Osteoarthritis, or “wear and tear” arthritis, is a debilitating joint disease affecting nearly one third of all American adults. Some people may experience only mild joint pain, while others endure severe chronic pain as their cartilage wears away leaving no cushion between their bones.
Fortunately, Jake Elkins has developed a sophisticated computational model that helps researchers predict improved results for patients receiving hip replacements.
Elkins is a sixth year MD/PhD student completing his PhD work in the department of Biomedical Engineering at the University of Iowa. Also an Institute for Clinical and Translational Linked Training Award (TL1) trainee, Elkins is preparing to defend his thesis next month and deliver five presentations at two national conferences shortly thereafter.
How did you become interested in orthopaedic biomechanics?
During college I wanted to be a nuclear engineer. After completing an engineering internship, I realized that I enjoyed the problem-solving aspects of the field, but I didn’t feel like it was a good fit. Suddenly I was a senior in the unnerving situation of not knowing what I wanted to be when I grew up. I’ve always been interested in medicine, so I volunteered at our Veteran’s Administration hospital just to gain some experience. I worked in the surgical department doing various tasks like preparing patients for surgery, scheduling operations, and fixing the copy machine.
I was fascinated by surgery and after watching a few I was allowed to scrub in and observe some procedures up close. The first time I helped a patient get a new knee, I was hooked. This was the moment I knew I wanted to become an orthopaedic surgeon. I volunteered with the orthopedic department for the rest of the year and when they offered to hire me as a surgical technician I couldn’t believe that I was actually going to get paid to do it.
What’s it like being a TL1 trainee at the University of Iowa?
I am always within arm’s reach of peers and mentors who remind me that while we all work in different fields, use different tools, explore different topics, and get excited about different science, we all strive for the same goal: to improve the quality of life for patients. The ICTS’s focus on truly translational science has motivated me to strive for the highest-quality and highest-impact work that I can possibly produce. This is an extremely supportive environment and if I ever have questions outside of my expertise, I know that someone here can help me.
You’re preparing to give five (5!) presentations. Tell us a little bit about that.
Advanced-stage osteoarthritis generally requires joint replacement to relieve debilitating pain and improve a patient’s quality of life. Conventional hip implants have a metal head that connects the joints within a plastic cup. The plastic wears down during routine use, making them best suited for older patients with less demanding lifestyles. However, disabling osteoarthritis also affects younger, more active patients, so orthopaedic implant manufacturers have developed several new generations of advanced metal and ceramic hip implants that are designed to last longer and take more abuse.
Unfortunately, several recent reports have indicated an unusually high failure rate among these implants. A significant knowledge gap obviously exists when it comes to understanding the biomechanics of these new devices and the objective of our recent research has been to bridge this gap using a computation model of hip replacement. We have successfully investigated several avenues of potential failure. We’ve also explored and quantified areas for improvement in regards to optimal surgical placement, edge-loading and scraping of metal implants, fracture of ceramic implants, bone impingement in large devices, and the effect of head size on implant performance. We will present these five topics at The Orthopaedic Research Society and The American Academy of Orthopaedic Surgeons conferences in San Francisco.
Your work seems very innovative in terms of using new imaging and assessment techniques. What is your guiding research purpose and what techniques are you using to get there?
Our collaborative research involves computational simulations, experimental simulations, and surgical observations. This research is translational because the information goes from the computer (bench) to the operating table (bedside). Its purpose is simply to guide surgeons to make the best possible decisions in terms of maximizing implant performance.
My area of research focuses on a numerical technique called Finite Element Analysis (FEA). The automotive and aeronautic industries, among others, use this type of method to design and develop their products. By using computers to simulate certain attributes, such as stiffness and strength, manufacturers avoid making defective products and save time, materials, and cost.
We used FEA to develop a robust model of total hip replacement to observe the impact of surgery, the individual patient, and the implant itself will have on an implant’s performance. We came up with three distinct inputs for the model. First, we used a patient’s anatomic details, including bones and soft tissues obtained from radiographic (CT) scans and radiographic studies, to build the model. Material properties of the soft tissues were determined from a series of cadaveric experimental studies. Next, we input the total hip replacement geometry, also obtained from radiographic studies. These files were then processed (meshed) and registered to the bony/soft-tissue anatomy. The final inputs were the joint loads and movements that we determined from motion-analysis and inverse-kinetics of several patients performing various daily tasks. This computational model has been extensively validated using both experimental and analytical techniques.
Dislocation is the most common cause of failure following total hip replacement surgery, so most of our initial work with the model related to investigating how surgical approach, surgical repair of the soft tissues, and surgical position of the components resisted dislocation. Many dislocations are a direct consequence of component impingement, a fulcrum-like action leading to the head dislocating from the cup. In addition to dislocation, we were also interested in determining other harmful consequences of impingement. We made several refinements of the model to better quantify the damage propensity that occurs alongside impingement, such as generation of wear debris and, in the case of ceramic implants, fracture. We found high body mass index and poorly positioned components led to substantially higher fractures in ceramic implants. Now we are focusing our research on outcome predictions using all metal total hip replacements. We have been able to identify component placement and implant sizes that minimize the potential for deleterious wear formation while maximizing implant stability.
Congratulations, that’s really exciting. This last question might be moot given how hard you’re working, but what kind of things do you like to do for fun?
When not at work, I try to spend as much time as possible with my family. I have an amazing and very patient wife, Jaymie, and two beautiful little girls, Maddie (two years old) and Tessa (eight months). I am also an avid woodworker. At any given time, except sometimes in January and February, I am working on a furniture project out in my garage.
Elkins JM, Pedersen DR, Callaghan JJ, Brown TD. (2011) Fracture Propagation Propensity of Ceramic Liners during Impingement – A Finite Element Analysis. J Arthroplasty (PMID: 21855277).
Elkins JM, Kruger KM, Pedersen DR, Callaghan JJ, Brown TD. (2011). Edge-Loading Severity as a Function of Cup Lip Radius in Metal-on-Metal Total Hips – A Finite Element Analysis. Journal of Orthopaedic Research (PMID 21812025).
Elkins JM, O'Brian MK, Stroud NJ, Pedersen DR, Callaghan JJ, Brown TD. (2011). Hard-on-hard total hip impingement causes extreme contact stress concentrations. Clin Orthop Relat Res 469 (2) 454-463.
Elkins JM, Stroud NJ, Rudert MJ, Tochigi Y, Pedersen DR, Ellis BJ, Callaghan JJ, Weiss JA, Brown TD. (2011). The Capsule’s Contribution to Total Hip Construct Stability – A Finite Element Analysis. William H. Harris Award Paper, Orthopaedic Research Society, J. Orthop. Res 29 (11) 1642-1648
Photo at middle-right is used with permission, courtesy of the Orthopaedic Research Society