How to Construct and Apply a Shoe to Compliment a Superficial Flexor Tenotomy in the Standing Horse
Indepth Equine Podiatry Symposium Notes
Written and presented January 2009 by R.F. (Ric) Redden, DVM
1. Introduction
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.
Fig 1. Once sedated the moderate luxation (A) becomes increasingly worse. The right leg (B) appeared to be slightly worse than the left. Sedation made it difficult for the filly to stand as both fetlocks were prone to severe knuckling. She preferred to keep moving.
Radiography
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.
Fig. 2. Using the radiograph as a blueprint, the details of the shoe should be drawn and measurements taken for the amount of material required for 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.
Fig. 3. The foot pattern (A) should be drawn on the template as indicated. Green arrows define nail holes (punched through template into the aluminum plate and drilled out with 9/16 drill bit). Red arrows define the size and location of the toe clips. Blue arrows mark the location of the first bend, and yellow arrows mark the
location of the second bend.
Fold the template (B) to represent the shoe to scale. A band saw (C) should be used to cut the shoe from the 0.6 cm aluminum plate.
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.
Fig. 4. The aluminum is heated to forging temperature. Aluminum has a low melting point. Check it often, as overheating will melt the aluminum.
Fig. 5. The first bend (A) is made over the face of the anvil along the punch markers transferred from the template. The second bend (B) is the heel height. The desired elevation and medial lateral balance should be adjusted while the aluminum is in the forging heat.
Fig. 6. The clips (A) should be cut in the aluminum along the lines drawn on the template. The clips (B) are initially pushed through the piece and forged to the desired height. The shoe is ready to be tested for optimum fetlock extension.
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.
Fig. 7. A toe extension/heel elevation shoe aids digital alignment prior to surgery and helps maximize gapping once the superficial tendon is severed.
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.
Fig. 8. Administer the nerve block as high on the metacarpal as possible to avoid edema at surgery site.
Surgery
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.
Fig 9. The mid-cannon incision (A) can be as small as 2.5-3.5 cm for adequate exposure. Metzenbaum scissors (B) are used to guide the retractors between the superficial and deep flexor tendons. The second retractor is inserted between the skin and superficial tendon. Once locked together, the tendon is easily severed using the retractors to protect the nerves and vessels.
Fig 9. The retractors (C) are made from stainless steel kitchen knives and are easy to make. The blades are thin and flexible, which is an advantage over the thicker, rigid retractors on the market. Note the radius is slightly different, which offers a reliable means of isolating the tendons and ligaments from the nerves and vessels.
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.
