ABSTRACT:
Total knee arthroplasty (TKA) is the gold standard to treat degenerative knee
joint conditions that do not improve with conservative treatment, and it yields
excellent clinical and functional outcomes. However, a small proportion of
patients report some dissatisfaction with their knees after surgery. Recently,
TKA underwent significant technological development with the introduction of new
biomechanical concepts and the incorporation of techniques to improve surgical
procedures. Moreover, the evolution in implant designs optimized for the
individual characteristics of the patients enables better surgical
customization. The current article presents the concepts, advantages, and
limitations to the development of customized implants, as well as TKA surgical
techniques involving automation (robotics) and computer-assisted navigation.
Although the medical literature showing promising outcomes with new TKA
technolo- gies is extensive, studies with longer follow-up and appropriate
methodologies are required to contribute to the demonstration of advantages in
knee arthroplasty outcomes.
Keywords: arthroplasty, replacement, knee; osteoarthritis, knee; prostheses and implants; robot surgery.
RESUMO:
A artroplastia total de joelho (ATJ) é o procedimento padrão-ouro para o
tratamento das patologias degenerativas articulares do joelho sem melhora com o
tratamento conservador, e resulta em desfechos clínicos e funcionais excelentes.
No entanto, uma parcela pequena dos pacientes relata alguma insatisfação com
seus joelhos após as cirurgias. Neste contexto, nos últimos anos, o
desenvolvimento tecnológico associado a este tratamento tem passado por
relevante introdução de novos conceitos biomecânicos e incorporações de
tecnologias que buscam o aprimoramento das técnicas cirúrgicas associado à
evolução de desenhos de implantes que otimizem as características individuais
dos pacientes para permitir melhor customização cirúrgica. O objetivo deste
artigo é apresentar conceitos, vantagens e limitações associadas ao
desenvolvimento dos implantes customizados, além das técnicas cirúrgicas de ATJ
associada à automação (robótica) e à navegação assistida por computação. Ainda
que exista ampla literatura médica que demonstra resultados promissores com as
novas tecnologias nas cirurgias de ATJ, são necessários estudos com maior
seguimento e metodologias adequadas a fim de contribuir com a demonstração de
vantagens nos desfechos cirúrgicos nas artroplastias de joelho.
Palavras-chave: artroplastia do joelho; cirurgia robótica; osteoartrite do joelho; próteses e implantes.
| Citation: Luzo MVM, Ferreira MC, Mestriner AB, de Palma IM, da Silveira Franciozi CE, Kubota MS. Technological Innovation in Total Knee Arthroplasty: Navigation, Robotics, and Customization. 60(4):1. doi:10.1055/s-0045-1810044 |
| Note: Study developed at the Knee Surgery Group, Department of Orthopedics and Traumatology, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil. |
| Financial Support The authors declare that they did not receive financial support from agencies in the public, private, or non-profit sectors to conduct the present study. |
|
Conflict of Interests
The authors have no conflict of interests to declare. |
| Received: February 05 2025; Accepted: March 27 2025 |
INTRODUCTION
Total knee arthroplasty (TKA) is the gold-standard surgery for the final stage of gonarthrosis. Even though its clinical outcomes are mostly favorable, it is estimated that approximately 10% of the patients remain dissatisfied with the procedure.1,2
Given the growing demand for TKA and its increasing performance on young adult patients,3 there is a clear need and search for higher-quality surgical outcomes aiming at implant longevity, a more physiological perception of the joint, better lower limb functionality, and less surgical trauma.4
In this context, new technological advances, such as specific instrumentation, guides, and computer-assisted (navigated) and/or automated (robotic) surgery, seek better customization. Moreover, these advances consider the phys- iology and balance of each patient’s ligaments to improve three-dimensional surgical planning, increasing the accura- cy of alignment and implant positioning.4
These concepts are being presented and introduced into the arthroplasty care market to improve the mechanical understanding of the lower limb, the articular and functional mapping of the knee, and the precision and surgical reliability to increase patient satisfaction. However, since the incorporation of new technologies usually increases costs, surgeons need to understand TKA innovations to develop a critical sense about their practices and visualize the proper use of these new tools to improve surgical outcomes.5,6
The present article aims to describe the new technologies in TKA, which involve navigation, robotics, and customized implants, as well as to discuss their current concepts, advantages, and limitations, to help the reader identify how they may contribute to technical development and improve TKA outcomes.
Customized Implants
The first devices for knee arthroplasty were introduced in the 1970s. Since then, they have undergone several changes, including surgical technique and implant design.7 An implant is based on the anatomical dimensional parameters of a defined population group, which may lead to inadequacies in the fit of prosthetic components to the joint anatomy in other populations. Studies involving non-Caucasian populations, such as Indians, Chinese, Malaysians, and Koreans, for example,8–12 have demonstrated diverse anthropometric relationships that differ from those presented by Caucasians. The comparison of these populations showed significant discrepancies in commercial prosthesis models, which can have a direct effect on arthroplasty outcomes.8–12 Anatomy can vary with gender, ethnicity, biotype, and acquired phenotypic alterations.
