Indepth Equine Podiatry Symposium Notes
How to Construct and Apply a Shoe to Compliment a Superficial Flexor Tenotomy in the Standing Horse
Written and presented January 2009 by R.F. (Ric) Redden, DVM
The treatment of superficial flexor contraction presents a challenge to veterinarians, farriers and their owners, as it can range from mild to severe. If the normal angle of the metacarpophalangeal (MCP) joint is 135 degrees, a mild case will approach 180 degrees but rarely flex cranially.1,3 Moderate cases will be flexed cranially at rest, but return to upright but normal positioning with movement and load.1,3 Severely affected horses have MCP joints that are flexed past 180 degrees at all times.1,3 Many different treatments are available, all with varying degrees of success.1-8 Authors report success on mild to moderate cases using combinations of superior and inferior check ligament desmotomies.1,3 In addition, some authors advocate superficial digital flexor tenotomies in severe cases.1,6-8 Two authors recommended shoes with a heel elevation and toe extension as part of therapy.1,3 Severe developmental superficial flexor contraction can frequently occur in fast-growing horses of various ages as well as in the unthrifty slow growing individuals and is particularly difficult to treat.1,3 Very young foals with congenital superficial flexor contraction respond much better to corrective methods.
Traditionally surgical correction requires general anesthesia, and application of a therapeutic shoe has not been reported as beneficial. In a study evaluating 15 cases of flexural deformity treated with ICL and SCL desmotomy with heel elevation and toe extension of 3.5cm, 8 of 10 mild to moderate cases responded to treatment and returned to their intended work.3 None of the five severe cases with severe deformity were able to work.3 Results relative to the goals of client and veterinarian are difficult to achieve, and relapse often occurs.1,2,3 Severing the superficial flexor tendon mid-cannon in the standing horse immediately after applying a therapeutic device to realign the digits presents several advantages over traditional surgical techniques. The standing approach reduces the risk of general anesthesia-related complications, hospitalization time and cost to the client. Less time and technical support is required for the veterinarian and there is a decreased need for surgical and anesthesia equipment and facilities, which increase the veterinarian's ability to provide more efficient cost related services.
The success of the standing superficial flexor tenotomy in the severe case is largely dependant on the degree of severity and chronicity of the case. The toe extension, heel elevation shoe/surgery combination improves fetlock angulation over other methods, resulting in a more favorable response. Splints used for 30 days post op maintain maximum angulation, and gradually stepping down the mechanical properties of the shoe over a 90 day shoeing period helps preserve favorable fetlock angulation. The combined benefits of this specific step by step protocol improve the prognosis for the severely contracted case. The purpose of this paper is to describe how to fabricate and apply an aluminum shoe to compliment the effects of a superficial flexor tenotomy in the standing horse for treatment of severe flexor contraction.
2. Materials and Methods
Fabrication and application of a therapeutic shoe is technique sensitive and requires the skills of an accomplished farrier. The farrier should have a working knowledge of the mechanical function of the superficial and deep flexors, be experienced with using radiographs as a blueprint to design the shoe and have experience forging aluminum. In most instances, the farrier and veterinarian will benefit from using a sling for the shoeing and surgery. Sedation is required for the shoeing applications and standing surgical procedure. Muscle relaxation (the result of sedation) in severely contracted animals makes it very difficult for them to stand; therefore the sling offers good support as well as restraint for individuals that are fractious and untrained.
A soft tissue lateral radiographs should be used to evaluate the foot and create a blueprint for designing the unique characteristics of the shoe.9 This has advantages over verbal or written instructions to the farrier as it helps prevent design flaws and miscommunications. To accurately evaluate soft tissue parameters such as the horn-lamellar (HL) zone, palmar angle (PA) and sole depth (SD), the primary beam should penetrate the foot proximal to the ground surface and distal to the palmar rim, be directed in a horizontal plane with the ground surface, perpendicular to the sagittal plane while maintaining zero film/subject distance to avoid unwarranted magnification. Visualizing the entire hoof capsule as well as bone is crucial for the farrier.
