What is carpal hyperextension?
Carpal hyperextension is an abnormality of the wrist (carpus) that causes increased extension of the joint.
The wrist consists of seven small bones, which move to allow motion between the paw and the limb. These bones are arranged in rows, dividing the carpus into several smaller joints. This entire structure is stabilized by several ligaments, found on both the front and the back of the carpus. In a healthy dog, these ligaments hold the carpus in place and maintain it at a normal angle when the dog is standing or walking.
Carpal hyperextension is caused by damage to these ligaments that stabilize the carpus. In a mild case of carpal hyperextension, the ligaments may only be stretched or strained; in a severe case, the ligaments may be completely torn. A lack of carpal stability leads the carpus to sag towards the ground, or become hyperextended, when the dog is bearing weight.
When you look at a dog from the side, a dog with a normal carpus will have straight, upright front legs ending at a small paw. In contrast, a dog with carpal extension will appear flatfooted, like a duck.
What causes carpal hyperextension?
There are several potential causes of carpal hyperextension in dogs.
In young dogs (usually less than 4 months of age), carpal hyperextension may be caused by a developmental abnormality. These dogs lack normal strength in the ligaments surrounding the carpus. Developmental factors that may cause carpal hyperextension include inadequate nutrition combined with rapid growth, or prolonged wearing of a cast or bandage. In some cases, however, no underlying cause can be identified. It is most often seen in large breed puppies. Both front legs, and possibly the hind legs, are typically affected.
Trauma is a common cause of carpal hyperextension in dogs. When a dog falls and lands primarily on his front legs, the force of landing can cause the carpus to bend more than usual, tearing the ligaments that stabilize this joint. Once these ligaments are torn, stability is lost.
"Trauma is a common cause of carpal hyperextension in dogs."
In older dogs, carpal hyperextension may also occur as a degenerative condition. In this scenario, the ligaments that stabilize the carpus degenerate with age, allowing hyperextension of the wrist. This condition is most common in large breed dogs.
What are the signs of carpal hyperextension?
Dogs with carpal hyperextension have a noticeable bend at the wrist, forcing their lower limb into an abnormally flattened position. In some cases, the dog may still run and play normally (albeit with an abnormal gait), while in more severe cases the dog may appear reluctant to move.
If carpal hyperextension is caused by trauma, it may be associated with pain and swelling. However, not all dogs with carpal hyperextension will act like they are in pain.
In some cases, pressure sores or ulcers may develop where the carpus contacts the ground. These sores may cause an increase in pain, while also causing your dog to lick or chew at the affected area. The sores can become infected.
How does a veterinarian diagnose carpal hyperextension?
In many cases, a tentative diagnosis of carpal hyperextension can be made based on initial observation. However, your veterinarian will perform a thorough physical exam, evaluate your dog’s overall health and examine all your dog’s bones and joints. Dogs with carpal hyperextension may also have abnormalities in other joints, so a thorough physical examination is important.
"Dogs with carpal hyperextension may also have abnormalities
in other joints, so a thorough physical examination is important."
Your veterinarian will likely recommend X-rays of the affected leg(s). Sedation or anesthesia is often required for these X-rays, to get good images that provide as much information as possible. Although ligaments cannot be viewed on X-rays, taking “stressed views” (in which the carpus is manipulated into various positions) can aid in the diagnosis of ligament damage by assessing the stability of the joint. X-rays can also be used to look for fractures of the small bones within the carpus.
Further imaging is often required to confirm the diagnosis and better characterize the specific ligament damage that is causing carpal hyperextension. Your veterinarian may refer you to a veterinary specialist for a CT scan or magnetic resonance imaging (MRI).
How is carpal hyperextension treated?
Treatment of carpal hyperextension depends upon the cause and severity of the condition.
In some cases of mild trauma, non-surgical treatment may be an option. Medical therapy typically involves a combination of splints and physical therapy, with the goal of restoring normal function to the stretched or sprained carpal ligaments. Developmental carpal hyperextension is not treated by splinting; rather, proper nutrition and adequate exercise will typically improve this condition in a couple of months. Ligament degeneration due to age is also often managed medically, with pain medication, physiotherapy, and other treatments.
"It is challenging, if not impossible, to repair damaged carpal ligaments, so this condition is typically treated with surgical fusion of the carpal joint, also referred to as carpal arthrodesis."
In many cases of severe or traumatic carpal extension, however, surgical repair is required. It is challenging, if not impossible, to repair damaged carpal ligaments, so this condition is typically treated with surgical fusion of the carpal joint, also referred to as carpal arthrodesis. In this surgery, your veterinarian will use a combination of plates and screws to immobilize the carpus in a functional position. In many cases, this means fusion of the entire carpus (known as a pancarpal arthrodesis), although partial carpal arthrodesis may be recommended in some scenarios. Although this surgery will prevent normal mobility at the carpal joint, it will provide stability and allow your dog to bear weight normally on the limb.
What post-surgical care is required after carpal arthrodesis surgery?
Your dog will need to wear a splint for six to eight weeks after surgery. This splint provides additional stability to the carpal joint as the metal plate fuses to your dog’s bones and the bones within the carpal joint fuse together. The plate and screws alone are not sufficient to support your dog’s full weight; they could fail if your dog immediately returns to normal activity.
While your dog is wearing the splint, you will be required to keep the splint clean and dry. Your veterinarian will provide you with instructions regarding proper splint care, but you should be prepared for approximately two months without swimming or grooming. You will be given guidelines for how to monitor your dog at home, in addition to having regular scheduled checks with your veterinarian.
Most dogs undergoing carpal arthrodesis can gradually return to their normal activities by approximately 12 weeks after surgery.