The Essential Total Knee

Abstract

Osteoarthritis (OA) is the single most common cause of disability in older adults. Total Knee Arthroplasty (TKA) is a surgical procedure that is beneficial to a majority of patients suffering from OA. Still many are not able to access TKA because it is expensive. And yet despite advancement in technology that have driven increase in total costs of knee devices many aspects of these newer design and material components continue to be debated. Logic 1.0 is an all-poly, cruciate retaining total knee device that incorporates essential design features that adhere to basic principles of proven long-term results in order to lower down costs. It is potentially a cost-effective device to resource challenged patients without compromising on good clinical outcomes.

1. Introduction

As early as the JI 9th century surgeons used pig bladder, nylon, and fascia lata to reconstruct damaged knees and apparently without success [1]. It was Fergusson (1860) in the latter part of this century who started the concept of resection arthroplasty. By resecting both articular surfaces of the distal femur and proximal tibia it allowed mobility between the segments with consequent formation of subchondral bone. This also presented with limited success since the procedure resulted in ligamentous laxity and subsequent joint instability.

In the mid-20th century (1958) Macintosh introduced the concept of hemiarthroplasty wherein he implanted acrylic material on the tibial plateau to correct genu varus or valgus. He posited that by correcting deformities of the knee stability may be restored and partially relieve patients of their painful joints.

McKeever introduced metallic plates with fixed tibial plateaus instead of acrylic materials with “good” results. In 1963, bone cement (Polymethyl Methacrylate) was introduced as a fixation device that revolutionized joint arthroplasty. Gunston contributed to a better understanding of the polyethylene ratio which proved vital in developing the “modem” total knee arthroplasty.

In 1969, Dr. John N. Insall along with Dr. Chitrajan Ranawat, Dr. Allan E. Inglis and Peter Walker, PhD developed and introduced the total condylar knee that allowed patients to move their knee naturally and painlessly. The design developed by Insall thus became the forerunner of the modern total knee because this was the first implant to address all aspects of the knee with anatomically shaped components. With its initial clinical success surgeons across the United States began to use them on their patients.

In the 1970s Freeman and colleagues came up with the list of standards that a knee prosthesis must attain: that components of the prosthesis should be unconstrained so that rotational forces and coronal varus-valgus stress cannot be transferred to the bone-implant interface. Freeman stressed that the amount of bony resection should take into account the possibility of performing arthrodesis in the event of failure of the index arthroplasty. Freeman, et al. emphasized the reduction of friction over the metal and polyethylene interface to lessen debris. They suggested that components should be able to spread the loads evenly over the bone-implant interface He advocated the importance of wear debris reduction in the longevity of the implant and emphasized the removal of dead spaces during surgery to prevent infections. Moreover, Freeman stated the importance of ligamentous balancing and achievement of ROIM (five degrees hyperextension to at least 90 degrees of flexion) which are still considered standard procedures in today’s arthroplasty systems.

2. Moving from success to significance

More than 50 years of history of the modern total knee and its clinical results are testimonies to the success of this medical device. Millions of knee arthritic patients worldwide have undergone total knee replacement₂ (TKR) since the 1970’s making this procedure one of the most successful man-made implants. The TKR procedure improves the quality of life for patients as evidenced by improved functional demands and a significant reduction in pain on the affected joint. Rehabilitation following TKR is a key component of its success and therefore progressive improvement in the range of motion and functional ability is observed over several weeks to months following the index surgery [2].

The demand for joint replacement surgery, specifically Total Knee Arthroplasty is expected to increase in many countries. This is largely due to an aging population and the obesity epidemic that knee osteoarthritis (OA) will increase in prevalence to 40% of the elderly population by 2025 [3, 4, 5, 6, 7, 8, 9]. In the U.S., Kurtz et al. predicted a 673% growth for TKR and a 174% increase for Total Hip Replacements from 2005 to 2030 [4]. Similarly, Ignacio et al. forecasted TKR volume of market expansion in the U.S. from 43–855% during the period from 2012 to 2050, respectively [5]. Similar trends in TKR demand are seen in the UK, Canada, Sweden, Australia, and New Zealand are predicted in the next two decades with varying degrees of estimates [6, 7, 8, 9].

