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ANGULAR LIMB DEVIATION
Overview
Angular limb deviation (ALD) is seen most commonly in young foals and is defined as a deviation from the normal axis of the limb in the frontal plane1-3. It can be described as the appearance of the foal as observed from the front or rear. There are two general terms used to describe the deviation. Valgus refers to a lateral (outward) deviation of the limb distal to, or below, the point of the deformity (Figure 1). Varus refers to medial (inward) deviation of the limb distal to the point of the deformity (Figure 2). The most common deviation seen in young foals is lateral deviation which originates at the level of the carpus (knee), known as carpus valgus (Figure 1).
Figure 1. Foal with a valgus deviation at the level of the carpus.
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Figure 2. Foal with a varus deviation at the level of the fetlock.
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Causes
ALD can be caused by perinatal factors such as premature birth, twin pregnancy, placentitis, perinatal soft tissue trauma and flaccidity of the soft tissue structures surrounding the joints1-3. These factors can potentially lead to improper development of the small bones, known as cuboidal bones, found within the knee and/or hocks (tarsus), and/or flaccidity (laxity) of the joints. Normally, most foals will be born with some degree of limb deviation, mostly due to ligament laxity and muscle weakness which usually will correct itself as the foal exercises. However if the cuboidal bones are not fully ossified (Figure 3), they run the risk of being crushed from exercise and the uneven load that is placed on the joint due to the laxity. Once ossification occurs, an ALD will result due to the abnormally shaped cuboidal bones.
Figure 3a. Incomplete ossification of the cuboidal bones of the carpus.
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Figure 3b. Incomplete ossification of the cuboidal bones of the tarsus.
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In addition, developmental factors such as unbalanced nutrition, and excessive exercise and/or trauma can result in ALD in older foals1-3. Feeding foals in groups (crib feeding) may lead to excessive grain intake by the dominant foals creating an imbalance in their diet (too much carbohydrates and protein). Nutritional imbalance may cause disproportionate growth across the growth plate, causing the deviation. Exercise is a very important element in the proper development and growth of foals. However, if the amount of exercise is excessive, this trauma can lead to microfractures and crushing of the growth plate, which will cause the development of ALD.
Incidence and Prevalence
Although all breeds are susceptible to the development of ALD, Thoroughbreds appear to be particularly affected. There have been reports of an incidence of up to 11% in foals of this breed. There is no gender predisposition.
Signs and Symptoms
Angular limb deviations are usually diagnosed by visual examination1. There is a break in the normal axis of the limb, either lateral or medial. It is important to examine the standing foal from the front, side and rear; and, observe the foal while walking in a straight line on a hard, level surface. In some cases, the affected joints will show varying amounts of effusion (joint swelling). If the deviation is secondary to inflammation at the level of the growth plate (physitis) there might be a hard, palpable swelling, either medial or lateral, at that level (Figure 4). Depending on the severity and chronicity, the inside or outside of the hoof wall might be excessively worn if the deviation is lateral (valgus) or medial (varus), respectively. In cases of incomplete ossification of the cuboidal bones with secondary crushing injury, lameness may be apparent.
Figure 4. Physitis at the level of the metaphyseal growth plate of the radius. Note the prominent swelling (white arrow) over the medial aspect of the distal radius.
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Risk Factors
Foals born prematurely or dysmature, and any foal born with an angular limb deformity, should be examined within the first 24 hours of birth to detect and treat joint flaccidity and/or incomplete ossification of the cuboidal bones, thereby preventing the development of ALD and other orthopedic conditions. Those who are showing ALD should be treated immediately using conservative management such as splints or casts in order to correct or control the angular deviation1-3.
Dominant foals fed in groups (crib feeding) are at a higher risk of developing ALD due to excessive grain intake which will result in dietary imbalance and disproportionate growth1-3.
Diagnostic Procedures and Imaging
Simple observation and examination of the foal will give a presumptive diagnosis1, 2. Manipulation of the limbs to correct the deformity will be helpful in order to rule in or out ALD due to excessive ligament/peri-articular laxity. Radiographs, although not needed in every case, are helpful in assessing the location (“pivot point”) and degree of deviation, condition of the cuboidal bones, appearance of the growth plates, and response to treatment (Figure 5). Two views, dorsal-palmar (cranial-caudal) and lateral-medial, should be taken centering the cassette on the affected joint. It is important to know that during follow-up radiographs, changes in the direction of the x-ray beam can alter the degree of deviation, making quantitative assessment of the response to treatment difficult. For this reason visual assessment of the limbs cannot be over-emphasized.
Figure 5. Dorsal-palmar radiograph of the carpus in a foal with valgus deformity.
