- The growth plates are much softer than other regions of the bones, therefore are more prone to injury
- The wrist or carpus is prone to developing an injury of the distal growth plate of the ulna, because it is “V” or cone-shaped
- If the dog is beyond the rapid growth phase then both radius and ulna bones must be cut to straighten the limb
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Growth plates, which are responsible for longitudinal bone growth are located near the ends of the bones and are found in animals less one year of age (see blue lines on bones in illustration right). The majority of a dog’s growth occurs during four to eight months of age. Usually by one year of age, when the pet is mature, the growth plates are closed and are not visible on x-rays. The growth plates are much softer than other regions of the bones, therefore are more prone to injury.
Since most of the longitudinal growth of bones occurs up to eight months of age, growth plate injuries that occur after this time are not as devastating. A growth plate is the weakest link in the bone construct, therefore is more susceptible to injury. A Salter-Harris classification of growth plate fracture has been described in humans and may to relate to prognosis in dogs and cats. A type 5 injury results in a crushing injury the growth plate resulting in damage to the cells responsible for growth of the bone. The result is a scar at the level of the growth plate and no additional growth of the bone occurs from this site. If the growth plate injury occurs in one of two paired bones (one bone grows and the other does not) the final outcome is usually devastating.
Mechanism of limb twisting
The wrist or carpus is prone to developing an injury of the growth plate of the distal ulna because it is is V or cone-shaped (see image right). An impact such as taking a fall and landing on the front limb with full force can drive this cone-shaped growth plate together and result in severe damage to the cells. This type of injury is common in short-legged dogs. Another injury can be due to damage to the blood supply to a section of the growth plate and a cartilaginous core will develop and the bone growth slows down or stops. Cartilaginous core formation is more common in giant breed dogs.
The growth plate at the distal (lower part) ulna bone is responsible for 90% of the longitudinal growth of the entire bone. Therefore, the ulna essentially stops growing. The radius bone, which is the parallel bone to the ulna, continues to grow. This causes a bowstring effect, with the radius being bent like a bow due to its continued growth and the ulna staying the same length like the string of the bow. The wrist therefore twists and the elbow joint also gets pulled out of alignment. The lameness in such a case comes primarily from the elbow incongruency, but also may be due to stress put on the collateral ligaments of the carpus. Another type of injury is closure of one side of the growth plate of the lower radius bone. In this situation the bone could twist toward or away from the midline of the pet (depending on which side of the growth plate is affected). This injury occurs when the limb is struck on one side of the foot. If the dog is still growing and the carpus is not twisted more than 25 degrees then removing a small section of the ulna bone and its associated covering (periosteum) will usually allow the limb to become straight again as the dog grows.
Signs and diagnosis
Angular limb deformities may affect both large and small breed dogs and signs are typically seen when the dog is less than one year of age. Lameness and twisting of the limb are the cardinal signs of an angular limb deformity. In some dogs, the elbow joint may be pulled out of alignment, thus causing swelling and pain in this joint. Bowing of the limb to the side may cause pain in the carpus joint due to excessive stresses put on the ligaments (medial collateral ligaments).
The diagnosis of an angular limb deformity is based on physical examination findings and x-rays of the affected forelimb. The surgeon likely will complete a CT scan of the affected and normal limbs, with your pet under sedation, in order to develop a precise surgical plan to correct the deformities. The surgeon may also submit the CT scan to a lab to make a 3D model and surgical guide to aid in the correction of the deformity. The images above show a twisted limb (left) and a straight limb (right).
The day of surgery
Our anesthesia and surgical team will prescribe a pain management program, both during and after surgery that will keep your companion comfortable. This may include a combination of general anesthesia, injectable analgesics, infiltration of a long-lasting local anesthetic (Nocita), oral analgesics and anti-inflammatory medication.
If the patient is still growing and the angular limb deformity is mild, a simple surgery involving removal of a part of the ulna bone will allow the limb to straighten (or at least not worsen) within a few months. Should the procedure not be done at this time, inevitable marked twisting of the limb will result.
If the patient is eight months of age or older, or if the deformity is severe, the limb must be surgically straightened. Timing of the surgical straightening procedure of the limb is important and will be decided upon by your pet’s surgeon.
Some surgeons prefer to use a 3D model and custom-made surgical guide during surgery, as this eliminates the intra-operative planning and shortens the surgical time (see images below). During corrective surgery, the ulna and radius bones are cut near the carpus, where the bones are twisted. Usually a wedge of bone is removed from the radius bone. The limb is then realigned to correct the deformity. The bones are held in place by means of a bone plate and screws or an external skeletal fixator.
At ASCM, the preferred method to secure the bones in place is with a bone plate and screws, as there is less postop care needed by the pet owner (see pre and post images to right). In most cases, the metal plate and screws are left in place, unless there is some indication to remove them once healing has taken place.
A second method of bone fixation is with an external skeletal fixator. This involves placement of pins through the skin and bone and these are fastened to external bars with a series of clamps. After full healing takes place, the apparatus is removed.
If the elbow joint has been pulled out of alignment by the shortened ulna, cutting the ulna bone will allow the elbow to come back into position.
After surgery, you can continue to give your pet a prescribed pain reliever to minimize discomfort. If a plate and screws have been used to secure the bones in place, a splint or cast may be used for period of time, pending the surgeon’s discretion. It’s also extremely important to limit your dog’s activity and exercise level during the post-operative period. Detailed instructions will be given to you after the surgery. The surgeon will monitor the healing process with a series of follow-up exams, depending on which method has been used to secure the bones in place. At eight weeks after the surgery, x-rays will be made to evaluate the healing of the bone.
Surgically correcting an angular limb deformity has the advantage of relieving carpus and elbow pain, and reducing arthritis from developing within the joints over time. The pet owner must understand that angular limb deformities are commonly complex, in three planes and may involve multiple levels of the bone. Therefore, following surgery, the deformity will be will be greatly improved upon, but may not be perfectly normal.
Uncommon complications following surgery include infection, nonhealing of the cut bones, breakage of the implants (metal plate, screws or pins), bone cancer (from leaving implants in place), cold sensitivity and fracture of the bone. In general, about 90 to 95% of the patients that have surgery will heal uneventfully.