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Primary knee arthroplasty: The pursuit to optimize patient outcomes
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In this second installment of a two-part Round Table discussion, we present a furtherance of advancing technologies that are advertised to enhance patient outcomes after primary total knee arthroplasty (TKA). The reader will appreciate that the opinions offered are not always in agreement, but overall reflect the desire to optimize patient care and long-term outcome.
In this conclusion to the discussion, we address the developments in robotics, patient-specific designs and evidence-based medicine that have impacted optimizing knee arthroplasty procedures.
A. Seth Greenwald, DPhil (Oxon)
Moderator
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A. Seth Greenwald, DPhil (Oxon)
Robert L Barrack, MD
John M. Cuckler, MD
Gerard Engh, MD
Adolph V. Lombardi Jr., MD, FACS
S. David Stulberg, MDA. Seth Greenwald, DPhil (Oxon): The elimination of standard instrumentation through the use of a surgeon-controlled tactile robotic arm with coordinates derived from a preoperative CT-guided bone resection and component placement in unicompartmental knee replacement (UKR) procedures is evolving. What are the upsides and caveats of this optimizing technology?
Robert L. Barrack, MD: Like computer-assisted surgery (CAS), this adds a great deal of time and expense to each case. Consistent clinical results are certainly attainable with modern instrumentation in the hands of experienced surgeons, which make this type of investment hard to justify.
John M. Cuckler, MD: Two forms of robotic surgery for knee arthroplasty are in use or under development: passive and surgeon-controlled technology. Both types of robotic surgery require a preoperative CAT or MRI scan for intraoperative guidance of the robotics.
Passive robotic surgery requires the application of an external frame to the femur and tibia, and initialization of the frame to anatomic landmarks, after which the robot performs the required cuts for the implants. This technology is expensive, adds significant time to the procedure and is not currently approved for use in the United States.
A robotically controlled milling technique for unicondylar arthroplasty has been developed, which “guides” the surgeon’s burr for femoral and tibial preparation (Rio, Mako Surgical). Increased precision in the alignment of the tibial component has been reported; however, no clinical data exist to validate this technique. Concerns exist over the cost and maintenance of the robotic unit and the additional cost of the preoperative CAT scan. This technology is approved in the United States and is currently being used largely as a marketing tool for surgeons and hospitals with this equipment.
The current health care environment may truncate the future of this technology.
Gerard A. Engh, MD: The major benefit of CT-guided bone preparation at the present time is safety. The robotic arm controls the safe zone that the surgeon works within.
The major limitations to this technology are the increased cost and surgical time to complete the surgical procedure.
Adolph V. Lombardi Jr., MD, FACS: The combination of CAS guidance with robotic arms is exciting technology currently in its infancy. This technology involves obtaining a preoperative CT scan, registering appropriate bony landmarks at the time of surgical intervention and then using the robotic arm, which utilizes a haptic field to guide the surgical procedure. The short-term data reveal that this is possible.
Currently, this technology is being utilized in UKA, and early data demonstrate it can be effective in proper orientation and placement of the components. Unfortunately, the UKA designs, which are being utilized with this technology, do not have the best track record of those currently available.
Mobile bearing UKA has demonstrated excellent long-term success from multiple centers. Currently, mobile-bearings represent 80% of the UKAs performed in the United States. Robotic arms have not been adapted to perform this specific arthroplasty. Furthermore, the robotic arms are cumbersome, expensive and time consuming in their present format. It is an exciting and evolving technology that will need to weather the test of time.
S. David Stulberg, MD: The use of robotic-assisted devices in TKA will and should continue to be explored. However, the efficacy, relative to well-designed manual or CAS-navigation instrumentation, of current robotic TKA/UKA devices has yet to be demonstrated and certainly has yet to be associated with improved mid- or long-term clinical outcomes.
