TREATMENT OF GROWTH DEFORMITIES IN THE YOUNG DOG

The most commonly affected area in growing dogs is the growth plates of the two bones in the forearm. Since the principles of treatment are the same for any bone this discussion will be limited to these bones.

The distal growth plates of the ulna contributes 85% of the growth while the proximal physis and cartilage of the ulnar articular surface of the elbow joint contributes only 15%. The distal radial physis contributes 70% and the proximal physis 30%. This disparity in growth between the two bones and their respective ends predisposes this area to growth problems. The most common causes of these problems are from fractures of the radius and ulna or diseases such as hypertrophic osteodystrophy and retained enchondral cartilage. The latter is most often seen in the distal ulnar physis in giant breed dogs. Growth in these physis can either be slowed or completely arrested. This is usually apparent from the radiographs and is an important distinction in planning treatment. Any time an immature dog is presented for a radius and ulnar fracture the owners should be advised of the possibility of closure of one or both of the distal growth plates. This will usually be apparent within 2 weeks on radiograph.

Regardless of which growth plate is affected the goal of treatment is to maintain length, preserve joint congruity (especially the elbow), and prevent and correct angular deformity. In planning treatment the surgeon should take into account the present angular and rotational deformity and joint incongruity and then consider how much further growth potential there is and what effect that will have on further deformity. In the young 3 to 4 month old animal with significant growth remaining the plan is to cut the slow growing bone to allow the other bone to grow unimpeded. Any deformities present can either be corrected at the same time or when the dogs growth stops. Mild deformities will sometimes correct themselves. If the deformity is severe then it can be corrected at the same time. In the older dog only the deformity itself must be corrected. Although the distal physis close until 12 to 14 months there is relatively small growth after 7 months and usually a final correction can be made at this age. Osteotomies ideally should be made at the area of greatest curvature. When using an External Skeletal Fixator (composed of pins that go from the outside through the skin and bone and are connected together by clamps on the outside of the limb) the limiting factor is the ability to place at least 2 pins in the distal fragment. The goal is to return the plane of the carpal joint to a parallel alignment with the elbow joint. This can be determined from the radiographs by drawing parallel lines through the joints and the deformity. This will determine the angle of the wedge to be removed and should be done for both planes, lateral and VD. If an ESF is to be used a simpler method is to place the transfixation pins parallel to the respective joints on either side of the osteotomy and when these pins are parallel in the fixator then the joint surfaces must be parallel also. Again all three planes of deformity must be considered angular, cranial bowing , and rotational when planning these corrections. With the use of an external or ring fixator a single osteotomy rather than a wedge can be performed. Also further adjustments can be made after surgery which cannot be done when using a plate.

Incongruity of the elbow joint can occur in either a distal ulnar or distal radial closure. Usually osteotomy of the offending bone and continuous weight bearing is enough to realign the elbow joint. A smooth pin can be placed in a proximal ulnar osteotomy to maintain axial alignment. The technique of distraction osteogenesis now allows the surgeon to perform the correction of the deformity and provide continued lengthening with one procedure. This technique can be utilized with bilateral external fixators using threaded bars or special ring fixators or a combination of both. Rings are especially useful in a short distal fragment where it is difficult to place two traditional transfixation pins.

DISTAL ULNAR GROWTH PLATE DISTURBANCES:

This is the most common form of growth disturbance and is seen most commonly after trauma, injury or growth disturbances. The cone shape of the distal ulnar physis concentrates and compressive forces and may explain the susceptibility of this physis to problems. The result of closure or retarded growth is a deformity of the distal radius and carpus as it grows around the stationary distal ulna. If the deformity is long standing then the carpus also internally rotates and bends caudally. Often there is significant deviation to the outsideat the carpus or foot while the elbow is spared. If not the elbow is pulled out of place and is painful so if the dog is very lame look for an elbow problem.

In young growing dogs a section of the ulna should be removed to relieve the pressure on the radius. Unless care is taken to remove all the periosteum with the excised section, especially along the radius, these dogs will bridge even a 3-4 cm gap within weeks. Fat grafts can be placed between the ends but meticulous removal of periosteum is more critical in preventing premature healing. If the osteotomy heals before growth ceases a second ostectomy is necessary. A smooth pin can be placed in the olecrenon in a proximal osteotomy to provide axial support. If there is severe concurrent angular deformity present this can be corrected at the same time but care must be taken to protect the distal radial physis to allow its full growth potential to be realized. If the deformity is mild it is better to wait until growth ceases to make the correction.
In older dogs a single correction is made as described above. It is necessary to transect the distal ulna when making the osteotomy at the point of greatest deformity in the radius. If there is elbow subluxation then a second osteotomy must be made in the proximal aspect of the ulna.
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DISTAL RADIAL GROWTH PLATE DISTURBANCES

These physeal abnormalities are usually secondary to trauma and often only the lateral aspect of the distal radial physis is affected. This causes the proximal or close end of the radius to pull away from the elbow joint. Occasionally the leg will appear straight and the articular surface of the distal radius will be angled in varus. An osteotomy of the radius is necessary to relieve pressure on the distal ulna and allow the radial head to realign with the humerus. A section of the radius can be removed or a distraction device can be used to move the proximal radius further proximal and prevent the osteotomy from healing before the dog stops growing. The radius can support weight alone better then the ulna so this added support is a good idea. If a significant angular deformity exists in the distal radius a corrective osteotomy can be performed at the same time as the distraction of the radius If the leg is significantly shorter at presentation in a young dog a distraction device should be placed on the leg, both the radius and ulna transected and distraction applied at between 1 to 2 mm a day to make up for present shortening and provide for continued growth. In an older dog a single radial osteotomy can be used to straighten the distal radius and slow distraction will return the radial head into proper alignment with the humerus. Some surgeons advocate shortening the ulna to bring the radial head in contact with the humerus in one procedure but this shortens the entire leg and although the dogs function well it seams counterproductive to add deformity to deformity when there are other options.

CLOSURE OF GROWTH PLATES OF BOTH BONES

This is usually secondary to trauma and if it occurs at an early age can lead to significant shortening as well as acting similar to a distal ulnar closure. This is because the proximal radial physis provides more overall growth then the proximal ulnar physis. The best treatment in an immature dog is osteotomy of both the radius and ulna and a distraction apparatus as described before. The use of a ring distractor allows small pins to be used and more even distraction in all three planes but requires special instrumentation. The biggest problem is in the osteotomies healing prematurely before natural growth ends. A second osteotomy and continued distraction is then necessary. Often owners will accept some shortening rather then undergo a second procedure. Since the distraction is done daily over a long period of time the owners must actively participate in the treatment and case selection is important.