Medical Device Daily Associate
CHICAGO – While the benefits of less-invasive knee replacement surgery may not be as dramatic as some direct-to-consumer advertising may claim, a panel of doctors at a session at the American Academy of Orthopaedic Surgeons (AAOS; Rosemont, Illinois) noted that the procedure has resulted in less scarring, diminished pain and faster recoveries for select patients.
The panel of experts discussed both the pros and cons of the increasingly popular procedure, how orthopedic surgeons are attempting to meet patients' growing demand for shorter incisions, and whether the less-invasive approach will ever totally take the place of traditional knee replacement surgery.
“I'd like to make the contention that advances in surgical technique, surgical instruments and the implants themselves allow many, but not all total knee replacements to be done with smaller skin incisions, and less cutting of the tendon and the muscle around the knee,“ said Robert Booth, MD, chief of orthopedic surgery at Pennsylvania Hospital (Philadelphia).
Less-invasive knee replacement surgery involves an incision of three to four inches as opposed to the 8-inch to 10-inch incision required for traditional surgery. Surgeons attempt to reach the knee without cutting into tendons, muscles and other tissues around the knee.
Booth described several of the different minimally invasive methods for performing minimally invasive surgical total knee replacement (MIS TKR). The first one he discussed was a mini medial arthrotomy (a surgical incision of a joint), a procedure in which an incision is made in the quadriceps about one to one-and-a-half inches above the knee cap.
Another approach, called the mini midvastus, involves an arthrotomy that goes up to the superior fold of the patella and then a short split of about one inch in the quadriceps.
Another promising approach he described is called the Quad-Sparing total knee replacement, which is trademarked by Zimmer (Warsaw, Indiana). This procedure involves a 3-inch to 5-inch incision, which extends up to the superior fold of the patella but entirely avoids the quad tendon and muscles altogether.
The final procedure he described is called the mini subvastus approach which involves making a short incision in the medial side of the knee joint capsule, with the remainder of the incision being made under the quadriceps muscle.
He said that at this time, “surgeons continue to debate the relative merits of each of those techniques, and each surgeon may associate various pluses and minuses with the various approaches.“
For MIS TKR, Booth said his institution uses the latter of the aforementioned techniques.
“I like to utilize that because I think it makes sense on an anatomic basis as it does preserve the quadriceps's muscle and tendon.“ He also noted that it makes sense on a scientific basis “because there are some randomized controlled trials that have been published on the subvastus approach that show that it does at least have some short-term benefits over the standard knee replacement.“
Booth told Medical Device Daily that he believes that while one approach may ultimately prove to be better than the others “there will probably be room for multiple approaches because each individual patient's needs may vary and dictate a different procedure.“ He added that while companies like Zimmer may attract more orthopedic surgeons to their Quad-Sparing technique due to its well-funded training program, the scientific data will ultimately dictate which procedure separates itself from the pack.
While he believes that minimally invasive total knee replacement is a good option for some patients, Booth acknowledged that it still has a ways to go before it can supplant the standard knee replacement procedure, which he noted “enjoys a demonstrated excellent track record that has proven reliable, reproducible and safe,“ stretching back more than three decades.
He also noted that less-invasive surgeries can take two- to three-times longer to perform than traditional operations, even if a surgeon has years of experience performing them. The protracted surgery may increase the risk of infections, blood clots and other complications, though these issues have not been a widespread problem up to this point.
Thus far these additional risks have not been a problem, according to Booth, though he emphasized the need for more evidence-based data on the efficacy of less-invasive surgery to determine if the procedure has long-term benefits for patients.
Additionally, he said, not all patients are good candidates for MIS TKR. Factors that he said may rule out some patients include prior surgery on the same knee, obesity, a recent history of deep vein thrombosis and other unstable medical conditions.
While there are still questions about MIS TKR, Booth predicted that within the next decade, “I think about half of all patients will be getting MIS operations on their knees.“
Presenting what he said was a “mildly dissenting view“ on MIS TKR was Mark Pagnano, MD, associate professor of orthopedics at the Mayo Clinic College of Medicine (Rochester, Minnesota).
Like the traditional surgery, he said the less-invasive approach has many of the same risks like infection and blood clots. But smaller incisions mean surgeons have to operate in a more compact area with a reduced field of vision.
“Any time surgery is performed with a smaller incision, the surgeon has fewer visual clues to guide them on techniques, such as the appropriate placement of the implant,“ said Pagnano. “Particular care must be taken during surgery not to damage tissue around the knee.“
He said reliable computer-assisted navigation systems are imperative to make the procedure safer when visibility is compromised. The length of the incision, however, is the least important factor in the successful outcome of the procedure. Smaller incisions necessitate more force on the tissues that may inhibit wound healing.
While medical device companies are fueling the demand for the procedure by advertising directly to patients, both experts agreed that smaller is not always better across the board. “Not every patient is right for the procedure,“ stressed Pagnano. “Patients who are obese, have a very stiff knee or a high degree of knee damage are not candidates for less-invasive knee replacement.“
He said what's not being talked about now is the great long-term success rate of the standard TKR procedure, only the length of the incision, length of hospital stay and time to recovery.
“Many surgeons show pictures of patients . . . being able to lift their leg right after the operation. That doesn't matter to me as much as whether my knee is going to last 20 years. We have to prove that [MIS TKR] really makes a difference not just in the short- term, but also in the long-term,“ he said, noting that the data thus far is not conclusive and that the debate needs to shift from techniques to results.
Despite his reservations about MIS TKR, Pagnano opined that as in hip replacement surgery, minimally invasive approaches will ultimately become the standard of care for TKR, particularly because a growing number of patients, perhaps spurred on by advertising, will demand it.
Booth mentioned that one positive outcome of the direct-to-consumer advertising is that patients are coming in earlier to get surgery; this can translate into a more successful operation.
Both doctors said that while the less-invasive approach to TKR has many advantages, it may be quite some time before it completely replaces the traditional method.
“Certainly not in the foreseeable future, as long as you have people who are overweight or who have already undergone multiple operations on their knee,“ said Pagnano. “But as techniques improve and evolve, we hope to make this type of surgery available to a wider range of patients.“