The Implant Boom: It’s Now Hip to Replace Your Hip

The number of joint replacement surgeries in the US is skyrocketing amongst the baby boomer population. Not only are joints being replaced due to fractures and severe pain, but also to facilitate the continuation of an active lifestyle. Previous generations might have reached for their canes, but baby boomers seem to be more likely to grab their running shoes, bikes, or swim goggles.

According to the National Hospital Discharge Survey (NCHS), the number of total hip replacement surgeries of patients 45 years or older in the United States has more than doubled from 2000 to 2010, but the total number of hip replacement surgeries for people between the ages of 45-64 has almost tripled during that same time! This is a dramatic change since many implants used for hip replacements haven’t been designed for active lifestyles. Additionally, much of the data indicating some prostheses should last more than 20 years is based on patients leading a more sedentary lifestyle.


While total hip replacement surgeries are seeing an increase in demand, 10-20% of the patients may require a revision surgery because of a failure or wearing-out of the prothesis, most commonly due to loosening of the implant stem. This loosening can be caused by bone resorption or loss of bone mass. Revision surgeries can be more complex, especially for elderly patients, and bone resorption can increase the risk of bone fracture. All of this is bad news for younger active patients who will need these prostheses to last several decades.


How can these problems be avoided in the future? By applying optimization and simulation technologies and methods to a hip implant can greatly improve the longevity and how it performs. Two ways of doing this are to include more dynamic load cases when designing the hip implant stem and focusing on reducing stress-shielding in the bone surrounding the implant.

When analyzing a design using computer simulation, it is important to include all the various load cases a product might see during its life cycle. The current load cases considered when designing hip implant stems might only involve daily activities such as standing, sitting, walking and climbing stairs. However, with an increasing number of younger patients having total hip replacement surgeries and older patients staying active later in life, additional load cases should be considered. In our study, we included jogging in addition to other standard daily activities, but biking, swimming, and other activities could be included during the design process. Adding these load cases could increase the longevity and performance of hip implant stems.

In considering additional load cases, improving the performance and compatibility with the natural body should also be considered. Most hip implant stems are made of titanium due to its biocompatibility, but titanium is roughly 6.5 times stiffer than the cortical bone of the human femur. When a solid titanium stem is implanted in the femur the load distribution will change in the remaining bone. Often the load into the bone will be reduced because the titanium stem is so much stiffer than the natural bone. This is referred to as stress-shielding. Per Wolff’s law, bone remodels itself to adapt to external loading. With a reduction in loading and stress in the surrounding bone, bone resorption and/or loss of bone mass can occur. Therefore, reducing stress-shielding should help reduce the number of revision surgeries.

Topology optimization optimizes the material distribution within a defined material volume based on the provided load cases, design constraints and objective. This optimization process illustrates where material can be removed and the optimal load paths for the various loads.  With the recent advances in additive manufacturing capacities, Altair has introduced lattice optimization which generates structural lattice can be incorporated in areas where the solid structure is not necessary. Each beam diameter of the lattice can be fine-tuned to achieve the design constraints and objective.

These technologies have been applied to the geometry of a general hip implant stem and the results were very promising. The goal of our study was to create a methodology and process to better tune the stiffness and strength of the hip implant stem while including load cases like jogging among the other standard daily activities.

We started by simulating a healthy femur, then a femur with a generic implant and finally a femur with an implant designed using topology and lattice optimization. The optimized prosthesis was designed for metal additive manufacturing which requires careful selection of the print direction, calculating overhang angles, maintaining minimum size parameters and reducing the need for printed support structures.

In the end, the stress-shielding caused by the implant was reduced by 57% when comparing the generic design and the optimized design. Furthermore, in the optimized design the stresses in the stem were kept below 575 MPa for all load cases including the jogging and two ISO standard fatigue load cases. For the grade of titanium, the implant was designed for, this would equate to an endurance limit of about 10,000,000 cycles or roughly jogging from Los Angeles to New York and back TWICE!

Coupling this optimization process with additive manufacturing can also provide some very exciting design freedom and customizability of these prostheses. For example, if you are working with a 200-pound male who enjoys water skiing and cycling, specific load cases based on individual activities and physiology could be configured to the optimization process. A customized design could be printed and in the surgeon’s hands the following week!

Solid-Lattice Hip Prosthesis Step Printed by EOS in Ti-6Al-4V

For more technical information regarding optimized hip replacement technologies, download the white paper here.