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When to Seek Veterinary Surgical Advice
Although a high percentage of foals with ALD respond favorably to conservative management, including rest, restricted exercise and corrective farriery, surgical intervention is recommended if the deviation is moderate to severe (>12º) (Figure 6). Foals that are born dysmature or premature should be examined by a veterinarian within the first 24 hours in order to assess the condition of the cuboidal bones and joints in general. In cases that surgical intervention is necessary, timing regarding when to perform the procedure(s) is extremely important since its success is directly related to the amount of growth left on the particular growth plate. Due to the fact that the growth plates of different long bones have different periods of maximal growth rate (cannon bone, tibia, and radius have their maximal growth during the first 2, 4, and 6 months of life, respectively) early communication with your veterinarian and equine surgeon can be invaluable to formulate a treatment plan, both medical and surgical. Find an ACVS Veterinary Surgeon.
Figure 6. Dorsal-palmar radiographs of the carpus in a foal with valgus deformity. The relative angle of the deviation has been calculated.
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Treatment Options and Aftercare
Non-surgical treatments1-3:
- Stall rest-
- Foals with incomplete ossification and straight limbs. Stall rest for a maximum period of 1-2 months. Repeat radiographs every 10-14 days in order to assess ossification.
- Foals with disproportionate growth at the level of the physis and ones with diaphyseal deformities. Stall rest for 4-6 weeks.
- Foals with flaccidity of periarticular supporting structures and normal ossification of the cuboidal bones can benefit from stall rest with a daily hand walk of 10-15 min for a 4-6 week period.
- Splints and casts are used to treat foals with incomplete ossification of the cuboidal bones of the carpus (“knee”) and tarsus (“hock”). The splint or cast should end at the level of or just above the fetlock in order to minimize tendon/ligament laxity and osteopenia (loss of bone density). The limb should be examined regularly for evidence of rub sores. Splints and bandages should be changed every 3-4 days, and casts should be changed every 10-14 days. It is very important to examine the limb for straightness and sores each time the splints and casts are changed.
- Corrective hoof trimming and glue-on shoes with lateral or medial extensions can be used alone or in combination with other treatment modalities.
Surgical treatments1-5:
- The objective of surgical intervention in cases of ALD is to return the affected limb to a more normal alignment. Common joints affected include the carpus, tarsus and fetlock. For carpal deformities, the growth plate responsible for the ALD is located at the level of the distal metaphysis of the radius; for tarsal (hock) deviations, it is the distal metaphyseal growth plate of the tibia; and, for the fetlock, it is the distal growth plate of the cannon bone and less often, the proximal growth plate of the first phalanx (P1). Surgical management should be considered for those foals which have not responded to conservative management, those with severe deformities, and those who are affected in a bone after its rapid growth rate is completed (cannon bone, ~2-3 months old; tibia, ~4 months old; and, radius, ~6 months old).
- Growth acceleration (“Periosteal Stripping”)1-3, also referred to as hemi-circumferential transection and periosteal stripping (elevation), is performed on the concave side of the affected limb. For example, in a foal with a valgus deformity, the concave aspect is the lateral side of the limb; with a varus deformity, it is medial. The division of the periosteum on the affected side is supposed to stimulate bone growth on that side, thus correcting the deformity. The theory is that by dividing the periosteum (a thick fibrous membrane that covers the entire bone with the exception of the joint surface) tension is released at the level of the growth plate resulting in new bone production and deposition on the operated side of the limb. Historically, this procedure resulted in a very high success rate (up to 80%) although recent studies have questioned its benefit when compared to conservative (non-surgical) management alone. Due to these recent studies4, some equine surgeons do not recommend performing the procedure although it is still widely performed with varying degrees of subjective success. The procedure is simple to perform with minimal instrumentation required. There have been no reports of over-correction with this procedure. Following surgery, the incision will be bandaged to prevent infection and/or seroma formation. The bandage should be changed every 2-3 days for 10-14 days (Figure 7). Stall rest is recommended for 2-3 weeks.
Figure 7. Light bandage of the distal radius following periosteal stripping procedure.
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- Growth retardation (“Transphyseal Bridging”) is performed either in young foals (<3 mo. old) with severe ALD or in foals with significant ALD in a bone after its rapid growth rate is completed. Growth retardation procedures are performed on the convex side of the deviated limb, ie, on the medial side for a valgus deformity and on the lateral side for a varus deformity. The goal is to create compression across the physis, retarding the growth on that side of the limb. The physis at the concave side will not be affected. Historically, there have been three different techniques used to create compression across the growth plate: staples; screws with cerclage wires in a figure 8 pattern; and, screws with a small 2.7 mm bone plate1-3. Recently, a fourth technique has been described in which a single screw is inserted across the growth plate to create the desired compression (“Transphyseal Screw Technique”)5. This latest technique has been shown to be successful in achieving adequate correction of the ALDs, with the advantage of a better cosmetic result. Post-operative care for patients treated by growth retardation procedures is similar to the periosteal stripping, with the one important exception: the implants used must be removed as soon as the deformity has been corrected. If the implants are left too long it is possible to overdo the amount of correction. Radiographs should be taken every 10-14 days in order to assess degree of correction (Figure 9 a and b), and to determine the timing of implant removal.
