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Foot management
Foot Management Scott Morrison, DVM Laminitis is managed by determining if the foot is in the acute stage, in which the bone has not yet displaced or in the chronic stage, in which the bone has displaced, either by rotation, sinking, or both. Chronic cases may be chronic, compensated (in which the coffin bone is to some degree stable but out of alignment) or chronic, uncompensated (the bone is still actively displacing, the laminae are still tearing and the sole corium beneath is still being compressed). Treatments and goals are different for each of these three categories. Laminitis usually causes mechanical failure limited to the toe region as a result of the powerful tensile forces acting on the dorsal regions of the foot. When laminae fail the DDFT continues to pull without opposition and the coffin bone rotates and displaces downwards. Baseline and subsequent lateral radiographs, as well as venograms, provide a basis for categorizing cases and to measure progress or deterioration. During the acute phase, the aim is to prevent the coffin bone from displacing or entering the chronic phase. Heel elevation that decreases the tensile force on the dorsal laminae and transfers load to the sole, frog and bars is recommended. Foot breakover should be moved to a more palmar position, since the tension on the DDFT is greatest during breakover. Cases recovering from the acute phase, without P3 displacement, may recover without significant damage. In chronic laminitis the coffin bone rotates, is displaced downwards and compresses the sole corium beneath it. Additionally, the coronary corium is pulled beneath the fixed hoof wall, is compressed and ceases to grow normally. Coronary band grooving and, in severe cases coronary band resection, can alleviate compression and return normal growth to the hoof wall. The hoof is trimmed to bring the coffin bone back to its normal position relative to the ground. The base of support is moved back toward the heel region, to preserve sole depth (especially in the toe area compressed by the rotated P3) and to ease breakover by decreasing tensile tearing of the dorsal laminae. Shoes can be fabricated to augment the foot trim. Where a plum line, dropped from the dorsal coronary band, intersects the ground, is the point of breakover that relieves most of the tension on the dorsal laminae. A deep digital flexor tenotomy, done in conjunction with proper trimming/shoeing, can be a cheaper and less time consuming way to achieve balance and rehabilitation. Secondary complications such as bruising, abscessation, osteomyelitis, seroma formation and coronary band shearing are features of unstable/uncompensated chronic laminitis and present greater therapeutic difficulties. Disinfected maggots (larval therapy), that debride necrotic tissue, are useful for treating deep seated hoof infections. Clin Tech Equine Pract 3:71-82 © 2004 Elsevier Inc. All rights reserved. KEYWORDS acute, chronic laminitis, lateral radiographs, venograms, heel elevation, foot breakover, horseshoes, coronary band grooving, coronary band resection, deep digital flexor tenotomy (DDFT), larval therapy
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ypical cases of laminitis, which are presented for foot management, are in either the acute or chronic phase of the disease. In either scenario we are dealing with a foot that has already accrued damage and is to some degree unstable and thus vulnerable to further insult. It is essential that the laminitic foot be treated delicately and appropriately for the best outcome. In managing laminitis it is important to determine if the foot is in the acute stage, in which the bone has not
Rood and Riddle Equine Hospital, Lexington, KY. Address reprint requests to Dr. Scott Morrison, Rood and Riddle Equine Hospital, Lexington, KY. E-mail: [email protected].
1534-7516/04/$-see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1053/j.ctep.2004.07.007
yet displaced or in the chronic stage, in which the bone has displaced, either by rotation, sinking, or both. The chronic stage can be further broken down into the chronic, compensated (in which the coffin bone is to some degree stable but out of alignment) and the chronic, uncompensated (the bone is still actively displacing, the laminae are still tearing and the sole corium beneath is still being compressed). Our treatments and goals are different for each of these three categories. To fully understand how to treat a laminitic foot, we must first understand some of the forces at play. The coffin bone is suspended in the hoof capsule primarily by the laminae and 71
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Figure 1 Lateral radiograph of a normal foot showing the relationship between the dorsal hoof wall and the distal phalanx.
is also to some degree supported by the arch of the sole, frog and bars. Although the laminae suspend the entire perimeter of P3, the overwhelming majority of chronic laminitis have mechanical failure limited to just the toe region. There are several theories for why most horses rotate at the toe rather than sink medially or laterally: 1) Laminar damage may be uniform but the forces acting on the foot create more tensile stress to the laminae in the toe region. Studies with force plates show that the horse during stance, primarily loads the dorso medial toe region. 2) The palmar aspects of the foot receive additional weight bearing from the frog and bars whereas the toe is primarily suspended by the laminae. 3) If one believes the decreased lamellar perfusion theory of laminitis, the blood flow to the foot supplies the heels first then supplies the toe last. Therefore if laminitis is caused by a decreased perfusion the anterior regions of the foot may be affected more severely. In observing the trends of hundreds of laminitic cases, it is the author’s belief that laminar damage is fairly uniform but the powerful tensile forces acting on the toe region cause the weakened laminae to fail first at the toe. This can be demonstrated by observing venogram patterns, growth ring changes, and regional mechanical failure following loading of different regions of a laminitic foot. When the horse is fully weight bearing and the fetlock is displaced downward, the deep digital flexor tendon (DDFT) is put under tension. As the DDFT is loaded, it pulls on its insertion site at the semilunar crest of the coffin bone. This causes the coffin bone to rotate downward around its center of articulation within the distal interphalangeal joint. The slight displacement of the coffin bone which occurs in the healthy foot is exaggerated when the laminae are weakened. A simplified view of the supporting structures of the coffin bone in the sagittal plane can be seen in Fig. 1. Basically the laminae suspend the dorsal regions of the coffin bone and the DDFT slings the palmar regions. If the laminae are compromised the DDFT continues to pull without opposition and the coffin bone rotates and displaces (Fig. 2).
Figure 2 Radiograph of laminitic foot with compromised laminae. The deep digital flexor tendon (DDFT) has pulled, without opposition, and the coffin bone has rotated and displaced downwards.
Likewise if the DDFT were to be severed the palmar aspect of the coffin bone would drop downward within the hoof capsule (Fig. 3).
Managing the Acute Laminitic Foot The acute phase is defined as the onset of foot pain and usually lasts up to 72 hours. Cases which are still showing clinical signs without improvement after the first 72 hours, are very likely to develop coffin bone displacement and enter the chronic phase. About 80% of horses are nursed successfully through the acute phase with conservative treatment. Like many other acute musculoskeletal injuries, our initial approach to treatment is immobilization of the compromised tissue, rest and systemic use of antiinflammatory medication. The problem with the acute condition is that we cannot accurately assess the extent of lamellar damage. For this reason all cases should be treated as emergencies and monitored carefully. Ideally the owner/manager should patiently and gently move the horse to a deeply bedded stall until a veterinarian/farrier can perform the initial examination and start the initial treatment. The initial examination should asses the coronary band for a palpable ledge, swelling or discharge. Additionally the foot should be cleaned of debris and rocks and the shoes removed if possible. If the foot is overgrown or neglected, it should be
Figure 3 Radiograph of foot with the DDFT severed. The palmar aspect of the coffin bone has dropped downwards within the hoof capsule.
Foot management quickly trimmed to back up the base of support. A baseline lateral radiograph should be taken at the first examination. This initial radiograph provides a basis to measure progress or deterioration. Some cases may have had previous episodes of laminitis and may have some old coffin bone displacement which is essential information gained from the initial radiograph. Care should be taken during the examination and radiograph not to stress the compromised laminae. The examination, foot trim, and radiography should be done with the horse in a deeply bedded stall or with the opposite foot supported and should be performed quickly and efficiently. The assistance of an experienced farrier will make this initial process a lot more efficient and less traumatic. Given the fact that the majority of chronic cases have mechanical failure limited to the toe region, the initial treatment should be aimed at mechanically relieving the tensile forces in this region. In the acute phase the foot is best managed with the use of temporary, easily removable devices that can be bandaged to the foot and nontraumatically applied and removed as needed. Nailing a shoe in place is contraindicated in this phase as it compresses the hoof capsule to some degree and can set off a cascade of events leading to further damage. Gluing a shoe on in this phase is also contraindicated as the horse is forced to hold the foot up for an extended period of time during the gluing procedure and this may prove harmful to the opposite foot. It is also extremely important not to confuse the situation with other complications that are occasionally associated with adhesives such as subsolar or submural infections or sole pressure. Additionally, removing adhered devices can cause unnecessary trauma to the already compromised fragile foot. The goal, during the acute phase, is to prevent the coffin bone from displacing or entering the chronic phase. This is best accomplished by decreasing tensile force on the anterior laminae and unloading the laminae to some degree by transferring load to the sole, frog and bars (providing axial support). There are several sole/frog support materials available on the market (eg, impression materials, foam, and rubber pads). Some are hard and some softer and more elastic. The harder materials offer more support and immobilization but are less forgiving to a thin, weak sole. The softer more elastic materials are more forgiving but offer less immobilization and support. A conscientious and thorough examination of the foot, appropriate selection and careful monitoring of the horse is essential for any device to be used effectively. The use of general support of the entire sole is a fairly safe approach as the weight is distributed over a large area. It is a good idea to “map out” the foot with hoof testers and trim the sole support materials away from painful areas of the foot. Materials such as Styrofoam blocks can be cut to fit the foot. However, additional Styrofoam has to be added daily as the horse crushes and maximally compresses the Styrofoam quickly. Rubber pads cut from gym mats are very useful and effective. This material compresses by 50% under the horse’s weight and resumes its normal shape when removed from the foot. These devices give the horse the ability to mold the material into the configuration that is most comfortable although most horses make a heel wedge out of them and sink more to either the medial or lateral side. More specific loading can be accomplished with frog support devices. Since a smaller area is the focus of weight distribution, great care must be taken in fitting and applying these devices.
