Carpal & Tarsal Hyperextension in Dogs and Cats
When the wrist or ankle collapses toward the floor and the paw goes flat.
A healthy wrist and hock sit at a slight spring-loaded angle that pushes the pet up off the ground. When the ligaments on the underside give way, the joint sinks and the paw flattens, a stance vets call palmigrade in the front leg and plantigrade in the back. It turns up after a fall, builds slowly with age, or creeps in when a sore knee or hip shifts load onto the joint. Most cases settle with the right mix of support, strengthening, and load management.
Carpal (wrist) and tarsal (hock) hyperextension happen when the small ligaments and fibrocartilage on the underside of the joint stretch or tear. The joint can no longer hold its normal standing angle, so it drops and the foot goes flat against the floor. Some cases come from a single hard landing; others build slowly as the tissue weakens with age, or as a pet unloads a sore knee or hip onto the opposite limb. Milder cases often do well with a brace, strengthening, and changes at home. Severe collapse, or any case where the top joint of the wrist is involved, usually needs surgery to fuse the joint. One condition it gets confused with is knuckling, where the paw folds under from a nerve problem. That looks similar at a glance but needs a completely different work-up.
Quick facts
- What it is: failure of the palmar (wrist) or plantar (hock) ligaments and fibrocartilage that normally stop the joint from over-extending. Under weight, the joint sinks toward the ground and the paw flattens.
- Who gets it: dogs of any size, from sporting dogs landing hard to older dogs whose ligaments have weakened. Collies and Shetland Sheepdogs are over-represented for the hock version. Cats get it mostly after high-rise falls, though a non-traumatic form is now recognised too.
- The hallmark sign: a flat-footed stance. The wrist or hock drops low, the paw splays, and the limb looks like it is sitting down at the joint. Usually worse after exercise or by the end of the day.
- Diagnosis: stressed X-rays (taken with the joint weight-bearing or held in extension) show which level of the joint gives way. The vet also flips the paw over to confirm the pet rights it at once, which separates this from a nerve cause.
- Treatment: bracing, strengthening, laser, and load management for milder cases; surgical fusion (arthrodesis) of the affected level when the collapse is severe or the top wrist joint is involved.
What carpal and tarsal hyperextension actually is
The carpus (wrist) and tarsus (hock) are not simple hinges. Each is a stack of small bones held in a spring-loaded angle by a web of ligaments and a pad of fibrocartilage on the underside, the palmar side in the front leg and the plantar side in the back. Those tissues are what stop the joint from folding flat when the pet lands or pushes off. When they stretch or tear, the support goes, and the joint sinks toward the floor every time weight goes through it.
Three things drive it. A single hard landing, a jump or a fall, can rupture the ligaments outright. Slow degeneration weakens the tissue over months to years, so the collapse creeps in with no injury the owner ever saw. And a painful joint elsewhere, a torn cruciate ligament in the knee for example, can push a dog to load the hock differently until it too begins to give way. That last route, functional hyperextension, matters because fixing the joint that hurts often takes the strain off the one that is collapsing.
How far the joint has dropped tells you a lot about what comes next. The strip below runs from a joint that only dips after hard exercise to one that rests flat on the ground.
Why this is not knuckling
Hyperextension and knuckling look almost opposite once you know what to watch. In hyperextension the joint sinks, but the paw stays the right way up with the pads on the floor. In knuckling the paw folds under, so the pet walks on the top of the foot, on the knuckles. One is the leg collapsing at the joint; the other is the foot in the wrong position.
The reason it matters is the cause. Hyperextension is a support problem in the ligaments, so it sits with the orthopaedic team. Knuckling is a signalling problem in the nerves, so it points to something like IVDD or degenerative myelopathy. Vets use a quick test: turn the paw so it rests on its top surface. A pet with intact nerves flips it back at once. A pet that leaves it upside down has lost position sense, and the work-up moves to the spine and nerves, not to the joint.
Hyperextension or knuckling? A side by side
Because the two get mixed up so often, and because they lead down completely different paths, here is the quick comparison.
| What to check | Hyperextension | Knuckling |
|---|---|---|
| What you see | Joint sinks toward the floor; paw stays flat, pads down | Paw folds under; pet walks on the top of the foot |
| Where the fault is | Ligaments and fibrocartilage under the joint | Nerves carrying position sense to the brain |
| Body system | Orthopaedic, a support failure | Neurological, a signalling failure |
| The paw-flip test | Corrected instantly | Slow to correct, or left upside down |
| Usual culprits | Falls, ageing ligaments, offloading a sore knee or hip | IVDD, degenerative myelopathy, FCE, nerve injury |
| First step | Stressed X-rays of the joint | Neurological exam and spinal imaging |
If the paw is flat and the joint is low, think ligaments. If the paw is flipping over, think nerves, and read our page on other neurological conditions before you go any further.