While most patients who underwent TKR are satisfied with the results of the procedure there is, however, twenty percent (20%) of patients who are dissatisfied with the outcomes [10].

This lack of patient satisfaction attracts new players into the implant industry offering innovations in all aspects of Total Knee Replacements. Innovations fuel change. Improvement of outcomes can be achieved through implant design, surgical techniques, biomaterial engineering, and enhanced pre-and post-operative care. Patients’ perception of quality of life and the procedure (TKR) are important parameters to measure satisfaction with TKRs [11, 12]. While there is the strong demand side of patient demographics (aging and obesity) that contribute significantly to osteoarthritis there also is the supply side that contributes as a driver to increasing costs of TKR. Global Market Insights (GMI) expects the TKR market to grow at 5% annually until 2030 with an estimated market size of USD 9 Billion in 2022. The Asia and the Pacific region represent potentially an even larger market size as it is where 60 percent of the world’s population live. By mere extrapolation of disease prevalence of degenerative osteoarthritis of the knee, it far outnumbers the population of the U.S. and the rest of the First World population combined [13]. But this is also home to a great number of poor economies where access to high-technology health services is a challenge. Economically, the region as a segment contributes to the highest annual growth of the implant industry at 8% impacted by several factors such as increasing privatization, expanding health insurance penetration, training, and attracting skilled orthopedic surgeons and nurses in the context of an aging population (Global Market Insights).

The WHO has set the world poverty index at USD 2.25 per person per day. While there is wide variability of TKR implant costs ranging from USD 1800 to USD 13,000 [14] the average TKR procedure (including hospital costs and professional fees) in the US alone is USD 24,000.00. If the market and economic forces alone are allowed to determine the availability of this life-improving technology it would ease out more than 90% (Pareto Principle) of the global patients suffering from this debilitating disease because of financial incapacity.

3. The “Modern” TKA

Today the modern condylar design of TKR has undergone subtle changes and still retains much of its original components as described by lnsall. lt consists of a femoral component usually made of cobalt chrome alloy, a metal tibial tray that inserts a UHM PE (ultra-high molecular weight polyethylene) plastic of various sizes and laterality, and a plastic patellar component all of which are grouted into bone using bone cement (PMMA or polymethylmethacrylate). However, there are as many iterations to the design as there are implant manufacturing companies. Proof of this is the expansion of knowledge in the field of knee arthroplasty. Surgical techniques and instrumentation have improved making TKR more surgeon-friendly. New biomaterials are discovered and biomechanical engineering has further our understanding of the kinematics of the human knee joint. Research and development pushed new products into the market. New implant companies have emerged and joined the fray in maximizing profits pushing TKR to.

3.1 USD P27 Billion industry by 2040

Akin to selling cars orthopedic implant companies appeal to different sectors of the market through segmentation strategies, market development, market penetration, etc. But unlike selling cars where the price is apparent and may be negotiated before purchase total knee implant pricing is most of the time hidden from the buyer or the patient. This information asymmetry explains partly the wide price elasticity of the implant across different markets around the globe. Furthermore, like most medical devices hospitals and surgeons negotiate the value of these products to be used on patients. Rarely are patients given the choice or advice as to the kind, type, or cost of implants to be implanted on them.

To be truly significant this device must be made accessible to a greater elderly population since osteoarthritis does not affect only those who can only afford TKA. A paradigm shift is necessary to veer away from market forces brought about by features of the device gleaned from research and development. The explosion of knowledge through open-source information technology has made it possible for surgeons and implant manufacturing companies to flatten the marketplace curve. It is, therefore, possible to rethink TIKA design that can address the needs of a greater population without compromising on quality and profitability. This thinking is counterintuitive. Companies exist to maximize profits from their products. But taking on the business model of Aravind, an enterprise that manufactures intra-ocular lenses (also a man-made device), it is possible to do business at the bottom of the pyramid [15].