The considerable expense of current robotic devices — which are greater than the expense of CAS navigation systems — is lacking supporting outcomes data. At the moment, the robotic devices are being used for marketing purposes in much the same way that minimally invasive surgery was used. As has happened with many of the CAS navigation developments, robotic systems are being used to sell implants. Early adopters of robotic devices should be encouraged to press for the evolution of effective, safe, cost-efficient systems that have open platforms, ie, can be used to insert any implant system.
Patient-specific designs
Greenwald: Patient-specific knee designs utilize a preoperative MRI to construct a 3-D model of the involved knee to assist in component sizing. Through the use of rapid prototyping technology, custom cutting jigs are also produced, which afford specific bone resection. Will this technology optimize initial outcomes and influence long-term procedure durability?
Barrack: The concept of patient-specific instrumentation utilizing preoperative MRI holds the greatest promise of the emerging technologies described in improving the efficiency and consistency of TKA. Overall, 10% to 20% of patients are not happy with the function and pain relief they attain following knee replacement. The cause is unclear, but one of the leading theories is that subtle degrees of malalignment occur in a substantial percentage of patients. There are preliminary clinical data that suggest that more consistent clinical improvement and patient satisfaction can be attained with custom guides. Whether this will consistently improve clinical results compared to standard instrumentation is a question that will require prospective randomized trials to answer. We plan to begin such a trial this year.
The other question is whether the components should be aligned with a mechanical axis model or the so-called flexion/extension axis, which is another issue that would require a similar prospective comparative study.
Cuckler: Patient-specific cutting guides have been reported to produce malalignment of TKA implants. No data exist to clinically validate either patient-specific cutting guides or the efficacy of custom implants; the increased cost of both the preoperative CAT or MRI studies and the custom implants may be the most limiting factor in the widespread adaptation of this technology.
Engh: Patient-specific instrumentation is undergoing rapid adaptation by all the major implant companies. In essence, the registration of bony landmarks is performed preoperatively, which eliminates the need for orientation of cutting blocks intraoperatively with conventional instrumentation. This is much more accurate, as these landmarks can be precisely located on an MRI. Surgical time is reduced and the intramedullary canals are not accessed. Another big advantage is that we know the correct size for the components and therefore can eliminate a great deal of instrumentation from the OR set up.
In terms of optimizing implant and extremity alignment, we should not alter time-honored principles for component alignment. The patient’s mechanical axis should be restored, not the anatomic axis, to minimize the risk of both component loosening and implant wear.
Lombardi: Patient-specific instruments represent a paradigm shift in TKA. However, there are two essential variations.
The majority of the techniques involve scanning, not only the knee but also the hip and the ankle. This allows for determination of appropriate component orientation to restore the mechanical axis, as well as appropriate component positioning in the sagittal plane. On the other hand, rotational alignment of the components can be determined from the MRI or CT scan of the knee.
The controversy involves one specific technology that only relies on an MRI of the knee. A 3-D model of the knee is created from an MRI, osteophytes are removed and shape matching is performed. The patient is, therefore, aligned back to the so-called “pre-arthritic” condition. Since the scan of the hip and ankle are not obtained, there is no information available to restore the mechanical axis.
On the other hand, the majority of systems do respect the mechanical axis, and algorithms are prepared such that the cutting guides are created to assist the surgeon in performing the appropriate resections to restore the mechanical axis and align the femoral component rotationally with the epicondylar axis. While the majority of systems survey the patient-specific desires prior to performance of the plan, only one system allows for active interaction of the surgeon with the planning software.
The surgeon is able to view the plan and modify it according to the specific needs of the patient. Once the plan is approved, the rapid prototyping technology is utilized to create the 3-D model of the patient’s knee. Cutting guides are made to match the patient’s anatomy and, on the femoral side, position the distal femoral resection, determine rotational alignment and place the four-in-one cutting block, and, on the tibia, determine appropriate resection.
Early outcomes of this technology are exciting. The number of outliers is diminished and the ability to restore the mechanical axis is enhanced. While the argument over added cost abounds, there must be consideration for the fact that this technology addresses specific concerns in the immediate operative period.
