Mayo studies squeaky hips, joint problems of superobese, shoulder relief for young and arthritic

February 27, 2009

ROCHESTER, Minn. -- Mayo Clinic orthopedic surgeons will contribute more than 100 presentations on their latest findings for improving orthopedic clinical care and scientific research at the annual meeting of the American Academy of Orthopedic Surgeons (AAOS) in Las Vegas, Feb. 25-March 1.

This AAOS event is the largest professional meeting of orthopedic surgeons in the U.S.

As such, it is a major resource for helping physicians and surgeons improve patient mobility and the care of bones, joints and muscles through the sharing of ideas and techniques.

Four brief highlights of Mayo Clinic Orthopedics' presentations, and the boldfaced time the embargo lifts for each, appear below:

As Obesity Epidemic Spreads, More Patients Feel It in Their Bones and Joints

Embargoed until Wednesday, Feb. 25, 2009, 9:30 a.m. PT/12:30 p.m. ET

Common sense suggests that extra body weight severely stresses bones and joints. But until the findings of a new Mayo Clinic study were presented today, no one had reported how this higher, unprecedented level of obesity in the U.S. affects total hip replacements, implanted to restore mobility and relieve the chronic pain of hip degeneration.

Mayo researchers found that obesity has a significant effect. "While technically feasible, there is a much higher complication rate -- more than 50 percent -- in hip replacement patients regarded as superobese," explains Mayo Clinic orthopedic surgeon David Lewallen, M.D., the senior researcher. "This suggests we must do much more to help these patients recover their health by helping them lose weight when possible prior to implant surgery."

Body Mass Index (BMI) is the measurement of choice for many physicians studying obesity. BMI uses a mathematical formula that takes into account a person's height and weight.

In this Mayo study, patients diagnosed as superobese had a BMI greater than 50. Generally, a BMI of 30 indicates obesity. A person 6-feet tall with a BMI of 30 would weigh about 225 pounds. A person that same height with a BMI of 50 would weigh 369 pounds.

In the study, 43 patients categorized as superobese underwent total hip arthroplasty from 1996 to 2006. This surgical procedure replaces a worn, fractured or damaged hip joint with a prosthetic implant. The patients had a BMI ranging from 50 to 77, and a mean age of 56.

Mayo followed them an average of three years to determine outcomes. Results showed:

• More than half (56.5 percent) experienced either surgical or medical complications, including prolonged wound drainage.
• Five of the 43 patients required a total of 15 re-operations to correct problems such as recurring dislocation of the implant, chronic infection and new bone fractures around the device.

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Knee Problems of the Superobese

Embargoed until Wednesday, Feb. 25, 2009, 9:30 a.m. PST/12:30 p.m. EST

The knee joint is especially vulnerable to injury in both healthy-weight active people and those who are overweight. But until today's Mayo Clinic presentation, no one had published results of what happens to knee implants under the stress of extreme extra weight known as superobesity. Superobesity is defined as having a Body Mass Index (BMI) that is greater than 50. Normal-weight BMI ranges from 19 to 25. http://www.cdc.gov/healthyweight/assessing/bmi/index.html

Replacing a knee joint is a common surgical procedure called total knee arthroplasty. What is less common is having a large enough group of superobese patients to comprise a statistically powerful sample to determine how implants fare in this population.

As a center of orthopedic excellence, Mayo Clinic surgeons treated 105 of these surgically and medically challenging patients between 1996 and 2006. The patients had a mean BMI of 53.6, and average age at the time of surgery was 61 years. Their outcomes were followed an average of three years after surgery.

Results showed:

• Overall, 40.6 percent had surgical complications and 14.3 percent had medical complications -- including two deaths after the surgery.
• Surgical complications included 20 knees that had prolonged wound drainage --increasing the chance of deep infection of the implant.
• Nineteen cases needed additional operations to trim slowly healing wound edges, treat deep infection or repair failed implants.

"As with hip replacement in the superobese patient, total knee arthroplasty also is associated with a markedly higher complication rate compared to patients of normal weights," says Mayo Clinic orthopedic surgeon David Lewallen, M.D., senior author on the study. "The real concern here is that clinicians and patients need to be aware of that fact when they are making treatment decisions. In general, this group of patients is in desperate circumstances -- and we really want to help them. To do that, we are trying to get the data out there that will guide management of the superobese patient. A big part of that has to be helping them lose weight prior to knee arthroplasty whenever possible."

VIDEO ALERT: Additional audio and video resources, including excerpts from an interview with Dr. David Lewallen describing the research, are available on the Mayo Clinic News Blog (http://newsblog.mayoclinic.org/2009/02/20/superobese-struggle-with-hip-and-knee-replacement/). These materials are also subject to embargo, but may be accessed in advance by journalists for incorporation into stories. The password for this post is: bmi2259.

