(Knock Knee)

Posting Date: 7-4-2005

Jodi Houser, Senior Veterinary Student

David E Anderson, DVM, MS, DACVS
Head and Associate Professor of Farm Animal Surgery
Director, International Camelid Initiative
Ohio State University
College of Veterinary Medicine
601 Vernon L Tharp Street
Columbus, Ohio 43210
Phone 614-292-6661
Fax: 614-292-3530

David E Anderson, DVM, MS, DACVS Head and Associate Professor of Farm Animal Surgery Director, International Camelid Initiative Ohio State University College of Veterinary Medicine 601 Vernon L Tharp Street Columbus, Ohio 43210 Phone 614-292-6661 Fax: 614-292-3530

What is an angular limb deformity (ALD)?

Angular limb deformity is defined as the valgus (e.g. outward or lateral) or varus (e.g. inward or medial) deviation of a limb. The deformity is named for the joint at which the deviation begins, and the direction in which the deviated portion of the limb extends. For example, the lateral deviation centered at the carpal joint would be termed carpal valgus. The lay terms for these carpal-centered conditions are knock-kneed (valgus) and bow-legged (varus).

What causes angular limb deformity?

Angular limb deformity can be congenital or acquired, but often the underlying issue is that one side of the bone is growing faster than the other side of the same bone. This excess growth occurs at the growth plate (physis). Growth plates occur at the ends of long bones, therefore a change in the physical growth rate leads to a change in the angle of the limb distal to the growth plate.

Some animals are born with ALD because of problems in utero such as malposition, trauma, improper growth of tendons and ligaments, or premature birth and inadequate formation of the tendons and ligaments essential to formation of strong bones. Another possible cause of ALD is excessive pulling of a cria because of dystocia (difficult birth) and an overzealous desire to get the cria out quickly.

Several major causes of ALD are those that occur shortly after the cria is born. These include insufficient Vitamin D during the period when the cria is growing most rapidly. Crias born during the fall and winter are more prone to ALD because of decreased sunlight and therefore the decreased ability to process Vitamin D through decreased ultraviolet light on the skin. Other reasons animals may develop ALD are any reason that causes asymmetric weight-bearing on a limb such as trauma, infection, inflammation of the joint, and decreased weight-bearing on the contralateral limb leading to compensation on the normal limb.

How is angular limb deformity diagnosed?

ALD often can be diagnosed on the clinical appearance of the limbs. However, presence of hair/fiber on the limb makes assessment of the angle difficult. Taping the limb, wetting down the fiber, or shearing the limb can facilitate visualization of the angle. Radiographs should be performed to evaluate the limb for origin of defect, angle of deviation, other problems with the bones or surrounding structures, soft tissue swelling, and closure of the growth plates.

How is angular limb deformity treated?

Treatment is determined based on the severity of deviation, age, and intended use of the animal. In those animals with joint laxity or instability caused by insufficient growth and development of the supporting structures of the bones, splints may be applied to correct the deformity. Splints are generally applied for 7-14 days. In those animals where the deformity is recognized early (e.g. < 3 months of age), medical treatment (e.g. Vitamin D) may be attempted. Late recognition of the deformity (e.g. > 6 months of age) warrants surgical therapy. Once the cria begins to grow rapidly, surgery is often necessary. The type of surgery performed must be decided by the veterinarian based on several factors including age, severity of deviation, possibility of overcorrection, chance of infection, and general temperament of the animal. Types of surgery performed for correction include periosteal stripping, transphyseal bridging, wedge ostectomy/osteotomy, and any combination of these.

Surgery performed only in those animals with actively growing bones

Periosteal stripping (also termed hemicircumferential periosteal transection and elevation) – the outer layer of bone is removed on the concave side (slower growing side) of the affected bone, close and proximal to the growth plate where the deviation occurs. This helps stimulate more growth of the bone on the shorter side of the bone, thus straightening the limb. This surgery does not involve any implants so the risk of infection is much lower and there is little to no risk of overcorrection. This surgery will only work when the bone is extremely actively growing. Thus, this surgery is only performed in crias less than 3 months old.

Transphyseal bridging – two bone screws are placed in the convex side (e.g. more rapidly growing side) of the bone of the affected limb, one directly above and one directly below the joint at which the deviation occurs. Once both screws are in place, a metal orthopedic wire is placed in a figure-eight configuration around the screws and the screws are then tightened down onto the bone. The skin is then closed over the metal implants. Once the leg is straight a second surgery must be performed to remove the implants to prevent overcorrection. Although transphyseal bridging may seem dramatic this is a simple, minimally invasive surgery and minimal pain is observed post-surgery. Risks with this type of surgery are infection or failure of the implants and most importantly, overcorrection of the limb deviation if the implants are not removed immediately when the bones have straightened out. Transphyseal bridging can be performed at any time during growth of the long bones but is most successful when done while the animal is less than 6-8 months old.

