Navigation Links
Engineering a better hip implant
Date:9/18/2012

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?

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."

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."


'/>"/>

Contact: Richard Lewis
richard-c-lewis@uiowa.edu
319-384-0012
University of Iowa
Source:Eurekalert

Related biology news :

1. UA engineering professor Shane Snyder to speak in Korea on international water quality
2. Engineering research centers awarded $55.5 million to innovate in nanoscale science and engineering
3. £30 million boost for biomedical engineering research
4. University of Minnesota engineering researchers discover new non-invasive method for diagnosing epilepsy
5. UA engineering professor uses aerospace materials to build endless pipeline
6. Genetic Engineering & Biotechnology News unveils Biotech Boulevard
7. Engineering technology reveals eating habits of giant dinosaurs
8. GEN reports on growth of tissue engineering revenues
9. Oligonucleotide Delivery: Biology, Engineering and Development Conference
10. Investigation of American Oriental Bioengineering, Inc. by Securities Lawyers at Goldfarb LLP Law Firm for Potential Shareholder Claim
11. NSF report detailing growth in graduate enrollment in science & engineering in the past decade
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:4/6/2017)... Forecasts by Product Type (EAC), Biometrics, Card-Based ... & Logistics, Government & Public Sector, Utilities / Energy ... Nuclear Power), Industrial, Retail, Business Organisation (BFSI), Hospitality & ... for a definitive report on the $27.9bn Access Control ... ...
(Date:4/5/2017)... April 4, 2017 KEY FINDINGS ... expand at a CAGR of 25.76% during the forecast ... the primary factor for the growth of the stem ... https://www.reportbuyer.com/product/4807905/ MARKET INSIGHTS The global stem cell ... application, and geography. The stem cell market of the ...
(Date:3/30/2017)... , March 30, 2017  On April 6-7, ... Hack the Genome hackathon at Microsoft,s headquarters ... two-day competition will focus on developing health and wellness ... Hack the Genome is the first ... tremendous. The world,s largest companies in the genomics, tech ...
Breaking Biology News(10 mins):
(Date:7/20/2017)... ... 2017 , ... Dr. Asher Kimchi, Founder and Chairman of the International ... at the 22nd World Congress on Heart Disease held in Vancouver, BC, Canada. In ... Distinguished Fellowship Awards. , Dr. Asher Kimchi, together with Co-Chairmen Dr. John A. Elefteriades ...
(Date:7/20/2017)... and PLYMOUTH, Minn., July 20, 2017 /PRNewswire/ ... , a personalized genetic evaluations company, today announced ... their partnership investigating a genetic mutation implicated in ... extend the partnership for a second case involving ... year, the KCNQ2 Cure Alliance and Pairnomix entered ...
(Date:7/18/2017)... ... , ... Sourcing custom glass or quartz parts can be a daunting task. ... execute your job can take many hours of emails, phone calls and on-line research. ... showcase the company’s capabilities and core custom categories, and enables you to start the ...
(Date:7/18/2017)... ... July 18, 2017 , ... Allotrope Foundation won the 2017 ... of the Allotrope Framework for commercial use. , The Bio-IT World Best Practices ... elevate the critical role of information technology in modern biomedical research, but also ...
Breaking Biology Technology: