Annually, some 15.000 hip fractures caused by a weakened bone tissue structure, occur among the elderly population in The Netherlands. The musculo-skeletal specialists are eager to understand the functioning of bone tissue and the origin of osteoporosis at an advanced age. Why do people lose bone volume as they grow older? In the Orthopaedics Research Laboratory at the Erasmus University of Rotterdam, the Dr. Weinans team is studying the bone tissue metabolism and its mechanical aspects.
Most people think bone is dead material but in fact it is not. The bone tissue supports the body and protects the interior organs against mechanical forces from outside. It also stores calcium and phosphates. Bones have to endure tremendous forces imposed upon them even in light physical exercise, which may amount in four to five times the entire body weight. A constant overload submits the bone structure to a hardly visible tear and wear. Yet, there is a continuous process of reparation and replacement going on to reinforce the structure. Bone can get more strength when it is put under stress regularly.
Each year, ten to twenty percent of our entire skeleton is being replaced by new bone. Hormones and signal molecules, located in specialised cells near the bone, play an important role in the process of demolishing and restoring. When people grow older, the bone structure changes, and the repair process is slowing down gradually. To analyse the bone structure and the processes of constant adaptation taking place, Dr. Weinans and his team developed a software programme which needs supercomputer power to run fast enough.
Normally, bone extremities consist of a kind of spongy structure. These are vulnerable spots for fractures. A number of methods have been developed to analyse the spongy bone. In the recent past, researchers studied histological samples under the microscope to measure the thickness and direction of the bony structures. Today, a micro-CT (computed tomography) scanner is used to generate 3D images from tiny pieces of spongy bone tissue, as to visualise the complete internal geometry. Researchers can describe this architecture mathematically by means of a volume rendered model.
One of the models developed in Rotterdam demonstrates what is happening when people get arthrosis. When the bone repair process is not functioning properly anymore, the bone tries to maintain its original power by filling up the holes, keeping its strength under pressure, but making it vulnerable for breaking. Even if the powerful supercomputer models are used, it is still not possible to grasp details down to the micro-level. At a macro-level however, the models already provide a lot of insight.
The team of Dr. Weinans applies the Finite Element Modelling (FEM) method to accurately calculate how the external forces are distributed over the bone and led through the spongy structure. In this way, it is possible to simulate the adaptive capacity of bone tissue to alternatively reduce and grow in order to learn and understand why this typical behaviour is disturbed in patients who are suffering from osteoporosis. Dr. Weinans anticipated that the new supercomputer will enable his team to create more refined simulations, and scale up the bone structure dimensions at a realistic level for simulation.