Cat fitted with bionic feet

25 June 2010

Surrey-based neuro-orthopaedic surgeon Noel Fitzpatrick performed the procedure with prosthetic technology developed by a team from University College London.

The design of the feet uses custom-made implants to ‘peg’ the ankle to the foot and mimics the way in which deer antler bone grows through skin.

These pegs, or ITAPs (intraosseous transcutaneous amputation prosthetics), were first developed by a team from University College London led by Prof Gordon Blunn, head of the Centre for Bio-Medical Engineering at UCL’s Institute of Orthopaedics and Musculoskeletal Science.

Working in partnership with UCL, Fitzpatrick has pioneered the use of these weight-bearing prosthetic implants, combining engineering mechanics with biology to give the cat, who is called Oscar, two new feet.

In a three-hour operation, the veterinary surgical team had to insert the ITAPs by drilling into one of the ankle bones in each of the back legs – an extremely delicate feat, which could have fractured the ankle joint before the procedure had even begun, and even more challenging as it had to be performed twice.

These artificial implants, which are attached to the bone at an amputation site, are coated with hydroxyapatite, a substance that encourages bone cells to grow onto the metal. The skin then grows over the special umbrella at the end of the ITAP to form a seal against bacteria and potentially fatal infections. The ITAP itself protrudes through the bone and skin, allowing the custom-built artificial paws to be securely attached.

Following successful surgery on 13 November, the focus of the veterinary team has turned to the slow process of rehabilitation and helping the cat to learn to walk again – firstly using external scaffolding anchored to the tibia for five weeks to protect the new implants until the ITAPs integrated into the bone and the skin grew onto the ITAP.

The medical team note the cat was trying to stand within a day of the operation and despite some problems with infection that had to be overcome, in less than four months it could stand and bear weight equally on all four limbs. It has since been fitted with a series of prototype new paws to ensure the best possible long term fit.

While full limb amputation procedures are common in humans and animals, and despite a range of technological and surgical advances, post-operation complications still arise when stump-socket exoprostheses (strap-ons) are used. These complications include infection, stump morbidity, abrasions and pressure sores and mobility problems associated with weight-bearing, often leading to fractures and limb failure.

What made Oscar’s operation so difficult was its feet were severed at the junction of the tarsus and metatarsus, which is the junction between the ankle bones and the arch of the foot. A cat stands up on its toes, whereas humans stand on the entire flat of the foot, so the ankle is the equivalent of the cat’s hock.

As Noel Fitzpatrick explained: ‘The real revolution with Oscar is because we have put a piece of metal and a flange into which skin grows into an extremely tight bone, with very narrow tolerances in the region of nanometres, rather than millimetres. We have then successfully managed to get the bone and skin to grow into the implant and we have developed an exoprosthesis that allows this implant to work as a see-saw on the bottom of an animal’s limbs to give him effectively normal gait. Oscar can now run and jump about as cats should do.’