There is a call to a horse which can't move", said my receptionist. "The owner says it is rooted to the spot".

When I arrived at the livery yard I found several worried people gathered around the stable of George, the pony in question. He was a three-year-old bay gelding about 14 hands high. He looked well-fed, with a shiny coat and was wearing a stable rug because the weather was still cold. He wore a mildly anxious expression.

His owner explained that they had taken him out of the stable earlier in the day while they mucked out his stable. He had walked fine for a short distance then as they put it "His leg had just seemed to lock".

They had had practically to drag him back to his stable, his leg stiff and the front of his hoof dragging on the ground. As he got back to the stable his leg had seemed to come right again and he had been fine until just before they rang.

When I examined him it was clear that he really could not move. As I worked my way down his leg I soon found why. Horses have a remarkable capacity to sleep standing up. They owe this to their ability to hook their kneecaps over the lower end of their thigh bone, so that even when they relax they do not fall over. Unfortunately George had managed to lock his knee cap even though he was not asleep.

Using both hands I tugged and pushed at his kneecap until all of a sudden there was a loud crack, his kneecap jumped back into its proper place and I felt his patellar ligaments relax and he was able to walk normally again.

When I was a student most cases of upward fixation of the patella, as the problem is called, were treated by an operation to cut the ligament. After this the horse would have to lie down to sleep. Modern thinking is that in many cases (including George's) this is a lifestyle disease caused by too much good food and not enough exercise.

I arranged for George to go on a strict diet - hay and one or two carrots only - and to start a programme of regular exercise. At first just ten minutes a day, building up to half an hour and then 45 minutes. Only if he had failed to respond would I have considered operating on him. At first his knee cap still locked slightly from time to time, but soon it stopped locking at all as he got fit. He has not had any more problems.

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