An angular limb deformity is a condition that results from the abnormal growth, or stunted growth, of one or more long bones, usually in the front legs of a young dog.
Causes of Angular Limb Deformities
Angular limb deformities can be caused by the premature closure of a growth plate (called a "physis"), by retained cartilaginous cores or by bony bridging (synostosis) between the radius and ulna. In dogs, these deformities typically occur in one or both front legs, although occasionally a hind leg is affected. To understand this condition, it is worthwhile to have a general understanding of canine forelimb anatomy, and of how long bones grow.
The lower part (forearm) of a dog's front leg (forelimb) has two long bones: the radius and the ulna. These are the largest paired bones in a dog's body. The radius is the main weight-bearing bone of the forearm. Above the radius and ulna is the elbow joint, which connects the lower long bones to the humerus (upper arm), which in turn articulates with the scapula (shoulder blade) to form the shoulder joint. Below the radius and ulna are a number of small bones, tendons and ligaments that form the carpus (in people, this is the wrist joint). Below the carpus is the paw, which is comprised of various joints and bones that are collectively referred to as the metacarpus, paralleling the body of the hand in people. At the very end of the forelimb are the toes – called digits or phalanges – which in people are the fingers of the hands.
Angular limb deformities typically come from abnormalities in the radius and/or ulna. In puppies, immature long bones are made of a shaft called the "diaphysis", which is the middle or center part of the bone. At both ends of the diaphysis is another area called the "metaphysis," and beyond that is the terminal end of the long bone, called the "epiphysis." The area between the metaphysis and epiphysis is called the "physis." It is also commonly referred to as a "growth plate." Longitudinal growth of the radius and ulna (and other long bones) comes almost entirely from the growth plates (physes), which have their own extensive blood supply that is separate from the blood supply that nourishes the central shaft (diaphysis) and the very ends (epiphyses) of the bones. The growth plates are cartilage made up of five separate developmental zones. Longitudinal growth, which causes the puppy to grow taller, comes from active division and growth of cartilage cells in the growth plates. Ultimately, those cartilage cells (called chondrocytes) degenerate, causing calcium to be deposited into the bony matrix of the area, which mineralizes and forms mature hard bone.
This growth process normally continues until the growth plates close. In dogs, the growth plates of the radius and ulna typically close between 6 and 9 months of age. The physis at the lower (distal) end of the ulna bone is responsible for most of the longitudinal growth of that bone. It also is particularly vulnerable to becoming crushed during trauma because of its unique shape.
Because of their intimate association and contribution to the same joints at either end, the paired radius and ulna bones need to grow in a synchronous manner for the foreleg to develop normally. Premature closure of a growth plate at the lower end of the radius or ulna (or rarely, the tibia in the hind leg) will cause the affected bone to stop growing earlier than it should. Because of their close connection, abnormally stunted growth of one of the long bones of the forearm will affect development of the other long bone, as well as the elbow and/or the carpus (wrist) joints. Put simply, if the ulna stops growing while the radius continues to grow, the radius will begin bowing at the top, rotating outward and suffering from what is called "valgus deformity," which is a twisting of the leg away from the midline of the dog's body. The dog's elbow and carpal (wrist) joints are commonly affected, as well.
Premature growth plate closure most commonly is caused by some traumatic injury to the affected limb of a young, growing puppy less than 9 months of age. Trauma can damage the vessels that normally provide the blood supply necessary for bone growth. Far less common causes of angular limb deformities are retained cartilage cores and bony bridging of the radius and ulna, which are beyond the scope of this article.
Prevention of Angular Limb Deformities
The best way to prevent angular limb deformities is to prevent any type of traumatic injury to the lower legs of growing dogs. Early recognition and treatment are essential to preventing (or at least minimizing) severe leg deformities, pain and discomfort in affected animals.
Angular limb deformities have become desired genetic characteristics of certain breeds, such as the Bassett Hound, Corgi, Dachshund and others. In those breeds, the limbs are "naturally" shortened and deformed, without traumatic injury causing premature closure of the growth plates.
Angular limb deformities typically become noticeable about 3 to 4 weeks after some sort of trauma to the affected leg. Owners usually bring their dog to the veterinarian not because of the traumatic event, but instead when they begin to notice deformity of the affected limb.
