Endoprosthetic surgery: modern and traditional approaches

Surgery is required if you need an artificial joint. Patients and doctors must select the type of surgery that’s best suited and choose between robot-assisted, traditional or minimally invasive surgical approaches. Post-operative risks should be kept to a minimum, while benefits should outweigh any possible complications.

Against the backdrop of digitization, 1992 brought the introduction of the ROBODOC surgical system, followed by the "Computer Assisted Surgical Planning and Robotics" system (CASPAR) in 1998. At the time, both were considered quintessential surgical procedures. Back then, the robot milled cavities for hip implants in the femur, which used to be the surgeon’s job. A 3D model of the endoprosthesis was created based on CT scans of the patient’s hip. Based on this model, the robot then calculated the respective toolpath, providing a custom fit of the endoprosthesis into the hollow of the natural bone. Nevertheless, ROBODOC and CASPAR ended up not standing the test of time. One reason for this: the units were too large and bulky. Another reason: Although the systems provided precision milling of the bone, they had no feel for the bone density, which normally allows the surgeon to determine whether the prosthesis fits tightly into the bone. What’s more, the robot exclusively focused on the bone and ignored the muscle tissue. If muscle tissue was injured in the process, patients would end up having severe walking difficulties and pain.

Still, robotic surgeries are on the rise in the age of digitization. Unlike the first-generation technology, which included ROBODOC and CASPAR, medicine is now in the third generation of robots. Not only are these medical robots smaller, but they are also able to tell the difference between bone cement and bone, which is crucial when it comes to the implantation of an endoprosthesis. A doctor does not have this ability. The benefit here is that the robot can remove the cement from the femoral canal, causing only minimal or no damage to the bone in the process. When combined with a navigation system, the robot can even remove residual cement from hard to reach areas – areas the surgeon has difficulties to get to as they are not visible to the naked eye. What’s more, robots are able to respond faster than their human counterparts.

It’s a question of time and evolution of technology before "Doctor Robot" gains the trust of patients versus garnering doubt and rejection. That’s where a detailed explanation by the physician can be helpful.

The average hip replacement surgery takes just 1-2 hours to perform and primarily depends on the qualities and skills of the surgeon. The surgical option is the foundation for a speedy and successful recovery of the artificial joint. There are two surgical approaches to hip replacement.

First, there is the traditional surgical approach, which is done either under general anesthesia or by using a spinal or an epidural block that blocks the sensation of the spinal nerves. The surgeon starts by removing the damaged bone and cartilage. Before the implant can be inserted, the joint surface cartilage must be machined (milled). A cemented joint prosthesis uses bone cement to help affix it to the bone. A cementless joint prosthesis is specially textured to allow the bone to grow into it and adhere over time.

In the minimally invasive procedure, the surgeon pushes aside the hip muscle rather than cutting it to replace the affected joints with the implant. This process protects the muscle and other tissues around the joint. Unlike the traditional method, the minimally invasive surgical approach has many advantages. Since surgeons only use one or two shorter incisions, there is less blood loss and less surrounding tissue damage, which in turn may lead to less pain and shorter recovery time, and a faster return to the activities of daily living. What’s more, the approach is suitable for each age group.

Revision surgeries are often necessary after the initial implantation of the endoprosthesis. The reason for this is inflammation due to a loose prosthesis. To find a solution, eleven research and industry partners have teamed up in the EvPro Project (Extracellular Vesicles Promoted Regenerative Osseointegration) and devised a biologically active coating. It is designed to help the implant to attach to the bone. The coating is able to control inflammation in and around the surface of the prosthesis and promotes bone regeneration. A combination of biodegradable, adaptive and nanofunctionalized biomaterials with extracellular vesicles – tiny intercellular bubbles enclosed by a protein shell – makes this possible. This coating is applied to the implant. The project is scheduled to be completed in December 2022. The goal is to minimize risks and complications that might occur after a hip replacement and reduce the number of revision surgeries.

A minimally invasive surgical approach is distinctly more effective and involves fewer risks for patients than the traditional method. This applies to both the first implantation and any surgical follow-ups. While a robotic system is able to provide effective assistance, the surgeon’s hands are undoubtedly far more sensitive. What’s more, it is very difficult to code human decision-making. But how long do we have before this might change? The fact is, we still have a long way to go before robots can autonomously perform surgical procedures and factor in the needs and requirements of the individual patient. For now, a human surgeon’s hands, blend of skills and personal qualities are still crucial in the operating room.