Part 4: Surgical techniques
used on Foal Limb Deviations/
Angular Limb Deformities
Where a foal has limb deformities, is surgical intervention a commonly used approach?
This is an important decision carried out by the treating veterinary surgeon. It is estimated that a high proportion of foals born with angular limb deformity can correct themselves. The estimated figures indicate that approximately 90% can correct themselves, approximately 5-7% require minor alterations e.g. trim, glue-on extensions, etc, and about 3-5% actually require surgery. Epiphysitis or joint problems can arise from too much stall rest or from irregular exercise schedules. What surgical techniques are used in Angular Limb Deformities in a foal?
Where conservative foot balancing methods of treating Angular Limb Deformities (ALD) have not been successful, there are certain types of surgical techniques which may be used. As already outlined, corrective shoeing may help to correct the deformed limb but if done incorrectly or in excess can cause degeneration of the articular cartilage and eventually arthritis. The surgical techniques involve manipulating bone growth using procedures such as Periosteal elevation (PE), surgical staples, etc. Basically this means one of two main approaches can be used depending on the type of limb deformity (ALD):a) Growth acceleration. This involves accelerating the growth on the other side by cutting and lifting the fibrous periosteal bone covering. The technique is known as Periosteal Elevation (PE).
b) Stopping or slowing up procedures by bridging the growth plate with staples and effectively causing halting the growth on one side of the bone.
In very severe cases, both of the above can be done. Most importantly, irrespective of the line of treatment decided upon, it must be done while the bone is still growing at the site where the angular deformity has arisen. This means in the case of with fetlocks, treatment must be done before three months of age and with knees and hocks before approximately four or five months. After these times any growth will be minimal and straightening of the legs will be unsatisfactory following surgery. What is Periosteal Elevation/Stripping?
All bones are covered by a fibrous layer or film called the periosteum. The Periosteal Elevation procedure involves making a small incision on the concave aspect of the relevant bone, incising the periosteum and elevating it away from the bone. Periosteal stripping is only beneficial in cases where the angular deformity is coming from an active growth plate, i.e. it would be ineffective in an older foal. How does Periosteal Elevation improve limb deformities in foals?
The exact mechanism that improves angular deformities after periosteal stripping is unknown. One theory is that after periosteal stripping, the blood supply to the affected growth plate is improved and this causes the bone on that side of the joint to grow faster Another belief is that the thickened periosteum acts as a bow string, and when cut, relieves the tension and allows the growth to resume. The procedure speeds the rate of growth on the side of the limb on which it is performed.Is the foal placed under general anaesthesia for the periosteal elevation operation on the knee?
Yes, as it would be difficult to carry out this operation efficiently under local anaesthetic.At what age should PE be carried out on a foal with ALD?
Periosteal elevation or stripping is beneficial up to the time that the growth plates close. However PE is most effective prior to four weeks in the fetlock area and four months in the knee area. It is generally recommended that if stripping is to be used alone, it should be performed at or prior to three weeks and three months for the fetlock and the knee. After the four weeks/four months guidelines, stripping should be combined with some type of transphyseal bridging for best results. Can over-correction occur in surgery?
No. The benefits of periosteal stripping are that the leg will never over-correct and that the procedure can be done more than once. The draw backs of periosteal stripping is that it is unlikely to provide enough straightening with legs that are deviated more than 15 degrees. Also stripping alone is unlikely to improve any type of rotational deviation i.e. where the leg is turned out or rotated.How are Surgical Staples used for angular limb deformities in foals?
This is referred to as Transphyseal Bridging. Transphyseal bridging may be used in a) Any case where the deformity is 15 degrees or greater, or
b) After four weeks in the distal fetlock and four months in the knee.
There are different techniques used to bridge the epiphysis. The basic principle/aim is to retard the growth of the convex surface of the limb by bridging the physis with some type of mechanical device such as bone screws and wires, staples, or bone screws and small bone plates. All of the techniques have their positive aspects and drawbacks. Surgeons preference usually dictates the method chosen. Transphyseal bridging can be used in any area that there is an active growth plate/physis, but as the animal gets older and the physis has less growth, the amount of straightening is diminished. Transphyseal bridging can and often is used in conjunction with periosteal stripping and corrective trimming/shoeing. Are there any disadvantages in the transphyseal bridging technique?
The major drawback to transphyseal bridging is that it requires a second surgery to remove the staples. The staples should be removed as soon as the leg is straight. If the implants are not removed, the angular deformity will over-correct, and the leg will acquire a deformity in the opposite direction. The staples can be placed at an angle to help correct rotational deformities. There are various types of staples and techniques used to achieve this growth arrest. Initial techniques described a staple placed in order to bridge the growth plate causing a tensional force, which greatly reduces growth on the convex side of the epiphysis. A further development was that of two screws placed horizontally into the bone, on either side of the growth plate and then joined with steel wire. This effectively achieves the same effect as the staple. More recently the ‘Single Screw Technique’ describes a screw being placed at a 60-degree angle to the bone through the epiphysis on the convex side of the limb. The tension created across the growth plate by the screw retards the growth until the deformity is corrected. Once the growth plates have closed or calcified, none of the above techniques will be useful.In summary breeding is an important consideration with regards to conformation. A high percentage of angular limb deformities are considered to be inherited. But while good conformation is not synonymous with success, a well-bred horse from a successful family can endure faulty conformation much better than a less well-bred horse.