One of the reasons that Bonnie is an indoor cat is that it's a safer place to be. Studies have shown that cats that are kept indoors all the time have longer, healthier lives.
Cats that venture outside are at risk of road accidents, fights with other animals, and viral infections carried by other cats. Bonnie has lived indoors since she was a kitten, and so far, she's been healthy and contented.
The accident happened just after New Year. Natalie was drinking coffee with friends in the sitting room, watching Bonnie play.
The young cat had taken a decoration off the Christmas tree, and was chasing it around the room, batting it in front of her, then pouncing on it. Bonnie often plays enthusiastically like this: it's her way of burning up energy indoors.
Bonnie was getting increasingly energetic with her new toy, throwing it into the air, then jumping after the toy to grab it with her paws, twisting and gyrating as she leapt.
After one particularly dramatic jump, she let out a yelp as she landed awkwardly, and she immediately stopped playing.
She fell over on her side, curling her leg up beneath her.
Natalie rushed over and picked her up to comfort her, but she continued to cry, and when she tried to walk, she couldn't put any weight on her right back leg.
Natalie rushed her in to the emergency vet, who reassured her that it seemed to be a nasty sprained joint: at least nothing had been broken.
She was given pain relief and advised to rest Bonnie. Two days later, Bonnie was still unable to walk on the leg properly, so Natalie brought her back to see me for a review. When I examined her, she cried when I pressed around her knee joint.
I admitted her for the day, to examine her carefully under anaesthesia, and to take x-rays of the affected area. My investigations confirmed the diagnosis that I had suspected.
Bonnie had suffered an injury that is rare in cats, but common in dogs and human football players: she had ruptured the cruciate ligaments in her right knee.
These ligaments hold the knee joint tightly together: when they are torn, the knee wobbles when the animal tries to stand on it. As well as pain, this causes the leg to be unstable.
In dogs and humans, surgery is needed to repair the damaged ligaments. In cats, because they are so small and light, a simpler approach of pain relief and rest is often enough to allow the knee to heal.
Bonnie was sent home with pain-relieving drops, and instructions to stop playing so vigorously for a few weeks.
There's a good chance that she'll make a full recovery with this approach, but a small number of cats continue to be lame because of the instability of the damaged knee.
In these cases, an operation is needed to carry out a surgical repair of the damaged ligaments.
This can be a complicated and expensive procedure, and we're hoping that Bonnie will be one of the lucky ones who heals naturally so that surgery is not needed.
Natalie's Christmas tree has now been taken down, and the decorations have been put away.
Bonnie is living a quieter life in January, and with luck, she'll soon be walking normally.
The cost of a major orthopaedic operation is not something that anyone would hope for at the start of a new year.
Bonnie still lives indoors: despite her recent mishap, it's still a safer place for her to be.
Owner: Natalie Waters from Bray
Animal: Bonnie, her two year old cat
Background: Bonnie injured her knee badly after falling while playing with a Christmas decoration