Empowering Innovation in Startups at Altair Nasdaq Entrepreneurial Event

The Startup ecosystem, made up of entrepreneurs, universities, investors, and researchers, is a community filled with innovative, thought provoking individuals driven by the desire to produce products and devices to provide a sustainable way of life. Last week Altair had the unique privilege of hosting an event at the Nasdaq Entrepreneurial Center in San Francisco, “Accelerate Your Startup to Market Leadership”, to introduce our technologies to this community through the lens of their peers. Special guest speakers provided their perspectives on the essence of a startup, their passion for innovation, and the importance of the virtual playground. As their stories of growth were presented, the audience was captivated by the possibilities of the advanced technologies Altair provides.

When designing for both near and far future, physical testing is not always possible. For example, when engineering robots to withstand the environment on Mars, how would one prototype and test these? It is as if simulation was made for the far future thinkers allowing them to apply physics and principles to these revolutionary ideas to build a better future. The event sought out to share these ideas through storytelling and inspiring illustrations.

As an opener to the event, Andrew Beebe presented on behalf of Obvious Ventures. Obvious Ventures has a 50-company portfolio focused on one mantra… World Positive Investing. This chant is a reminder of the company’s focus on tackling systemic world challenges. These challenges fit into three main categories: healthy living, people power, and sustainable systems. From diamond harvesting to air taxis, Obvious Ventures is pushing the technological envelope, defining, designing, and testing through simulation.  As an example, Beebe shared the story of Lilium, a company in their portfolio designing vertical lift electric jet air taxis to transport individuals short commuting distances. This technology is powered by Altair software as noted by Patrick Nathen, Lilium Co-Founder and Head of Calculation & Design. “Altair OptiStruct® helps our engineers to develop robust and lightweight aircraft structures in a more efficient way through its Integrated Analysis & Optimization approach which prepares us for certification.”

Following this provocative overview, Doug Harp, Global VP of IoT at Altair, took the stage sharing a much different approach to startups with his previous company, CANDI Controls, whose technology was recently acquired by Altair. His unique perspective shed light on the failures and successes of a startup in an emerging market. CANDI, expanded to Cloud Assisted Network Device Integration, provides software that easily connects systems and equipment with cloud-based monitoring and control services to help organizations improve performance, conserve resources, and cut operational costs. Although cutting edge in nature as a first to market company, Harp shared the ups and downs of deployment. One take away was the importance of focusing on where the technology fits into the entire package. With IoT, there are thousands of parts which make up the infrastructure. The challenge for Harp was to enable the end user through strong partnerships with complimentary technology. His guidance was candid and encouraging, allowing the audience to reflect on their own endeavors.

Rolo Bikes was represented next through the eyes of its founder, Adam Wais. Wais and his partner set out to design the highest performance road racing bicycles manufactured to date. Unabashedly using Altair’s technology, they did just that, producing an ultra-lightweight bike while hitting extremely rigorous stiffness requirements and impeccable handling. Wais shared the Altair technology used throughout the product development process and reiterated the following statements he had previously made. “We chose Altair HyperWorks for our project because we think that it offers us the most powerful tools for our optimization and development tasks within one suite. In addition, the use of HyperWorks enabled us to develop our own simulation tools for virtual testing. When we realized that we could use additional engineering support and manpower in our development and optimization process it was a natural choice for us to work with Altair ProductDesign, since the company’s engineers are very familiar with HyperWorks and have tremendous expertise in designing and optimizing composite materials. Working with Altair ProductDesign and using the HyperWorks suite has enabled us to develop the highest performance in the world with respect to weight, stiffness, and comfort. This project was completed in record time with close to no prototypes.”

Learn more about Rolo & watch the Rolo Bike video

Wais’ enthusiasm was followed by the introduction to the Altair Startup Program. This program is designed specifically for startups to aid in the development and advancement of product engineering. The audience was exposed to many Altair solutions, including electromagnetics, structural analysis, IoT enablement, CFD, and the entire extensive suite of tools available through the program. With the significant discount for these early adopters and the expansive solution offerings by Altair, a true partnership can be formed at the early stages of the product life cycle. This 80% discount also includes the 50+ Altair software partners and 16 hours of consulting with our highly experience CAE engineers. This left the audience feeling empowered by the opportunities in front of them as they reflected on the stories of their peers and mentors and the possibilities the Altair Startup Program can provide.

For more information on the Altair Startup Program, check out:

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