Overview of Carpal Hyperextension in Cats
Carpal hyperextension injuries in cats produce a breakdown of the ligaments that support the back of the carpal joint in the wrist resulting in collapse from the normal upright position. The injury can produce a non-weight bearing lameness that progresses to a point that demonstrates the broken-down appearance of the carpus. The lameness usually persists and leads to significant arthritic changes in the affected joints. The carpus is commonly referred to as the “wrist” of a cat.
There is no breed, age or sex predisposition. Most commonly, the disease is the result of landing on the front legs from a significant height such as a second story window.
What to Watch For
Sudden onset of front leg lameness
Swelling in the wrist
Change in gait and stance, such that the cat appears to be walking “flatter” on the wrist
Diagnosis of Hyperextension Injuries to the Carpus
Following a thorough discussion of your cat’s medical history and a full physical examination, your veterinarian will perform an orthopedic evaluation.
In the early stage, the carpus is swollen and painful and may be accompanied by instability. If your cat can use the leg, the collapse of the wrist joint may be apparent.
Standard X-rays of the carpus may not show the area of the abnormality.
Full assessment of the level of the problem in the carpal joint requires stress radiographs. Under sedation or anesthesia, the carpus is overextended to highlight the level of the joint at which the instability has occurred.
The are no specific laboratory abnormalities with this disorder, but blood work and urinalysis may be obtained as part of a work up prior to a general anesthesia. In cases of known or suspected trauma, chest X-rays may also be obtained.
Treatment of Hyperextension Injuries to the Carpus
Medical management is often unrewarding, so carpal hyperextension injuries are best treated surgically. This involves making an incision over the damaged joint, removing the articular cartilage from the affected joint and other joints nearby to allow the bone across the joint to fuse. The bones can be held in place to allow this fusion to occur (arthrodesis) by a metal plate and screws, pins, or even placed in a cast alone.
Your cat will receive injectable pain-killers (analgesics) during the period of hospitalization, and will probably be sent home with oral medications to reduce pain and inflammation.
Home Care and Prevention
Your cat will usually be in a splint or cast, regardless of the surgical fixation technique. You will need to keep the bandage clean and dry. The toes at the bottom of the dressing should be checked daily for swelling, pain or discomfort.
If the bandage gets wet, creates sore spots at the top or bottom, begins to smell, or seems to bother your cat, it will need to be changed.
Strict rest is important for the first six to eight weeks following surgery. Follow-up X-rays of the surgery will be arranged with your veterinarian to assess the healing, to time removal of the cast or splint, and to set up a program for gradual increase in exercise.
Depending on the type of surgery performed, your cat will not have complete range of motion in the carpus or even no motion whatsoever.
Carpal hyperextension injuries are usually the result of a significant fall from a height. To prevent this, make sure that windows are secure in second floor rooms that your cat can access.
In-depth Information on Feline Carpal Hyperextension
Acute sprains of the carpus can produce swelling and pain that result in significant lameness, but this should resolve with rest, anti-inflammatory medications and/or hot/cold packing, over a few days to a week. Also, there should be no instability.
Fracture of the bones within or around the carpus will also produce swelling and pain, but this does not resolve and may produce instability or “crunchiness” (crepitus) on manipulation of the fracture. There is normally no hyperextension of the carpus. Plain X-rays should define these kinds of fracture.
Damage to the medial or lateral collateral ligaments, the ligaments that run down the sides of the carpus, will produce sudden onset of pain or swelling, but instability, if present, will be produced in a side-to-side plane, not front-to-back as with a hyperextension injury. Stress radiographs in a side-to-side direction will help define a damaged medial or lateral collateral ligament.
Following a medical history (which will often include a description of falling from a height or some other trauma), and general physical examination (to ensure that no other more serious life threatening problems exist), your pet will be given an orthopedic evaluation.
Your cat may or may not use the leg to walk. If he/she does, then the carpus usually appears to be dropped to the ground, sometimes being completely flat to the ground.
On palpation of the carpus, there is usually swelling, or joint thickening (in longer standing injuries), pain, and, if your pet allows, increased extension beyond the normal limit. This finding would suggest a hyperextension injury but it may be difficult to tell at which level of the joint the problem exists.
There are three important rows of joints that make up the carpus of the cat. The radio-carpal joint is the largest and most important at the top. This is the joint that allows the majority of carpal flexion. Below is the middle carpal joints and the carpo-metacarpal joints, both of which contribute far less to carpal motion.
