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April 20, 2021updated 14 Feb 2022 10:44am

Growing up with implants

Medical implants may not always be suitable for children, as most are a fixed size and cannot grow in line with the child’s body. Abi Millar runs through some of the ways researchers are addressing this problem.

By Abi Millar

Medical implants – which run the gamut from orthopaedic implants to cardiac devices – can be lifesaving for patients. However, when we think about the patients who might benefit, more often than not we’re thinking of adults. Historically speaking, children and adolescents have been an underserved population.

Clearly, the situation will vary depending on what type of implant the child requires. However, there is a key problem with using medical implants in a young patient – the child is going to grow, whereas the implant is going to stay the same size. The implants will therefore need to be replaced at some point, forcing the child to endure multiple surgeries.

While there is a clear need for specially designed paediatric implants, the area has been somewhat neglected simply because the market isn’t large. Children require implants less frequently than adults do, and therefore haven’t reaped the benefits of all the investment and innovation occurring in this space.

It is only relatively recently that medical device manufacturers have grown wise to this problem and have turned their attention to children growing up with implants. Below, we round up some of the key developments in the field.

Orthopaedic implants

By and large, children’s bodies have a remarkable ability to heal and correct problems, meaning bone fractures don’t always require reconstructive surgery. However, surgical procedures are becoming more common, bringing with them new techniques suitable for young patients.

In an osteosynthetic surgery, bone fragments are stabilised with mechanical implants, often using materials like titanium. These devices will eventually need to be removed, or the child’s growth would be impeded. One possible solution, requiring no additional surgeries, might be biodegradable implants that the child’s body could absorb once the bone has healed.

While the few studies in the field have shown promising results, research remains thin on the ground. “The knowledge created so far is insufficient to recommend application and requires further investigation,” concluded a 2018 review of the evidence.

In other cases, the need for orthopaedic implants is more acute. For instance, children with osteogenesis imperfecta (brittle bone disease) experience frequent bone fractures and may require rodding surgery. This involves placing a straight metal rod lengthwise into the middle section of the bone, usually in the long bones of the arms and legs.

In the past, fixed-length rods were the only option available. These didn’t grow with the bone, meaning children would need further procedures further down the line. More recently, surgeons have started to use telescopic rods, which are anchored at the top and bottom of the bones and lengthen over time. While these are more expensive than regular rods, they can postpone or even prevent the need for rod replacement.

Dental implants

When an adult patient loses a tooth, dental implants are a commonly used alternative to dentures. These include titanium screws, placed directly in the jawbone to replace the missing tooth root. Although expensive, they can last a lifetime if cared for properly and are often credited as returning the patient’s confidence.

Unfortunately, these devices are not usually recommended for children and adolescents who lose one of their permanent teeth. This is because the jawbone is still growing, meaning the implant could shift out of its desired location and impact the growth of the surrounding teeth. In some cases, implants can be fitted in girls at 15 and boys at 17, but generally, the procedure wouldn’t be performed till early adulthood.

Younger patients may be given removable dentures, or sometimes a fixed prosthetic tooth instead. However, the prosthesis will likely loosen over time, and requires replacing as the shape of the mouth changes.

Dental implants have been used in children – for instance by placing a metal implant in the jawbone that restricts its growth in that area – but this can be challenging and may require input from multiple specialists. It may be more suitable for children who have lost multiple teeth, rather than just one.

A 2020 mini-review concluded: “A multidisciplinary approach including the involvement of an orthodontist, pedodontist and a periodontist or an implantologist skilled in soft and hard tissue management around implants with a comprehensive treatment plan may be able to successfully place dental implants with a satisfactory long term outcome in children.”

Cardiac implants

For children with certain heart conditions, multiple surgeries are unavoidable. Valve defects, for instance, are treated through a procedure called a valve annuloplasty, which involves implanting a medical device to tighten the valve. Around 1,000 procedures of this kind are performed in children in the US every year.

Adults with this condition can be treated with a prosthetic ring. However, this device isn’t suitable for children, as the ring would restrict the growth of the heart. Surgeons must use less durable, suture-based techniques, which come with their own problems – the sutures can break through the tissue over time, forcing the need for follow-up surgery.

In 2017, researchers from Boston Children’s Hospital and Brigham and Women’s Hospital reported on a new, growth-accommodating implant that might address this issue. Their proof-of-concept device – a tubular, expanding ring – would be able to grow along with the child.

The ring consists of a braided sleeve, which is able to elongate and accommodate growth, along with a degradable inner core. It is currently in preclinical development.

“Medical implants and devices are rarely designed with children in mind, and as a result, they almost never accommodate growth,” said Pedro del Nido, chief of cardiac surgery at Boston Children’s and co-senior author on the study.

“So, we’ve created an environment here where individuals with expertise and interest in medical devices can come together and collaborate towards developing materials for pediatric surgery.”

Encouragingly, the materials used might have much wider applicability and may be suitable, not just for paediatric heart surgery, but also for orthopaedics. The device could be adapted for a wide range of growth-accommodating implants throughout a child’s body.

In a 2020 follow-up paper, co-author Dr Eric Feins explained that while efforts to develop growth-accommodating implants have been underway for years, these haven’t translated into real-world applications. At present, very few devices are available for clinical use and there is an evident gap in the market.

“Surgeons are constantly faced with the challenge of palliating and repairing heart defects while also accounting for somatic growth. If we are unable to translate innovation to the bedside, growth will continue to be a major challenge in our field,” he wrote.

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