Ten years ago, it was sometimes difficult for Bart van der Wal: another young patient with hip dysplasia, another person who was facing major surgery. As an orthopedic surgeon, he saw, in various hospitals in the center of the country, what the standard treatment at the time meant for young people.
The operation, a pelvic tilt or so-called Ganz osteotomy, was effective but drastic. During such an operation, surgeons use special chisels to make extremely precise cuts in the bone surrounding the hip socket until the hip socket is loose and can be rotated. This way they could combat pain and premature osteoarthritis, in the hope of delaying a completely new hip – a prosthesis – for as long as possible. Van der Wal did not perform these operations himself, but saw up close that patients had to recuperate for months. That was nagging. Couldn’t it have been done differently?
Van der Wal is now a professor of orthopedics at the LUMC in Leiden, but in 2016 he still worked as a surgeon at the UMC Utrecht. There he knocked on the door of Björn Meij, professor of companion animal surgery at the faculty of veterinary medicine around the corner, with the question: did he know an animal model with the same condition? “I see that every week,” Meij replied: “That’s the dog.”
Van der Wal: “It involved young people. We wondered: should we really keep doing this? It worked, but it was a major operation with a long recovery.”
In the Netherlands, doctors at clinics check babies’ hips three times in the first six months. An ultrasound is only performed if hip dysplasia is suspected – something that is done as standard for every baby in Germany. That is also not a foolproof screening: in about half of the people who later undergo a pelvic tilt, the first ultrasound showed no abnormality. Complaints only arise during puberty or much later. Pain in the groin is a well-known symptom, often on both sides. But pain on the side of the hip or in the buttock also occurs, because surrounding muscles try to compensate for the unstable joint. What connects all these complaints is the same underlying problem: the acetabulum is not deep enough, causing the femoral head to wear out faster than normal. The damage accumulates, with the risk that someone with hip dysplasia will develop osteoarthritis at a young age.
For young patients with hip dysplasia, this often means a trade-off. Some can learn to live with the complaints with physiotherapy, others become so limited that a pelvic tilt is their only option. Before the turn of the century, surgeons still had to completely saw through the pelvis in three places in order to tilt the acetabulum. Thanks to special software, this operation is now a lot more refined than ten years ago. Only one notch is needed in the bone and the pelvic ring itself remains intact. However, pelvic tilt is still known as a complex and difficult operation, in which few surgeons are skilled.
Make the joint more stable
Meij immediately recognized that dilemma. He himself had been performing pelvic tilts for almost twenty years, but on dogs with hip dysplasia. He knew the pain after the operation, the long rehabilitation process, the weeks in which animals carefully got back on their feet and the complications. Van der Wal showed his idea on the basis of a sketch. He drew the femoral head and the acetabulum and pointed out what he was missing: sufficient coverage. What if you could enlarge it without sawing through the pelvis? Not a new hip, not a prosthesis, but a way to make the existing joint more stable. “The aim was mainly to gain time,” says Van der Wal. “If you can slow down the wear and tear before things really go wrong, you may be able to postpone a complete hip replacement for twenty years.”
An example of a 3D printed hip socket, an attachment that deepens the hip socket.
Illustration UMC Utrecht
Van der Wal and Meij put together a team to further develop the idea, including a pediatric orthopedist and a biomechanical engineer. Because there was no regular financing available for such an experimental process, Van der Wal founded a company to make the research possible – he has a minority interest in it.
At that time, the UMC Utrecht had already gained experience with 3D-printed skull implants, to close holes in the skull that arise during brain operations or to correct forehead deformities. But a 3D-printed hip socket – in technical terms a ‘pandak’, an attachment that deepens the hip socket – was a different matter. While a skull implant mainly had to fill a cavity, a hip implant not only had to fit perfectly, but also had to withstand heavy, moving loads for years.
Charlie, a nine-month-old Labrador retriever, was the first candidate for the new procedure. They started cautiously. First one hip: “We thought: caution is the order of the day,” says Meij. “But after seven or eight dogs we saw how quickly they recovered. That was a world of difference compared to the pelvic tilt. Within six hours after the operation they were back on their feet.”
Meij soon decided to perform the procedure on both hips at the same time as standard. The results were so convincing that the university clinic now offers the operation in dogs as a standard treatment.
Now, barely ten years later, the next step is to perform the operation on humans. But dogs are not people – and so that step remains exciting, Meij acknowledges. “A dog is a quadruped and distributes its weight over four legs. In humans, the entire body weight ends up on two hips. What that means for recovery remains to be seen.”
Still, you have to be careful. History has shown us that implants can fail
The operation takes place in the context of a so-called safety study, a study that is primarily aimed at determining the safety of a new medical intervention. The intention is for five young people with hip dysplasia to receive the new hip socket from the 3D printer. “The first patient is a 36-year-old man,” says orthopedic surgeon Rintje Agricola. He will perform the operation this Friday at the Anna Hospital in Geldrop.
Agricola was not involved in the development of the implant or the research, but was involved in another study into hip dysplasia. At Erasmus MC, he and other scientists follow ten thousand growing children in Rotterdam, the Generation R cohort. The team now sees something unexpected there, says Agricola. “After the second growth spurt, roughly between the ages of twelve and fifteen, we also see hip dysplasia on scans in as many as 15 percent,” he says. “That does not mean that all these young people will develop complaints or need treatment, but it does show that hip dysplasia can also develop later. This percentage is considerably higher than the 1 to 4 percent assumed by the Dutch guidelines.”
Geert Ensing sees this in his daily practice. He is an orthopedic surgeon at the Wilhelmina Hospital in Assen and is considered the specialist in the Netherlands in the field of the modernized pelvic tilt, the Ganz osteotomy, for people with hip dysplasia. He performs the operation almost a hundred times a year, with success: “Almost all our patients can regain full weight on their hip three months after the pelvic tilt.”
Ensing sees the new 3D hip socket as an interesting concept, but emphasizes that the current procedure – which is now also performed with 3D software – will remain the standard for the time being. “That is the consensus treatment. Until there is evidence that something else works better.”
That evidence must be carefully constructed, he believes. Orthopedics has many innovations that do not last: “If this works, it would be a nice addition to the current gold standard for some patients. However, you have to be careful. Orthopedics is a mechanical profession and history has taught us that implants can fail.”
Ensing especially hopes that doctors will learn to recognize the image earlier. According to him, hip dysplasia in young adults is still often missed. As a result, patients suffer from complaints for an average of five years before the correct diagnosis is made. During those years, they regularly ended up in a medical no man’s land, he says. “People are told to stop exercising, or that their complaints are related to something like fibromyalgia. They are sent from pillar to post. When they eventually know what the cause is and that something can be done, it is often a huge relief.”
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