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Primary knee arthroplasty: The pursuit to optimize and document patient outcomes
The success of knee replacement procedures has contributed to its widening application to younger, more active patient populations in the United States and globally. While pain relief and restoration of function remain the two cardinal rules of these procedures, there is increasing emphasis on in vivo device longevity as well as the continuity of successful patient outcomes. With advancing knee replacement technologies and their additional costs, procedure reimbursement from both Centers for Medicare and Medicaid Services (CMS) and private insurers is dependent on the assurance of good intermediate and long-term patient outcome.
In this first installment of a two-part Round Table discussion, we address some of these technologies and their relevance to optimizing knee arthroplasty procedures. It brings together four orthopedic surgeons whose collective experiences are intended to provide reader insight into realizing this goal.
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, MDSeth Greenwald, DPhil (Oxon): With the past as prologue, what knee designs and material choices offer the prospect of long-term in vivo durability?
Robert L. Barrack, MD: There is good data to support a minimally constrained, condylar resurfacing-type component, cemented, with a keel or I-beams stemmed tibial component. The current standard femoral component is cobalt chromium (CoCr), the tibia can be titanium alloy or CoCr, but should have a durable locking mechanism and smooth backside to minimize wear.
John M. Cuckler, MD: Highly crosslinked polyethylene (PE) is now being marketed by multiple manufacturers for tibial inserts. Second-generation crosslinked PE tibial bearings are also now available. Thus far, there are no clinical data to validate the use of these materials; however, substantial data exists from in vitro testing to suggest that these materials may improve the long-term results of total knee arthroplasty (TKA). Long-term follow-up will be necessary to validate the results of these tests.
Alternate materials for the femoral-tibial wear couple are also marketed or in development. The principle alternate material currently commercially available is surface oxidized zirconium (ZrO [Oxinium, Smith & Nephew]). Laboratory data from knee simulator testing suggests that this material reduces wear of conventional PE by approximately 50%. However, a recent report found no difference in wear between CoCr and ZrO in TKR based on characterization of number and size of PE particles in joint fluid. Simulator testing of wear comparing CoCr with ZrO against highly crosslinked PE suggests that highly crosslinked PE has a larger effect on wear reduction than that of ZrO.
No clinical data exist to show improvement in clinical results when comparing mobile- vs. fixed-bearing TKA. No decrease in PE wear has been realized for mobile bearings through in vitro wear studies for TKA, although reduction in PE wear has been reported for unicondylar knee replacement with mobile bearings. Complications of mobile bearing designs include bearing dislocation, fracture and osteolysis. Mobile bearing designs are more expensive than conventional fixed bearing TKAs, and are more demanding of gap balancing technique.
Gerard Engh, MD: We now have clear evidence that with good PE the prospect of long-term durability is excellent for both fixed- and mobile bearing designs with partial and full knee arthroplasty.
The problems of fatigue wear have been corrected with sterilization processes that eliminate the formation of free radicals and subsequent susceptibility to oxidation that can reduce the mechanical toughness of PE. The established benefits of reduced abrasive wear of total hip implants with newer highly crosslinked PE remains unproven with total knee components.
Adolph V. Lombardi Jr., MD, FACS: With respect to long-term in vivo durability of TKA, the bearing surface remains the Achilles’ heel. In the face of appropriate alignment, aseptic loosening without wear and osteolysis is relatively unknown. Over the past 10 to 15 years much has been learned with respect to PE manufacturing techniques.
One manufacturing technique of PE which has exhibited excellent long-term durability is direct compression molding. Multiple reports of several different designs that utilize direct compression molded PE have demonstrated minimal wear, even in articulations that have been described as flat-on-flat surfaces.
Techniques of direct compression PE molding have now been adapted to modular bearings with the hope of enhancing the durability of modular systems. These modular systems have been plagued by concerns over backside wear. However, recent data has emerged demonstrating a significant decrease in the severity and intensity of backside wear in direct compression molded PE inserts.
In addition to direct compression molded PE there has been a great deal of work in the field of highly crosslinked PE. The original highly crosslinked PEs required melting in order to quench the free radicals. This melting process affected the mechanical properties of the PE. Newer techniques have evolved that allow for the use of vitamin E to quench the free radicals. Highly crosslinked PE that has been treated with vitamin E to quench the free radicals demonstrates mechanical properties similar to conventional PE. The superior wear and mechanical properties of this material have been demonstrated extensively in the laboratory and offer promise for improved articulation in both total hip and knee arthroplasty.
