| Introduction | History and physical examination | Ligamentous laxity | Cuboidal bone hypoplasia | Disparity in long bone growth | References | About the author
Take-home message
- Most foals with angular limb deformities self-correct.
- Angular limb deformities due to underdeveloped cuboidal bones may carry a poor prognosis.
- Periosteal stripping is not an effective treatment.
- Transphyseal bridging techniques are indicated in foals that do not self-correct.
Introduction
Developmental orthopedic disease has become the recent "catch phrase" that encompasses a number of orthopedic conditions affecting the growing horse. Conditions included under this umbrella are angular limb deformities, flexural deformities and osteochondrosis. While the predisposing factors and the underlying pathophysiologic mechanisms for each of these conditions may be inter-related, the management techniques employed are condition specific. Angular limb deformities represent a deviation of the limb in a sagittal plane (viewed from in front or behind). Most foals have less than ideal conformation at birth; however, only a small number of affected foals actually require active medical management to resolve their deformities. Clearly, the focus needs to be on identifying and managing this latter group of foals.
The following paragraphs are intended to convey an understanding of the mechanisms responsible for angulation and the treatment modalities that can be employed.
Three basic mechanisms can be responsible for the presence or development of an angular limb deformity in the foal. The first, and by far the most common, are deformities that result from a greater than normal degree of laxity in the ligaments supporting the medial and lateral aspects of the joints. Inadequate development of the cuboidal bones of the carpus (knee) and tarsus (hock) is potentially the most devastating manifestation of angular deformity. While deformities that develop due to a medial-to-lateral disparity in long growth may require surgical management, but generally carry an excellent prognosis.
History and Physical Examination
The assessment of foals with angular limb deformities should always begin with collection of a complete patient description and history. The foal should be observed standing at rest and at a walk to establish whether the angulation displayed is consistent or variable in nature. The affected limb(s) should be palpated to evaluate degree of ligamentous laxity and the presence of pain or swelling. Radiographs should be made to allow evaluation of the cuboidal bones and objective measurement of the angle of deviation.
Angular Limb Deformities - Ligamentous Laxity
Angular limb deformities due to ligamentous laxity are typically present and most pronounced at birth. The carpal and tarsal joints are most commonly involved and, in severe cases, the stifle joints can be angled as well. Examination of the foal at rest reveals excessive medial to lateral mobility of the involved joints. At a walk, the deformity may be consistent in direction and severity, or variable in both severity and direction. Manipulation does not elicit a painful response. Radiographs are morphologically normal and the geometric pivot point is located within the joint.
The majority of angular deformities due to ligamentous laxity resolve spontaneously over the first few days of life. The conservative clinician may recommend a short period of stall confinement. There are cases where mechanical support in the form of a stiff bandage or a splint may be indicated (foal's carpii are rubbing against each other); however, those cases are rare. In addition to the possible negative implications of bandages and splints, the clinician also needs to be aware that mechanical support may slow the resolution of the laxity.
Angular Limb Deformities - Cuboidal Bone Hypoplasia
Angular limb deformities caused by cuboidal bone hypoplasia carry the potential for the poorest prognosis. Under normal circumstances, the small bones of the carpus and the tarsus achieve their adult shape within 30 days of birth. Foals with underdeveloped cuboidal bones are clearly skeletally immature; however, skeletal immaturity does not correlate well with gestational age. This condition can occur in otherwise healthy foals, but in Western Canada, these foals often suffer from the well known, but poorly understood "hypothyroid foal syndrome." With the exception of foals with hypothyroid syndrome, normal foals with underdeveloped cuboidal bones have a good prognosis if therapeutic intervention is undertaken before permanent deformity occurs.
Foals with hypoplastic cuboidal bones generally have mild to moderately severe angular limb deformity that is inconsistent in severity. Manipulation of the affected limbs reveals an impression of ligamentous laxity, though the force needed to create deformity is greater than in foals with ligamentous laxity. Radiographic assessment confirms the presence of inadequately ossified cuboidal bones and a geometric pivot point within the joint. In severe cases, the proximal growth plate of the metacarpus and metatarsus (cannon bones) may still be present (should be closed before birth). Deviation in the front limbs usually occurs in a medial-to-lateral direction, but in the rear limbs, the abnormality is best seen from the side.
Foals with underdeveloped cuboidal bones should be restricted to box stall confinement. If the foal is especially active, additional support, in the form of a splint or tube cast, should be provided to mechanically protect the essentially cartilaginous cuboidal bones. In otherwise normal foals, the ossification process proceeds rapidly and most affected foals need only be confined for a period of 14 -21 days. Hypothyroid foals seem to respond more slowly. Radiographic evaluations should be repeated at 7 to 10 day intervals.
