Osseointegrated Implants for Amputees: Reduced Infection Risk
Osseointegrated implants, those press-fitted directly into the femur, are a promising development for those having to undergo amputation. Osseointegration pioneer Munjed Al Muderis, MB ChB, FRACS, FAOrthA, an orthopedic surgeon at Macquarie University Hospital in Sydney, Australia, has just published research in The Journal of Bone and Joint Surgery indicating that there are minimal risks for severe infection with osseointegrated implants.
Dr. Muderis and his colleagues made use of a new infection classification system, and tracked adverse events in 86 patients (91 implants) who received an osseointegrated implant. For each patient, the procedure in two stages: a porous-coated implant was placed in the femur bone, then an opening was created to attach the prosthesis. The results: 31 patients had no side effects or complications related to the osseointegration system, 29 patients developed a grade one or two infection, successfully managed with “simple measures;” 26 patients had no infection, but reported other complications such as problems with the orthopedic hardware, problems with skin and soft tissue, or fracture of the femur bone; there were no patients who experienced a grade three or four infection, according to the June 1 press release.
Dr. Al Muderis told OTW, “The Dutch team visited the designer Dr. Hans Grundi at the same time I visited him in 2009. We both started the process in the same time and established our units separately but with some similarities. We continued to exchange information and ideas throughout the time and we visited each other’s units frequently. Few years ago I suggested to Dr Jan Paul Frolke to unify our protocols and he was positive about it. We started working on this paper and few other projects that will be published in the future.”
“The main highlight of this study that it is for the first time we could establish a proper pathway to identifying infection rate, severity and mode of treatment for osseointegration patients. The classification system that we established would potentially help in making osseointegration for amputees feared less and more accessible to a wider group of surgeons and centers around the world so that more amputees will benefit from it.”
As for what is new about this infection classification system, Dr. Al Muderis said, “Osseointegration surgery has been performed for more than 20 years on amputees in Sweden and Germany, however to date there has not been any uniform way to identify and grade infection with this technique. We have established the OGAAP (Osseointegration Group of Australia Accelerated Protocol), part of which is the infection classification system. It is a simple way to identify, grade and treat any kind of infection in the osseointegrated limb. The classification system is of 0-4 grade and each grade has three modes of treatment except grade 4 where the treatment of choice is explantation (removal of implant).”
“This classification system enables the management of infections associated with osseointegration to be standard and simple even by local medical practitioners, especially that significant percentage of patients live remotely from the osseointegration centers.”
Asked about the simple measures used for the 29 patients who developed an infection, he noted, “Simple measures including short course of oral antibiotics such as Keflex for one week, Epsom salt baths twice per day for 20-30 minutes each and exposure of the skin implant interface to the sun for 20 minutes each day.”
“I would like to make the wider surgical community become more familiar with this technique, its advantages and the risks associated with it. Proper setup of multidisciplinary teams would minimize the risks and secure a more successful outcome of such technology. We are at the bottleneck when it comes to osseointegration. In the not so far future this technology will be readily available to the wider community of amputees if we continue following the measured steps that we are taking.”
As for how other complications (orthopedic hardware, problems with skin and soft tissue, fracture of the femur bone) affect how osseointegration is done in the future, Dr. Al Muderis says, “This technology, like any new technology, is all about calculated risk. The progress in implant design is continuous to make the implant more durable and longer lasting. I am confident that with the new generation of the titanium implants OPL (osseointegration prosthetic limb) system that we have developed the implant strength has significantly increased; also the bone implant interface has become much more biomechanically compatible with less stress shielding and more load distribution along the osseointegration surface. The skin implant interface, we have achieved significant improvements especially with the surface coating of titanium niobium oxides (bacterial repellant) and potentially new generation of coating with nano particles we would achieve less chance of infection. Also the soft tissue surgical technique where we minimize the soft tissue at the skin implant interface bringing the skin as close to the bone end, this helped in reducing the infection rate further with the new generation of bone recessed implants (Type B OPL system) Figure 1.”
“The development of neck of femur supporting implants (Type C OPL System) Figure 2, reduces significantly any chance of bone fractures with osseointegration, this system has the capability to insert a supplement screw into the femoral neck and head as an extra support to the femur from breakage in case of fall or direct trauma to the leg.”