Surgery performed when growth plates are closed

Wedge ostectomy/osteotomy – a wedge of bone is removed from the convex side of the bone so that the two edges where the wedge was removed will grow toward each other. This will straighten the bone by shortening the side of the bone that has grown too fast. This procedure is performed after the growth plates have closed because the other two procedures require actively growing bone to be successful. Risks association with this surgery are non-union of the bone edges, pathologic fracture, and infection.

How much time should it take for the limb to be straight after transphyseal bridging?

The time for a limb to become straight following surgery varies by individual animal. According to the cases seen at The Ohio State University Veterinary Teaching Hospital since 2001, the average correction of a carpal valgus angular limb deformity is 0.23 degrees/day, or about 1 degree correction every 4 days. Obviously there are reasons why a particular limb may take longer or shorter to correct, such as the age of the animal, health status, and type of surgery performed. The numbers stated above serve as a general guide but not as a definitive healing time. Animals should be observed daily following surgery for straightening of the limb and should be returned immediately for removal of implants following transphyseal bridging as soon as the limb appears straight.

What is the best way to prevent angular limb deformity?

Starting with the period in which the cria is not yet born, the dam must be given adequate nutrition and reduce stress to prevent premature birth. Assistance with birthing should not be done unless absolutely necessary. When the dam is in difficult labor, do not pull excessively on the limbs to get the cria out. Call the veterinarian if there is any question that the dam might be experiencing a dystocia.

Once the cria is born, it is important to supplement the diet with Vitamin D in order to ensure adequate growth and formation of the bones. This can be done by injection every 60 days or by oral supplementation given every 2 to 4 weeks. Crias born in the spring are much less dependent on supplemental Vitamin D as they receive adequate sunlight. If the cria is born in the fall or winter this is especially important due to decreased sunlight when the cria is actively growing. Crias contained indoors for prolonged period (e.g. injury, etc.) require supplemental Vitamin D.

Other causes of ALD, such as trauma and infection, may be more difficult to prevent. Good facilities free of clutter and debris and careful watch of young stock to prevent injury are good measures to take in any situation. If the ALD is suspected to be heritable because of congenital malformation of bone, tendons, ligaments, etc. or other crias from the same parent are experiencing similar disease, it is important to consult your veterinarian to discuss if the crias should not be used as breeding animals.

Outcomes of 41 Cases of Carpal Valgus and 2 Cases of Carpal Varus Angular Limb Deformity in Camelids and Their Surgical Correction at The Ohio State University Veterinary Teaching Hospital (OSUVTH) from 2001-2005

Between the years of 2001-2005, 18 alpacas and 5 llamas representing 43 angular limb deformity (ALD) surgeries were presented to the teaching hospital for evaluation and surgical correction of their ALD. The animals ranged in age from 2 weeks to 16 months at time of surgery with a mean age of 22 weeks at surgery. The angle of deviation ranged from 4 degrees to 29 degrees with a mean angle of deviation of 10 degrees. The average time to correction (straightening) of the limb was 53 days after surgery. Of the 43 surgeries performed, 32 were transphyseal bridging alone, 2 were transphyseal bridging plus periosteal stripping, 5 were wedge ostectomy, and 4 were periosteal stripping plus ulnar wedge ostectomy.

Age

Age is a critical factor when evaluating patients with angular limb deformity. For growth plates in the distal limb (radius, ulna, tibia), there is maximal active physeal growth from birth to 10 weeks of age. From that point, the rate of growth steadily declines until 60 weeks of age at which physeal growth essentially stops. For this reason, it is important to evaluate animals with ALD as soon as possible so that surgery may be attempted at an age at which maximal effective straightening will occur. In the cases seen at OSUVTH, 6 animals presented were under the age of 10 weeks and their outcome was 0.32 degrees of correction per day, which was faster correction than the average of all of the cases. One animal presented over the age of 15 months (60 weeks) and correction of the ALD was 0.24 degrees/day. This may be because this animal was very close in age to the point where physeal growth stops but had sufficient physeal growth to allow correction. These numbers show an age correlation to outcome of surgery in that the younger animals seemed to heal faster than the older animals receiving the same treatment

Angle of Deviation

As stated in other similar studies, angle of deviation does not have a significant effect on rate of correction, but only on the amount of time until correction is achieved. The average rate of healing did not change significantly based on the severity of deviation except in one case. In one

13-month-old female alpaca the angle of deviation was 29° and 26° in the right and left carpi, respectively. No healing was noted in the ALD 14 days post-surgery and the alpaca developed fractures in each carpus at the point of screw insertion and was euthanized. The next highest angle of deviation was 19° and this leg healed following transphyseal bridging according to the average time of healing. This data may suggest that there is a certain point (between 19-29°?) at which the deviation is severe enough that surgical correction alone cannot fix the problem.