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Figure 4 Heel elevation can be provided by using a glue-on cuff riveted to a plastic wedge pad (Nanric, Inc).
General guidelines are to fit the frog support full width to the frog and extending it forward to a vertical plum line dropped from the base of the extensor process to the ground surface. Decreasing tensile force on the anterior laminae is best accomplished by addressing the pull of the DDFT. There are two ways to decrease the influence of the DDFT on the coffin bone. One is by elevating the heel to shorten the distance between origin and insertion. The second is by moving the breakover point to a more palmar position, since the tension on the DDFT is greatest during breakover. In the acute case in which the patient will be confined to a stall, elevating the heels is most effective. It is assumed that elevating the heel decreases strain tension on the DDFT. Consequently the internal tensile force of the coffin bone against the anterior laminae should be decreased as well. Heel elevation can be provided with the use of the Redden Ultimate Cuff, Dalmer Clog, or a block of wood or plastic wedge pads riveted together (Fig. 4). Whenever we alter the position of the hoof with artificial aids such as wedges, we put additional stress on other regions of the foot. A heel wedge will load the quarters and heels. Most horses show immediate improvement after the application of a 10° wedge combined with sole/arch support. If they don’t show immediate improvement or become worse, I become suspicious that the external regions of the dorsal wall and sole are overloaded with the heel elevation (ballerina effect). This can be ruled out by removing (trimming out) the sole support material from the toe regions and re-applying the cuff. The occasional horse will still appear worse with a wedge, even with the dorsal sole relieved. These cases usually have severe lamellar damage and may be sinking. I attribute this to the ball in a box scenario. If we place a ball (the coffin bone) in a box (the hoof capsule) then raise one end of the box, the ball will roll forward within the box. If this is the coffin bone and the tilted (wedged) hoof capsule, the coffin bone may be compressing the dorsal structures (laminae, sole corium) between itself and the hoof wall. In these cases, I keep the foot flat and use axial support only. The important thing to remember is that we cannot recommend a prescription for every case. In the end careful reading of the patient will dictate which treatments are suitable and which are causing more damage. Each foot is unique and every case is different so careful monitoring, immediately after the application of the device, is crucial.
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Figure 6 Modified cuff and heel wedge to give the foot a rocker action and an “air wedge” in the heel region. The heels of the wedge have been beveled with a rasp or grinder and the point of breakover has been brought back.
Figure 5 A laminitic foot with overloading of the quarters and heels. At the quarters and heels the growth rings are compressed more than those of the toe.
Post Placement Monitoring In the acute stage the extent of lamellar damage is unknown and because of this careful monitoring of the foot in the acute or early chronic phase is essential. Early detection of regional overloading or lamellar failure is critical. The hoof capsule (wall and sole) is continuously growing and replacing itself. Hoof capsule growth is monitored at the coronary band and sole regions. A healthy foot has continuous even hoofwall growth from the coronary band. Thus, a hoof growth ring should be parallel to the coronary band in the heel, quarter, and toe regions. A sign of lamellar damage or structural failure is a decreased or absent growth of wall or sole tissue. As the coffin bone rotates and is displaced downwards the sole corium beneath it is compressed and fails to grow. Additionally the coronary corium is pulled beneath the fixed hoof wall; this creates a palpable ledge proximal to the hoofwall. If the displacement is severe enough, the coronary band shears and separates. An early sign of coronary band damage is slowed or ceased hoofwall growth especially in the toe region. Often the acute laminitic foot is wedged to decrease tensile strain on the anterior laminae. When the foot is artificially propped up with wedges the ground reaction force (GRF) is moved toward the heel and quarter regions. If the laminae in these regions are weakened, occasionally signs of overloading or compression of the quarters and heels appear (Fig. 5). The slowed hoof wall growth will be seen most in the palmar quarters and then normal growth resumes in the heel region. The reason for this growth pattern is that the palmar processes of the coffin bone end in the palmar quarter region. The hoofwall behind the bone column is unaffected by the compressive forces of the horse’s weight. Once overloading of the quarters is detected the height of the wedge should be slowly decreased. The heels of the wedge can be beveled down with a rasp or grinder; additionally the point of breakover can be brought further back. This combination of changes gives the foot a rocker action and an “air wedge” (Fig. 6) in the heel region which may put less force on the heels while achieving heel elevation.
The mechanics of this shoe have not been objectively studied. It is unknown if an “air wedge” puts less force on the heel compared with a conventional solid wedge. In an attempt to prevent progression of coronary band damage or to prevent a shear lesion from forming, the use of coronary band grooving can alleviate compression and even speed up hoofwall growth in a given region (Fig. 7). In addition to the daily monitoring of the coronary band, radiographs should be taken every 7 days to monitor sole growth or loss. The hallmark of foot stability is even hoofwall growth and healthy restoration of sole tissue (which can only be monitored with consistent good quality radiographs). Clinical improvement alone can be misleading as some severe cases with a lot of vascular/nerve damage can go through a period of comfort (6-8 weeks) while the foot is numb and undergoing necrosis. Improving clinical signs coupled with regenerating wall and sole offer a superior prognosis. Once the horse is walking sound with the assistance of axial (sole/ frog) support and wedging for 7 to 10 days, we slowly decrease the dosage of antiinflammatory medication. The horse must walk sound without analgesics or antiinflammatory medications for at least 7 days before we begin to wean the patient from mechanical support. Initially the 10° wedge is reduced by 50% and monitored closely. If the comfort level significantly decreases then the 5° wedge is replaced and decreased by smaller increments. Once the wedge is reduced the horse must walk sound for 5 to 7 days before another
Figure 7 Foot showing coronary band grooving.
Foot management
75 ment of the farrier is essential in determining how much to trim in each particular foot. Cases that recover from the acute phase without any displacement are expected to make 100% recovery without any known permanent damage. However, we should cautiously rehabilitate these cases and slowly increase their activity level 30 to 45 days after the acute episode has resolved. Cases which develop coffin bone displacement are put into the chronic laminitis category (compromised/ uncompromised) and should be restructured and treated as such.
Restructuring the Chronic Laminitic Foot
Figure 8 A shoe made and fitted to provide the required degree of breakover.
reduction is attempted. Once the horse is weaned from the mechanical support the patient is either left barefoot with specific trimming or shod depending on the foot type and depth of sole. In either event the foot must be trimmed or shod to increase palmar support or move the GRF toward the heel region. Additionally the breakover point must be kept behind diseased or compromised toe tissue, therefore decreasing tensile force on the dorsal laminae. My general guideline for achieving this is to drop a vertical plum line from the most dorsal aspect of the coronary band toward the ground surface. The foot should be gently rolled or rockered from this point forward. Each foot should be treated individually. Some severely affected feet are so anatomically compromised they cannot be trimmed in this way, in which case a shoe is made and fitted to the foot to provide the required degree of breakover (Fig. 8). The dorsal sole region should not be excessively invaded with this trimming pattern. Experience and the good judg-
As mentioned earlier chronic laminitis can be categorized as compensated or uncompensated. Compensated is the foot which has had pedal bone displacement in the past but has compensated or stabilized to some degree. The foot regenerates or maintains sole depth and continues to regenerate hoofwall all around the coronary band. This foot has remodeled and altered its growth pattern to compensate for the weakened laminar attachments. This foot may have a high heel or increased growth in the heel region and slowed growth in the toe region. This irregular growth pattern is a direct consequence of and is the foot’s way of compensating for the imbalance between lamellar strength and rotational forces on the coffin bone. Essentially the growth pattern has reestablished a balance between the pull of the DDFT and the strength of the anterior lamellar attachments. Consequently, the position of the coffin bone is at a more acute angle to the ground (Fig. 9). The tip of the coffin bone often suffers remodeling and demineralization due to excessive ground force derived from this abnormal angle. This foot has patent blood supply to all regions of the foot. The health of the coronary band and sole corium is intact. Although this foot maintains sole growth, often the anterior sole mass is thin or compressed to some degree. Our goal is to restructure or remodel the compensated foundered foot over time. Eventually we plan to create a foot
Figure 9 Radiographs showing feet in which the position of the coffin bone is at a more acute angle than normal, to the ground.