Technological development promotes more “personalized” orthopedic therapies focused on the specific conditions of each subject. Although a contemporary trend, therapeutic individualization dates to Hippocrates, who said, “It is more important to know what sort of person has a disease than to know what sort of disease a person has.”13
Individualized medicine is increasingly present in arthroplasty to obtain better outcomes. Personalized TKA is encouraged by four main pillars: 1) a mechanical axis better adapted to individual biomechanics14,15 2) anatomical variations that do not fit into predefined implant formats due to joint phenotypic variability; 3) technological evolution enabling better knowledge and intraoperative biomechanical assessment; and 4) commercial pressure from manufacturers to mass-market their new products.16
Customized components with physiological coating respect geometry and bone limits, avoiding anatomical hyperor hypodimensioning and reducing the chances of impacts and friction in soft tissues or lack of adequate joint coverage, resulting in more physiological kinematics. However, even when advocating for individualized anatomophysiological joint restoration, it is necessary to reflect that, at times, the natural biomechanics of a given patient may be a causal or risk factor for joint pain and dysfunction.
Customized implants enable personalized definitions of the trochlear groove, favoring patellofemoral kinematics regardless of femoral condylar shapes, which can be manufactured with individual curvature radii. This customization enhances the kinematic benefit of the implant and may contribute to reducing the need for compensation to modify femoral rotation and balance the flexion gap. This condition depends on the absence of ligamentous tension asymmetries requiring soft tissue release to reestablish gap balance.17–19
The physiological and anatomical reestablishment of the posterior condylar curvature increases the flexion and extension gaps. It is worth highlighting the influence of the femoral condylar curvature radius, as its relationship with the posterior capsule also interferes with the dimensioning of the extension gap, a condition the surgeon must keep in mind when dimensioning the offset during arthroplasty planning in patients with flexed or hyperextended knees.20,21 For a physiological arthroplasty, in which the patient does not perceive their “artificial” knee in daily routines, a specific questionnaire has been developed to measure this outcome.22
Conceptually, customized TKA should maintain or seek to restore: 1) the perception of a normal joint; 2) “functional” biomechanics (when the native anatomy is not deemed pathological), namely: a) native kinematic axes; b) native orientation of the joint line; c) native tension of soft tissues; and d) native joint kinematics and kinetics during daily activities; 3) adequate mechanical stress transfer between interfaces; 4) native articular range of motion; 5) macroand microstability of the joint; 6) polyethylene resistance to wear and solid implant fixation, contributing to its survival without activity restriction; and 7) provide fast and complication-free recovery.2
Customized implants gave rise to new conceptual challenges to the TKA classic technical principles, which are binary between the measured resection and the gap-balancing techniques.23 As such, Lee et al.24 proposed a new concept dissociated from the principles of sections perpendicular to the femoral and tibial mechanical axes and called it kinematic alignment; it aims to obtain a joint profile closer to that of the native joint by recreating the three kinematic axes of the knee, which are parallel and perpendicular to the native articular lines. Later, other concepts were introduced, including the inverted kinematic alignment, unrestricted kinematic alignment, functional alignment, and modified kinematic alignment.24,25 All of these new technical definitions share the manipulation of more “physiological” joint tensions and lines and potential bone section compensations for small asymmetries in ligament tensions. In other words, we now question the concepts previously established by Insall et al.26 as to whether to restore all native anatomy and ligament laxity. Technological innovations, such as computer-assisted surgery (CAS) and automation, have favored new perceptions and understandings, leading to the current conceptual development for a patient-specific approach, and are promising for optimizing TKA evolution and outcomes. It is worth emphasizing that Krackow, Krena, and Hungerford conceived the concept of anatomical alignment in the 1980s for use with prosthesis preserving the posterior cruciate ligament. This concept was forgotten, largely due to the premature wear of the polished polyethylene used at the time. The advent of new and better materials and the incorporation of navigation-assisted technology and robotics have resulted in a better understanding and use of the anatomical alignment technique.25
We must mention that the customized TKA concept does not have universal application. In many patients, degenerative arthritic disease can lead to joint and limb deformities and anatomical and biomechanical variations, such as shortening and lengthening of soft tissues and extraand intraarticular deformities that make it difficult or impossible to identify physiological kinematics to be restored. In addition, analyzing whether the patient’s anatomical and physiological mechanical condition can negatively interfere with the implant’s longevity requires critical judgment.27 Therefore, Vendittoli et al.2 stated that customized TKA does not mean reproducing the patient’s anatomy routinely, but offers a more qualified surgical solution to address the disease with a personalized implant technology.
Given all the considerations and advantageous theoretical concepts on customized implants, we still need further clinical evidence to demonstrate superior outcomes of these implants. Müller et al.28 and Saeed et al.29 demonstrated that customized TKA did not yield benefits superior to those of conventional implants, and they found a higher early revision rate among personalized implants. Moret et al.30 did not find significant differences in clinical outcomes between customized and conventional implants. However, personalized implants presented better alignment to the neutral axis of the limb, with better adjustment and positioning.