Unfortunately, cuboidal bone hypoplasia may go undetected. In those foals, the presenting complaint is often the sudden appearance of a moderate to severe angulation. These foals often have swelling over the carpus or tarsus and frequently object to manipulation of the affected joints. Radiographs reveal misshapen but completely ossified cuboidal bones with a geometric pivot point located within the joint. Regrettably, while the angulation may be resolved using one of the techniques described for the management of growth disparities, the involved joints will become arthritic. Foals with permanent cuboidal bone deformity in the carpii are candidates for euthanasia unless they have value as breeding animals. Foals with tarsal involvement may be able to perform athletically if the affected joints undergo fusion; however, they inevitably suffer through some variable length period of lameness.
Angular Limb Deformities - Disparity in Long Bone Growth
Angular limb deformities caused by a disparity between medial and lateral long bone growth may be present at birth or the deformity may be an acquired developmental condition. In either case, there is an imbalance between the growth occurring at the medial and lateral aspects of the physis (growth plate) of the affected bone. The most common deformity is a lateral (valgus) deformity originating at the carpus. Other affected areas can include the distal metacarpus/metatarsus, and the distal tibia (hock).
Uterine positioning is believed to be the major cause of congenital deformities. The foal is restricted to cramped quarters and medial-to-lateral stress maintained over a period of time essentially compresses one side of the physis allowing overgrowth of the opposite side and development of angulation. Foals that are born straight, but later develop angulation are believed to have undergone some degree of growth plate injury.
Physical examination will reveal a constant angulation. Palpation and manipulation does not elicit a painful response and there is no swelling or laxity of the involved joint. Radiographic evaluation confirms the presence of normally shaped cuboidal bones and the geometric pivot point is located proximal (above) the joint. A complete and accurate history will elucidate one of six possible scenarios:
1. Congential deformity that is:
a. Improving
b. Static
c. Worsening
2. Acquired Deformity that is:
a. Improving
b. Static
c. Worsening
The collection of the above information will allow the clinician to develop a logical approach to management of the condition. The window of opportunity for dealing with deformities arising from the distal radius is large; however, there is a degree of urgency when the deformity is at the distal cannon bone because there is little growth potential in that bone after the foal is 100 days of age.
The majority of foals with angular limb deformities caused by growth disparity of the long bones will spontaneously correct. The challenge for the veterinarian is to identify which foals are likely to require more aggressive intervention and to implement corrective measures while there is still sufficient growth to allow correction. Exercise restriction and corrective hoof care are consistent treatment recommendations that help to reduce the biomechanical stress on the angled limb. In many cases, this conservative approach is sufficient to allow resolution of the deformity. Foals that are severely affected or foals that fail to respond to confinement and corrective hoof trimming are candidates for surgical treatment.
Prior to 1980, the preferred surgical approach was the placement of a temporary transphyseal bridge. This involved placing a staple or a pair of screws connected by a wire across the side of the physis that is growing too fast. The transphyseal bridge compresses the growth plate, restricting growth while allowing the slow growing side to essentially catch up, thereby resolving the angulation. The transphyseal bridging techniques are effective; however, a second surgery is required to remove the implants when the limb is straight. Beginning in 1980, the periosteal stripping procedure appeared on the scene. This procedure is performed on the side of the growth plate that is growing too slow. The proponents of the technique believe that manipulation of the periosteum stimulates growth and subsequent resolution of the deformity. Some 20 years later, the efficacy of the periosteal stripping procedure is being drawn into question. Since its' introduction, there have been numerous reports detailing its use though none of those reports critically evaluates the technique's utility. Foals undergoing periosteal stripping procedures are exercise restricted and corrective hoof care is routinely applied begging the question, "is the observed correction due to exercise restriction, corrective hoof care, periosteal stripping or a combination?" Two research groups have recently presented results of experimental work that clearly does not support the continued use of periosteal stripping as a treatment modality in the management of angular limb deformities in foals.
Dr. Donnie Slone at Peterson and Smith Equine Hospital in Ocala, Florida repeated the original experiment of Auer who reported the creation of angular deformities with periosteal stripping followed by correction of said deformities with a second periosteal stripping procedure. Auer was not able to detect any difference between medial and lateral bone growth at the distal radial growth plate and, he believed he had created and corrected a deformity and attributed the correction to growth at the proximal radial growth plate. Dr. Slone was not able to produce an angular limb deformity by performing a periosteal stripping procedure and detected no change in medial-to-lateral growth at either the proximal or distal growth plates.