76 with a coffin bone that has reestablished its normal orientation relative to the ground and maintains adequate sole depth and even parallel hoofwall growth from all around the coronary band. To achieve this, we must come up with a mechanical plan to restore balance between the rotational forces on the coffin bone (the pull of the DDFT and the horse’s body weight), and the compromised lamellar attachments. In each foot this mechanical formula will be slightly different. As stated earlier, the pull of the DDFT is a major component of the rotational forces acting on the coffin bone. Reason would dictate that the coffin bone can’t be forced into proper alignment simply by lowering the heels to achieve alignment. Doing this would increase the tension of the DDFT and can make the foot unstable, unbalanced and worsen laminar inflammation that can lead to further displacement. The foot can achieve normal alignment by mechanically promoting more wall/sole growth in the dorsal region and decreased need for increased growth in the palmar regions. The foot eventually reestablishes alignment through its altered growth patterns. Re-alignment can’t be forced into the foot with aggressive trimming. A combination of heel elevation, axial sole/frog support, and improved breakover is all that is usually needed to rebalance the foundered foot. The first step in re-balancing the foot is the foot trim. The second step is shoe fabrication and application. Foot Trim Our initial foot trim pattern and goals are similar for every foundered (rotated) foot. We want to move the base of support back toward the heel region, preserve anterior sole depth and ease breakover to decrease tensile tearing of the anterior laminae. The foot trim should be applied to each foot in varying degrees depending on the foot type and foot mass. Whatever mechanical goals cannot be achieved with trimming alone should be fabricated into the shoe. Some feet have very little depth to work with and can only be gently cleaned up, therefore all the mechanics need to be built into the shoe. On the other hand, some feet have a lot of depth and mass and all of our mechanical goals can be achieved with the trim alone. With the limitations and restrictions of each foot type in mind, our method of moving the base of support palmarly is simply achieved by rasping the heels down (Fig. 10). As the heels grow, they tend to migrate forward, thus shifting the base of support dorsally. The consequence of lowering the heels is the potential of increased tension on the DDFT and increased rotational forces. This process should be done modestly if you plan to leave the horse barefoot. However, if a shoe is going to be made and applied, the heels can be safely moved back to the widest part of the frog and the heel height difference can be supplied with a wedge or a rail. The second component of the trim is to create easy foot breakover to decrease tension and tearing of the anterior laminae. As a general rule, I prefer the breakover point be set behind the diseased tissue. Therefore I use the dorsal coronary band as a starting point or reference point. A plum line is dropped from the dorsal coronary band to the ground. If the foot breaks over at this point, the majority of the anterior laminae are relieved of breakover force/tension. The foot should only be gently rolled or rockered from this point forward. Care should be taken not to excessively invade sole
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Figure 10 Foot with the heels lowered to move the base of support palmarly.
mass to achieve this pattern. If the sole mass is thin beneath the tip of P3 then the foot should only be rockered from a point just in front of the tip of P3 and a shoe can be applied which has the breakover point forged into it further back. The breakover point can be slowly worked back with each trimming or shoeing as foot depth increases. The reason for incorporating the rolled or rockered toe into the foot that is going to be shod is that I plan on eventually getting this foot out of shoes and barefoot. Having the trim pattern already in the foot makes the transition from shoes to barefoot easy. Keeping the toe rolled or rockered aids in preventing dirt and debris from packing into the widened white line in the toe region and causing seedy toe or a gravel. The quarters should be heavily rolled as well. This aids in medial–lateral breakover which reduces the painful twisting or torque force on the laminae. The sole, frog, and bars should only be cleaned of exfoliating, weak tissue. The structure of these tissues should not be invaded. Shoeing The role of shoes is to enhance the mechanics of the basic foot trim. Additionally, the shoe can offer additional support and provide heel elevation if necessary. There are various shoe modifications (Table 1) that can be incorporated into the design of a shoe to achieve our goals. With these tools at hand we can now formulate a treatment plan with the aim of achieving a balance between diseased laminae and the rotational forces (DDFT, body weight) exerted on the foot. We can implement various shoe/trim modifications to decrease the rotational forces and change the growth pattern of the foot and eventually have a coffin bone that is re-aligned with the ground and a foot that builds and maintains an adequate and even thickness of sole mass. For most average size feet (5 inch diameter) the combination of a 1/4-inch to 1/2-inch elevating heel rail, with the breakover point set underneath the dorsal coronary band, is all that is required to slowly restructure the foot over time. The hoof heel height should not be reduced/trimmed by much more than the rail height (1/4 inch to 1/2 inch) at each shoeing. The
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Table 1 The Modifications that Can Be Incorporated into the Design of a Shoe
Axial Support Heartbar Heel Plate Sole Support Materials Foot Cast
Decrease DDFT Tension/Lamellar Tension Rails Roller Motion Shoe Wedge Pads Rolled Toe Open Toe Shoe Rockered Toe
Protection Wide Web Toe Plate Treatment Plate Pads Foot Cast
Increase Base of Support Extended Heels Eggbar Straight Bar Heel Trim
With these tools at hand we can now formulate a treatment plan with the aim of achieving a balance between diseased laminae and the rotational forces (DDFT, body weight) exerted on the foot. We can implement various shoe/trim modifications to decrease the rotational forces and change the growth pattern of the foot and eventually have a coffin bone that is re-aligned with the ground.
chance of putting too much tension of the DDFT by lowering the heels is counteracted by replacing the lost angle with rails and easing breakover significantly (Fig. 11A and B). The need for additional support and protection is variable and dictated by each case. If the sole is extremely thin or prolapsed, it is a good idea to offer protection in the form of a solid plate welded into the shoe or with a removable treatment (hospital) plate. If the integrity of the heels and quarters are weak or uncertain, it is a good idea to offer additional support with heartbars shoes, silicone sole support material, heel plates, etc. (Fig. 12). As the horse’s foot is monitored in the weeks postshoeing, we should see more even wall growth and an increased dorsal sole depth (Fig. 13A and B). Failure of the foot to respond clinically or radiographically
to shoeing mechanics may warrant more aggressive mechanics or a deep digital flexor tenotomy to restore balance to the foot. A deep digital flexor tenotomy, done in conjunction with proper trimming/shoeing, can be an excellent treatment option for some cases (see below). Often the tenotomy can be a faster way to achieve balance and rehabilitation of the foot. In many cases the tenotomy can be cheaper and less time consuming for the owner. We are able to get most chronic compensated cases barefoot and comfortable in one to two shoeings post tenotomy thus eliminating the need for long term expensive special shoeing. Following restoration of normal pedal bone alignment and proper foot mass, the posttenotomy foot is maintained with trimming alone, every 6 weeks, as described earlier. The foot should be trimmed to ease break over and maintain coffin bone alignment. Periodic radiographs are recommended to check pedal bone position. Restructuring the Chronic Uncompensated Laminitic Foot Restructuring the unstable/uncompensated foot is often very difficult. This foot type has massive vascular damage, secondary infections, and loss of important tissue generating structures, such as coronary and sole corium.
Figure 11 Heartbar shoe with a square, rockered toe to supply ease of breakover and rails to elevate the heels. Ground surface view (A) and side view (B).
Figure 12 If the heels and quarters are weak they can be supported by the addition of silicone support material to the palmar sole.
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mechanics alone, a deep digital flexor tenotomy may be warranted. Trying to treat a penetrated coffin bone with shoeing alone takes far too long; the bone suffers too much inflammation and demineralization and there is chronic, relentless pain for the animal. A deep digital flexor tenotomy is the fastest way to counteract the rotational forces and restore perfusion and tissue mass to the dorsal regions of the foot. The horse’s future soundness will not be determined by the fact it has had a tenotomy. However, it is limited by the pathology within the foot and preservation of a healthy coffin bone should be a priority.
Deep Digital Flexor Tenotomy and De-Rotation Shoeing The transection of the deep digital flexor tendon allows us to immediately re-align the coffin bone in relation to the ground surface. I prefer to shoe the horse before surgery because often the shoe must be glued on and the surgical preparation for the tenotomy often gets the foot wet and unsuitable for gluing. The goal for de-rotation shoeing is to glue a shoe, which is parallel to the ground surface of the coffin bone, onto the foot. Additionally the shoe should also provide heel extension to prevent the toe from hyperextending following transection of the DDFT. Using the lateral radiograph as a blueprint (Fig. 14A), several measurements should be made to assure proper shoe alignment. For an average size foot, at
Figure 13 Post-shoeing, there should be even wall growth below the coronary band (A) and increased dorsal sole depth (B).