4. Connecting the dots and trimming the tree

The purpose of a total knee implant in particular and total knee replacement (TKR) in general is to relieve pain and improve mobility of patients suffering from severe degenerative osteoarthritis of the knee. The ideal implant choice should provide reliable survivorship and functional outcomes while being cost conscious.

After half a century of the modern TKR and millions of successful surgeries that have impacted positively people’s lives worldwide access to this life-improving procedure is still a challenge because of cost. Knee implant cost contributes to almost one-third of the cost of TKIR. Referring to Figure 1 on the Total Knee Replacement Market one can conclude that there are numerous designs, materials, and principles or techniques each espousing superior or better results than the other. Numerous comparisons of laboratory and clinical results are published every year and are now available on the Internet. This technology has made it possible for even start-up ideas and companies to challenge existing norms in the industry.

Figure 1.

Total knee replacement market (taken from GMI).

Random clinical trials are the standard for determining the efficacy and effectiveness of one device or the other, however, long-term results and implant survivorship is the core determinant of success. There is no one perfect TKR device. However, through the robust experiences of arthroplasty surgeons who have trail-blazed new concepts and shared their knowledge we can now with confidence know what works and what does not. It was Steve Jobs who said that we can only connect the dots by looking backward. It is in this spirit of looking backward that we hope to simplify and perhaps make TKR more accessible to more people who suffer from this debilitating disease.

5. Unresolved issues in TIKR

5.1 All-Poly Tibia (APT) versus Metal-Backed Tibia (MBT)

The standard TKR as described above consists of a metal femoral component, a tibial tray (also referred to as metal backed), and a polyethylene plastic that sits on the tibial tray. The articulation between the plastic and the femoral component allows the gliding motion of the femur over the tibial surface, thus, replacing the painful grating between bone on bone in the knee joint.

2Early clinical results of all-polyethylene (AP) monobloc tibial components were good with survival rates up to 10 years or even more [16]. But these early designs had high failure rates of up to 17% at 2 years, due to deformed plastic AP tibial components resulting in delamination and loosening at the implant-tibia interface [17].

In vitro, biomechanical, and laboratory studies of the newer metal-backed tibial components showed decreased tensile strains in the stem and bending of the tibial component. This design afforded a more effective distribution of eccentric loads to the inferior surface of the tibial plastic. Metal backing also afforded the ability to incorporate metal augments for bone loss as opposed to bone grafting with autografts or allografts, potential for porous coating for uncemented use, modularity during polyethylene exchange during surgery or in cases of periprosthetic infections [18]. With these theoretical advantages emanating from laboratory and biomechanical experiments the orthopedic community embraced this design espoused by implant manufacturing companies in Europe and the U.S. Today only 1.4% of all TKAs in the UK use AP tibial components and mostly have been completely phased out [19].

The metal-backed (MB) tibial components are not without their inherent problems. Earlier literature reviews revealed that clinically they have the potential for backside wear increasing volumetric wear of the plastic. This also increased tensile stresses at the bone-implant interface during eccentric loading dispelling earlier laboratory results advocated for this design. Dislodging of the plastic from the metal tray also happened but was not very common necessitating early revisions. Increased bony resection is also required to accommodate a reduced polyethylene thickness. Moreover, the manufacturing costs of tibia designs are higher making them more expensive [20].

Ultra-High Molecular Weight Polyethylene (UHMWPE) continues to be used as a tibial liner. Although ceramic technology is being introduced as an alternative to address volumetric wear it has yet to gain traction in the market. Advances in this area included the use of gas plasma ethyl oxide in sterilization to avoid oxygen-free radical generation. The earlier UHMPE were sterilized using gamma radiation resulting in oxidation and deoxidation of the surface resulting in delamination resulting to early poor clinical results. The introduction of the use of gas plasma sterilization along with vacuum packaging significantly improved the performance of UHMWPE with reduced surface oxidation and better wear performance in vivo [21].