S. David Stulberg, MD: I think that we need to recognize that the 15- to 20-year survivorship of primary TKA performed by experienced surgeons using both cruciate retaining and cruciate sacrificing implants and instruments designed and manufactured in the late 1980s and early 1990s is between 90% and 95%. The many implant and surgical technique modifications currently being proposed and evaluated must offer evidence that this level of survivorship will be increased. Although patients undergoing TKA 15 to 20 years ago may have been less active, older and smaller than a significant number of patients currently undergoing TKA, and though the expectations of those early patients may have been lower than those of current patients, the impact of these factors (activity, age, size) on TKA durability is not clearly understood. Therefore, any claim that new implant and instrument designs will positively affect durability in the presence of these factors must not be overstated.
The characteristics of knee design which are associated with long-term in vivo durability include:
- articular surface congruency of either cruciate retaining or posterior stabilized implants;
- minimal motion between the PE and tibial base plate or elimination of motion, as in monoblock implants;
- non-aged, compression molded PE with moderate crosslinking, sterilized in an inert environment;
- CoCr tibial and CoCr or ceramic coated (Oxinium) femoral components;
- mobile bearing implants; and
- congruous, capacious patellar-femoral designs.
In order to be associated with long-term in vivo durability, these designs must be inserted with instrumentation that assures consistent alignment, soft tissue balance in flexion and extension and appropriate stability.
New concepts currently being explored — including high-flexion designs, highly crosslinked PE, custom-made implant and instrument designs, navigation and robotic-assisted instrumentation — must achieve or surpass the results obtained with the design characteristics obtainable by the implant and instrument systems with established clinical results.
Knee pathologies
Greenwald: What specific knee pathologies influence your choice of implant?
Barrack: While I prefer a cruciate retaining component for the majority of primary knees, I will utilize a cruciate substituting design in patients with more than mild flexion contracture, and more than moderate degrees of varus or valgus as well as for post-patellectomy patients.
Cuckler: A posterior stabilized, cruciate sacrificing, design is preferred for the majority of patients, as better correction of flexion contractures is obtained with the posterior stabilized designs. More normal roll-back is observed with these designs. Severe deformity and inflammatory arthritis are relative indications for posterior stabilized designs.
Young patients, those under age 65, with minimal deformity are good candidates for cruciate retaining designs as bone stock will be preserved for future revision surgery.
Engh: I am a strong advocate for partial knee arthroplasty for those patients that do not have clear evidence of significant pathology on both sides of the knee. Knees with degenerative arthritis fail either in progressive varus or valgus.
The unloaded compartment in many cases of degenerative arthritis rarely shows the significant changes that warrant a full knee arthroplasty.
I believe we will see substantial growth in the unicondylar market as surgeons gain experience with unicondylar and bicondylar implants and as new technologies are developed to ensure component positioning, alignment and fixation.
In my practice, total knee implants are primarily for patients who have clear degenerative changes in both tibiofemoral compartments. Age-related changes such as yellowing or mild fraying of cartilage are not indications for full knee arthroplasty. Fixed angular deformity greater than 10°, flexion contractures greater than 15°, and/or knee flexion less than 100° are best served with TKA. I also favor partial knee implants in patients with attenuated or even absent ACLs, unless they have clinical episodes of knee instability.
Lombardi: Whether to retain or sacrifice and substitute for the PCL remains an ongoing controversy in TKA. The pathological approach to the PCL decision can influence one’s choice of implants. While the majority of knees can be performed with cruciate retaining devices, those knees with rather significant deformity, either varus or valgus combined with flexion contracture, may be handled best with a cruciate substituting device.
Occasionally, a patient presents with incompetence of the medial or lateral collateral ligament or with a rather significant valgus malalignment which may require the use of a more stabilized implant such as a posterior stabilized constrained device.
Stulberg: Knee pathologies which influence my choice of implants include: bone stock status; preoperative range of motion less than 20° to 30°; presence of fixed angular deformity, flexion greater than 20°; varus/valgus greater than 20+°; neurologic abnormality; extra-articular deformity; and the presence of TKA implants
Pain management
Greenwald: Can multimodal pain management protocols following primary TKA influence longer-term patient outcomes?
Barrack: The greatest impact of multimodal pain management is improving the patient’s level of comfort and satisfaction with the perioperative experience.
It is possible that optimal multimodal protocols will lower the incidence of problems with long-term stiffness and associated discomfort; however, there is not sufficient long-term data to support this at the present time.