Figure 8. Anteroposterior radiographs of a foal with carpal valgus deformity following transphyseal bridging procedure.
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Figure 9a. Dorsal-palmar radiograph of a foal with carpal valgus deformity following transphyseal screw procedure.
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Figure 9b. Dorsal-plantar radiograph of a foal with tarsal valgus deformity following transphyseal screw procedure.
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Corrective Osteotomy or Ostectomy is used for correction of angular limb deformities once the growth plates have closed1. Also, it is used to treat patients with rotational and diaphyseal deviations, primarily of the cannon bone (third metacarpal/metatarsal bones). There are two main techniques described in the literature: the closing wedge and step ostectomies. The step ostectomies are currently the preferred techniques. The step osteotomies can be performed in both the frontal and sagittal planes, performing a Z-plasty of the affected bone. A wedge of bone is usually removed in order to provide proper correction, and it is stabilized using bone plates and screws.
Potential Complications Following Treatment
Some deviations may not be corrected if the period of maximal growth of the particular growth plate has elapsed or there is plastic deformation of the cuboidal bones due to incomplete ossification1,3. Although overcorrection of an ALD has not been reported following periosteal stripping procedures, it is possible to do this with growth retardation (transphyseal bridging) procedures. For this reason, the operated limb(s) should be monitored very closely on a daily basis. As soon as the ALD appears corrected, radiographs can be taken to verify the observation and the implants should be removed as soon as possible.
Prognosis
Prognosis for foals with ALD can vary greatly depending on the underlying condition, degree of deviation, joint affected, and future use of the horse1,3,6,7. Foals with mild to moderate deviations but with complete ossification of the cuboidal bones have a good chance of having the deviation corrected. Those with peri-articular laxity tend to correct themselves within the first several weeks of life. The condition which can have perhaps the most profound effect on the athletic future of the horse is incomplete ossification of the cuboidal bones because of the degree of deviation that this can create and the potential for the development of osteoarthritis (degenerative joint disease). Generally speaking, foals with carpal deformities tend to do better than those with tarsal deviations. Based on past studies, 73% of the foals born with incomplete ossification of the tarsal bones developed a valgus deformity as a consequence6,7. Out of this group, only 32% of the foals were able to reach their intended use. This was due to crushing of the incompletely ossified cuboidal bones found in the hock (tarsus), which resulted in varying degrees on osteoarthritis (degenerative joint disease) of the distal intertarsal and tarsometatarsal (lower hock) joints.
—Jose Garcia Lopez, VMD
Diplomate ACVS
Posted 4/29/2005
Updated 6/17/2008 by Dr. Garcia Lopez
References:
1. Auer JA: Angular Limb Deformities. In: Equine Surgery, 3rd edn, Eds JA Auer and JA Stick. Saunders Elsevier, St. Louis. 2006: pp 1130-1149.
2. Parente EJ, García-López J: Angular Limb Deformities. In: Diagnosis and Management of Lameness in the Horse, Eds MW Ross and SJ Dyson. Saunders, Philadelphia. 2003: pp 557-561.
3. Hunt RJ: Angular Limb Deformities. In: Current Techniques in Equine Surgery and Lameness, 2nd edn, Eds NA White and JN Moore. Saunders, Philadelphia. 1998: pp 323- 326.
4. Read EK, Read MR, Townsend HG, et al: Effect of hemi-circumferential periosteal transection and elevation in foals with experimentally induced angular limb deformities. J Am Vet Med Assoc 221:536-40, 2002.
5. Hunt RJ: New Techniques in Transphyseal Bridging. Proceedings of the American College of Veterinary Surgeons Symposium, 2006: pp 168-169.
6. Dutton DM, Watkins JP, Walker MA, et al: Incomplete ossification of the tarsal bones in foals: 22 cases (1988- 1996). J Am Vet Med Assoc 213:1590-4, 1998.
7. Dutton DM, Watkins JP, Honnas CM, et al: Treatment response and athletic outcome of foals with tarsal valgus deformities: 39 cases (1988- 1997). J Am Vet Med Assoc 215:1481-4, 1999.
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