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 dog. 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 reverts to its original collapsed state.
By fusing the bones across the site that has been damaged, the ligament becomes superfluous, 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 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 dog to be much more functional than without surgery. In theory, dogs with a partial arthrodesis should have greater function. Some dogs 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, or 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 are 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 are 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 at 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.