Signs to watch for
Most owners notice the shape of the leg before anything else. The signs run from a subtle dip that only shows after a long walk to a wrist or hock that rests on the ground.
- A wrist or hock that looks lower or more "sat down" than the matching leg on the other side
- A flat-footed stance: the paw splays and the back of the joint drops toward the floor, clearest when the pet stands still
- A dip or bounce in the joint at the moment the foot takes weight during a walk
- The stance gets worse as the pet tires, after a long walk, or towards the end of the day
- On slippery tile or marble the legs splay further and the pet scrabbles to push off
- A callus, bald patch, or raw skin over the back of the wrist or hock where it now touches the ground
- In cats: a sudden change after a fall from a window ledge or balcony, or a slow flattening of the front legs with no injury you saw
One leg or both can be affected. When it is one leg, watch the other closely, since the pet often overloads the good limb and can start to break it down too.
How AURA helps
The job is to take load off the failing ligaments, build up the muscles that help hold the joint steady, calm the inflammation, and support the pet through surgery and back to walking if it comes to that. That work carries on whether the joint is braced or fused.
Not sure if the leg is collapsing or knuckling?
Send us a short video of your pet standing and walking. We can usually tell a joint that is sinking from a paw that is folding under, and point you to the right next step.
Brace, fuse, or manage?
This is the question every owner asks, and the honest answer follows the severity strip above and, for the wrist, which level has given way.
Milder and functional cases, Grade I to II or a joint that is dropping only because a sore knee or hip is loading it wrong, are often managed without an operation. You treat the primary problem first, add a well-fitted carpal or tarsal brace for support during activity, build strength, keep the pet lean, and sort the floors at home. Plenty of pets hold steady like this for years.
Severe cases, Grade III to IV and any wrist case where the top level has failed (the antebrachiocarpal joint, where the wrist meets the forearm), usually do best with surgery to fuse the joint, an operation called arthrodesis. Fusing removes the painful, unstable movement and gives back a limb the pet can stand and walk on. A partial fusion is used when only the lower levels have gone; a full fusion, called pancarpal, is needed when the top joint is involved. Most dogs walk comfortably again once it has healed.
Worth being clear about one thing: a brace supports the joint but does not repair a torn ligament. The palmar and plantar ligaments sit under so much tension during weight-bearing that a full tear will not heal back to its old strength on its own. That is why severe collapses lean surgical, and why the sooner a borderline case is assessed, the more options stay open.
Day to day: protecting the joint
Whether the joint is braced, fused, or simply being watched, a few habits at home make a real difference to how comfortable your pet stays.
Sort out the floors
Tile, marble, and polished parquet are the enemy of a joint that already wants to splay. Lay runners, rugs, or rubber-backed mats along the routes your pet uses most, and add a ramp so they stop jumping down off the sofa, the bed, or into the car. Keep the fur between the pads trimmed and the nails short so the foot can actually grip.
Use the brace properly
A carpal or tarsal brace supports the joint during activity, but only if it fits. Too loose does nothing; too tight rubs a sore. Build wear time up slowly, check the skin over the joint every day for pressure marks, and take it off at night unless your vet says otherwise. Bring it to rehab so we can check the fit against how the leg is loading.
Keep them light and strong
Every extra kilo lands on a joint that can no longer hold its own angle. A lean body weight, plus the strengthening from rehab, is the cheapest support there is. Short, frequent, controlled activity beats one long weekend outing, and it slows the arthritis that tends to settle into a joint that has been collapsing for a while.
Outlook
It depends on the cause and how far the joint has dropped. Milder and functional cases often hold steady for years once the primary problem is treated and the joint is supported, and cats with a traumatic carpal injury caught early tend to do well too.
Severe collapse and top-joint involvement do best with surgical fusion, and most pets walk comfortably again on a fused limb and get back to normal life. Left alone, a severe collapse tends to get worse over time: the joint keeps sinking, the skin over the contact point breaks down, and arthritis sets into the joints around it.
Because the tissue does not grow back to full strength once it has torn, this is usually a condition you manage rather than one you cure outright. The goal is a comfortable, stable, weight-bearing limb, and for most dogs and cats that is a realistic one.
What to ask your vet
Worth a screenshot before the appointment:
- Which joint is collapsing, and which level of it, on the stressed X-rays?
- Is this a ligament problem, or is a nerve problem making the paw knuckle instead?
- Is the collapse the main issue, or is my pet offloading a sore knee, hip, or the other leg onto it?
- For this severity, would you manage it with a brace and rehab, or is surgical fusion the better long-term answer?
- If we brace, what type and fit do you recommend, and how do I check for pressure sores?
- What body weight and activity level should I aim for to take strain off the joint?
