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:4/26/2016)... 27, 2016 Research and ... Biometrics Market 2016-2020"  report to their offering.  , ... The analysts forecast the global multimodal biometrics ... during the period 2016-2020.  Multimodal biometrics ... such as the healthcare, BFSI, transportation, automotive, and ...
(Date:4/15/2016)... 15, 2016 Research and ... Biometrics Market 2016-2020,"  report to their offering.  , ... , ,The global gait biometrics market is expected ... the period 2016-2020. Gait analysis generates ... be used to compute factors that are not ...
(Date:3/31/2016)... 2016   LegacyXChange, ... "Company") LegacyXChange is excited to release its ... to be launched online site for trading 100% guaranteed ... will also provide potential shareholders a sense of the ... an industry that is notorious for fraud. The video ...
Breaking Biology News(10 mins):
(Date:6/24/2016)... ... 2016 , ... Researchers at the Universita Politecnica delle Marche in Ancona combed ... pleural mesothelioma. Their findings are the subject of a new article on the Surviving ... signposts in the blood, lung fluid or tissue of mesothelioma patients that can help ...
(Date:6/23/2016)... 23, 2016 /PRNewswire/ - FACIT has announced the ... biotechnology company, Propellon Therapeutics Inc. ("Propellon" or ... of a portfolio of first-in-class WDR5 inhibitors for ... as WDR5 represent an exciting class of therapies, ... medicine for cancer patients. Substantial advances have been ...
(Date:6/23/2016)... -- The Prostate Cancer Foundation (PCF) is pleased to announce 24 new ... prostate cancer. Members of the Class of 2016 were selected from a pool ... Read More About the Class of 2016 PCF Young Investigators ... ... ...
(Date:6/23/2016)... ... June 23, 2016 , ... STACS DNA Inc., the sample tracking software company, ... Crime Laboratory, has joined STACS DNA as a Field Application Specialist. , “I ... President and COO of STACS DNA. “In further expanding our capacity as a scientific ...
Breaking Biology Technology: