A cat that suddenly drags a hind leg needs to be seen within 4 hours, and 4 hours is not a formality. In saddle thrombus a clot has landed at the aortic trifurcation and the leg muscle is losing blood from that minute; the gap between 4 hours and 12 hours is often the difference between a leg that recovers and a leg that does not. Three groups explain almost every case: a clot, a spinal or nerve lesion, and an orthopaedic injury. Each runs on its own clock — minutes for a clot, hours for a compressed cord, days for a fracture that still has blood flow.
Why the line is 4 hours and not 24
Skeletal muscle tolerates roughly 4 to 6 hours of complete ischaemia before the damage becomes irreversible, and the nerves in the leg fail sooner than the muscle does. A paw that is cold, hard and pale at hour 3 can often still be saved; the same paw at hour 12 usually cannot. Waiting overnight to see whether it improves is the most common mistake owners make, and it converts a treatable clot into an amputation or a euthanasia decision. If the cat is dragging 1 leg and cries when you touch it, you are at hour 1, not hour 6, whatever the clock on the wall says.
Check a femoral pulse in 30 seconds
Put 2 fingers on the inner thigh, halfway between the hip and the knee, and press lightly against the bone. You are feeling for a beat under the fingers, not for the cat's heartbeat. Compare left with right at the same moment: a normal cat has a strong pulse on both sides at 180 to 220 beats per minute. An absent or clearly weaker pulse on 1 side is the single strongest sign of a clot, and it is worth more than an X-ray. Then lift the paw. Pads that are pale grey or blue, and a capillary refill over 2 seconds, point the same way. A paw that is 2 to 3 °C cooler than the front foot is a clot until proven otherwise.
Cause 1: saddle thrombus
The clot usually forms in a heart with hypertrophic cardiomyopathy, travels down the aorta and jams at the trifurcation, which is why 1 or both hind legs are affected and the front legs never are. Onset is sudden, often under 5 minutes, and the cat is in real pain: vocalising, panting, dragging, refusing to let the leg be touched, with firm calf muscles and cool pads. A murmur is absent in roughly 1 in 3 cats, so a quiet chest does not rule it out. Treatment starts with pain control, then an antiplatelet such as clopidogrel at 18.75 mg per cat every 24 hours, heparin in some protocols, and oxygen plus diuretics if the cat is in heart failure. The first 4 hours are about pain and perfusion; the next 48 hours are about reperfusion, which can bring potassium over 7 mEq/L and rhythm disturbances.
Cause 2: spinal or nerve lesion
Here the leg is weak rather than cold. A fibrocartilaginous embolus, disc extrusion, fracture of the spine, trauma, toxoplasmosis or spinal lymphoma can compress or infarct the cord, and the signs are usually symmetric, or worse on 1 side, with a normal pulse and normal pad temperature. Look for knuckling: the cat drags the top of the foot rather than the whole leg, and the limb scuffs in an arc. Deep pain perception is the dividing line. A cat that pulls the leg away when a toe is pinched has a far better chance than one that does not, and loss of deep pain for over 48 hours carries a poor prognosis. High-dose steroids that were standard in the 1990s are no longer recommended for cord injury, so ask what is being given and why. Sudden wobbliness without dragging belongs in the wobbly walk workup instead.
Cause 3: orthopaedic injury
A fractured femur, a dislocated hip, a torn cruciate or a bite-wound abscess produces a cat that will not bear weight but still has warm pads and a pulse on both sides. Onset is tied to a jump, a fall, a road or a fight, and the cat often hides for 6 to 12 hours before anyone notices. A sprain settles in 7 to 10 days with rest and pain relief; a fracture wants repair within 3 to 5 days, before the bone ends round off and the repair gets harder; a cruciate repair means 8 to 12 weeks of controlled activity. A cat with a bite wound over the hip can look orthopaedic for 2 days and then turn into an abscess with a fever of 40 °C.
Six signs that separate them
Read down the columns rather than across. One absent pulse decides more than 5 other findings, and the paw temperature in the fourth row is the cheapest test in the table. The third row counts how many of the 2 hind legs have a pulse you can feel. If 2 columns disagree, treat it as a clot until a vet says otherwise, because that is the only group where an hour changes the outcome.
| Sign | Clot | Spinal | Orthopaedic | Act within (hours) |
|---|---|---|---|---|
| Onset (min) | under 5 | 5 to 60 | 0 to 30 | 4 |
| Pain on touch (0-10) | 8 to 10 | 2 to 5 | 6 to 9 | 4 |
| Femoral pulses felt (of 2) | 0 to 1 | 2 | 2 | 1 |
| Pad temperature (C below) | 2 to 3 | 0 | 0 | 1 |
| Hind legs affected | 1 to 2 | 1 to 2 | 1 | 4 |
| Deep pain lost at (hours) | 24 to 48 | 0 to 48 | 0 | 48 |
The first 60 minutes at home
- Carrier, not arms: a painful cat bites the person holding it, and a struggling cat worsens reperfusion.
- No massage and no heat pad on a numb leg; a cat cannot feel a burn and will not pull away.
- No aspirin from the cabinet. It is not the first-line antiplatelet any more and it adds bleeding risk to whatever the clinic will give.
- Write down the exact minute you first saw the drag, and photograph the paw next to the other one.
- Bring every medicine box, including supplements and flea products, and mention any toxin exposure; the toxin lookup covers the common household ones.
Five steps in the next hour
- Check both femoral pulses for 30 seconds and note which side is weaker.
- Compare paw temperature and pad colour between the 2 hind feet.
- Time the onset, and photograph the gait for 15 seconds.
- Call the clinic and say: hind limb drag, onset 1 hour ago, pulse absent on the left.
- Ask for pain relief before the exam, and read the hind leg drag checklist on the way so nothing is left out at the desk.
Frequently asked
The cat is dragging a leg but does not seem to be in pain. Is it still urgent?
Yes. A spinal lesion or a nerve infarct can be nearly painless, and a clot that has already killed the nerve may hurt less than one that has just landed. Urgency is set by perfusion and by the cord, not by how loudly the cat complains. Check both femoral pulses, compare paw temperature, and be at the clinic inside 4 hours if either side is weak or cold.
Can a cat recover from saddle thrombus without surgery?
Some do. Treatment is medical: strong pain control, an antiplatelet such as clopidogrel at 18.75 mg per cat daily, oxygen and diuretics if there is heart failure, and monitoring for the potassium spike and rhythm changes that come with reperfusion over the next 48 hours. Recovery depends on how much muscle died before blood returned, which is why the first 4 hours carry so much weight.
How do I tell a sprain from a clot at home?
Temperature and pulse, not the limp. A sprain has warm pads, a pulse on both sides, and pain that is worst over a joint or a muscle belly. A clot has a paw that is 2 to 3 °C cooler than the other side, pads that look grey or blue, an absent femoral pulse, and a cat that will not let the limb be handled at all. Any of those 4 means a clinic now.