When to call your vet
Recovery or not, contact your vet promptly if:
- The joint suddenly drops much lower or the leg gives way: a ligament or the fibrocartilage may have torn further
- Raw, weeping, or smelly skin appears over the collapsed joint: a pressure sore has broken down and can get infected
- The paw starts folding under instead of sitting flat: this points to a nerve problem rather than the ligaments, and needs a different work-up
- The brace leaves rubs or swelling, or the pet chews at it constantly: the fit is wrong and is doing more harm than good
- Both matching legs start to collapse over a short time: suggests a whole-body cause, or in cats a metabolic one such as diabetes
- Your pet stops putting weight on the limb or cries when it is touched: pain at this level needs same-week assessment
Common questions
What is the difference between hyperextension and knuckling?
They look alike but they are opposites once you know the tell. In hyperextension the joint sinks toward the floor while the paw stays flat, pads down, so it is a support failure in the ligaments. In knuckling the paw folds under and the pet walks on the top of the foot, so it is a signalling failure in the nerves. The quickest check is to turn the paw onto its top surface: a pet with normal nerves flips it back at once, while a knuckling pet leaves it upside down. Hyperextension is worked up with X-rays of the joint; knuckling sends you to the spine and nerves.
Can a brace fix carpal or tarsal hyperextension, or does my dog need surgery?
It depends on how far the joint has dropped and, in the wrist, which level has gone. Mild cases, and joints that are only collapsing because a sore knee or hip is loading them wrong, often do well with a brace, strengthening, and weight control. A brace supports the joint, but it cannot mend a torn ligament, because the tissue sits under too much tension to heal back to full strength. Severe collapse, or any case where the top wrist joint has failed, usually needs surgery to fuse the joint. Most dogs walk comfortably again once a fusion has healed.
My cat is walking flat on its wrists after a fall. Is that the same thing?
Very likely, yes. Cats mostly get carpal hyperextension from a fall, often from a window ledge or balcony, which is common enough in high-rise Singapore homes. The impact tears the ligaments and fibrocartilage under the wrist, and the joint drops into a flat, palmigrade stance. It is a ligament injury rather than a nerve one, so the paw stays the right way up. Get it checked soon: stressed X-rays show how bad the damage is, and early cases have more options. Some cats do well with support and rest; others need surgery to stabilise the joint.
My older cat is walking on its hocks. Is this hyperextension?
It might be, but there is a common look-alike in cats that needs a different fix. Diabetes can damage the nerves to the back legs and drop the hocks into a flat, plantigrade stance, walking on the heels. That is a nerve and metabolic problem, so the first step is a blood test for diabetes, not a brace. True tarsal hyperextension from failed ligaments can look similar, so the vet will check the nerves and take X-rays to tell them apart. If it is diabetic, getting the blood sugar under control is what turns the stance around, with rehab alongside to support it.
Does hyperextension hurt my pet?
Often less than you would expect from how the leg looks, at least early on. A slowly collapsing joint can be more uncomfortable than sharply painful at first, which is part of why owners miss it. Pain builds as the joint keeps dropping: the surrounding tissues get overstretched, arthritis settles into the nearby joints, and the skin over the contact point rubs raw once the joint reaches the ground. A sudden traumatic tear does hurt sharply. Either way, comfort improves once the joint is supported or fused and the load comes off the failing ligaments.
Can hydrotherapy and physio really help a collapsed joint, or is it just for after surgery?
Both, and it is not only for after an operation. The joint leans on muscle as well as ligament for support, so building the muscles around the carpus or tarsus takes some of the strain off the tissue that has failed. On the underwater treadmill the water carries part of the body weight, so your pet can rebuild strength and a normal step without the impact that would stress the joint. Physio adds balance and proprioception work so the limb loads evenly. For braced and managed cases this can hold a joint steady for years; for surgical cases it is how the limb comes back.
Sources
- Nakladal B, vom Hagen F, Brunnberg M, Gross M, Nietz H, Brunnberg L. Carpal joint injuries in cats: an epidemiological study. Vet Comp Orthop Traumatol. 2013;26(5):333–339. PubMed
- Marks TA, Meeson RL, Paran E, Hayes G, Yeadon R, Cerna P, Morris C, Langley-Hobbs SJ. Idiopathic carpal hyperextension in 12 cats (2018–2025). J Feline Med Surg. 2026. JFMS
- Bilateral functional tarsal hyperextension associated with stifle pathology improved following stifle stabilization in a dog: a case report. Vet Sci. 2026;13(6):518. MDPI
- Treatment of medial instability of the carpometacarpal and tarsometatarsal joints using the Isolock system in two dogs. PMC. PubMed Central
- Levine D, Millis DL (eds). Canine Rehabilitation and Physical Therapy. 2nd ed. Saunders/Elsevier; 2013.
- VCA Animal Hospitals. Carpal hyperextension in dogs and in cats (client education). VCA
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