The Corrective Surgery Debate
(Photo : Annet Becker)
Early assessment and close monitoring of a foal’s conformation is crucial so that measures can be taken to improve any abnormalities. However, one particular treatment, ‘corrective surgery’, has become so commonly performed on even minor conformational imperfections that many are now questioning whether it is being carried out too frequently and whether its disclosure at the yearling sales should be mandatory. James Tate BVMS MRCVS writes the following report for the UK’s Thoroughbred Owner & Breeder.
Knock-kneed or bow-legged
‘Angular limb deformities’ are conformational abnormalities seen most commonly in thoroughbred foals that require early recognition and treatment.
They occur more frequently in front legs, are seen when viewing the foal from the front or back and are broadly categorised into two types – ‘valgus’ and ‘varus’. A valgus conformation is where the limb deviates away from midline, for example, a foal with valgus conformation of its knees is often described as being ‘knock-kneed’. A varus conformation is where the limb deviates towards midline, for example, a foal with varus conformation of its knees is often described as being ‘bow-legged’.
Angular limb deformities occur most commonly at the knee (carpus) but also quite frequently at the fetlock joint or the hock. The degree of the deformity is usually evaluated by repeated visual examination but can also be measured and assessed using x-rays. The main problem is often an imbalance of growth in the growth plates. For example, if the outside of the growth plate just above the knee is growing slower than the inside, then the foal’s leg will deviate away from midline and so develop a carpal valgus conformation – knock-kneed.
Congenital and acquired deformities
These conformational deformities are broadly grouped into congenital or acquired forms, with congenital deformities being present at birth and acquired deformities usually appearing at a few weeks of age.
Congenital abnormalities are caused by either laxity of joint ligaments or incomplete formation of the small bones of the knee or hock. Careful palpation of joints should establish the presence of joint laxity and the conformation of such foals can usually be corrected successfully with conservative management, even in relatively severe cases.
Incomplete formation of the knee or hock bones is typically found in premature foals and so x-rays should be performed as a routine.
Conservative management of angular limb deformities is successful in most foals and, in fact, a degree of carpal valgus conformation is normal in a newborn foal.
Therapy consists of restricting exercise to box rest with a limited turnout period per day, providing a firm bedding and turnout pasture, as well as corrective hoof trimming and, if necessary, the use of glue-on extensions that force the foal to straighten its legs. This allows the growth plates to be stimulated but prevents stress and compression on the affected side of the growth plate. If the affected limb of a newborn foal can be manually ‘straightened’ because it is being caused by joint laxity, then conservative management will usually be successful. More severe cases are treated with splints or limb casts, but these should be used with caution and changed regularly to avoid skin rubs.
Acquired angular limb deformities are caused by asymmetrical bone growth from the growth plate, with one side of the growth plate growing faster than the other. Sometimes the cause of such deformities is not known, but it can be the result of injury to one side of the growth plate, uneven loading on one leg due to lameness of the other leg, inappropriate nutrition (for example, too much nutrition or an incorrect calcium/phosphorous ratio), excessive exercise, or improper foot-trimming.
Whilst affected foals can also be treated conservatively, this is when many foals are booked in for surgery.
Corrective surgery – more now than ever
There are two surgical treatments that should be used for the more severe cases but which are now being used more than ever.
Both techniques depend on continued growth in order to straighten the leg and so should ideally be carried out before the foal is two months old (especially in fetlock deformities) and in severe cases the techniques can be performed together.
The first surgical technique is a periosteal elevation, which is carried out on the side of the growth plate that is not growing fast enough and its aim is to stimulate growth on this side of the growth plate. The outer surface of the bone (the periosteum) is thought to have a restraining influence on growth and by removing a strip of periosteum over the slow-growing side of the growth plate, growth is stimulated. For example, periosteal elevations are performed on the outside of the knee in a foal with carpal valgus, or the inside of the knee in a foal with carpal varus. An inverted ‘T-shaped’ incision is usually made approximately 2.5cm above the growth plate and its maximum effect is seen after approximately two months.
It has a few advantages over the second surgical technique described below in that it is a one-off surgery, it is minimally invasive and there appears to be little risk of over-correction, although some argue that this is because it is not that effective. Indeed, recent research has suggested that foals with the mild deformities currently treated by periosteal elevation generally improve without the need for surgery if treated with box rest and corrective farriery alone.
The second surgical technique works in the opposite way to a periosteal elevation, in that it slows down the side of the growth plate that is growing too fast.
Temporary transphyseal bridging is the insertion of metal implants to slow down
the growth of one side of the growth plate to allow the other side to catch up.
Traditionally, a staple is inserted over the growth plate or two screws are placed either side of the growth plate and either wires or plates join them together.
However, more recently, a new method of inserting a single screw across the growth plate has been developed, as it has the advantage of a better cosmetic result. All of these methods are very effective.
However, the metal implants must be removed as soon as the leg is straight, otherwise over-correction and deviation in the opposite direction may occur.
There is no doubt that, if left untreated, severe angular limb deformities cause big problems for horses and the result is often osteoarthritis of the joints which have been put under excessive pressure by the poorly balanced limb.
Veterinary surgeons have become so proficient at these corrective surgeries that they are becoming very widely used, even for minor conformational abnormalities. Therefore, the possible disadvantages must be discussed.
Are there any downsides to such surgery?
In 2006, Santschi et al reported on their findings from studying the conformation of 199 thoroughbred foals from birth to yearling auction age, and found that knee and fetlock conformations change greatly with foals, generally becoming less carpal valgus and more fetlock varus as they become older.
This could lead the reader to suggest that it may be difficult to ‘correct’ a foal’s conformation to exactly the right degree as its conformation is likely to alter after corrective surgery has had its effect. However, in reality veterinary surgeons are now so good at judging these corrective surgeries that this is rarely a problem. The only significant practical downside of the surgeries seems to be the minimal scars and white hairs that can be left after the procedures, if the breeder is unlucky – although one or two do attempt to fix this with a little boot polish at the sales!
From an auction sale point of view, these corrective surgeries are excellent and have very few disadvantages.
However, the final important issue is whether performing all of these corrective surgeries is good for the racing careers of the horses concerned or, indeed, the breed as a whole.
In 2004, Anderson, McIlwraith and Douay published a paper in the Equine Veterinary Journal on the role of conformation in musculoskeletal problems in the racing thoroughbred, and the highly-respected Professor Wayne McIlwraith presented his findings at the Thoroughbred Racing and Breeding Seminar at Cheltenham racecourse.
He made two significant points. First, he came to the slightly unexpected conclusion that a degree of carpal valgus, which many are currently ‘correcting’, is actually a good thing and may serve as a protective mechanism for soundness.
Second, he argued that we should try to “manipulate Mother Nature” when we need to and suggested that corrective surgery is not always helpful and can actually contribute to unsoundness.
Widespread use does spark some concerns
In summary, corrective surgeries are excellent procedures for the treatment of extreme angular limb deformities. However, their widespread use leads everyone involved in the thoroughbred industry to have two serious concerns.
First, is it correct to be performing so many surgeries? Second, should vendors be made to disclose which yearlings at the auction sales have had such corrective surgeries?
The second concern is exactly what the North American Consignors and Commercial Breeders Association have been suggesting for some time.