Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Engineering a better hip implant

19.09.2012
UI team learns thigh size is a reason why hip implants fail
University of Iowa researchers have determined that thigh size in obese people is a reason their hip implants are more likely to fail.

In a study, the team simulated hip dislocations as they occur in humans and determined that increased thigh girth creates hip instability in morbidly obese patients (those with a body mass index (BMI) greater than 40). The researchers propose that surgeons modify surgical procedures to minimize the chance of dislocation in obese patients and consider other designs for hip replacement implants.

“We have shown that morbidly obese patients’ thighs are so large that they are actually pushing each other outward and forcing the implant out of its socket,” says Jacob Elkins, a UI graduate student and first author of the paper published in the journal Clinical Orthopaedics and Related Research. “Studies have shown up to a 6.9-fold higher dislocation rate for morbidly obese patients compared to normal weight patients.
Total hip replacement gives mobility back to people who experience debilitating hip joint pain. According to the National Institute of Arthritis and Musculoskeletal and Skin Disease (NIAMS), 231,000 total hip replacements are performed annually in the U.S. and more than 90 percent of these do not require follow-up repair or replacement. But when an implant fails, it is painful, and costly. Studies have shown that dislocation ranks as the most common reason for failed implants, according to Medicare hospital discharge data.

A hip implant is a ball-in-socket mechanism, designed to simulate a human hip joint. However, it lacks the connective tissue that stabilizes a normal hip joint, meaning the ball portion of the implant can sometimes “pop out.”

Clinical studies point to an increased dislocation risk among obese patients with total hip replacements, but the reasons have remained unclear. Dislocation requires extreme range of motion, such as flexing at the waist. Given the reduced range of motion in the obese, why do they experience more dislocations?

Engineering a better hip implant

Using a computational model he created to understand how a hip implant works in patients, Elkins and research collaborators analyzed 146 healthy adults and six cadaver pelvises. They examined the effects of thigh-on-thigh pressure on the hip implant during a wide range of movements from sitting to standing. With the ability to simulate movements in human bodies of varying sizes, the team could test different implants. They also looked at the various implants’ performances in different body types. They used a hip-center-to-hip-center distance of 200 millimeters as a basis for their analyses of thigh girth for eight different BMIs, ranging from 20 to 55.

The research team ran computations to examine the joint stability of several different hip implants. They tested two femoral head sizes (28 and 36 millimeters), normal versus high-offset femoral neck, and multiple cup abduction angles.

The researchers report three main findings: 1) thigh soft tissue impingement increased the risk of dislocation for BMIs of 40 or greater; 2) implants with a larger femoral head diameter did not substantially improve joint stability; 3) using an implant with a high-offset femoral stem decreased the dislocation risk.

“The larger your legs are, the more force that goes through the hip joint,” Elkins says. “It’s a simple concept. When your thighs are real big, they push on the hips.”

Recommendations for surgeons

Surgeons treating obese hip implant patients can use the study findings to select better implant designs and modify their surgical procedures to minimize the chance of dislocation in obese patients, the researchers say.

“The number one thing surgeons can do is what is called a ‘high offset femoral stem,’” says senior author Thomas Brown, UI professor of orthopaedic surgery, referring to the portion of the implant that attaches to the patient’s upper thigh bone, or femur. “Basically, the implant’s femoral stem is longer, so it effectively shifts the leg further away from the center rotation of the joint. The thighs then would need to move even further inward before they would abut one another and generate the forces necessary for dislocation.”

The study, titled “Morbid obesity may increase dislocation in total hip patients: A biomechanical analysis,” was published online on Aug. 21. Elkins is in the UI’s College of Engineering Biomechanical Engineering Program and the Carver College of Medicine’s Medical Scientist Training Program.

Other authors are Matej Daniel, assistant professor at Czech Technical University in Prague, Czech Republic, and former Fulbright Research Scholar at UI Hospitals and Clinics; Douglas Pedersen, UI research associate professor of orthopaedic surgery; Bhupinder Singh, UI doctoral candidate in physical therapy; John Yack, UI associate professor of physical therapy; and John Callaghan, UI professor of orthopaedic surgery.

The National Institutes of Health, the Veterans Administration, and the National Center for Resource Resources funded the research.
Contacts
Jacob Elkins, Orthopaedics and Rehabilitation, 319-594-4800
John Riehl, Graduate College, 319-384-1309

Richard Lewis | EurekAlert!
Further information:
http://www.uiowa.edu
http://now.uiowa.edu/2012/09/engineering-better-hip-implant

More articles from Materials Sciences:

nachricht An innovative high-performance material: biofibers made from green lacewing silk
20.01.2017 | Fraunhofer-Institut für Angewandte Polymerforschung IAP

nachricht Treated carbon pulls radioactive elements from water
20.01.2017 | Rice University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>