horses (36.2%) were pasture sound. The 14 cases that underwent deep flexor tenotomy were in this group.

10. Discussion

This glue-on technique for shoeing chronically laminitic horses is quick, simple, atraumatic, inexpensive and logical. Using radiographic guidance, the shoe is bonded to the foot in a manner that realigns the third phalanx relative to the ground surface. By also raising the heels, this approach decreases tension in the DDFT and along with the appropriate breakover is thought to minimise tension and leverage on the dorsal hoof wall during breakover, and relieves focal compression of the solar and coronary corium, which in turn reduces pain and promotes horn growth. This procedure is more effective and allows greater flexibility and precision in realigning the third phalanx than any other technique I have used. It can be tailored to the specific requirements of each foot simply by using more or less of the composite as needed.

The importance of having a good lateral radiograph from which to work cannot be overstated (Fig 4). Without a lateral radiograph, it is impossible to determine the precise orientation of the distal phalanx, and thus the degree of intervention necessary to realign the third phalanx with the ground surface. The primary reason this glue-on shoeing technique may be less than satisfactory in inexperienced hands is failure to achieve the desired angle between the shoe and the hoof, and thus realignment of the third phalanx along with failure to relieve DDFT tension. This mistake can be avoided by studying the lateral radiograph and deciding how to orient the shoe in relation to the bearing surface of the hoof before commencing.

Fig 4: Radiographs indicating before and after realignment.

Although few of the horses with chronic laminitis returned to their former level of athletic use, all horses treated with this technique have become more comfortable. All are at least pasture sound and able to move about freely with minimal analgesic medication. In many of the laminitic horses treated in this practice, permanent vascular and structural damage within the foot prevents full recovery, regardless of which technique is used to realign the third phalanx and support the foot.

In summary, effective management of chronic laminitis involves restoring the alignment of the third phalanx relative to the ground surface. Clinical experience has shown the glueon shoeing technique described here to be a simple and atraumatic method of effectively realigning the distal phalanx, and thus improving comfort and hoof growth in horses with chronic laminitis.

Manufacturers' Addresses

• ¹ Equilox International, Pine Island, Minnesota 55963, USA.
• ² Nanric, Inc., Versailles, Kentucky 40383, USA.

References

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