The initial approach to the unstable foot is often similar to the acute laminitic foot. I usually perform a venogram as part of my initial diagnostic workup to better asses the extent of instability and tissue compression (Fig. 14A and B). The information gained from the external examination of the foot, venogram, and radiographs will dictate which treatment modalities need to be implemented. There is no way to describe a systematic approach to dealing with every severe laminitic foot. Each case is different and every foot is unique. Treating laminitic feet requires experience, good judgment, and a well coordinated effort by the farrier, veterinarian, and owner/manager, combined with good nursing care. The short-term goal, for the unstable laminitic foot, is to preserve the integrity of the coronary band and sole corium and thus its vasculature. Our ultimate goal is to maintain health of the coffin bone and eventually re-establish normal coffin bone alignment and adequate sole depth. It is important to realize that the secondary complications such as bruising, abscessation, osteomyelitis, seroma formation and coronary band shearing are a consequence of digital instability and tissue compression. For this reason, we cannot successfully resolve these problems without formulating a plan to relieve the displacement forces and realign the coffin bone. Depending on the extent of damage, most cases can be treated by re-balancing the foundered foot with the shoeing mechanics described in the compensated and acute conditions. If the coffin bone has penetrated the sole corium or if the foot fails to show continuous improvement with shoeing
Figure 14 A plain radiograph (A) and a venogram (B) are taken to better asses the extent of hoof instability, coffin bone rotation and tissue compression.
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79 have two reference points, we can transfer the line of the shoe from the radiographs to the foot. We can draw a line on the hoof capsule that guides us in trimming the foot and in placing the shoe. The shoe is forged from aluminum or a keg shoe is used with a heel plate welded in (Fig. 15). The heel plate will help hold in the sole support and offer additional support to the palmar aspects of the foot. The sole support material is mixed and applied to the sole. The shoe is firmly placed onto the foot at the same angle as on the radiographs (Fig. 16A). Often impression material is molded at this stage into a toe wedge to achieve proper shoe alignment. Once the proper angle is achieved, the shoe is glued in place using fiberglass cloth impregnated with adhesive. The shoe is only glued in the heel and quarter regions and the toe is left open (Fig. 16B). Gluing the toe is contraindicated in a laminitic foot. This shoeing method is adequate for most cases with severe mechanical failure limited to the toe region. These feet generally respond with significant dorsal sole growth (Fig. 16C) over the next 4 to 6 weeks. If however, the foot is showing damage in either heel or quarter region, such as medial or lateral sinking, I will set my shoe slightly lower on the side of the foot opposite to that which is sinking. For example, if the foot has sunk to the medial side, I set the shoe into the sole support slightly lower on the lateral side to shift the foot’s weight distribution to the lateral heel.
Figure 15 A keg shoe with a welded in heel plate to help hold sole support material and offer additional support to the palmar aspects of the foot.
Preservation of the Coronary Band
least 3/4 inch of sole depth should be left beneath the most palmar aspect of the palmar process. A line should be drawn from this point parallel to the ground surface of the coffin. This line will represent the shoe. The line can be transferred from the radiograph to the hoof capsule using the following technique: On the radiographs measure the distance from the ground to a point where the line intersects the hoof capsule in the heel region. Measure this distance on the hoof and notch the hoof capsule at that point. Next, drop a plum line from the dorsal coronary band to the ground surface on the foot, notch this point on the hoof capsule. On the radiograph, drop the same plum line and note where this line intersects the line that represents the shoe. This often is below the ground surface of the hoof capsule so we need to measure the distance below the hoof that these two lines intersect. Now that we
With severe displacement and instability the coronary band is often internally compressed. As the displacement advances, the coronary band shears or separates as the soft tissue structures further displace beneath the fixed rigid hoof capsule. In coronary band compression, the coronary corium is still intact but hoof wall growth has slowed in this region. Coronary band compression can occur anywhere in the toe in a rotational displacement or in the quarters in a foot which is sinking medially, laterally, or vertically (Fig. 17). Proper shoeing mechanics should first be implemented. Additionally the technique of coronary band grooving has proven to be a good adjunct treatment in this scenario. Use the hoof wall growth rings as a guide to determine which area to groove. Following the constricted growth rings, groove the hoof wall using a Dremmel with a 1/4-inch diameter burr, just distal to the coronary groove. The entire wall thickness is carefully grooved until small areas of hemorrhage are evident (Fig. 17). This technique can prevent the coronary band from
Figure 16 Shoeing for feet with chronic uncompensated laminitis. The shoe is firmly placed onto the foot at the same angle as determined by the radiograph (A). Then the shoe is glued in place, using fiberglass cloth impregnated with adhesive, leaving the toe open (B). Significant dorsal sole growth (C) over the next. 4-6 weeks is the usual response.
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Figure 19 To regenerate the coronary band and thus proper hoof wall growth after a shear lesion the proximal hoof wall is resected.
Figure 17 Coronary band shearing and separation occurring in the quarters of a foot which is sinking medially. Coronary band grooving was performed in the medial quarter.
developing a shear lesion, if caught early, and can speed up hoof growth in that region (Fig. 18). If the coronary band develops a shear lesion and significant compression, often the coronary band cannot regenerate because of severe pinching and impingement by the proximal hoof wall. When coronary band separation is followed by
Figure 18 A foot that was grooved beneath the medial coronary band to prevent a coronary band shear lesion. Hoof growth has been restored (Same foot as in figure 17).
swelling and pain, a proximal hoof wall resection is required to regenerate the coronary band and thus proper hoof wall growth (Fig. 19). A semielliptical outline is drawn on the hoof capsule over the area to be resected. The resected area should include all areas below the shear lesion, tapering off to healthy coronary band in either end. The resected area should be about 1/2 inch to 1 inch distal to the coronary band (Fig. 19). A Dremmel or the oscillating blade of a cast cutter is used to cut through the hoof wall. Then, using forceps, the transected piece of hoof is removed and the area firmly packed with antiseptic soaked gauze. Following the resection the area should epithelialize within 5 to 10 days. True stratum medium should be regenerated by the coronary band over the next couple of months (Fig. 20). Failure of the tissue to epithelialize or continued impingement of the corium by the proximal aspect of the transected walls is an indication for further, more distal resection. Often the use of a foot cast is required if resections are needed in the quarter and heel regions. Immobilization of the hoof capsule
Figure 20 After proximal hoof wall resection the stratum medium, over the next couple of months, is regenerated by the coronary band.
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Figure 21 A foot after complete hoof capsule ablation (A). The yellow zones are areas of epithelialization. Months later hoof wall below the coronary band has regenerated (B).
and more uniform weight distribution by the cast may help stabilize the foot for epithelialization to occur. Topical products containing zinc may speed up epithelialization. Extra cellular (A-cell; A-Cell Vet) matrix products may also be beneficial. They act as a scaffold for epithelial cells to migrate across, thus speeding up the epithelialization process.
Medial or Lateral Sinking (Displacement): Depending on lower limb conformation, occasionally a laminitic foot will sink to either the medial or lateral side. Some of these cases are caused by the use of wedges to prevent rotation in the acute stage. Although wedging does decrease the rotational forces on the coffin bone and thus the tension on the dorsal laminae, heel wedges shift the GRF to the heels and put stress on the quarters. In some of our efforts to decrease rotation, we may cause sinking in the quarters. Once medial or lateral sinking is detected, the wedge should be removed and the horse placed into a soft rubber pad. This allows the horse to mold the rubber pad into the most comfortable configuration and take stress off the compromised areas. Coronary grooving should also be implemented at this stage in the appropriate regions. In cases which are vertically sinking, I prefer to place them into a foot cast with 1/2 inch carpet felt, soaked in antiseptic, placed on the sole surface. After the foot cast is set, I place hoof reconstruction adhesive on the ground surface forming a mild dome shape. This allows the foot to breakover in all directions and loads the axial regions of the foot and unloads the hoof wall perimeter. Euthanasia is indicated when the vertical displacement advances and shear lesions form around the entire proximal hoof wall perimeter. In some unilateral cases or in special circumstances, complete hoof capsule ablation combined with a lower limb cast or transfixation pin cast has successfully re-habilitated some feet to reasonable pasture soundness. Following hoof capsule ablation or partial hoof wall resection, the hoof heals first through laminar epithelialization (Fig. 21A). Completion of this process can vary from weeks to months depending on the amount of compression on the
exposed area. The hoof wall can take several months to begin regenerating from the coronary band (Fig. 21B). Dealing with infections while the hoof wall is regenerating can be very challenging. The extent to which these feet can be rehabilitated is questionable. The laminar attachments will always be to some degree compromised. For this reason, these cases must be intensely managed and monitored. Often special footing, shoes, boots, and exercise restrictions are necessary throughout the remainder of the horse’s life.