Despite the popularity of metal-backed tibias a few surgeons managed to keep interest in using AP tibial components, especially those in Europe. In the Swedish Knee Arthroplasty Registry [22], the paper reviewed 27,722 cruciate-retaining TKRs using a press-fit condylar prosthesis with either a metal-backed or PE tibia operated between 1999 and 2011. These were followed up for 4.5 years (0–12.5 years). 60.9% were female (16,896), 39.1% were male (10,837). In all cases, 57.7% (16,011) were metal-backed and 42.3% (11,722) were all PE. With revision as an endpoint, the all-polyethylene tibial component had slightly superior, unadjusted 10-year survival compared with 96.6% (95% Cl, 96.2% to 96.9%; p = 0.002). They concluded that these all-polyethylene tibial components were at least as good as or superior to metal-backed tibial components concerning implant survivorship at 10 years in cruciate-retaining total knee replacements” [22].

Recent published reports in 2023, included a total of 14 RCTs with 1367 TKA for all-polyethylene and metal-backed tibial components groups. The all-polyethylene group demonstrated statistically significant differences in five-year survivorship (OR 0.27; 95% CII0.10--0.75; p-value 0.01) and stairs climbing score (OR - 2.07; 95% Cl - 3.27 0.87; p-value 0.0007) when compared to the metal-backed group. Based on the results, the all-polyethylene implant should be considered a viable choice for primary knee replacement [23, 24].

Newer studies have begun highlighting the economic advantages of APT implants, especially in patients undergoing primary, uncomplicated TKA. The use of APT implants in younger patients and those with a body mass index>35 has not been extensively studied, but the existing literature suggests the use of APT implants in these cohorts to be equally acceptable. With modern implant design and instrumentation, rising utilization of TKA along with the current and future economic strain on health care, the increased use of APT implants could result in massive savings without sacrificing positive patient outcomes [23].

3With recent overwhelming evidence pointing to a distinct advantage of APT over M BT in terms of cost savings without sacrificing good clinical results the Essential TKR design, therefore, should include an all polyethylene tibial component over a metal-backed one.

6. Posterior stabilized versus cruciate retaining design

The controversy and debate regarding the superiority of cruciate retaining (CR) versus a posterior stabilized (PS). TKR still rages on. The issue at hand is which design affords greater stability of the knee with good functional outcomes.

To date, many surgeons select a prosthesis based on experience and training [25].

A meta-analysis of 14 RCTs on this topic written by Chao et al. concluded “that PS and CR TKA had no significant difference in Knee Society knee Score (KSS), pain score (KSPS), Hospital for Special Surgery score (HSS), kinematic characteristics including postoperative component alignment, tibial posterior slope and joint line, and complication rate. However, PS TIKA is superior to CR TIKA regarding post-operative knee range of motion (ROM)”. Whether this superiority matters or not in clinical practice still needs further investigation and longer follow-up [26].

While arthroplasty surgeons are familiar with these issues the author believes that choices may go beyond the merits of each design or even the surgeon’s preference. Costs are a strong consideration in countries where access to these technologies is a challenge. Manufacturing costs of an all-poly CR are lesser by 20% compared to a posterior stabilized poly because of a more complex design of the latter. Injection or compression molding of polyethylene is used by certain manufacturers where volume demand is anticipated. The downside is the high cost of production to cover the iterations in the inventory of the plastic tibial components due to the demand for its sizes both in its aspect ratios and thickness. To obviate these manufacturers today utilize CNC (computer numerical control) in manufacturing implants. This results in decreased production cost, increased scalability, and diminished material wastage. CNC enables contour machining of complicated designs including 3D printing. This enabling technology allows surgeons and manufacturers to choose and develop cost-effective, high-quality all poly CR with the confidence of expecting good long-term clinical results [27].

