Veterinarians at Rood and Riddle Equine Hospital answer your questions about sales and healthcare of Thoroughbred auction yearlings, weanlings, 2-year-olds and breeding stock. Email us at [email protected] if you have a question for a veterinarian.
QUESTION: “I've got a weanling who's got a mild to moderate conformation issue in the knees or ankles. How do I decide whether to try to correct with trimming/shoeing vs going the surgical route?”
DR. SCOTT MORRISON: I assume by “mild to moderate conformation issue” you are referring to angular deformities of the fetlock and knees. Angular deformities are classified as valgus or varus. Valgus- limb deviation occurs lateral to axis of limb. An example of this would be a knock-kneed conformation in which the knees are “in” and the foot is “out”. A varus limb deviation occurs medial to axis of the limb; an example of this would be the bowlegged conformation, in which the knees are “out” and the foot is “in”. Angular limb deformities are common in the newborn foal. The normal newborn foal should have a moderate carpal/tarsal and fetlock valgus conformation and slight outward rotation of all four limbs. This is nature's way of providing a wide base of support and stability for the newborn foal. As the foal strengthens and matures the limbs straighten to improve the mechanical efficiency of the limb. So, there is a physiologic mechanism naturally in place to encourage a limb to straighten with time. As foals mature, the limb should be developing a straighter appearance with time. That should be the trend.
The majority of limb growth occurs at the growth plate (physis) just above the knee at the end of the radius. A lesser amount of growth occurs at the physis just above the fetlock or ankle at the end of the cannon bone. These are the two growth plates that we are most often concerned with in the growing horse. Frequent monitoring of the developing limb is paramount to successfully manage the conformation in foals, recognizing that abnormal conformation which is not improving at the correct pace, getting worse with time, or the development of a new deviation, requires us to implement an effective treatment plan.
Growth plates provide the most rapid growth, which slows down as the growth plates eventually close with age. So, we have the most influence on correcting deformities at a younger age while the foals are fairly malleable. Closure times vary for different growth plates and dictate when we can influence or manipulate them. For instance the growth plate in the ankle closes around four to five months of age and the growth plates at the knees closes around 18 to 24 months of age.
Unfortunately if your foal has an angular deformity of the ankle, there is little we can do at weanling age to influence it. At this age if there is an angular deformity of the ankle, I would make sure the foot has a good robust, shape which provides support to the lower limb. Dysfunctional feet, which break up and don't maintain a good shape, can make a mild to moderate lower limb angular deformity look much worse. Trimming feet to encourage a nice round shape helps, including trimming heels back to the widest part of the frog, rounding up or beveling the entire perimeter of the hoof wall and doing a roll or rocker toe. The rocker or roll toe trim encourages the foot to break over in the center, and also creates a round hoof capsule shape.
An understanding of the tools available to alter physeal growth, and the limitations of each, are necessary to effectively implement a foal management plan. In order to straighten an angular deformity, you can either encourage growth on the concave side of the limb or slow growth on the convex side to straighten the limb.
These are the most common options:
1) Trimming and the use of hoof extensions can alter the forces on the limb's growth plates. For instance, an extension placed on the outside (lateral) of the hoof will shift the weight or force to that side of the limb. That will create more force or compression on the growth plate in that region, slowing the growth on the outside (laterally) and decreasing force on the inside (medially) of the limb, speeding growth in that region of the growth plate. Trimming the foot so that it is higher on one side has a similar effect as an extension.
Hoof extensions and trimming are more effective for fetlocks and have less impact on structures further up the limb, such as the knees.
2) Surgical techniques to slow physeal growth, also known as transphyseal bridging techniques (screw and wire, single screw, staple)
3) Techniques to accelerate growth (periosteal stripping, injections, shock wave). The effectiveness of many of these techniques to accelerate physeal growth
If the knees of your weanling have a “mild to moderate” valgus angular deformity, chances are these will improve with time. Exceptions to this would be if there were signs of physitis, or damage to the growth plate. If that's the case, there will most likely be signs of heat, swelling and pain of the physis. Your veterinarian should examine and possibly radiograph to assess the degree of damage. Cases that have inflammation or damage to the growth plate are telling you that the self-correcting mechanism is overloaded, and may need additional help to correct. This may be in the form of restricted exercise, decreasing body weight, anti-inflammatories, shoeing with extensions or in cases that are not responding, possibly surgery.
If your weanling is developing a moderate carpal varus, at this age I would use a small lateral extension to help correct or prevent it from worsening. Since this growth plate stays open and growing until 18 to 22 months of age, you have time to monitor it and treat conservatively. We try not to do corrective surgery on the knees at this age unless they are severe or if they are developing a severe case of physitis. Ideally, you would try to manage it with trimming and extensions until the spring/summer when the weanling becomes at least 12 to 13 months old. At that time if the limb is not improving, I would consider a transphyseal bridge. The reason for not doing a transphyseal bridge earlier is the fear of causing premature closure and physitis of the growth plate. This more of a concern when using a single screw technique in which the screw actually goes into the growth plate as opposed to the other techniques which do not invade the actual growth plate (screw and wire or the staple).
Working closely with your veterinarian to monitor the conformation of your young growing horse will give you the best opportunity to produce a conformationally correct athlete.
Dr. Scott Morrison is both a veterinarian and a farrier, having graduated from both Virginia Maryland Regional College of Veterinary Medicine and the Eastern School of Farriery. He helped develop Rood and Riddle's Podiatry Center, now oversees the podiatry department and is a shareholder in the hospital.
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