Infections in the Foundered Foot Due to chronic tissue damage and decreased perfusion to certain areas of the foot, tissue necrosis and infection is a common sequel in severe laminitic cases. Infections can vary from a gravel or seedy toe due to the stretched white line, subsolar/submural abscessation to osteomyelitis of P-3. Most
Figure 22 Necrotic/infected tissue from this chronically foundered foot is being removed by disinfected maggots.
82 superficial infections are resolved with alleviation of tissue compression and re-alignment of the coffin bone. Deeper infections are often more difficult to resolve. Methods to treat osteomyelitis of P-3 include surgical debridement, regional limb perfusion, systemic antibiotic therapy, and larval therapy. I have had great success treating chronic infections with gentle surgical debridement followed by larval therapy and appropriate antibiotic therapy (Fig. 22). Formulating a me-
S. Morrison chanical plan with shoeing and surgery is a critical first step to alleviate compromised tissue and restore perfusion before any other treatment can be effective. Disinfected maggots, that debride necrotic tissue, are used in larval therapy. This has the advantage of removing only necrotic/infected tissue without structurally compromising the fragile foot, as sometimes occurs with deep surgical debridement.
T
ypical cases of laminitis, which are presented for foot management, are in either the acute or chronic phase of the disease. In either scenario we are dealing with a foot that has already accrued damage and is to some degree unstable and thus vulnerable to further insult. It is essential that the laminitic foot be treated delicately and appropriately for the best outcome. In managing laminitis it is important to determine if the foot is in the acute stage, in which the bone has not
Rood and Riddle Equine Hospital, Lexington, KY. Address reprint requests to Dr. Scott Morrison, Rood and Riddle Equine Hospital, Lexington, KY. E-mail: [email protected].
1534-7516/04/$-see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1053/j.ctep.2004.07.007
yet displaced or in the chronic stage, in which the bone has displaced, either by rotation, sinking, or both. The chronic stage can be further broken down into the chronic, compensated (in which the coffin bone is to some degree stable but out of alignment) and the chronic, uncompensated (the bone is still actively displacing, the laminae are still tearing and the sole corium beneath is still being compressed). Our treatments and goals are different for each of these three categories. To fully understand how to treat a laminitic foot, we must first understand some of the forces at play. The coffin bone is suspended in the hoof capsule primarily by the laminae and 71
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Figure 1 Lateral radiograph of a normal foot showing the relationship between the dorsal hoof wall and the distal phalanx.
is also to some degree supported by the arch of the sole, frog and bars. Although the laminae suspend the entire perimeter of P3, the overwhelming majority of chronic laminitis have mechanical failure limited to just the toe region. There are several theories for why most horses rotate at the toe rather than sink medially or laterally: 1) Laminar damage may be uniform but the forces acting on the foot create more tensile stress to the laminae in the toe region. Studies with force plates show that the horse during stance, primarily loads the dorso medial toe region. 2) The palmar aspects of the foot receive additional weight bearing from the frog and bars whereas the toe is primarily suspended by the laminae. 3) If one believes the decreased lamellar perfusion theory of laminitis, the blood flow to the foot supplies the heels first then supplies the toe last. Therefore if laminitis is caused by a decreased perfusion the anterior regions of the foot may be affected more severely. In observing the trends of hundreds of laminitic cases, it is the author’s belief that laminar damage is fairly uniform but the powerful tensile forces acting on the toe region cause the weakened laminae to fail first at the toe. This can be demonstrated by observing venogram patterns, growth ring changes, and regional mechanical failure following loading of different regions of a laminitic foot. When the horse is fully weight bearing and the fetlock is displaced downward, the deep digital flexor tendon (DDFT) is put under tension. As the DDFT is loaded, it pulls on its insertion site at the semilunar crest of the coffin bone. This causes the coffin bone to rotate downward around its center of articulation within the distal interphalangeal joint. The slight displacement of the coffin bone which occurs in the healthy foot is exaggerated when the laminae are weakened. A simplified view of the supporting structures of the coffin bone in the sagittal plane can be seen in Fig. 1. Basically the laminae suspend the dorsal regions of the coffin bone and the DDFT slings the palmar regions. If the laminae are compromised the DDFT continues to pull without opposition and the coffin bone rotates and displaces (Fig. 2).
Figure 2 Radiograph of laminitic foot with compromised laminae. The deep digital flexor tendon (DDFT) has pulled, without opposition, and the coffin bone has rotated and displaced downwards.
Likewise if the DDFT were to be severed the palmar aspect of the coffin bone would drop downward within the hoof capsule (Fig. 3).
Managing the Acute Laminitic Foot The acute phase is defined as the onset of foot pain and usually lasts up to 72 hours. Cases which are still showing clinical signs without improvement after the first 72 hours, are very likely to develop coffin bone displacement and enter the chronic phase. About 80% of horses are nursed successfully through the acute phase with conservative treatment. Like many other acute musculoskeletal injuries, our initial approach to treatment is immobilization of the compromised tissue, rest and systemic use of antiinflammatory medication. The problem with the acute condition is that we cannot accurately assess the extent of lamellar damage. For this reason all cases should be treated as emergencies and monitored carefully. Ideally the owner/manager should patiently and gently move the horse to a deeply bedded stall until a veterinarian/farrier can perform the initial examination and start the initial treatment. The initial examination should asses the coronary band for a palpable ledge, swelling or discharge. Additionally the foot should be cleaned of debris and rocks and the shoes removed if possible. If the foot is overgrown or neglected, it should be
Figure 3 Radiograph of foot with the DDFT severed. The palmar aspect of the coffin bone has dropped downwards within the hoof capsule.
Foot management quickly trimmed to back up the base of support. A baseline lateral radiograph should be taken at the first examination. This initial radiograph provides a basis to measure progress or deterioration. Some cases may have had previous episodes of laminitis and may have some old coffin bone displacement which is essential information gained from the initial radiograph. Care should be taken during the examination and radiograph not to stress the compromised laminae. The examination, foot trim, and radiography should be done with the horse in a deeply bedded stall or with the opposite foot supported and should be performed quickly and efficiently. The assistance of an experienced farrier will make this initial process a lot more efficient and less traumatic. Given the fact that the majority of chronic cases have mechanical failure limited to the toe region, the initial treatment should be aimed at mechanically relieving the tensile forces in this region. In the acute phase the foot is best managed with the use of temporary, easily removable devices that can be bandaged to the foot and nontraumatically applied and removed as needed. Nailing a shoe in place is contraindicated in this phase as it compresses the hoof capsule to some degree and can set off a cascade of events leading to further damage. Gluing a shoe on in this phase is also contraindicated as the horse is forced to hold the foot up for an extended period of time during the gluing procedure and this may prove harmful to the opposite foot. It is also extremely important not to confuse the situation with other complications that are occasionally associated with adhesives such as subsolar or submural infections or sole pressure. Additionally, removing adhered devices can cause unnecessary trauma to the already compromised fragile foot. The goal, during the acute phase, is to prevent the coffin bone from displacing or entering the chronic phase. This is best accomplished by decreasing tensile force on the anterior laminae and unloading the laminae to some degree by transferring load to the sole, frog and bars (providing axial support). There are several sole/frog support materials available on the market (eg, impression materials, foam, and rubber pads). Some are hard and some softer and more elastic. The harder materials offer more support and immobilization but are less forgiving to a thin, weak sole. The softer more elastic materials are more forgiving but offer less immobilization and support. A conscientious and thorough examination of the foot, appropriate selection and careful monitoring of the horse is essential for any device to be used effectively. The use of general support of the entire sole is a fairly safe approach as the weight is distributed over a large area. It is a good idea to “map out” the foot with hoof testers and trim the sole support materials away from painful areas of the foot. Materials such as Styrofoam blocks can be cut to fit the foot. However, additional Styrofoam has to be added daily as the horse crushes and maximally compresses the Styrofoam quickly. Rubber pads cut from gym mats are very useful and effective. This material compresses by 50% under the horse’s weight and resumes its normal shape when removed from the foot. These devices give the horse the ability to mold the material into the configuration that is most comfortable although most horses make a heel wedge out of them and sink more to either the medial or lateral side. More specific loading can be accomplished with frog support devices. Since a smaller area is the focus of weight distribution, great care must be taken in fitting and applying these devices.
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Figure 4 Heel elevation can be provided by using a glue-on cuff riveted to a plastic wedge pad (Nanric, Inc).
