Since the early 1900s, surgeons have been using metal implants in healthcare, typically to treat bone diseases including osteoarthritis and inflammatory rheumatoid arthritis, as well as in reconstruction therapy.
Though a long-established technology, traditional implants often cause challenges for patients and surgeons. One area being worked on is smart implants, which improve patient outcomes and bring the technology into the modern age.
Implants can be smart in two ways, either by being additively manufactured to produce patient specific implants (PSIs) from computed tomography data, or by incorporating sensors. Still in the early phases of development, inbuilt sensors could collect patient-specific data, enabling surgeons and other healthcare professionals to tailor treatment to the needs of individual patients.
One of the key challenges that traditional implants present is loosening. Particularly common following joint replacement procedures, loosening can be a result of poor osseointegration – the structural and functional connection of the implant with the patient’s bone.
Another limitation of traditional metal implants is that they are only manufactured in a discrete number of shapes and sizes. Therefore, it is unlikely patients will receive an implant that fits them accurately. This can cause poor physical function and contribute to loosening.
Poor physical function can also occur because of stress shielding – the process whereby metal implants remove stress from the patient’s bone. The bone responds by reducing in density and therefore becomes weaker.
The increasing incidence of obesity is one reason joint replacements are becoming more common in young people. This poses longevity issues as implants can reach their maximum lifespan and need replacing several times.
To combat these issues, researchers and engineers have been developing implants in new ways, using techniques such as additive manufacturing (AM). The technology aims to improve the form, fit and function of implants.
Because AM builds an implant layer by layer, it’s possible to produce PSIs that are a more accurate fit for the patient. The manufacturing method also has fewer geometric constraints than subtractive manufacturing. PSIs designed and manufactured according to a patient’s CT scan encourage the implant to integrate with the bone, reducing the risk of loosening. As a result, patients are less likely to suffer pain or require revision surgeries.
As well as being able to manufacture an exact shape, AM enables surgeons to control additional properties of the material. They can design implants that mimic the patient’s bone stiffness, density and trabecular structure, which can reduce stress shielding and improve osseointegration and physical function further.
Implants can also be made smarter by adding sensors. This allows clinicians to accurately measure patient data, such as temperature, which is the key to evidence-based medicine.
Sensors can also be incorporated into bone reinforcement implants, which are used to help fractures heal. In this example, sensors can measure the strain exerted on the implant, which indicates the extent the fracture has healed. From this information, surgeons can determine the best time to progress the patient to the next stage of therapy and could identify healing problems earlier than currently possible.
As implant loosening can be affected by non-compliance with physiotherapy, technology has been developed to overcome this. Incorporating accelerometers to monitor the movement of patients would allow healthcare professionals to obtain data remotely. This could be used to determine whether a patient is complying with their prescribed physiotherapy and rest regime.
One institute developing technology in this field is a collaboration between Renishaw and Western University in Ontario, Canada, who have set up the Additive Design in Surgical Solutions (ADEISS) Centre to bring together clinicians and academics to generate novel 3D printed medical devices. ADEISS recently showcased the smart hip concept, which uses temperature sensors and accelerometers to collect patient data that can be communicated to a remote device.
By making use of advanced sensor technology, there is now potential for the development of implants that can detect an infection and subsequently secrete the appropriate dose of antibiotic to treat it. This could reduce the number of patients admitted to hospital.
For widespread clinical adoption of smart implants, there are still challenges to overcome. Clinicians must run clinical studies to collect data on the safety and performance the implants offer. This must all be done in line with regulations such as the EU Regulation on Medical Devices. A further key consideration is the processing of personal data in smart implants and how that data is used.
The treatment of bone diseases and injuries has come a long way since the days of bone setters and blacksmiths. Patients can now receive metal implants designed to their individual requirements. Pioneering research is improving the technology, so the uptake of additively manufactured and data-driven implants is set to rise, improving outcomes for patients and hospitals.