What this means
You notice weak hind legs when your cat creeps along crouched, its legs buckle, it tumbles on landing or it struggles to jump onto the sofa. Sometimes the hindquarters look narrower because the muscles are thinning. Write down whether the weakness came on suddenly or grew slowly, whether both legs are weak, and whether your cat controls urination and bowel movements.
Weak hind legs in a young animal are often linked to an inherited or developmental condition: the nerve signals do not reach the muscles as they should, because the spinal cord or its nerves formed abnormally or because nerve cells slowly die off. The cat stays just as curious and affectionate, only moving is harder. A vet needs to assess these conditions, and there is no need to guess the cause or how it will go.
Weak hind legs are not necessarily a sign of old age. A cat that stops jumping up or struggles to stand is very often in pain and is not simply getting old. Sudden weakness in the hind legs, pain, or cold, dragging legs can mean a blood clot and is an emergency, so it is not something to wait out.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your cat.
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A lower spine and spinal cord that formed abnormally
When a kitten is born with differences in the spine or spinal cord, the nerves that control the back legs may work incompletely. It is an inherited condition.
About the condition: Manx syndrome -
Inherited loss of the nerves that drive the muscles
In a young cat the nerve cells in the spinal cord die off, so the muscles weaken and shrink, especially in the back legs.
About the condition: Spinal muscular atrophy -
A blood clot blocking the blood supply to the back legs
A clot can suddenly cut off the blood to the legs. They become weak or paralysed, painful and cold.
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Damage to the spinal cord or spine
After a fall, a blow or a road accident the spine or spinal cord can be damaged. The back legs may weaken or stop working altogether.
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Muscle weakness from another illness
Low potassium in the blood or another illness can weaken the muscles all over the body, with the back legs giving way first.
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Pain in the hips or knees
Sore joints make a cat protect its back legs, so they look weak. The cat has often stopped jumping up as well.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the weakness came on suddenly or grew slowly
- Whether both back legs are weak or only one
- Whether your cat controls urination and bowel movements
- Whether the legs are cold, swollen or sore to the touch
- Whether the back legs tremble or your cat tires quickly
- Whether your cat was born without a tail or with a very short one
When to book a routine visit
Book a visit if a young cat or kitten has weak hind legs, struggles to jump or tires quickly, and especially if urination or bowel movements are also affected. If the weakness appeared suddenly, go straight away. When getting a kitten, ask the breeder about the parents' health testing.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Manx syndrome Nerves and muscles An inherited condition of the spine and nerves that can affect cats born with a very short or absent tail. The lower spine and spinal cord form abnormally, which can disturb the movement of the back legs, urination and bowel movements.
- Spinal muscular atrophy Nerves and muscles An inherited disease in which the nerve cells in the spinal cord that tell the muscles to move slowly die off, so the muscles weaken and shrink. The first signs appear in young cats.
Body systems: Nerves and muscles