General guidelines are to fit the frog support full width to the frog and extending it forward to a vertical plum line dropped from the base of the extensor process to the ground surface. Decreasing tensile force on the anterior laminae is best accomplished by addressing the pull of the DDFT. There are two ways to decrease the influence of the DDFT on the coffin bone. One is by elevating the heel to shorten the distance between origin and insertion. The second is by moving the breakover point to a more palmar position, since the tension on the DDFT is greatest during breakover. In the acute case in which the patient will be confined to a stall, elevating the heels is most effective. It is assumed that elevating the heel decreases strain tension on the DDFT. Consequently the internal tensile force of the coffin bone against the anterior laminae should be decreased as well. Heel elevation can be provided with the use of the Redden Ultimate Cuff, Dalmer Clog, or a block of wood or plastic wedge pads riveted together (Fig. 4). Whenever we alter the position of the hoof with artificial aids such as wedges, we put additional stress on other regions of the foot. A heel wedge will load the quarters and heels. Most horses show immediate improvement after the application of a 10° wedge combined with sole/arch support. If they don’t show immediate improvement or become worse, I become suspicious that the external regions of the dorsal wall and sole are overloaded with the heel elevation (ballerina effect). This can be ruled out by removing (trimming out) the sole support material from the toe regions and re-applying the cuff. The occasional horse will still appear worse with a wedge, even with the dorsal sole relieved. These cases usually have severe lamellar damage and may be sinking. I attribute this to the ball in a box scenario. If we place a ball (the coffin bone) in a box (the hoof capsule) then raise one end of the box, the ball will roll forward within the box. If this is the coffin bone and the tilted (wedged) hoof capsule, the coffin bone may be compressing the dorsal structures (laminae, sole corium) between itself and the hoof wall. In these cases, I keep the foot flat and use axial support only. The important thing to remember is that we cannot recommend a prescription for every case. In the end careful reading of the patient will dictate which treatments are suitable and which are causing more damage. Each foot is unique and every case is different so careful monitoring, immediately after the application of the device, is crucial.
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Figure 6 Modified cuff and heel wedge to give the foot a rocker action and an “air wedge” in the heel region. The heels of the wedge have been beveled with a rasp or grinder and the point of breakover has been brought back.
Figure 5 A laminitic foot with overloading of the quarters and heels. At the quarters and heels the growth rings are compressed more than those of the toe.
Post Placement Monitoring In the acute stage the extent of lamellar damage is unknown and because of this careful monitoring of the foot in the acute or early chronic phase is essential. Early detection of regional overloading or lamellar failure is critical. The hoof capsule (wall and sole) is continuously growing and replacing itself. Hoof capsule growth is monitored at the coronary band and sole regions. A healthy foot has continuous even hoofwall growth from the coronary band. Thus, a hoof growth ring should be parallel to the coronary band in the heel, quarter, and toe regions. A sign of lamellar damage or structural failure is a decreased or absent growth of wall or sole tissue. As the coffin bone rotates and is displaced downwards the sole corium beneath it is compressed and fails to grow. Additionally the coronary corium is pulled beneath the fixed hoof wall; this creates a palpable ledge proximal to the hoofwall. If the displacement is severe enough, the coronary band shears and separates. An early sign of coronary band damage is slowed or ceased hoofwall growth especially in the toe region. Often the acute laminitic foot is wedged to decrease tensile strain on the anterior laminae. When the foot is artificially propped up with wedges the ground reaction force (GRF) is moved toward the heel and quarter regions. If the laminae in these regions are weakened, occasionally signs of overloading or compression of the quarters and heels appear (Fig. 5). The slowed hoof wall growth will be seen most in the palmar quarters and then normal growth resumes in the heel region. The reason for this growth pattern is that the palmar processes of the coffin bone end in the palmar quarter region. The hoofwall behind the bone column is unaffected by the compressive forces of the horse’s weight. Once overloading of the quarters is detected the height of the wedge should be slowly decreased. The heels of the wedge can be beveled down with a rasp or grinder; additionally the point of breakover can be brought further back. This combination of changes gives the foot a rocker action and an “air wedge” (Fig. 6) in the heel region which may put less force on the heels while achieving heel elevation.
The mechanics of this shoe have not been objectively studied. It is unknown if an “air wedge” puts less force on the heel compared with a conventional solid wedge. In an attempt to prevent progression of coronary band damage or to prevent a shear lesion from forming, the use of coronary band grooving can alleviate compression and even speed up hoofwall growth in a given region (Fig. 7). In addition to the daily monitoring of the coronary band, radiographs should be taken every 7 days to monitor sole growth or loss. The hallmark of foot stability is even hoofwall growth and healthy restoration of sole tissue (which can only be monitored with consistent good quality radiographs). Clinical improvement alone can be misleading as some severe cases with a lot of vascular/nerve damage can go through a period of comfort (6-8 weeks) while the foot is numb and undergoing necrosis. Improving clinical signs coupled with regenerating wall and sole offer a superior prognosis. Once the horse is walking sound with the assistance of axial (sole/ frog) support and wedging for 7 to 10 days, we slowly decrease the dosage of antiinflammatory medication. The horse must walk sound without analgesics or antiinflammatory medications for at least 7 days before we begin to wean the patient from mechanical support. Initially the 10° wedge is reduced by 50% and monitored closely. If the comfort level significantly decreases then the 5° wedge is replaced and decreased by smaller increments. Once the wedge is reduced the horse must walk sound for 5 to 7 days before another
Figure 7 Foot showing coronary band grooving.
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75 ment of the farrier is essential in determining how much to trim in each particular foot. Cases that recover from the acute phase without any displacement are expected to make 100% recovery without any known permanent damage. However, we should cautiously rehabilitate these cases and slowly increase their activity level 30 to 45 days after the acute episode has resolved. Cases which develop coffin bone displacement are put into the chronic laminitis category (compromised/ uncompromised) and should be restructured and treated as such.
Restructuring the Chronic Laminitic Foot
Figure 8 A shoe made and fitted to provide the required degree of breakover.
reduction is attempted. Once the horse is weaned from the mechanical support the patient is either left barefoot with specific trimming or shod depending on the foot type and depth of sole. In either event the foot must be trimmed or shod to increase palmar support or move the GRF toward the heel region. Additionally the breakover point must be kept behind diseased or compromised toe tissue, therefore decreasing tensile force on the dorsal laminae. My general guideline for achieving this is to drop a vertical plum line from the most dorsal aspect of the coronary band toward the ground surface. The foot should be gently rolled or rockered from this point forward. Each foot should be treated individually. Some severely affected feet are so anatomically compromised they cannot be trimmed in this way, in which case a shoe is made and fitted to the foot to provide the required degree of breakover (Fig. 8). The dorsal sole region should not be excessively invaded with this trimming pattern. Experience and the good judg-
As mentioned earlier chronic laminitis can be categorized as compensated or uncompensated. Compensated is the foot which has had pedal bone displacement in the past but has compensated or stabilized to some degree. The foot regenerates or maintains sole depth and continues to regenerate hoofwall all around the coronary band. This foot has remodeled and altered its growth pattern to compensate for the weakened laminar attachments. This foot may have a high heel or increased growth in the heel region and slowed growth in the toe region. This irregular growth pattern is a direct consequence of and is the foot’s way of compensating for the imbalance between lamellar strength and rotational forces on the coffin bone. Essentially the growth pattern has reestablished a balance between the pull of the DDFT and the strength of the anterior lamellar attachments. Consequently, the position of the coffin bone is at a more acute angle to the ground (Fig. 9). The tip of the coffin bone often suffers remodeling and demineralization due to excessive ground force derived from this abnormal angle. This foot has patent blood supply to all regions of the foot. The health of the coronary band and sole corium is intact. Although this foot maintains sole growth, often the anterior sole mass is thin or compressed to some degree. Our goal is to restructure or remodel the compensated foundered foot over time. Eventually we plan to create a foot
Figure 9 Radiographs showing feet in which the position of the coffin bone is at a more acute angle than normal, to the ground.