Symptoms of Angular Limb Deformities
Clinical signs of angular limb deformities include one or more of the following:
Bowing of the affected leg (usually bows in a cranial, or frontward, direction, towards the dog's head)
Outward rotation of the affected leg (angular deviation)
Shortening of the affected leg
Pain on palpation of the elbow and/or carpal (wrist) joints (due to malalignment/incongruity of the joint)
Reduced range of motion in the elbow and/or carpal joints
These signs become increasingly obvious over time.
Dogs at Increased Risk
Angular limb deformities – especially those caused by premature closure of one or more growth plates – are usually first seen in young dogs under 9 months of age. However, older dogs who did not have appropriate treatment when they were puppies can present with angular limb deformities. Mature dogs will require a different surgical treatment than will puppies.
Angular limb deformities typically are obvious to owners once they begin to develop. The underlying cause of the abnormality usually is trauma, which probably occurred several weeks before signs of the deformity become apparent.
How Angular Limb Deformities are Diagnosed
Diagnosis of angular limb deformities is best made based upon history, clinical presentation and radiographs (X-rays). Radiographs of both front legs (even if only one is affected), from the shoulder joints all the way down to the toes and from several different views, are essential to enable the attending veterinarian to assess and fully understand the anatomical and physiological processes causing the particular dog's limb abnormalities. Radiographs will show any bone deformities and closure of the growth plates. They are also important to rule in or out any fractures, ligament or tendon damage or retained cartilaginous cores, which can also cause lameness and limb deformities.
Most veterinarians will also recommend routine blood work, including a complete blood count and a serum biochemistry profile, together with a urinalysis, to assess the dog's overall health. If the only problem is premature closure of a growth plate, the results of those tests should be completely normal.
Angular limb deformities can be diagnosed based on visible appearance. However, the real challenge is to determine and diagnose the underlying cause of the abnormality, so that appropriate treatment can begin.
The goals of treating angular limb deformities are to prevent or correct the bone and joint abnormalities, reduce the dog's discomfort and maintain as much leg length as possible.
The most commonly reported treatment for an angular limb deformity, caused by premature closure of a distal ulnar growth plate or otherwise, is surgical correction. The particular surgical approach will depend upon the age of the animal (whether its growth plates are still growing or are already closed), and on the nature and extent of the existing deformity. Young dogs with developing forelimb deformities may benefit from a procedure called an ostectomy; if the ulna is affected, the procedure is referred to as a distal ulnectomy. An ostectomy involves surgically removing a several centimeter section of the affected long bone (usually the ulna), to allow unrestrained growth of the other long bone (usually, the radius). Think of cutting a one inch piece out of the center of a chicken drumstick bone, leaving the two remaining end-pieces of the bone intact. That, essentially, is what is done with an ulnar ostectomy. Because the ulna and radius are so intimately connected, creating this surgical gap in the non-growing ulna allows the still growing radius to lengthen normally. The space created by this procedure typically is packed with a graft of fat collected from the dog's flank area, to prevent premature union of the now two separate pieces of the affected bone. Hopefully, this will facilitate spontaneous correction of the distortion of the radial bone, by permitting it to continue growing normally because it is no longer restricted by a shortened, solid ulna.
Mature dogs with limb deformities that were not corrected during their youth may be candidates for a surgical procedure called a corrective closing radial wedge osteotomy. An osteotomy involves making a surgical cut (transection) through the entire width of the affected long bone, without removing a full-cut section of that bone. The transection can be stabilized with either internal or external fixative devices, such as metal pins, wires, screws and/or plates. If the elbow joint is severely affected, additional surgery can be performed to realign the bones forming that joint.
The affected limb will be bandaged for protection after surgery. The dog will be placed on cage rest and exercise restriction for at least 6 weeks. Physical therapy is also important to reduce the chances of post-operative complications. The dog should be reevaluated radiographically (with X-rays) every few weeks, until s/he has stopped growing. If bony bridges occur between the radius and ulna, or if the first surgery is not cosmetically or functionally successful by the time of skeletal maturity, the surgery may need to be repeated.
Of course, the selection of any specific surgical or other treatment will depend upon the particular growth plate affected, the extent of the limb deformity, the age of the dog, the professional assessment of the attending veterinary surgeon and the commitment and financial wherewithal of the owner.
The overall prognosis for young dogs with angular limb deformities is good to guarded. Puppies whose premature physeal closure is caught early have a good chance of complete recovery following surgical correction. Older dogs with severe leg deformities have a more guarded prognosis, even with attempted surgical correction.