Creating the Blueprint
Using the radiographs as a blueprint, draw the shoe on the film. The foot should be trimmed flat, preferably with a 2-3 degree PA and as much foot mass as possible. Most cases will have a PA of zero to 5 degrees, which requires very little foot preparation. The toe extension should be extended 2.5 cm beyond the toe and the heel extension to the bulb of the heel. The heel height should be approximately 1/3 the length of the ground surface of the foot and heel support surface should be approximately 2.5-5 cm wide. Measure the entire shoe length on your blueprint and cut a piece of cardboard 15 cm wide and slightly longer than the length of the previously measured shoe material. An aluminum plate (0.6 cm thick) is used by the author to fabricate the shoe as it is lightweight, easy to forge and can be modified without heat. The cardboard template should be used to facilitate fabrication of the shoe.
Trace the foot on the template and mark the point of each fold. Remove the foot and mark appropriate nail holes on the template. The toe clips should be drawn on the template. Fold the template as if shaping the shoe and match it to the blueprint (radiograph). Transfer the template nail holes and bend marks to the aluminum plate using a center punch. Turn the plate over and stamp each nail hole using a farrier's forepunch. A band saw should be used to cut the aluminum to the desired shape.
The plate should be placed in the gas forge nail side down and heated to forging temperature. Aluminum melts at a very low temperature relative to steel, so check it frequently to prevent overheating. The heel support fold is the first to be made over the face of the anvil followed by the heel bend. Feet wider than 7.6 cm require an aluminum strut welded or riveted down the center of the shoe to prevent sag.
While in the forging heat the heel height can be adjusted and the clips pulled. Using the cardboard template to position and pre-test the clip shape and location enhances the ease of fabrication. The clips prevent stress on the nail attachment and facilitate fitting and adjusting prior to nailing.
Once fabricated, the foot should be placed on the shoe and the fetlock joint tested for range of motion. The fetlock should be easily pushed into a slightly extended position once the shoe is in place. Final adjustments to the shoe should be made at this time before the shoe is nailed on. Once attached to the foot, the assistant should apply firm, steady pressure on the carpus, maintaining the slightly extended fetlock until the superficial flexor is severed. The patient should be sedated with .25cc. .0056 mg/kg detomidine HCL, the tendon area clipped, local anesthetic injected over the palmar nerves at the level of the proximal cannon and the limb surgically prepped.
The mid-cannon area offers a quick, easy approach, good results and minimal cosmetic disfigurement (a noticeable dimple or notch will appear where the ends of the tendon retract). A 3.5 cm incision should be made along the lateral edge of the superficial tendon. A pair of metzenbaum scissors should be used to gently separate the superficial flexor from the DDF. A curved, blunt retractor is placed between the superficial and the deep. A second one should be placed between the skin and superficial tendon. Connecting the two retractors, the tendon should be isolated and severed using a #15 blade. The skin should be closed with an inverted mattress stitch and the leg bandaged with a sterile post op bandage.
Once the tendon is severed, the fetlock should resume an angle of 140 degrees to 150 degrees. However, it is important that the fetlock remain in this position for several weeks to allow time for the severed ends to fibrous securely to the DDF. To prevent the fetlock from inadvertently flexing into the knuckled over position, a custom-fitted splint should be used along the flexor side of the limb for several weeks. Maintaining the desired digital alignment and fetlock position is made possible with the mechanical benefits of the shoe and tenotomy combined.
A roll of soft cast padding should be applied over the bandaged limb as a release aid before applying the casting tape splint. One roll of 12.7 cm fiberglass casting tape should be unrolled and folded on itself several times to accommodate the length of the splint. Casting tape should be placed on the posterior side of the limb approximately 5 cm distal to the accessory carpal and just proximal to the bulbs of the heel. A piece of felt 1.3 cm thick should be placed under the cast material at the proximal and distal ends. The wet splint should be formed to the limb using a roll of vetwrap followed by a roll of 10.2 cm elastic tape to securely anchor it to the bandage, all the while holding the limb in its most desirable position.