76 with a coffin bone that has reestablished its normal orientation relative to the ground and maintains adequate sole depth and even parallel hoofwall growth from all around the coronary band. To achieve this, we must come up with a mechanical plan to restore balance between the rotational forces on the coffin bone (the pull of the DDFT and the horse’s body weight), and the compromised lamellar attachments. In each foot this mechanical formula will be slightly different. As stated earlier, the pull of the DDFT is a major component of the rotational forces acting on the coffin bone. Reason would dictate that the coffin bone can’t be forced into proper alignment simply by lowering the heels to achieve alignment. Doing this would increase the tension of the DDFT and can make the foot unstable, unbalanced and worsen laminar inflammation that can lead to further displacement. The foot can achieve normal alignment by mechanically promoting more wall/sole growth in the dorsal region and decreased need for increased growth in the palmar regions. The foot eventually reestablishes alignment through its altered growth patterns. Re-alignment can’t be forced into the foot with aggressive trimming. A combination of heel elevation, axial sole/frog support, and improved breakover is all that is usually needed to rebalance the foundered foot. The first step in re-balancing the foot is the foot trim. The second step is shoe fabrication and application. Foot Trim Our initial foot trim pattern and goals are similar for every foundered (rotated) foot. We want to move the base of support back toward the heel region, preserve anterior sole depth and ease breakover to decrease tensile tearing of the anterior laminae. The foot trim should be applied to each foot in varying degrees depending on the foot type and foot mass. Whatever mechanical goals cannot be achieved with trimming alone should be fabricated into the shoe. Some feet have very little depth to work with and can only be gently cleaned up, therefore all the mechanics need to be built into the shoe. On the other hand, some feet have a lot of depth and mass and all of our mechanical goals can be achieved with the trim alone. With the limitations and restrictions of each foot type in mind, our method of moving the base of support palmarly is simply achieved by rasping the heels down (Fig. 10). As the heels grow, they tend to migrate forward, thus shifting the base of support dorsally. The consequence of lowering the heels is the potential of increased tension on the DDFT and increased rotational forces. This process should be done modestly if you plan to leave the horse barefoot. However, if a shoe is going to be made and applied, the heels can be safely moved back to the widest part of the frog and the heel height difference can be supplied with a wedge or a rail. The second component of the trim is to create easy foot breakover to decrease tension and tearing of the anterior laminae. As a general rule, I prefer the breakover point be set behind the diseased tissue. Therefore I use the dorsal coronary band as a starting point or reference point. A plum line is dropped from the dorsal coronary band to the ground. If the foot breaks over at this point, the majority of the anterior laminae are relieved of breakover force/tension. The foot should only be gently rolled or rockered from this point forward. Care should be taken not to excessively invade sole
S. Morrison
Figure 10 Foot with the heels lowered to move the base of support palmarly.
mass to achieve this pattern. If the sole mass is thin beneath the tip of P3 then the foot should only be rockered from a point just in front of the tip of P3 and a shoe can be applied which has the breakover point forged into it further back. The breakover point can be slowly worked back with each trimming or shoeing as foot depth increases. The reason for incorporating the rolled or rockered toe into the foot that is going to be shod is that I plan on eventually getting this foot out of shoes and barefoot. Having the trim pattern already in the foot makes the transition from shoes to barefoot easy. Keeping the toe rolled or rockered aids in preventing dirt and debris from packing into the widened white line in the toe region and causing seedy toe or a gravel. The quarters should be heavily rolled as well. This aids in medial–lateral breakover which reduces the painful twisting or torque force on the laminae. The sole, frog, and bars should only be cleaned of exfoliating, weak tissue. The structure of these tissues should not be invaded. Shoeing The role of shoes is to enhance the mechanics of the basic foot trim. Additionally, the shoe can offer additional support and provide heel elevation if necessary. There are various shoe modifications (Table 1) that can be incorporated into the design of a shoe to achieve our goals. With these tools at hand we can now formulate a treatment plan with the aim of achieving a balance between diseased laminae and the rotational forces (DDFT, body weight) exerted on the foot. We can implement various shoe/trim modifications to decrease the rotational forces and change the growth pattern of the foot and eventually have a coffin bone that is re-aligned with the ground and a foot that builds and maintains an adequate and even thickness of sole mass. For most average size feet (5 inch diameter) the combination of a 1/4-inch to 1/2-inch elevating heel rail, with the breakover point set underneath the dorsal coronary band, is all that is required to slowly restructure the foot over time. The hoof heel height should not be reduced/trimmed by much more than the rail height (1/4 inch to 1/2 inch) at each shoeing. The
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Table 1 The Modifications that Can Be Incorporated into the Design of a Shoe
Axial Support Heartbar Heel Plate Sole Support Materials Foot Cast
Decrease DDFT Tension/Lamellar Tension Rails Roller Motion Shoe Wedge Pads Rolled Toe Open Toe Shoe Rockered Toe
Protection Wide Web Toe Plate Treatment Plate Pads Foot Cast
Increase Base of Support Extended Heels Eggbar Straight Bar Heel Trim
With these tools at hand we can now formulate a treatment plan with the aim of achieving a balance between diseased laminae and the rotational forces (DDFT, body weight) exerted on the foot. We can implement various shoe/trim modifications to decrease the rotational forces and change the growth pattern of the foot and eventually have a coffin bone that is re-aligned with the ground.
chance of putting too much tension of the DDFT by lowering the heels is counteracted by replacing the lost angle with rails and easing breakover significantly (Fig. 11A and B). The need for additional support and protection is variable and dictated by each case. If the sole is extremely thin or prolapsed, it is a good idea to offer protection in the form of a solid plate welded into the shoe or with a removable treatment (hospital) plate. If the integrity of the heels and quarters are weak or uncertain, it is a good idea to offer additional support with heartbars shoes, silicone sole support material, heel plates, etc. (Fig. 12). As the horse’s foot is monitored in the weeks postshoeing, we should see more even wall growth and an increased dorsal sole depth (Fig. 13A and B). Failure of the foot to respond clinically or radiographically
to shoeing mechanics may warrant more aggressive mechanics or a deep digital flexor tenotomy to restore balance to the foot. A deep digital flexor tenotomy, done in conjunction with proper trimming/shoeing, can be an excellent treatment option for some cases (see below). Often the tenotomy can be a faster way to achieve balance and rehabilitation of the foot. In many cases the tenotomy can be cheaper and less time consuming for the owner. We are able to get most chronic compensated cases barefoot and comfortable in one to two shoeings post tenotomy thus eliminating the need for long term expensive special shoeing. Following restoration of normal pedal bone alignment and proper foot mass, the posttenotomy foot is maintained with trimming alone, every 6 weeks, as described earlier. The foot should be trimmed to ease break over and maintain coffin bone alignment. Periodic radiographs are recommended to check pedal bone position. Restructuring the Chronic Uncompensated Laminitic Foot Restructuring the unstable/uncompensated foot is often very difficult. This foot type has massive vascular damage, secondary infections, and loss of important tissue generating structures, such as coronary and sole corium.
Figure 11 Heartbar shoe with a square, rockered toe to supply ease of breakover and rails to elevate the heels. Ground surface view (A) and side view (B).
Figure 12 If the heels and quarters are weak they can be supported by the addition of silicone support material to the palmar sole.
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mechanics alone, a deep digital flexor tenotomy may be warranted. Trying to treat a penetrated coffin bone with shoeing alone takes far too long; the bone suffers too much inflammation and demineralization and there is chronic, relentless pain for the animal. A deep digital flexor tenotomy is the fastest way to counteract the rotational forces and restore perfusion and tissue mass to the dorsal regions of the foot. The horse’s future soundness will not be determined by the fact it has had a tenotomy. However, it is limited by the pathology within the foot and preservation of a healthy coffin bone should be a priority.
Deep Digital Flexor Tenotomy and De-Rotation Shoeing The transection of the deep digital flexor tendon allows us to immediately re-align the coffin bone in relation to the ground surface. I prefer to shoe the horse before surgery because often the shoe must be glued on and the surgical preparation for the tenotomy often gets the foot wet and unsuitable for gluing. The goal for de-rotation shoeing is to glue a shoe, which is parallel to the ground surface of the coffin bone, onto the foot. Additionally the shoe should also provide heel extension to prevent the toe from hyperextending following transection of the DDFT. Using the lateral radiograph as a blueprint (Fig. 14A), several measurements should be made to assure proper shoe alignment. For an average size foot, at
Figure 13 Post-shoeing, there should be even wall growth below the coronary band (A) and increased dorsal sole depth (B).
The initial approach to the unstable foot is often similar to the acute laminitic foot. I usually perform a venogram as part of my initial diagnostic workup to better asses the extent of instability and tissue compression (Fig. 14A and B). The information gained from the external examination of the foot, venogram, and radiographs will dictate which treatment modalities need to be implemented. There is no way to describe a systematic approach to dealing with every severe laminitic foot. Each case is different and every foot is unique. Treating laminitic feet requires experience, good judgment, and a well coordinated effort by the farrier, veterinarian, and owner/manager, combined with good nursing care. The short-term goal, for the unstable laminitic foot, is to preserve the integrity of the coronary band and sole corium and thus its vasculature. Our ultimate goal is to maintain health of the coffin bone and eventually re-establish normal coffin bone alignment and adequate sole depth. It is important to realize that the secondary complications such as bruising, abscessation, osteomyelitis, seroma formation and coronary band shearing are a consequence of digital instability and tissue compression. For this reason, we cannot successfully resolve these problems without formulating a plan to relieve the displacement forces and realign the coffin bone. Depending on the extent of damage, most cases can be treated by re-balancing the foundered foot with the shoeing mechanics described in the compensated and acute conditions. If the coffin bone has penetrated the sole corium or if the foot fails to show continuous improvement with shoeing
Figure 14 A plain radiograph (A) and a venogram (B) are taken to better asses the extent of hoof instability, coffin bone rotation and tissue compression.