It is important to define which joint(s) are affected as this will impact the surgical management that is appropriate.
On plain x-rays, obtained by sedation or under general anesthesia, malalignment of joints or small chip fractures may be seen together with swelling around the affected joints. But to really define the problem, the carpus has to be stressed, that is hyperflexed and hyperextended and then x-rayed in these positions. The resulting x-rays should define the joint(s) that have been damaged.
It is important to remember that in a hyperextension injury, the small ligaments that interconnect the little bones of the carpus on its underside have been torn and damaged. These ligaments are extremely small and undertake massive stresses and strains during regular activity by your pet. There is no way to just stitch these back together, or to make a prosthetic replacement that would be as strong and effective.
For this reason, medical management usually yields poor results. If the leg is placed in a splint or cast, the torn ligaments can only heal with scar tissue. This is unlikely to mature to something as strong as the regular ligament, so commonly, after removal of the splint, the leg rapidly collapses back to how it was before.
By fusing the bones across the site that has been damaged, the ligament becomes redundant, at a cost of decreased or no range of motion at the carpus.
If the radio-carpal joint, the largest joint, has been damaged, then a complete fusion across the carpus or pancarpal arthrodesis is indicated. This will leave the carpus with a fixed lower limb, held in normal extension of about 10 degrees.
If the radio-carpal joint is intact, and the hyperextension exists at one or both of the remaining lower joints, then a partial arthrodesis can be performed. This will allow for a reasonable amount of carpal flexion and extension, although this will be decreased from normal.
Both techniques will allow your cat to be much more functional than without surgery. In theory, cats with a partial arthrodesis should have greater function. Some pets may develop lameness after increased exercise and some may retain a low-grade lameness, though not as bad as before the surgery.
To allow bone fusion, the articular cartilage is removed from the affected joint and this area is then packed with bone graft, harvested from the humerus (upper arm bone), usually on the affected front leg. This will mean that there is a small incision at the shoulder region. The bone graft will speed up the bridging across the old joint.
Often metal plates will be used to span across the joint, fixed in place using screws. Alternatively, metal pins can stabilize the bones across a joint. The plates or pins will be supported by a splint or cast as well.
A splint or cast may need significant adjustment for the first few days after surgery due to the amount of swelling of the toes, which can be very significant. For this reason, a soft padded bandage may be used for the first few days until some of the early swelling subsides. A large amount of swelling is extremely common due to performing surgery so close to the toes.
Follow-up Care for Cats with Carpal Hyperextension
The toes can be seen at the bottom of the bandage and they may be somewhat swollen, but your veterinarian will guide you as to how much swelling is normal, and when to be concerned. Although swollen, the toes are not normally painful. However, they may sweat and become moist, necessitating cleaning with a moist cotton ball.
The swelling subsides dramatically within the first week, so your cat may require a cast change to enable a better fit and support. Your cat should not place any weight on the limb initially, but he can begin to do so gradually over the next few weeks.
Strict rest is essential, which means no going up or down stairs and no jumping on or off furniture. Avoid slippery surfaces such as tile, linoleum or hardwood floors.
The incision over the front of the wrist and down the paw cannot be seen under the splint or cast. For this reason, look for any discharge seeping through the bandages, any foul smell, or your cat pulling or biting at the bandages. If you have concerns, have the cast checked by your veterinarian. Stitches or staples can be removed 10 to 14 days after surgery.
X-rays of the carpus will be redone around six weeks after the procedure to assess healing. Depending on how things look, the cast may be reduced to a splint, or even a soft padded support bandage for a few more weeks; in this way, slowly downgrading the amount of external support so that the healing fusing bones have to work a little harder. The carpus may be X-rayed again in four to six weeks.
All external support may be removed from eight to 12 weeks depending on the damage, the type of fixation, the age of the cat, and so forth. If the plate or pins are not causing any problems, they can stay where they are. In some cases, pins may back out and need to be removed, or plates, particularly in partial fusion, may impinge on the large radio-carpal joint, and are better off being removed.
In order to create a hyperextension injury to the carpus, a significant downward force must be applied against the ligaments holding up the back of the wrist. Depending on the size of the pet, certain household falls may create the kind of conditions necessary for just this sort of injury to occur. A cat could fall from a tree and therefore may be much better off kept indoors. Also, cats should not be allowed near an open upstairs window. These simple limitations on activity can help reduce the likelihood of this type of injury occurring to your pet.