Top story of 2008: Future TKA may include ‘smart’ implants, alternative bearing surfaces

An article in the November/December issue of Orthopaedics Today Europe titled, “Future TKA may see ‘smart’ implants and new alternative bearing surfaces,” was the most-read Orthopaedics Today Europe article in 2008 on our Web site, ORTHOSuperSite.com.

To determine the top-read articles of 2008 from Orthopaedics Today Europe, the editors calculated the number of times an article was opened on the ORTHOSuperSite.com Web site (ie, the number of “hits” that article received). The Web site contains articles from Orthopaedics Today Europe, Orthopedics Today (the U.S. edition), and the peer-reviewed journals Orthopedics and The Journal of Knee Surgery.

Below, we included a list and short overview of the top 5 most-read articles from Orthopaedics Today Europe that appeared on our Web site in 2008. We hope you enjoy the range of topics represented, and please use the key phrase listed at the end of each article to find the complete stories posted on our Web site.

– Robert Trace,
Orthopaedics Today Europe Managing Editor

1. The future of TKA: Smart implants, new bearings

Although a cobalt chromium femoral component on a polyethylene tibial component remains the gold standard for total knee replacement, the future may include the use of innovative alternative bearings and “smart” implants.

In an article that first appeared in the November/December issue of Orthopaedics Today Europe, Jean-Yves Jenny, MD, of Illkirch-Graffenstaden, France, noted that the main problem with the current gold standard is polyethylene (PE) wear. While some researchers have found lower wear rates with highly crosslinked PE, variance exists between PE components.

Conventional cobalt-chromium is placed on a polyethylene TKR. Image: Jenny J-Y

“Highly crosslinked polyethylene may be more frequently used in the future, when the cost increase is contained,” Jenny said. “This might be the case because the technology of polyethylene is not very costly. On the other hand, alternative materials for femoral components might remain experimental because of the problem of increased cost, except for patients with allergy problems.”

He highlighted alumina as the only real alternative for the metallic femoral component and noted that some researchers believe that it might exhibit good wear resistance.

Zirconium-coated components could provide another alternative, he said. Although an in vitro study from researchers in Japan showed that zirconium-coated femoral explants were not destroyed by a PE gliding surface, another study revealed a statistically higher rate of radiolucent lines at the tibial site when using these implants.

In the future, smart implants could also help surgeons improve TKR.

“A smart implant is anything that is going to communicate information to the heath care provider,” William M. Mihalko, MD, PhD, said. “That information can be anything from the serial and catalog number of the implant to forces, wear and number of gait cycles, which can give the surgeon some type of idea if that patient is starting down a pattern of aseptic loosening or severe wear.”

The implants could make it easier to track patients and identify those with recalled implants. However, he cited cost as an overriding factor to implementation.

2. Long-term ACL results similar in patients treated operatively, conservatively

Dutch patients who underwent anterior cruciate ligament reconstruction (ACL) for a ligament rupture showed 10-year results that were similar to those of patients who received conservative care, according to a paper presented at the American Academy of Orthopaedic Surgeons 75th Annual Meeting in early 2008.

The only significant difference between the two groups was in the level of stability; patients who received bone-patella-tendon-bone (BPTB) ACL reconstruction had higher stability marks. Both groups presented with a high number of meniscal lesions, said Duncan Meuffels, MD, of the Erasmus University Medical Center in Rotterdam, Netherlands.

The two groups of patients were pair-matched based on age, gender and Tegner activity score before injury. Fifty patients were pair-matched for the investigation.

“We found no statistically significant difference between patients treated conservatively and those treated with surgery, according to objective and subjective functional outcomes, degenerative changes in the knee or other lesions involving the knee,” he said. “The only difference we could see was that the patients who were treated operatively had better stability of the knee and a 1-point higher Tegner score.”

There was no significant difference among the groups in the one-leg hop test results collected post-treatment. There was, however, a 48% incidence of osteoarthritis symptoms in the operative group vs. 28% in the conservative group, although the researchers said they will continue to follow this.

“The stabilized knee does not yet seem to give rise to more radiographic OA at this long-term follow-up,” he said.

3. The potential of plasma-rich growth factors explored

Some surgeons are looking to biologic treatment options, such as plasma rich in growth factors, to aid in the healing of orthopaedic surgery and trauma cases.

In his editorial in the September/October issue of Orthopaedics Today Europe, Ramon Cugat, MD, PhD, of Barcelona, noted that growth factors, or growth differentiation factors (GDFs), are soluble, diffusible polypeptides that control the differentiation, growth and phenotype of many different types of cells. Growth factors attach to specific membrane receptors on a cell’s surface to transmit a specific signal, such as migration, differentiation or activation. Each growth factor has one or more specific actions in a specific cell depending on the environmental circumstances, Cugat wrote. Growth factors are multifunctional and are involved in cell regeneration and repair and regulate key cell processes.