Interestingly, at the same time, Dr. Emma Read and our research group at the Western College of Veterinary Medicine were developing an angular limb deformity model with the purpose of using that model to assess the utility of periosteal stripping. Temporary transphyseal bridges were placed across the lateral aspect of the distal radial physis in 10 normal foals at 30 days of age. By approximately 90 days of age, all of the foals had developed lateral deviations of 15 degrees or more. The transphyseal bridges were removed and periosteal stripping was performed on one limb, the contralateral limb served as a control. The foals were exercise restricted and medial-to-lateral hoof balance was maintained by rasping the hoof bi-weekly. Over the ensuing 10 - 12 weeks, the deformities in the treated and control limbs corrected at the same rate. This confirmed our hypothesis that periosteal stripping is no more effective than exercise restriction and corrective hoof trimming alone.
While we recognize the limitation of using an experimental model to evaluate treatment modalities in clinical disease, we believe this model closely simulates the congenital condition where compression of the physis is believed to be the active player in the development of the condition. At the most recent American College of Veterinary Surgeons Symposium (October 2001), Dr. Slone reported similar findings based on a controlled trial in clinically affected foals. Undoubtedly, those that dispute our work will call for more extensive controlled clinical trials; however, the author would submit that beyond Auer's original work, there is no scientifically sound evidence in the literature that supports those who advocate periosteal stripping as a treatment modality in the management of angular limb deformities in foals.
As the controversy continues, the reader needs to be aware not only of the medical implications, but also the financial implications that abandonment of the periosteal stripping technique may have on veterinary practices. In some practice areas, large percentages of foals undergo the procedure on a nearly prophylactic basis.
Future efforts need to be focused on identifying that small group of foals that are not going to respond to conservative management. Until that information is available, the clinician must rely on currently available intervention considerations which include:
1. Age of the foal
2. Anatomic site involved
3. Severity of the deformity
4. Status of the deformity
a. Congenital or Acquired
b. Improving, Static, or Worsening
In general, a less aggressive approach can be taken to deformities arising from the distal radius because the window of opportunity for correction is large. The author's current intervention criteria are:
Radius:
< 15 degrees; < 4-6 weeks, Not Worsening
- Confine and Corrective Hoof Care
> 15 degrees; > 4-6 weeks, Static or Worsening
- Transphyseal Bridge
Metacarpus/Metatarsus:
< 4 degrees; < 2 weeks
- Confine and Corrective Hoof Care
>4 degrees; > 2 weeks
- Transphyseal Bridge
Using this approach, there is little risk in giving the foal with a deformity at the carpus an opportunity to self-correct. The more aggressive tactic for dealing with deformities at the fetlock avoids missing the smaller window of growth opportunity.
Older foals with deformities at the fetlock can be corrected by performing an osteotomy of the cannon bone (cut and re-align). This major procedure is effective; however, the economic constraints often limit its application.
References
1. Auer JA, Martens RJ. Periosteal transection and periosteal stripping for correction of angular limb deformities in foals. Am J Vet Res 1982; 43:1530-1534.
2. Slone DE, Roberts CT, Hughes FE. Restricted exercise and transphyseal bridging for correction of angular limb deformities. Proc Am Assoc Eq Pract 2000; 46: 126-127.
3. Read EK, Read MR, Clark CR, Pharr JW, Wilson DG. An evaluation of hemicircumferential periosteal transection and elevation in an angular limb deformity model. Vet Surg 2001; 30:505.
About the Author
Dr. David Wilson received his veterinary degree at the Western College of Veterinary Medicine. He later completed an internship in Equine Medicine and Surgery at Iowa State University and a residency in Large Animal Surgery at the University of Florida. He was certified by the American College of Veterinary Surgeons in 1987. Dr. Wilson was on faculty at the University of Wisconsin-Madison's School of Veterinary Medicine from 1984-1999 before returning to the WCVM where he now serves as a faculty member.
This information was presented at, and appears in the Proceedings of, the 2002 Alberta Horse Breeders and Owners Conference.
This information is maintained by of the Horse Industry Section of Alberta Agriculture in conjunction with Sylvia
David G. Wilson, DVM, Diplomate ACVS
Professor, Large Animal Clinical Sciences
Western College of Veterinary Medicine
University of Saskatchewan |