Glimmer of hope from the university lab for recipients of artificial hips
In children, dislocation of the hip joint - inherited or caused by damage in the womb - is the most common skeletal malformation of all. In old age, on the other hand, hips are often worn out and worn out, because our hip joints constantly transmit forces that are many times our body weight. A new type of artificial hip joint has now been developed at Chemnitz University of Technology. In Germany, every 25th person has to reckon with the fate of having to rely on a hip joint made of metal, plastic or ceramic. Around 80,000 artificial hip joints are implanted in Germany every year. Worldwide there are even almost one million artificial hip recipients who are spared a life in a wheelchair or a stiff pelvis. The routine operation is considered harmless - but it does not always bring relief. Every fifth patient subsequently complains of pain. It is not uncommon for the connection between the inner prosthesis and the surrounding bone to be unstable. Then another operation is necessary. Even in the best-case scenario, an artificial hip lasts 15 years – a problem especially for younger patients. One reason for the lack of durability is that the metal or ceramic prosthesis anchored lengthwise in the femur is often perceived as a disturbance by the bone that surrounds it. This begins to grow in the middle area, while bone substance is broken down in the upper area. As a result, the artificial joint puts a completely different strain on the femur than the natural hip.
A new type of artificial hip joint that mechanical engineers at Chemnitz University of Technology have developed and which the body tolerates much better than previous artificial hips now promises a remedy. Significantly involved in the development was Dr. Gamal Baroud. With the help of the computer, he succeeded in designing a completely new artificial joint. It takes into account the stress conditions in the bone and restores them as far as possible - a prerequisite for a significantly longer durability.
First, Dr. Baroud worked to determine the exact stresses on the individual bones in the pelvic area. To do this, he "disassembled" the femur on the computer into more than 3000 cube-shaped sections. This method, which is used to calculate the statics of houses, for example, is called the “Finite Element Method” (FEM). It enables deformations and stresses to be precisely determined. The scientist then applied the method to conventional hip prostheses. Result: Because the bones and prosthesis have different degrees of stiffness, they load the thigh unevenly: excessively in some areas, but hardly at all in others. This is the reason for bone remodeling and subsequent loss of stability. Doctors speak of "aseptic loosening" here, and sooner or later another operation will be necessary.
The Baroud hip – which he himself calls a femoral neck total hip prosthesis – consists of several parts and essentially consists of a shaft and a titanium bushing. However, the socket is not inserted lengthwise, but diagonally towards the body in the neck of the femur, the upper end of the femur. With its elastic collar, it is supported on the particularly strong outer area of the bone, the so-called cortical bone. The elastic shaft protrudes into this socket. It also has a flexible collar that rests on the socket collar and thus also absorbs the pressure. Shaft and bush are loosely screwed together from the outside. The decisive advantage of the new hip is its flexibility: The flexible shaft and the two collars distribute the forces much better and over a larger area than conventional hip prostheses. Minimal displacements, which can sometimes occur when overloading occurs, only act between the individual parts of the prosthesis, but not between the prosthesis and the bone, as was previously the case. Therefore, no undesired soft tissue is formed, which otherwise usually leads to great difficulties. The harmful bone remodeling that leads to the aseptic loosening already mentioned is also avoided. Even with particularly strong forces, such as those that can occur in a fall, Dr. Baroud calculates that the new artificial joint can be completed without any problems. And should it ever be necessary to implant a conventional prosthesis later for whatever reason, this is also possible since the bone mass is retained. The Baroud Hip is also easy to craft since all parts are rotationally symmetrical.
The Heidelberger Verlag Spektrum der Wissenschaft is the operator of this portal. Its online and print magazines, including "Spektrum der Wissenschaft", "Gehirn&Geist" and "Spektrum – Die Woche", report on current research findings.