Type of Surgery

As stated above, 4 different combinations of three surgical procedures were performed in the cases at OSUVTH. In the cases of the transphyseal bridging alone 29 of 32 fully corrected with an average correction rate of 0.23°/day, 2 of 32 did not have any follow-up care at OSUVTH, and 1 of 32 overcorrected from a 10° valgus to a 10° varus deformity over the course of 15 months. Overcorrection occurred because the implants remained in the carpus and the owner did not notice the change in angle until it was too late. This last outcome demonstrates the importance of bringing the animal in as soon as possible to have the implants removed once the limb is straight to prevent overcorrection in the opposite direction. In the 2 surgeries that included transphyseal bridging and periosteal stripping, both healed with an average of 0.2°/day. This combination of surgery did not seem to provide more impetus for the bone to straighten compared with transphyseal bridging alone. On the side of the transphyseal bridge the growth is being retarded and on the side of the periosteal stripping growth is being promoted. However, this was only one animal and two limbs so it is difficult to draw a sound conclusion on the anticipated outcome of this combination surgery. In the 5 cases of wedge ostectomy, 1 of these surgeries overcorrected, 2 of these surgeries showed no healing at all after 14 days, and the remaining two surgeries fully corrected. The 4 surgeries that included periosteal stripping and wedge ostectomy included no follow-up at OSUVTH and therefore the outcome is unable to be determined. As with the other combination surgery, it could be hypothesized that a combination surgery may heal faster than one surgery alone although this was not proven in the cases above.

Time to Re-evaluate

Other than the case that did not return for re-evaluation for 15 months, the longest duration of time between surgery and re-evaluation was 4.5 months with the shortest time being 2 weeks to re-evaluation. Therefore, this data suggests that if the animal has not been re-evaluated within 4 months, re-evaluation should be scheduled. Based on the average of 0.25°/day of correction and the maximum angle of deviation of 19° in these 43 cases, the longest time to re-evaluation should be about 76 days (2.5 months).

Other Factors

Several other factors involved in clinical outcome of the cases were also observed. Concurrent illness was evaluated as a possible confounding factor involved in time to correction of the angular limb deformity. Of the 23 llamas and alpacas undergoing surgical correction of ALD at the OSUVTH, concurrent diagnoses were as follows: M. Hemollama (1), Rickets Disease (2), Trichuris vulpis (1), and vague illness with fever and weight loss (1). Difficult birth was a common factor among the animals undergoing surgical correction for ALD, with 5 confirmed dystocias out of 23 animals. Owners stated that the front limbs were pulled at birth on 3 of the 5 confirmed dystocias and 1 cria was confirmed with bilateral carpal flexion. More animals were likely involved in dystocias, however the medical records did not confirm this presumption. 2 of the 23 animals were confirmed to be premature, although the time premature was not noted in the medical record. It is well established that prematurity predisposes animals to ALD because the tendons and ligaments are not fully developed at birth.

Outcome

Of the 43 limbs that received surgical correction at OSUVTH, most fully corrected (30 out of 35 that included re-evaluation at OSUVTH). 3 out of 35 had healed to within 6° of normal at the time of re-evaluation and may have continued to straighten after that time. The transphyseal bridging procedure alone is by far the most commonly performed procedure and shows promising and consistent results. This surgery requires that the owners are compliant and bring the animal back in for re-evaluation as soon as the limb straightens. This procedure should continue to be very successful in correction of angular limb deformity in camelids.

REFERENCES

Anderson, David E, DVM, MS, Diplomate ACVS, “Common Surgical Procedures in Camelids.”

Burba, Daniel J., DVM, Diplomate ACVS, “Angular Limb Deformities Can Cripple Foals.” Louisiana State University School of Veterinary Medicine Equine Health Studies Newsletter, Volume 8, Number 1. Winter 1999.

Hendrickson, DVM, MS, Diplomate ACVS, “Angular Limb Deformities and Physitis.”

Smith, Brad, DVM, PhD, “Hypophosphatemic Rickets in the Llama.”

Smith, Bradford P., DVM, Diplomate ACVIM, Large Animal Internal Medicine. St. Louis, Mosby, 2002.

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