ACL Surgery Not One-Size-Fits-All
Researchers from Hospital for Special Surgery (HSS) and the Sheba Medical Center in Israel have found that when it comes to anterior cruciate ligament (ACL) ruptures, things are pretty nuanced as far as subluxation, load, and the anterolateral ligament. Their work involved 12 cadaver knees that were loaded using a robotic manipulator to simulate clinical tests of the pivot shift and anterior stability. Recordings were taken with the ACL intact, sectioned, and with both the ACL and anterolateral ligament sectioned. The researchers analyzed and studied the in situ loads borne by the ACL and anterolateral ligament in the ACL-intact knee and borne by the anterolateral ligament in the ACL-sectioned knee.
Co-author Ran Thein, M.D. told OTW, “There was broad speculation of the role of the anterolateral capsule, including the anterolateral ligament (ALL), in resisting the pivot at the time that this work was conducted from winter 2014 to summer 2014. Although previous studies indicated that the ALL does resist uniplanar rotatory loads, particularly in knee flexion, no controlled laboratory studies were available at the time addressing the question of whether or not this tissue resists complicated multiplanar loads such as those applied during a pivot shift exam. This study was designed to address this question.”
“We found that the ALL does indeed carry force in the ACL deficient knee in response to multiplanar torques that capture a subset of those applied during a pivot shift exam and during tests of anterior stability. However, we were most interested to find that the ALL, on average, does not begin to engage or start to bear appreciable load until the tibia is subluxed outside of the physiological envelope of motion of the intact knee. This left us questioning the role of the ALL in resisting pivot-type loads in well-reconstructed knees. We were also intrigued by the observation that a small subset of knees (basically one knee in our cohort) was much more reliant on the ALL for resisting subluxation in the ACL-sectioned knee. We speculate that this leaves us with the challenge as surgeons of identifying the small subset of knees who may be more reliant on their ALLs for stability and treating these individuals appropriately. Thus, these findings reinforce the notion that surgical treatment for ACL rupture is not a one-size-fits-all procedure.”
Asked about the challenges involved in running the study, he noted, “This was a time consuming and multidisciplinary study which can be done only when engineers and physicians are working together day and night. I want to acknowledge the hard work of all of my co-authors in this multidisciplinary effort. I am glad I had the opportunity to conduct the study at the Hospital for Special Surgery, where such cross-disciplinary collaboration is fostered, enabling the biomechanics team led by Carl Imhauser, Ph.D. to collaborate closely with sports medicine physicians like Andrew Pearle, M.D. and Thomas Wickiewicz, M.D. from the orthopedic department.”
Cup Placement Matters When it Comes to Loosening
Does location of cup placement affect total hip arthroplasty outcomes in patients with hip dysplasia? “Yes, ” says new work from Mayo Clinic. Chad Watts, M.D., chief resident in Orthopedic Surgery at Mayo Clinic in Rochester, Minnesota, was a co-author on this new research. He told OTW, “This work is a follow-up to previous research on the same cohort of 117 patients with Crowe type-II dysplasia who underwent 145 cemented total hip arthroplasties (THA) between 1969 and 1980. Our goal was to assess the long-term effects of hip center on component loosening and aseptic revision. We had 49 patients (60 hips) who were still alive at a mean of 36 years.”
“We found that recreating an anatomic hip center did improve implant survival, likely due to improved biomechanical forces which can affect interface stress and polyethylene wear. The overall cumulative incidence of aseptic revision at 35 years was 32% for acetabular components and 21% for femoral stems. Those patients who had a high hip center had an increased risk of failure, as we predicted.”
“Importantly, all of the implants in this study were cemented, which is in contrast to contemporary practice. While we don’t have as long of follow-up on uncemented components, it is possible that contemporary implants with biologic fixation and highly cross linked polyethylene may better tolerate a higher hip center. There are a couple of papers suggesting slight superior placement of about one centimeter is well tolerated, particularly if raising the hip center leads to better bony coverage.”
“When confronted with superior acetabular wear, the intraoperative decision would be, ‘Do you try to keep the cup low where the biomechanics are more favorable? Or do you place it superiorly where the bone quality may be better?’ With cemented implants we now know long-term outcomes are better with a lower, more anatomic hip center; we don’t know about uncemented components yet.”
“While our study had follow-up of 36 years, the longest study evaluating hip center using primary uncemented components is about 15 years. It will be important to continue to make similar observations of uncemented components in the upcoming decades. Hopefully these results will help guide orthopaedic surgeons when confronted with acetabular dysplasia.”
