Normal stance for a dog – on their ‘tip toes’ compared to human beings
As you probably have noticed, dogs and cats walk a bit differently compared to human beings – cats and dogs walk on the tip of their toes.
What is hyperextension?
This diagram shows where the carpus and hock are in a dog or cat
What causes carpal hyperextension? Carpal hyperextension is normally an acute phenomenon caused by a traumatic event that ruptures the palmar ligaments in a front foot, such as falling from a significant height. In other cases it is more of a slow phenomenon due to degeneration of the ligaments, where the dog becomes progressively palmigrade (this tends to happen to older dogs).
Fig 1: Hyperflexion of the front left leg
What is really important is for your vet to differentiate these two scenarios from a different condition known as flexural deformity in puppies. With this condition, puppies can suffer from hyperflexion (ie buckling over) (Fig 1), although normally the condition results in hyperextension causing ‘dropping’ of the carpus (wrist) and a palmigrade stance (Fig 2).
In puppies, the hyperextension is due to the looseness of the carpal flexor tendons associated with poor muscle tone.
Can carpal hyperextension be treated?
Fig 2: Carpal hyperextension
Treatment depends on the reason for the palmigrade stance.
When the reason for the hyperextension is a traumatic rupture or a degeneration of the palmar ligaments, it is important to know that the palmar ligaments do not heal well following injury, and if a splint or a cast is applied the problem will persist. In these cases the only solution is surgery, where the wrist is fused in a functional position (10 degrees of extension) in a procedure known as ‘arthrodesis’. This is normally achieved with surgery by using one or two plates and screws, and although this procedure has associated complications, it has a good prognosis. (Fig 3)
Fig 3: This x-ray shows a dog’s carpus after arthrodesis surgery. You can see the plates and pins which hold the wrist in place
Can cats be affected by carpal hyperextension? Adult cats can suffer from carpal hyperextension as well, and usually this is associated with a fall from a significant height. Treatment is similar to dogs, and fusion of the wrist is the treatment of choice. Some concern was raised in the past regarding the functional outcome that this procedure would have in cats, based on the perception that they have more movement in the wrist joint compared to dogs. A recent study showed that cats cope well with fusion of the wrist although they may experience some mild difficulty climbing and it is likely that they will have a reduction in their height of jump. Kittens don’t suffer from flexor tendon laxity (looseness).
Fig 4: This x-ray shows a dog’s hock following surgery to fuse the joint together. You can see the plates and pins which have been used to achieve this
Can the hock be affected by hyperextension? Dropped hock is normally associated with Achilles tendon problems. In a similar situation to the wrist issues, this could be the result of a traumatic event affecting the Achilles tendon (road traffic accident or sharp object cutting it) or more commonly a degeneration of the tendon where a swelling progressively develops at the level of the tendon insertion – with time this will result in a progressive ‘dropped hock’.
It is important to mention that some medical conditions can cause both hocks to drop (such as diabetes in cats).
Can dropped hock be treated? Treatment in traumatic cases consists of tendon stitching and temporary immobilisation of the hock, which has a good prognosis. If we are dealing with a degeneration of the hock, temporary immobilisation can be attempted, hoping that functional scarring of the tendon would occur, although in my personal experience these dogs may get better initially, but the problem tends to relapse and functional fusion of the hock joint (with a plate and screws) is likely to be required (Fig 4).
About Nacho Calvo
Ignacio (Nacho) Calvo graduated from Cordoba University in 2000. He has worked in Madrid, Dublin and Glasgow University, where he was the Head of Small Animal Orthopaedics. He is now Senior Surgeon at Fitzpatrick Referrals in Surrey. His main clinical and research interests are orthopaedic disease in cats, tibial tuberosity advancement (TTA), total hip replacement and arthroscopy.
The Veterinary Expert| Pet Health
The veterinary expert provides information about important conditions of dogs and cats such as arthrits, hip dysplasia, cruciate disease, diabetes, epilepsy and fits.