7. Patellar surfacing versus non-patellar resurfacing

The appropriate management of the patella during primary TKA remains debatable. There is a wide divergence of approaches to the patellae during TKA as reflected by differing attitudes of surgeons worldwide. These attitudes are a result of differences in geographic locations and the influence of education and training, influences based on how thick or thin the patient’s patella is, financial considerations, and hospital policies. Majority of North American surgeons routinely resurface patellae during primary TKA while this occurs less (35%) among surgeons outside the U.S. while several research papers on the subject reported similar outcomes for both procedures [28].

Since 2013, more and more RCTs, retrospective studies, and even meta-analyses and systematic reviews have been carried out. Still, no clear conclusion has been drawn [29, 30]. However, from the financial point of view, there is less cost per implant when surgeons do not perform resurfacing making non patellar resurfacing a more attractive option.

8. Symmetrical versus asymmetrical components

According to Bildenglas in his report in the Journal of Arthroplasty regarding this matter, he mentioned that “Despite the excellent success of earlier TKR designs (Total Condylar Knee, J&J) which had symmetrical femoral components, the majority of modern designs feature a more anatomic and asymmetric femoral prosthesis. A raised phalange, an angle trochlear groove, or both are thought to improve patellar tracking. Laboratory studies, however, suggest that surgical technique may be a dominant factor in determining patella-femoral kinematics. The component design has not been proven to be significant. A prosthesis with asymmetric femoral components may cost more”.

The literature reviewed in this article found no advantage of asymmetric anatomic femoral designs over symmetrical femoral components in primary TKR [31]. Similarly, Ashril, et al., published in the Knee Journal an analysis of 185 TKR (95 Kinematic and 87 Kinemax plus knees) performed between 1991 and 1993. The difference in design introduced a broader trochlear groove, and from an asymmetric to a symmetrical femoral component. All patients were followed up for 5 years using the Bristol. Knee Scoring and radiographs. The results showed no difference between the two groups scor s (85 vs. 86). However, the symmetrical trochlear group performed greater improvement in ROM (14 vs. 4 degrees; P < 0.05). It concluded that symmetrical femoral components with off set patella diminished patella-femoral complications without detectable disadvantage versus the anatomic asymmetrical design [32].

On the other hand, universal tibial implants whether metal backed or all-poly monoblock designs can be places on either left or right proximal tibias. Outcomes studies of this design are numerous and attest to its longevity, long eveity and good clinical results [33]. This design also affords decrease inventory and instrumentation do not adversely affect outcomes [34]. And some studies show improved proximal tibia coverage, less risk for over-stuffing, better rotation using symmetrical tibial implants [33, 35].

9. Essential total knee design

More than half a century of good clinical results, since lnsall and his colleagues introduced the “modern “total knee, is a testimony to the success of this procedure. Since then several design concepts and features have been introduced into the market to address the 20% “dissatisfaction” of patients from their artificial knees. Many critical papers use outcomes-based results on patients’ perceptions of their problems. And yet the orthopedic community still utilizes several scoring methods to define success without concurrence as to objective functional results versus the patient’s subjective experience of TKA. From the macro-economic perspective, there is also the demand to create more value for TIKA as this is expected to increase in the next half century with the exponential increase of the elderly population worldwide.

Total Knee Replacement is an expensive procedure. This is not accessible to more than half of the world’s elderly considering that most of these surgeries are performed in more affluent economies. However, the author personally believes that TKA is too good not to be shared with everyone who needs it.

Research and development drive costs. Every new development imputed on the design of TKA also increases its cost. Still, controversies abound because in hindsight open access to orthopedic knowledge has questioned and compared the long-term clinical results of one design principle to the other. By distilling orthopedic knowledge and being critical of costs it is possible to design TKA that is cost effective.

The Essential Total Knee is an all-polyethylene symmetrical component with a minimum of 10 mm thickness with a single, central post and flanged to resist rotational and torsional forces. It is cruciate retaining and unconstrained. Metal-backing in this design is removed to lower the cost of production and the total cost of the implant.