Cases that exhibit the most extreme form of the deformity stand with the feet well in front of the body and exhibit full range flexion of the metacarpophalangeal joint and extension of the distal interphalangeal joint and require a series of custom fit splints to gain optimum fetlock angulation over the first few weeks post op. Gaining a few degrees with each change is beneficial and improves the long term results.
Stall rest should be prescribed for 7-10 days followed by hand walking with the bandage and splint in place for approximately 30-45 days. The therapeutic shoe should be reset in 4-6 weeks, and the heel height and toe extension reduced by half. The third shoeing should require a 3 degrees wedge shoe (toe slightly extended) when a zero PA is present or a flat shoe when a 3-4 degree PA is present. A breakover enhanced shoe should not be used on this deformity as it enhances the knuckle effect. A firm fitted bandage should be worn for 90 days with a wean down schedule for optimum cosmetic results. Free exercise in a paddock can be resumed after 3-4 months.
The author has used the combination shoe and surgery technique to treat over 11 cases of severe superficial flexor deformity. Eleven cases reviewed consisted of 1 weanling, 8 yearlings and two 2 year olds. The weanling and 5 yearlings were quarter horses, 2 yearlings were Paso Finos and 1 was an American Saddlebred. Two 2 year olds were Tennessee Walking horses. Results were based on fetlock angulation obtained at the time of surgery and six months and one year follow up and were categorized as good (140 degrees to 150 degrees), moderate (150 degrees to 170 degrees) or poor (170 degrees and higher).
The weanling was presented with severe flexure contraction and distal interphalangeal extension, showed moderate response and was reported pasture sound one year later. The 8 yearlings had various degrees of contraction ranging from moderate to severe. Six had a good response and 1 Paso Fino had a moderate response. The Saddlebred relapsed and returned for a second surgery several months later and was eventually euthanized due to poor response. Seven were reported as being riding sound as two year olds. Of the 2 year olds, 1 had a good response and was sound for riding one year later. One had a relapse and returned 6 months following the initial surgery for a second surgery. Favorable results were not obtained and the horse was euthanized several months later.
The primary goal of the traditional surgical approach is to set the fetlock in a position less than 180 degrees. However, with the surgical approach described here the author's goal is to achieve a fetlock angle of 140 degrees to 150 degrees. This is made possible by use of the therapeutic shoe to realign the digits immediately prior to surgery. This step by step protocol procedure maximized gapping of the tendon ends, assuring improved positioning during the fibrosing phase and helped prevent relapse.
Veterinarians and farriers are becoming more familiar with the advantages of working together, combining mechanical applications of farrier services with surgical protocols. Using a sling in select cases to provide support and restraint can also facilitate application of the shoe and aid in fine tuning the therapeutic device, which requires body weight of the conscious horse to properly fit and evaluate. The sling also provides the veterinarian with a quick, easy means to immediately evaluate the combining effects of the shoeing-surgery protocol.
The extended toe of the therapeutic shoe apparently enhances extensor function. The elevated heel adequately reduces DDF tension, in turn reducing mal-alignment and offering loading through the digits. 10-13 Severing the superficial flexor tendon with the digit held in this position offers additional favorable fetlock extension and maximizes gapping of the tendon ends. Utilizing the restrictive nature of the splint assures fetlock extension for the time required for fibrosing of the tendon ends, thereby reducing the risk of relapse.
The disadvantages of this method are that it requires a technique sensitive precise mechanical appliance provided by a qualified farrier and the presence of the veterinarian to provide radiographs, professional input, sedation and surgery. Good horsemanship skills are a prerequisite for treating horses in a sling and performing standing surgery as the lack of adequate experience with horses can lead to serious injury to veterinarians and assistants. However, the advantages seem to outweigh the disadvantages. The standing superficial flexor tenotomy following application of a specific therapeutic shoe is a useful and simple technique for the vet and farrier team.
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