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'Squeaky' Hip Implants

Embargoed until Thursday, Feb. 26, 2009, 9 a.m. PST/Noon EST

With the growing success of joint replacement surgeries, patients have become accustomed to certain indignities related to having a metal replacement part in a hip, knee or shoulder. For example, they tend to set off airport metal detectors and attract attention of security personnel. Now, there's more.

To the acoustical signature of the orthopedic implant detected by a security sweep, add the distinctive "hip squeak." The sound is associated with implants made of a material known as alumina ceramic-on-ceramic -- and is audible to the person with the implant and those nearby.

While the hip squeak was previously known to experts, its precise cause has been a mystery. The Mayo Clinic Biomechanics Laboratory report released today sheds light on the potential causes of the squeak, thus guiding means of eliminating it.

After 11,000 cycles of tests in a mechanical simulator that reproduced the flexion and extension motions of the hip, Mayo Clinic investigators concluded that:

• Squeaking occurred when the film fluid between the two moving surfaces was disrupted.
• Disruption could be caused by the presence of particles that originate from wear and tear, or from imperfect alignment or positioning of implant surfaces.
• Squeaking occurred especially quickly under highest pressure on the artificial joint.
• Once squeaking started, it didn't stop -- and was constant at all frequencies tested.

According to Robert Trousdale, M.D., the lead Mayo investigator: "Adding a small amount of lubricant solved the problem in the lab. Our research is helpful because it can be applied to devising a solution to the squeak problem. Most likely that will consist of improving the design of implants so they have less chance of material transfer and disruption, which appears to be an important aspect in the basis of the squeak."

VIDEO ALERT: Additional audio and video resources, including excerpts from an interview with Dr. Robert Trousdale describing the research, are available on the Mayo Clinic News Blog (http://newsblog.mayoclinic.org/2009/02/20/squeaky-hip-implants/). These materials are also subject to embargo, but may be accessed in advance by journalists for incorporation into stories. The password for this post is: hip226q.

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Relief for Early Shoulder Arthritis

Embargoed until Friday, Feb. 27, 2009, 8:30 a.m. PST/11:30 a.m. EST

Young and middle-age adults tend to interpret chronic shoulder pain as the result of athletic and overuse injuries and shrug them off. But a subset of those patients under age 50 can't easily shrug away the pain, because it hurts too much.

A new Mayo Clinic study presented today concludes that those 50 and younger who experience chronic shoulder pain related to arthritic changes in the glenohumeral (shoulder) joint can benefit markedly in terms of pain relief and improved mobility from shoulder joint replacement surgery. The procedure is known as arthroplasty. Typically, arthritic degeneration of the shoulder joint is expected in people 65 years and older. How joint replacement affects a younger patient group was not known until this Mayo study.

The Mayo Clinic team studied the outcomes of 23 total shoulder arthroplasties performed between 1986 and 2005 and 10 procedures that replaced only the humeral head. All patients were

50 or younger and had chronic shoulder pain caused by arthritis. All patients were followed for two years after surgery to determine outcomes.

Results indicated:

• Long-term pain relief was significant.
• Key motions were improved, such as raising the hands above the head.
• Five patients needed more surgery, known as revision surgery, because of arthritic changes and/or infection.

Commented John Sperling, M.D., lead orthopedic surgeon on the Mayo team, "For the young patient with shoulder arthritis, clinical outcomes are favorable for both total shoulder arthroplasty and partial arthroplasty in terms of pain reduction and improved motion -- but revision rates are high."

VIDEO ALERT: Additional audio and video resources, including excerpts from an interview with Dr. John Sperling describing the research, are available on the Mayo Clinic News Blog (http://newsblog.mayoclinic.org/2009/02/19/relief-for-early-shoulder-arthritis/). These materials are also subject to embargo, but may be accessed in advance by journalists for incorporation into stories. The password for this post is: sprl0227.At the academy's annual meeting, Mayo Clinic orthopedic surgeons will give 20 presentations in the AAOS General Scientific Section and 19 in the Symposia, lead 22 Podium Presentations, give 40 Instructional Course Lectures, and present 21 Poster Presentations and Scientific Exhibits. On Specialty Day, Saturday, Feb. 28, Mayo orthopedic surgeons will give 25 presentations.

For More Information

To learn more about Mayo Clinic Orthopedics, see: http://www.mayoclinic.org/orthopedicsurgery-rst/

To obtain the latest news releases from Mayo Clinic, go to www.mayoclinic.org/news. MayoClinic.com (www.mayoclinic.com) is available as a resource for your health stories.

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