Ramon Cugat

Made by platelets, macrophages and endothelial cells, platelet-derived growth factors (PDGFs) are proteins that are stored in platelets’ alpha granules and are released when the platelets are grouped together. Recent research on tendons indicated that the PRGF hastens tendon cell proliferation, plays a role in the synthesis of Type I collagen and has an angiogenetic action.

“In conclusion, much research and many clinical applications have been carried out in the 43 years since Marshall Urist discovered BMP-7, and a field of research and therapeutical applications seems to be opening up,” Cugat wrote. “However, coinciding with reflections made by Sanchez et al, it is fundamental to arrive at a consensus about the technique for obtaining PRGF and to agree on the final biological efficiency of PRGF.

“Of course, we must standardize procedures and perform more well-designed clinical trials to help further evaluation of the therapeutic impact of PRGF,” he wrote.

4. VTE rate after total hip arthroplasty decreased with 35-day drug regimen

The results of a phase-3 study show a substantial reduction in venous thromboembolic events after elective total hip arthroplasty using a novel prophylactic regimen for 35 days compared to a 12-day regimen using enoxaparin.

The investigators also found no significant increase in complications using the extended rivaroxaban (Xarelto) treatment, an oral, direct Factor Xa inhibitor being developed by Bayer HealthCare AG and Johnson Pharmaceutical Research & Development LLC.

“In major venous thromboembolism (VTE) … it is associated with an 80% reduction in the frequency of symptomatic VTE, but there was no significant increase in bleeding complications associated with continuing prophylaxis for up to 35 days,” said Ajay K. Kakkar, PhD, FRCS, a co-author of the RECORD2 trial (Regulation of Coagulation in Major Orthopaedic surgery reducing the Risk of DVT and PE).

The investigators also discovered a 5.1% incidence of major VTE in the enoxaparin group compared to a 0.6% incidence for the rivaroxaban group.

Patients in the rivaroxaban group received 10 mg once daily of the pharmacologic, starting 6 to 8 hours postoperatively, and continued the regimen for 35±4 days. The comparison group received a subcutaneous injection of enoxaparin (40 mg once daily) for 12±2 days postoperatively, and began their treatment the night before surgery.

In addition, the results of the RECORD1 trial, which compared the outcomes of both prophylactic regimens for 35±4 days after THA, revealed a 3.7% total VTE rate with enoxaparin and a 1.1% rate with rivaroxaban. That study also showed that rivaroxaban substantially reduced the incidence of major VTE from 2.0% to 0.2%.

“This is the first study to compare extended prophylaxis for 35 days with rivaroxaban vs. enoxaparin,” said Bengt Eriksson, MD, a co-author of the RECORD2 trial. “The primary endpoint was reduced by 70% with rivaroxaban compared to enoxaparin. This was also consistent with the results seen for major VTE … and there was no indication of any compromise in safety.”

5. Most patients should expect TKR implants to activate airport security systems

British investigators reported that patients with total knee replacements are more likely to set off walk-through airport security scanners because of the metal in their implants.

Consequently, their orthopaedists and family practitioners can help by warning them that this may occur and what they should expect at the next level of airport security, said lead investigator Iain McNamara, MRCS, of the University of Cambridge, England.

Investigators found that 90% of patients experienced their implants setting off walk-through airport detectors.

Data from a British study showed that 90% of orthopaedic implants were detected by hand-held and arched walk-through scanners like these at a London airport. Image: McNamara I

“If it was a bilateral total knee replacement (TKR), then this number went to 100%,” McNamara said during his presentation at the 9th European Federation of National Associations of Orthopaedics and Traumatology Congress in Nice.

The study consisted of a phone survey of patients who underwent TKR within a 2-year period and a live test at a London airport involving several loose orthopaedic implants and patient volunteers with various implants.

“Interestingly, of those patients who had unicompartmental knee replacements (UKRs), either one side or both sides performed, none … actually activated the metal detectors,” he said.

Investigators also examined how sensitive security systems were to non-elective implants, such as titanium trauma implants.

Investigators surveyed 150 patients (61 men, 89 women) who had 111 TKRs, 20 UKRs, 17 bilateral TKRs and two bilateral UKRs.

Among them, 69 patients had flown on airplanes since their knee surgery and 47 patients had a TKR, 90% of which activated walk-through detectors.

According to results of the telephone survey, “More than 60% of our patients felt anxious about being stopped at security and also the possibility of a physical examination and public embarrassment,” McNamara said.

When asked whether they would like to receive a card to show airport security personnel stating they have a metal prosthesis, more than 80% said they would, particularly if it enabled them to bypass the larger, more public scanners and be checked individually with a handheld scanner or in private.