- First: The more trays that are open, the higher the risk for contamination. Utilizing this technology one can decrease the number of trays opened to perform a knee arthroplasty from six or seven to perhaps one or two. Not only does this reduce contamination to the patient, but it also decreases the burden to central sterile and decreases the number of minutes required to turn the room over between cases.
- Second: There is no capital expenditure. There is no need to bring a computer into the operating room, place pins and arrays and introduce additional personnel who may also contaminate the environment to perform this operative intervention. All of the perioperative planning has been performed prior to the patient even entering the operating room.
- Third: Since the surgeon has reviewed the 3-D anatomy of patient preoperatively, the surgical intervention proceeds in a more efficient manner with reduction in operative time. Not only is this reduction in operative time beneficial for the patient who now spends less time under anesthesia, but it is also beneficial for the hospital since less OR time reduces costs. Additionally, the decrease in OR time before the procedure combined with the decrease in turnover time allows the surgeon to be more efficient and perform perhaps one or two more operative interventions. This results in our ability to take care of the ever-increasing surgical burden of total joint arthroplasty and allows the hospital and, ultimately, the physician to be more profitable.
There are continued refinements in this technique, and certainly the future of this technology is to customize the implants for each specific patient.
Stulberg: Patient-specific knee designs, like CAS navigation and robotic technologies, are stimulating ideas that will encourage us to explore important issues related to TKA/UKA surgery. The marketing of these devices for widespread use is not wise and is likely to be associated with outcomes that are inferior to those achievable with current implants and instruments. Patient-specific designs require a rigorous understanding of the technologies that underlie them and a clear demonstration that outcomes associated with their use justify their use.
Evidence-based medicine
Greenwald: The Centers for Medicare & Medicaid Services (CMS) is increasingly focused on evidence-based outcome studies that confer long-term durability and function, reducing the cost burden of revision. Despite this, will these advantages be affordable in our health care system?
Barrack: The burden will be on surgeons and manufacturers to prove that the investment in additional technology or implant costs can be justified by some tangible clinical benefit and/or increased overall efficiency in lower cost for the entire procedure or episode of care.
Cuckler: Long-term data, greater than 20 years, are necessary to demonstrate significant improvement of existing conventional technologies, designs and instrumentation. Support for such studies may not ever be available under current political and economic conditions.
Engh: We have clear evidence that traditional knee implants with nonirradiated and irradiated polyethylene in an inert environment perform well in our Medicare population and rarely fail from wear. The focus going forward should be to find implants that safely allow higher levels of function and durability and accommodate the more-active lifestyles of a younger patient population. If payers do not adequately reimburse for these more expensive implants, innovation will be stymied. The ultimate cost burden could be greater with subsequent revision surgery.
Lombardi: CMS and the majority of surgeons are focused on evidence-based outcome studies. Surgeons, physicians, insurance carriers and the government all want the best for each and every patient. We are all striving for maximization of implant durability. This desire promotes young minds to innovate and adopt new techniques for delivery of health care.
We are all aware of the ever-increasing demand for TKA. In light of this, we must strive for better articulating surfaces, improved surgical techniques and ways to reduce the time expenditure to perform these operative interventions. We must also enhance the perioperative recovery. It is only by attention to all of these details that we will succeed in taking care of the ever-demanding baby boomer population.
Stulberg: The use of evidence-based outcome tools to guide medical/surgical care is here to stay, whether we like it or not. As a recent editorial in The New England Journal of Medicine suggested, the best use of these tools is as guidelines, not edicts. Unfortunately, it will be much easier for policymakers to install evidence-based outcome tools as requirements and leave physicians and patients to figure out how to work with them to optimize personalized care.
Our best hope is to help fashion tools that incorporate the opportunity for implant/technology development. Surrogate outcome measurements that accurately reflect improvements in technology need to be developed to supplement the conventional outcome measurements embedded in current evidence-based tools. The arthroplasty/joint reconstruction community should be vigorous and proactive in developing, validating and promoting these surrogates in order to assure that new technologies continue to emerge.
