SIEMENS

It's part of the daily routine at every orthopedics practice: Older people complain about hips, knees and other joints that are becoming increasingly painful. X-rays or computed tomography (CT) scans reveal the condition of a joint. If the orthopedist diagnoses advanced wear of a bone, cartilage, or socket, the only thing that can provide relief from chronic pain is an artificial joint.

The number of orthopedic procedures continues to rise due to increasing life expectancy. In the U.S., joint diseases are the second most common chronic ailment overall, and the most common among women. According to the German Society for Orthopedics and Traumatology, approximately 200,000 joint and hip replacements are now performed each year in Germany.

Until now, manufacturers of artificial joints have been unable to quickly and cost effectively manufacture prosthetic parts as custom-tailored products for individual patients. Although most machining and milling systems are computer controlled, they are designed to produce only standard components of a specific size and shape. The process for the production of custom implants, on the other hand, is hardly automated. Off-the-shelf prosthetics are thus produced in advance, with hospitals typically having a large inventory of models on hand.

Depending on the type and extent of the joint disease, the surgeon implants the best-fitting partial prosthesis or a complete replacement joint using PMMA (polymethyl methacrylate) bone cement or a cement-free joining technology. Here, the guiding principle is to preserve as much of the natural bone as possible, in order to keep the entire musculoskeletal system stable.

But prefabricated hip and knee joints pose a serious disadvantage. Only rarely do they precisely match the anatomical form of the bone part to be replaced. As a result, the surgeon has to work the patient's bone to ensure that the implant is securely held. This often results in loss of bone substance. As a result, if the artificial joint needs to be subsequently replaced, many patients will no longer be able to benefit from standard components. “In these situations, it isn't easy to achieve clean fixation again,” says Thomas Schneider, an orthopedic surgeon in Gundelfingen, Germany.

Digital Customization. A better approach is to use custom implants that have been tailor-made for the individual patient. Producing made-to-measure prostheses has always been very time-consuming and expensive, however, due to the numerous manual work steps involved. That is now expected to change thanks to the introduction of an optimized process chain. The chain begins with Siemens CT scanners, which now offer a resolution of 0.3 mm, resulting in images that show the three-dimensional form of diseased joints very precisely. Such 3D scans are ideally suited for producing an exact model of damaged or destroyed sections of bone and joint surfaces.

For Karsten Schwarz, head of Application Engineering at Siemens Industry's Technology and Application Center (TAC) in Erlangen, such digital data are the first step in a process chain for which Siemens has put together a complete technology package. “We have succeeded in integrating the production of complex hip, knee and dental implants into a continuous process chain,” says Schwarz. This was accomplished by borrowing an established practice from the manufacturing industry: three-dimensional planning of a workpiece on a computer, followed by automatic production of the piece by a special machine tool.

Whereas the conventional approach doesn't include patient-specific design data for custom-fitted implants, anatomically-tailored models of bone components, cartilage, and joints can be created on screen using 3D CT data and the NX-CAD/CAM software from Siemens PLM.

Doctors can thus use digitalized X-ray images to plan an operation—before forwarding the data to a production center, where the implant is modeled on a computer and a set of commands for a milling machine are generated. In addition, a simulation program runs through the entire production sequence. This does two things. First, it ensures that the production process can be completed without problems, and second, precise optimization helps to eliminate waste of expensive raw materials such as titanium and cobalt-chromium alloy.

If everything proceeds smoothly, and with the desired quality and speed, the simulation program gives the green light. A machine tool then mills a custom hip joint from a block of titanium in about 30 minutes, and fine finishing gives the joint the final form that is desired. The heart of the process is a system provided by Siemens Industry. Here, software relies on special algorithms to primarily control the milling, turning and grinding of very high-strength materials. Siemens development engineers proudly point out how quickly and flexibly the entire manufacturing procedure can be adapted. “In the future,” predicts Schwarz, “ we won't be able to imagine what it would be like not to have custom transplants with perfect fit and surface quality.”

Optimized Production. Manufacturing specialists are convinced that a high degree of process chain automation can make it possible for custom prostheses to be manufactured at substantially lower costs. Flexible and networked machining centers could be ideally matched to one another and would offer substantial savings potential in terms of the costs of inventory, labor, and materials. Today, orders for tailored prosthetic implants are placed with specialized plants only in the case of serious hip diseases or severe malalignment of the legs, but the integrated production process and its associated low production costs open the door to custom implants for patients suffering from a range of other conditions.

All in all, patients stand to benefit substantially from personalized implants. A major reason for this is that such implants are far better matched to the user's biomechanics. This reduces wear on the prosthesis and helps to prevent shaft loosening, which can result from anchorage fatigue or insufficient stabilization of a joint.