Foot management
79 have two reference points, we can transfer the line of the shoe from the radiographs to the foot. We can draw a line on the hoof capsule that guides us in trimming the foot and in placing the shoe. The shoe is forged from aluminum or a keg shoe is used with a heel plate welded in (Fig. 15). The heel plate will help hold in the sole support and offer additional support to the palmar aspects of the foot. The sole support material is mixed and applied to the sole. The shoe is firmly placed onto the foot at the same angle as on the radiographs (Fig. 16A). Often impression material is molded at this stage into a toe wedge to achieve proper shoe alignment. Once the proper angle is achieved, the shoe is glued in place using fiberglass cloth impregnated with adhesive. The shoe is only glued in the heel and quarter regions and the toe is left open (Fig. 16B). Gluing the toe is contraindicated in a laminitic foot. This shoeing method is adequate for most cases with severe mechanical failure limited to the toe region. These feet generally respond with significant dorsal sole growth (Fig. 16C) over the next 4 to 6 weeks. If however, the foot is showing damage in either heel or quarter region, such as medial or lateral sinking, I will set my shoe slightly lower on the side of the foot opposite to that which is sinking. For example, if the foot has sunk to the medial side, I set the shoe into the sole support slightly lower on the lateral side to shift the foot’s weight distribution to the lateral heel.
Figure 15 A keg shoe with a welded in heel plate to help hold sole support material and offer additional support to the palmar aspects of the foot.
Preservation of the Coronary Band
least 3/4 inch of sole depth should be left beneath the most palmar aspect of the palmar process. A line should be drawn from this point parallel to the ground surface of the coffin. This line will represent the shoe. The line can be transferred from the radiograph to the hoof capsule using the following technique: On the radiographs measure the distance from the ground to a point where the line intersects the hoof capsule in the heel region. Measure this distance on the hoof and notch the hoof capsule at that point. Next, drop a plum line from the dorsal coronary band to the ground surface on the foot, notch this point on the hoof capsule. On the radiograph, drop the same plum line and note where this line intersects the line that represents the shoe. This often is below the ground surface of the hoof capsule so we need to measure the distance below the hoof that these two lines intersect. Now that we
With severe displacement and instability the coronary band is often internally compressed. As the displacement advances, the coronary band shears or separates as the soft tissue structures further displace beneath the fixed rigid hoof capsule. In coronary band compression, the coronary corium is still intact but hoof wall growth has slowed in this region. Coronary band compression can occur anywhere in the toe in a rotational displacement or in the quarters in a foot which is sinking medially, laterally, or vertically (Fig. 17). Proper shoeing mechanics should first be implemented. Additionally the technique of coronary band grooving has proven to be a good adjunct treatment in this scenario. Use the hoof wall growth rings as a guide to determine which area to groove. Following the constricted growth rings, groove the hoof wall using a Dremmel with a 1/4-inch diameter burr, just distal to the coronary groove. The entire wall thickness is carefully grooved until small areas of hemorrhage are evident (Fig. 17). This technique can prevent the coronary band from
Figure 16 Shoeing for feet with chronic uncompensated laminitis. The shoe is firmly placed onto the foot at the same angle as determined by the radiograph (A). Then the shoe is glued in place, using fiberglass cloth impregnated with adhesive, leaving the toe open (B). Significant dorsal sole growth (C) over the next. 4-6 weeks is the usual response.
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Figure 19 To regenerate the coronary band and thus proper hoof wall growth after a shear lesion the proximal hoof wall is resected.
Figure 17 Coronary band shearing and separation occurring in the quarters of a foot which is sinking medially. Coronary band grooving was performed in the medial quarter.
developing a shear lesion, if caught early, and can speed up hoof growth in that region (Fig. 18). If the coronary band develops a shear lesion and significant compression, often the coronary band cannot regenerate because of severe pinching and impingement by the proximal hoof wall. When coronary band separation is followed by
Figure 18 A foot that was grooved beneath the medial coronary band to prevent a coronary band shear lesion. Hoof growth has been restored (Same foot as in figure 17).
swelling and pain, a proximal hoof wall resection is required to regenerate the coronary band and thus proper hoof wall growth (Fig. 19). A semielliptical outline is drawn on the hoof capsule over the area to be resected. The resected area should include all areas below the shear lesion, tapering off to healthy coronary band in either end. The resected area should be about 1/2 inch to 1 inch distal to the coronary band (Fig. 19). A Dremmel or the oscillating blade of a cast cutter is used to cut through the hoof wall. Then, using forceps, the transected piece of hoof is removed and the area firmly packed with antiseptic soaked gauze. Following the resection the area should epithelialize within 5 to 10 days. True stratum medium should be regenerated by the coronary band over the next couple of months (Fig. 20). Failure of the tissue to epithelialize or continued impingement of the corium by the proximal aspect of the transected walls is an indication for further, more distal resection. Often the use of a foot cast is required if resections are needed in the quarter and heel regions. Immobilization of the hoof capsule
Figure 20 After proximal hoof wall resection the stratum medium, over the next couple of months, is regenerated by the coronary band.
Foot management
81
Figure 21 A foot after complete hoof capsule ablation (A). The yellow zones are areas of epithelialization. Months later hoof wall below the coronary band has regenerated (B).
and more uniform weight distribution by the cast may help stabilize the foot for epithelialization to occur. Topical products containing zinc may speed up epithelialization. Extra cellular (A-cell; A-Cell Vet) matrix products may also be beneficial. They act as a scaffold for epithelial cells to migrate across, thus speeding up the epithelialization process.
Medial or Lateral Sinking (Displacement): Depending on lower limb conformation, occasionally a laminitic foot will sink to either the medial or lateral side. Some of these cases are caused by the use of wedges to prevent rotation in the acute stage. Although wedging does decrease the rotational forces on the coffin bone and thus the tension on the dorsal laminae, heel wedges shift the GRF to the heels and put stress on the quarters. In some of our efforts to decrease rotation, we may cause sinking in the quarters. Once medial or lateral sinking is detected, the wedge should be removed and the horse placed into a soft rubber pad. This allows the horse to mold the rubber pad into the most comfortable configuration and take stress off the compromised areas. Coronary grooving should also be implemented at this stage in the appropriate regions. In cases which are vertically sinking, I prefer to place them into a foot cast with 1/2 inch carpet felt, soaked in antiseptic, placed on the sole surface. After the foot cast is set, I place hoof reconstruction adhesive on the ground surface forming a mild dome shape. This allows the foot to breakover in all directions and loads the axial regions of the foot and unloads the hoof wall perimeter. Euthanasia is indicated when the vertical displacement advances and shear lesions form around the entire proximal hoof wall perimeter. In some unilateral cases or in special circumstances, complete hoof capsule ablation combined with a lower limb cast or transfixation pin cast has successfully re-habilitated some feet to reasonable pasture soundness. Following hoof capsule ablation or partial hoof wall resection, the hoof heals first through laminar epithelialization (Fig. 21A). Completion of this process can vary from weeks to months depending on the amount of compression on the
exposed area. The hoof wall can take several months to begin regenerating from the coronary band (Fig. 21B). Dealing with infections while the hoof wall is regenerating can be very challenging. The extent to which these feet can be rehabilitated is questionable. The laminar attachments will always be to some degree compromised. For this reason, these cases must be intensely managed and monitored. Often special footing, shoes, boots, and exercise restrictions are necessary throughout the remainder of the horse’s life.
Infections in the Foundered Foot Due to chronic tissue damage and decreased perfusion to certain areas of the foot, tissue necrosis and infection is a common sequel in severe laminitic cases. Infections can vary from a gravel or seedy toe due to the stretched white line, subsolar/submural abscessation to osteomyelitis of P-3. Most
Figure 22 Necrotic/infected tissue from this chronically foundered foot is being removed by disinfected maggots.
82 superficial infections are resolved with alleviation of tissue compression and re-alignment of the coffin bone. Deeper infections are often more difficult to resolve. Methods to treat osteomyelitis of P-3 include surgical debridement, regional limb perfusion, systemic antibiotic therapy, and larval therapy. I have had great success treating chronic infections with gentle surgical debridement followed by larval therapy and appropriate antibiotic therapy (Fig. 22). Formulating a me-
S. Morrison chanical plan with shoeing and surgery is a critical first step to alleviate compromised tissue and restore perfusion before any other treatment can be effective. Disinfected maggots, that debride necrotic tissue, are used in larval therapy. This has the advantage of removing only necrotic/infected tissue without structurally compromising the fragile foot, as sometimes occurs with deep surgical debridement.