Cuckler: There is no evidence that improved pain management strategies affect the long-term outcome of TKA. Hospital stay may be shortened; early postoperative rehabilitation may be facilitated, and improved patient satisfaction may result.
No single strategy has been demonstrated superior to another; improvements in anesthetic techniques (regional anesthetic) and the use of selective nerve blocks are probably the most efficacious pain management changes.
Engh: I don’t believe multimodal pain management has any influence in the longevity of a knee implant. Recovery is quicker and the hospital stay shorter. The outcome in terms of knee function and range of motion may be improved, but these benefits do not equate to better durability of the implant.
Lombardi: Perhaps the most significant success of the minimally invasive movement has been the establishment of multimodal pain management protocols following primary total joint arthroplasty. These are designed to effectively treat the patient’s acute perioperative pain and usually involve a combination of an oral anti-inflammatory agent, a regional anesthetic, a local anesthetic and oral narcotic therapy. These protocols have demonstrated high success and significant patient satisfaction.
Patients whose arthroplasty is performed utilizing a multimodal pain management protocol generally seem to have a positive attitude about their perioperative care. Since outcomes are generally the perception of the patient, there may be an ongoing perception by the patient of a satisfactory outcome based on the diminution of pain and discomfort experienced at the time of the surgical procedure. This would be an indirect influence on long-term patient outcome.
There are no direct influences on long-term patient outcomes secondary to multimodal pain management.
Stulberg: Pain management programs that focus on the perioperative period can help patients achieve early range of motion greater than 90° and can help patients overcome early fears of rehabilitation. Well-designed pain management programs can also reduce nausea, a common deterrent to effect early rehabilitation efforts. These effects can have an impact on longer-term function.
Moreover, some patients who have inadequate pain management in the first few weeks following surgery can struggle with their recovery. These patients can often be helped with aggressive pain management intervention, including in selected cases, re-admission and the use of regional anesthetics.
Computer assisted surgery
Greenwald: Do computer-assisted surgery (CAS) systems assure good intermediate- and long-term results, or are they of doubtful clinical benefit?
Barrack: The data on the clinical benefit of CAS is not compelling. A number of studies show a higher degree of consistency in attaining coronal alignment with fewer outliers; however, there is no convincing evidence that this has been a clinical benefit in terms of function or longevity. In addition, most studies do not support improvement in rotational alignment, which is probably at least as important clinically as coronal alignment. I believe there are inherent inaccuracies in CAS due to variability in the registration of landmarks. Also, I do not believe that the additional time and expense warrant its use at the current time except in clinical trials or among experts that are trying to develop this technology.
Cuckler: Substantial data exist demonstrating improvements in alignment of TKA implants using computed navigation guidance. However, no improvement in clinical results has been demonstrated at short- to intermediate-term follow-up. In addition, concerns have arisen over the increased cost of computer navigation compared with a conventional technique, which will probably doom the technology given the current status of declining reimbursement for joint replacement procedures.
Complications of computer navigation reportedly include postoperative fracture through holes in the femur and tibia resulting from the reference guides necessary for this technique. Concerns have been expressed over the learning curve, initialization technique, cost, accuracy, and the effects of case volume on the precision of CAS.
Engh: At the present time, the clinical benefits are doubtful with surgical navigation. An experienced surgeon is quite good at navigation and soft tissue balance without CAS. The experienced surgeon is also quite good at relatively accurate registration of anatomic landmarks. The occasional arthroplasty surgeon finds that navigation adds complexity to the surgical procedure which increases surgical time and potential errors.
Lombardi: CAS systems have arisen out of the need to enhance the surgeon’s technical ability to perform TKA. While one recent manuscript has suggested that the restoration of the mechanical axis is not imperative for long-term success of TKA, the majority of articles and conventional wisdom have demonstrated that restoration of mechanical axis is significant to the long- term durability and success of TKA.
With this premise, CAS systems have been developed to increase the accuracy of placement. Indeed multiple reports have been published demonstrating that the number of outliers is significantly decreased when CAS systems are utilized over standard mechanical intramedullary and extramedullary alignment systems. This significant decrease in the number of outliers should enhance the overall performance of the TKA. This, however, has not been demonstrated definitively in the literature.
The most significant drawback to CAS systems is the fact that anatomic landmarks must be identified by the surgeon and registered with the computer. Pins must be placed and secured, operative time is always increased and there is not only an associated cost for the computer, but also for the increased operative time.
