Additional Developments in One of Med-Tech's Key Sectors

Keeping you up to date in recent developments in orthopedics

Discovering that thigh size is a reason why hip implants fail may lead to better design . . . University of Iowa (Iowa City) 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; Bethesda, Maryland), 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. 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 vs. high-offset femoral neck, and multiple cup abduction angles. The researchers report three main findings: thigh soft tissue impingement increased the risk of dislocation for BMIs of 40 or greater; implants with a larger femoral head diameter did not substantially improve joint stability; using an implant with a high-offset femoral stem decreased the dislocation risk. 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.

Virtual foot set to help healing . . . An advanced virtual model of the human foot has been created by researches to drive forward improvements in treating serious injuries and illness. The 3-D model depicts bones, joints, ligaments, muscles and tendons in an unprecedented level of detail. It will be used to develop advanced treatments for conditions ranging from foot and ankle problems to amputations. The EUR 3.7 million a-footprint project is being led by Glasgow Caledonian University (GCU; Glasgow, Scotland). Researchers worked in partnership with the Maastricht University (Maastricht, the Netherlands) and Danish biomechanical firm AnyBody Technology on what had been named the Glasgow/Maastricht Foot Model.It is estimated that 200 million Europeans suffer from disabling foot and ankle conditions and the model should lead to more efficient orthotic devices, cutting recovery times and reducing symptoms. It will also have aplications in treating flat feet or foot drop - which prevents recovering stroke patients from moving their ankles and toes. GCU's Professor Jim Woodburn, who is the project co-ordinator, said: “Previous to this development, most computer models of the human body ended in a black rectangle - the foot was simply too complicated to model. The Glasgow/Maastricht foot is a game-changer. “It opens the door to a huge range of applications, including the manufacture of better and more efficient orthotics, resulting in quicker recovery times, reduced symptoms and improved functional ability for those suffering from conditions which afflict the foot and lower leg,“ Woodburn said. The simulation can be used to test potential cures as well as developing new orthotic devices, using 3-D printing techniques.

Gene discovery has potential for development of new medicines to prevent the most common fractures . . . A big international study has identified a special gene that regulates bone density and bone strength. The gene can be used as a risk marker for fractures and opens up opportunities for preventive medicine against fractures. The study, led by the Sahlgrenska Academy, University of Gothenburg, Sweden, was published in the journal PLoS Genetics. The international study, which involved more than 50 researchers from Europe, North America and Australia and was led by Associate Professor Mattias Lorentzon and Professor Claes Ohlsson at the Sahlgrenska Academy, University of Gothenburg, is based on extensive genetic analyses of the genetic material of 10,000 patients and experimental studies in mice. Through the combined studies, researchers have succeeded in identifying a special gene, Wnt16, with a strong link to bone density and so-called cortical bone thickness, which is decisive to bone strength. The genetic variation studied by the international research network could predict, for example, the risk of a forearm fracture in a large patient group of older women. “In the experimental study, we could then establish that the gene had a crucial effect on the thickness and density of the femur. In mice without the Wnt16 gene, the strength of the femur was up to 61 per cent lower,“ according to Mattias Lorentzon at the Institute of Medicine, the Sahlgrenska Academy, University of Gothenburg. The discovery opens up opportunities to develop new medicines to prevent the most common fractures. “Low cortical bone mass is a decisive factor in, for example, hip and forearm fractures. Unfortunately, the treatments currently used for brittleness of the bones have very little effect on the cortical bone mass,“ says Mattias Lorentzon. “If we can learn to stimulate the signaling routes of the Wnt16 gene, we could strengthen the skeleton in these parts too, thereby preventing the most common and serious fractures. The discovery of Wnt16 and its regulation of cortical bone mass is therefore very important,“ according to Mattias Lorentzon.

Study of spinal injury data may help surgeons treat injured soldiers and civilians . . . Spinal injuries are among the most disabling conditions affecting wounded members of the U.S. military. Yet until recently, the nature of those injuries had not been adequately explored. In a new study recently published in the Journal of Bone and Joint Surgery (JBJS), a team of orthopedic surgeons reviewed more than eight years of data on back, spinal column, and spinal cord injuries sustained by American military personnel while serving in Iraq or Afghanistan. The injuries were then categorized according to anatomic location, neurological involvement, the cause of the injury, and accompanying wounds. The resulting analysis is an important first step in helping orthopedic surgeons develop treatment plans for these service members, as well as for severely injured civilians who sustain similar disabling injuries. Of 10,979 evacuated combat casualties, 598 (5.45%) sustained a total of 2,101 spinal injuries. Explosions accounted for 56% of spine injuries, motor vehicle collisions for 29%, and gunshots for 15%. Additionally, 92% of all injuries were fractures and 84% of patients sustained their wounds as a result of combat. In 17% of injuries to the spine, the spinal cord also was injured, and 53% of all gunshot wounds to the spine resulted in a spinal cord injury. Spinal injuries were frequently accompanied by injuries to the abdomen, chest, head, and face. “In these current military conflicts, the latest technologies in body armor, helmets, and other protective devices have helped save many soldiers' lives,“ said James Blair, MD, an orthopedic surgery chief resident in the Department of Orthopaedics and Rehabilitation, Brooke Army Medical Center (Fort Sam Houston, Texas). “We also have access to advanced life-saving techniques in the field and medical evacuation strategies that are keeping many more service members alive. “But when a person survives an explosion or vehicle collision, there has still been a great deal of force on the body,“ Blair adds. “Many of those survivors are coming to us with severe injuries to their spine and back. We needed to describe and characterize these injuries so recommendations can be made on how to provide the most effective treatment and rehabilitation for our wounded warriors.“ Although the survival rate is high for such injuries, the disability rate also is quite high. This affects not only the service members, but also their families and the U.S. healthcare system. Therefore, the study's authors note, further research is required to improve future outcomes for those with spinal injuries.

— Compiled by Holland Johnson, MDD Executive Editor