The thread is harvested from 30mm long cocoons grown in silk farms. It is processed at the firms' Oxfordshire laboratory where the fibroin is extracted from the silk fibres - identical to those found in a shirt or tie - and bonded with water particles. When complete, the implants are 15 per cent fibroin and 85 per cent water.
This forms a strong, rubber-like material which can be shaped like cartilage and cut to fit individual knees.
At present, surgeons are reluctant to replace torn or worn knee cartilage with a full knee replacement in patients under the age of 60 because prosthetic implants tend to wear out within ten to 15 years in young, more active, individuals. Besides this, a knee replacement is a major operation involving a large incision, and second and third implants are not always as successful as the original ones.
It leaves orthopaedic surgeons such as Professor Ashley Blom - who is about to trial the silk implant in the next few weeks - with a dilemma. He says: "We have a lot of younger people with knee problems due to worn or torn knee cartilages who suffer and can't lead fully active lives.
"We try to do our best for them by taking out cartilage which can't be saved and preserve the rest, but they very often have to cope with decreased mobility and early onset of osteoarthritis." Nick Skaer, chief executive of Orthox Implants, the firm behind the new technology says the aim is to help younger victims of knee damage.
"We want to help those out there who suffer a sporting injury in their 20s then go on to develop early arthritis. The implant may help prevent the knee joint from deteriorating by repairing the cartilage in the first place. That way we can hopefully avert the need for knee replacement surgery completely."
The first trial - to be carried out at North Bristol NHS Trust - will deal with the meniscal cartilage, known as the "shock absorber" of the knee. This double-horseshoe of cartilage sits at the top of the tibia, the lower leg bone. It can be torn during sporting activity and can sometimes require surgical removal, causing instability and a cascade of complications. These include damage to the articular cartilage, the smooth tissue which covers the lower end of the thigh bone, which can hasten osteoarthritis.
A second implant has already been designed to replace this articular cartilage, and experiments with this will follow the trial on the meniscal patches.
In the laboratory, scientists have seen patients' cartilage - none of which is removed in the operation - grow into the implant and form a strong union.
The procedure is carried out via a keyhole incision and patients could be fit enough to carry out their normal activities within weeks.
Prof Blom is hopeful that silkworm cartilage implants will reduce the number of knee implant operations carried out in the UK.
"Recovery from the replacement operation can take between six months and a year, and patients frequently face complications.
"We are talking about major surgery and sometimes we have to go back in with revision surgery which means more time out for the patient. If successful, the implants could save the NHS money by repairing cartilage before it progresses to osteoarthritis and the need for a replacement knee."
With replacement knee operations predicted to increase by five times in the next 15 years, cartilage implants could save the NHS tens of millions a year.
Following the trial - which ends next year - the implant is likely to be offered routinely in about two years time.
"All our lab results have been good and we are extremely optimistic we have found a solution that works," says Skaer.
- Daily Mail
