Indepth Equine Podiatry Symposium Notes
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.
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.
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.