The femoral component may or not be symmetrical although a symmetrical femoral design is more cost effective in terms of inventory considerations as it does away with having stock a left or right side. The aspect ratios of these components have to be taken into consideration depending on the race of the host knee. Asian knees are generally more circular than Caucasian or Black African knees [34, 36, 37]. The Essential Knee is non-patellar resurfacing TKA. Intuitively, this design consideration will remove the need for patellar resurfacing instruments and lower total costs by eliminating plastic patellar button inventory.

There has been renewed interest in cementless total knees, but currently, the majority of these procedures are cemented [38]. However, cementless systems are more expensive as the manufacturing process entails more complicated steps to ensure the ingrowth of bone into the implant. It also must utilize the metal backing of the PE insert as bones do not grow into plastic. Although P PMA must be used as grouting material on both the femoral and tibial components in the Essential Knee design its cost only covers 3–5% of the latter’s total knee system.

By incorporating these design concepts in total knee replacement, the cost of the implant is effectively decreased by at least 60 to 70 percent. As in any company, market forces entail that their products must be able to maximize profits to offer value to its owners or shareholders. A lower-cost implant, however, can still maintain a profitable margin while making available these implants to a greater number of patients through cost incentives.

The Essential Knee principles are incorporated in this Logic 1.0 TKA system designed and developed by Dr. Rene Catan. Since ₄2013, over 300 patients have received this implant performed over several hospital operating theaters. Logic 1.0 is an all-poly, cruciate-retaining total knee, non-patellar resurfacing device that incorporates essential design features that adhere to the basic principles of proven long-term results at lower costs. It is an cost effective device for resource-challenged patients without compromising on good clinical outcomes.

4In a study conducted by the author, a total of 72 implants were followed up on 62 patients with three-year follow-up. Ten (10) patients received bilateral knee replacements at index surgery. Thirty-five (35) implants were fitted in the left knee while 37 implants were fixed in the right. The study group is comprised of 22.5% men and 77.4% women with a male-to-female ratio of 1:3. The mean age of the patients was 69.4 years at index surgery. One (1) had revision for periprosthetic joint infection and one (1) had patellar instability resulting in a complication rate of 1.38% each. Performance at 3 years is 98.61% successful. A comparison of means AKSS using Student’s T test with significance at p < 0.05 before surgery and after 3 years follow-up was done. Clinical AKSS improved from 48.46 to 94.29 (p-value 0.0031) before TKA and at 3 years follow-up, respectively.

Functional AKSS score improved from 44.99 to 93. 49 (p-value 0.028) and the range of motion likewise increased from 88.82” to 106.53” (p-value 0.0350). The author concluded showed excellent outcomes in terms of performance (98.61%), increased range of motion of the knee, improved clinical results, and enhanced functionality of patients [39].

10. Information gap

The author believes that the physician’s primary role in treating his patients includes making his services available to those who need them. Because who is there to treat if there are no patients?

Access to health services, therefore, is key in the context of health delivery. Many of us have gone on medical missions in far-flung places or even advocated for our patients in our local health facility because we believe and subscribe individually to the Hippocratic Oath of “using my power to help the sick to the best of my ability and judgment”.

Ability is a result of constant training and education. Judgment comes from experience, and wisdom to be able to choose from the body of scientific knowledge for the benefit of our patients. Unfortunately, Surgeons are unable to discern which of two similar products is more expensive because we are swayed by marketing strategies highlighting newer technologies imputed on the product rather than its results.

2Thus, controversies still abound in TKA implant design. This suggests a dearth of knowledge of the cost of the device. According to Gardezi, et al.,” This may result in a surgeon, consciously or subconsciously, choosing a less expensive product over a more expensive one, yet functionally similar. Or recommending a product to patients or hospitals if pricing and cost-benefit analysis are available in decision-making product over a more expensive, yet functionally-similar product, or vice versa₂, or recommending The financial impact of this on patients could be substantial, as medical device costs can vary drastically between similar products. Increased transparency and education regarding medical device costs could help to better address and mitigate this knowledge gap” [40].