Future advances
Greenwald: What lies beyond this discussion in emerging technologies that may further improve knee arthroplasty outcomes in both active and senior patient populations?
Barrack: The quality and consistency of the results of current TKA does not match that of hip replacement: 20% or more of patients are dissatisfied with their level of function and pain relief, and a high percentage of revisions are occurring prior to 5 years with a substantial number related to technical factors.
Our greatest challenge, presently, is not producing the ultra-high performance knee, but achieving a higher degree of consistency and improving surgical technique to maximize functional results and minimize a number of early failures.
Cuckler: Biologic resurfacing of early degenerative changes will become a reality within the next 20 years, thus moving the demand curve for TKR to the right on the timeline. However, the metal-PE resurfacing-type implant will remain the cornerstone for prosthetic management of advanced degenerative joint disease.
Engh: The biggest variable in outcomes with knee implants is the surgeon variable. New technology such as patient-specific instruments should improve the accuracy of bone cuts, but do not restore knee kinematics. When we change the hard tissue anatomy with an implant, we alter the soft tissue balance. Integrating the bone preparation with soft tissue tensioning and sensing devices will evolve and allow the soft tissues to guide knee kinematics, rather than trying to control knee kinematics with posts and cams and constraints built into the components.
Lombardi: We have focused on current implant designs and improved techniques to position these implants in the most minimally traumatic fashion. This will certainly enhance the patient’s early outcomes and should ultimately enhance long-term durability. Unfortunately, kinematically these Charcot joints which we create with metal and plastic leave little to be desired. The challenge for the future is to design implants with new materials that kinematically will approach the normal knee.
Stulberg: I would anticipate that the most successful emerging technologies in joint reconstruction would be built on the foundations of currently available, successful technologies and not on currently exciting but unproven technologies. For example, I would expect that drug-eluting implants would be a feasible and attractive technology development that could be used with current implant designs. However, substances that appear to have a positive effect on articular cartilage degeneration, while appealing and attention getting, are unlikely to alter the natural history of the degenerative diseases being successfully treated by current replacement techniques. I would anticipate that MIS and CAS would continue to develop and interact, but that the acceptance of these technologies will require outcomes, both in terms of clinical efficacy and user efficacy, that are convincing.
For more information:Robert L. Barrack, MD, can be contacted at Washington University School of Medicine, Dept. of Orthopedics, Campus Box 8233, 660 S Euclid Ave., Saint Louis, MO 63110; 314-747-2562; e-mail: pouchera@wudosis.wustl.edu. He is a consultant for and has intellectual property rights with Smith & Nephew.
John M. Cuckler, MD, can be reached at Brookwood Medical Plaza, 513 Brookwood Blvd., Suite 375, Homewood, AL 35209; 205-802-4577; e-mail:juckler@charter.net. He is a consultant for, receives teaching and speaking relationship with and has intellectual property rights with Biomet.
Gerard A. Engh, MD, can be reached at 2501 Parkers Lane, Suite 200, Alexandria, VA 22306; 703-619-4431; e-mail: jerry@andersonclinic.com. He is a consultant for Smith & Nephew and has intellectual property rights with DePuy.
A. Seth Greenwald, D Phil(Oxon), can be reached at Orthopaedic Research Laboratories, 2310 Superior Ave. East, Cleveland, OH 44114; 216-523-7004; e-mail: seth@orl-inc.com.
Adolph V. Lombardi Jr., MD, FACS, can be reached at Joint Implant Surgeons Inc., 7277 Smith’s Mill Road-Suite 200, New Albany, OH 43054: 614-221-6331; e-mail: joanneadams0625@gmail.com. He is a consultant for and has intellectual property rights with Biomet.
S. David Stulberg, MD, can be reached at 680 N. Lake Shore Drive, Suite 924, Chicago, IL 60611; 312-664-6848; e-mail: jointsurg@northwestern.edu. He receives royalties from Biomet.