Stulberg: CAS systems do not assure clinical results. Thus far, a positive impact of CAS on clinical function has not been convincingly demonstrated. However, the use of CAS by knee surgeons familiar with the principles and goals of TKA surgery has been shown to be associated with implant and limb alignment that is highly consistent and accurate (ie, achieves the goals sought by the surgeons).
In addition, CAS has been associated with a number of positive developments in TKA surgery, including: improved use of manual instruments by surgeons familiar with CAS techniques; retention of accuracy of implant and limb alignment when combined with MIS techniques; improvements in manual instrument design; and expanded opportunities for instruction of knee surgery.
CAS technologies are the foundation for currently evolving custom-made implants and instruments and for emerging robotic technologies. Surgeons familiar with CAS navigation will be in the best position to understand and utilize these newer CAS technologies. Current CAS navigation tools are still cumbersome and time consuming for the inexperienced user. However, the use of computer technologies in TKA surgery is here to stay.
Minimally invasive surgery
Greenwald: What is the influence of minimally invasive surgery (MIS) on long-term knee implant durability?
Barrack: MIS surgery has the potential to improve short-term patient satisfaction and return to function. There is no evidence that there is any clinical advantage beyond 3 to 6 months. A far greater concern is the potential for an increase in short-term failures due to malalignment, instability and marginal fixation.
The results of MIS are probably more predictable when performed by experienced, higher-volume surgeons. Patient selection is a factor and patients with complex deformities or those with previous incisions, high body mass index or fragile skin are among groups that should be avoided.
Cuckler: There are no data to suggest that MIS techniques improve the durability of the TKA. MIS surgery produces a shorter scar — perhaps a cosmetic advantage — but is performed at the risk of implant malposition, wound complications and imprecise soft tissue balance.
Engh: The long-term durability of knee implants certainly is not improved and probably is negatively impacted with minimally invasive techniques.
The advantages, if any, are possibly a quicker recovery and a smaller scar. When exposure is altered as with MIS, the potential for component malposition, soft tissue injury and altered fixation are increased. Any of these could have a deleterious impact on implant survivorship. I know of no study that even suggests that long-term durability will be improved.
Surgeons use MIS because the patient perceives a quicker recovery with less pain. High-volume surgeons are capable of performing MIS surgery safely, but I believe it would be ludicrous to suggest that MIS improves long-term durability.
Lombardi: The most significant benefit derived from MIS movement has been a better understanding of the perioperative process. Surgeons have learned the necessity to pay particular attention in the preoperative period to understanding the expectations of the patient and aligning the goals and expectations of the patient, family and surgeon.
During the operative intervention, not only have surgeons paid enhanced attention to minimizing trauma to the soft tissues, they have also come to the understanding that a local anesthetic injected into the soft tissues can be extremely beneficial to managing the acute postoperative pain. Surgeons and patients interested in MIS have also forced anesthesia to develop new protocols for regional and local anesthetics. These regimens have effectively changed the entire perioperative experience for the patients. It has certainly led to enhancement in patient satisfaction.
Having said this, the surgeon should not be a slave to the length of the incision. It is more important to implant the components in proper position and alignment than to minimize the surgical incision. It is better for the patient and surgeon to focus the other aspects of the MIS movement which have effectively improved the perioperative process for all of our patients.
Stulberg: As currently conceived, small incision surgery to implant conventional TKA devices does not alter either short- or long-term patient outcomes. The use of small incision surgery to insert unicompartmental devices, however, appears to be possible without compromising clinical or radiographic results and may be beneficial.
The application of small incision surgery has produced some positive benefits including: improvements in instrumentation; the recognition that patellar eversion is not necessary or perhaps even desirable; establishing multimodal pain management programs and an emphasis on the role of effective pain management; the development of rapid rehabilitation programs; and the acceptance by patients that rapid recovery is achievable and desirable after TKA.
Unfortunately, the marketing of the concepts of MIS-TKA has resulted in many cases in confusing patients with regard to the issues important to the safe and effective performance of TKA.
Editor’s note: See Part 2 of the Round Table in our January 2010 issue.
For more information:
- Robert A. 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 receives royalties from Smith & Nephew and research support from Stryker, Biomet, Smith & Nephew Wright Medical, MCS and Medtronic.
- John M. Cuckler, MD, can be reached at Brookwood Medical Plaza, 513 Brookwood Blvd. Suite 375, Homewood, AL 35209; 205-802-4577; e-mail: jcuckler@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.
- 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: lombardiav@joint-surgeons.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.