It is worth emphasizing the need for better research methodologies and study designs in prospective comparisons between personalized and conventional implants to clarify the understanding of the outcomes of customized and classic surgical techniques.
Computer-Assisted (Navigated) and Automated (Robotic) Arthroplasty
In the late 1970s and early 1980s, surgical and biomechanical concepts on resulting limb alignment and ligament balancing after knee arthroplasty showed greater scientific solidity, favoring the development of better implants and optimizing surgical performance.26 The early 1990s witnessed the development of the surgical technique for computer-assisted (CA)-TKA. The principle of this technology is the identification of intraoperative anatomical references, such as the centers of the femoral head, of the knee, and of the ankle, providing real-time frontal and lateral views of the mechanical axis of the lower limb for better intraoperative control of the patient’s limb axis. The first navigated TKA was performed on January 21, 1997.31 This technology aims to facilitate the anatomomechanical interpretation of the patient’s limb, favoring the technical decisions taken by the surgeon to define the best strategy for joint kinematics and implant positioning.
Navigation-assisted TKAs have evolved technologically and have enabled the surgeon to intraoperatively identify much more than the final resulting limb axis, as they now enable the precise angulation of the femoral and tibial sections, the rotational positioning of the femoral and tibial components, the dimensions of the extension and flexion gaps, and the sizing of the implants. The introduction of CA technology into TKA has enable surgeons to have a broader understanding, better intraoperative joint control, and greater procedural accuracy in planning; this knowledge has contributed to the development of new mechanical concepts of the resulting limb alignment.25 As such, the concepts of femoral and tibial sections, previously perpendicular to the mechanical axis in conventional mechanical alignment, became more flexible. This flexibility enables joint stability by reducing or avoiding soft tissue releases, that is, enabling a “thin” bone section adjustment compensating for small ligament imbalances through the inclination of the joint line about the mechanical axis, being closer to the anatomy of the native knee.14
Identifying the potential to increase the accuracy of CATKA with surgical precision to perform bone sections, robotic orthopedic surgery has undergone significant development in recent years. In addition, it has managed to increase the quality and practicality of the procedure.32
Robotic TKA (rTKA) uses software to convert the patient’s anatomical records into a three-dimensional knee joint reconstruction, enabling the surgeon to plan the procedure and perform the sections precisely. Therefore, rTKA is a surgical technique uniting CA navigation and robotic automation assistance for the positioning and/or performance of the sections.14,32–34 There are two rTKA subgroups: active (autonomous) rTKA, in which automation is complete and independent of the surgeon’s action to perform the planned femoral and tibial sections, and semiactive (semiautonomous) robotic system, which is more widespread globally and currently available in Brazil, in which the surgeon has the overall control of bone resection assisted by the precision of automation through the positioning of bone-cutting guides or by a robotic arm helping the surgeon control the force, range of reach, and direction of the saw blade within programmed limits.34
In a summarized and succinct manner, the main conceptual difference between CA-TKA and rTKA is that the former is a procedure in which the surgeon positions the guides and performs the sections assisted by computer monitoring. And rTKA is a CA-TKA assisted by automation regarding the positioning of cutting guides and/or the performance of the bone sections. The main benefit of rTKA is the precise and reproducible bone sections due to a robotic interface, regardless of the system. In addition, it enables the measurement of gaps according to the planning of the bone sections and the implant positioning during surgery.4 The main advantages of rTKA are the accuracy of bone sections as planned, contributing to the ideal implant positioning and joint balance by the exact measurement of the flexion and extension gaps.
There are no absolute indications or contraindications for rTKA or CA-TKA. Nonetheless, these technologies stand out and have an advantage over the conventional technique in patients with diaphyseal bone deformities and intramedullary rods, which hinder the classic surgery.
Patients with joint deformities and bone defects can also benefit from navigation, as this technology enables the surgeon to visualize the multiple possibilities of sections and implant sizing during planning and intraoperatively.
Some automation systems depend on preoperative radiographic examination for the software to interpret the threedimensional joint reconstruction that will match the anatomical points identified by the surgeon. However, depending on the robotic CA system, the surgery may not require prior radiological mapping, enabling the capture of all anatomical references and spatial identification of the knee and lower limb during the procedure.
It is worth noting that CA-TKA enables precise critical control of many concepts and technical elements relevant to the functional behavior of the knee to promote mechanical and kinematic predictability to the operated limb before and after bone sections, including:- The posterior sagittal tibial slope to form the flexion gap;
- The degree of rotation of the femoral component to equalize the flexion gap between the medial and lateral femorotibial compartments and potential notching of the anterior femoral cortex;
- The dimensioning and proportionality between the extension and flexion gaps according to the dimensions of the femoral component and the tibial polyethylene;
- The size of the femoral component and its relationship with the dimensioning of the flexion gap;
- The positioning of the femoral implant in the sagittal plane;
- The ability to interchange the femoral and tibial implants;
- The resulting angulation of the lower limb about the mechanical axis per planned adjustments;
- The resulting sagittal of the lower limb in neutral, recurved, or flexed positions;
- The dimensioning of the distal and posterior femoral and proximal tibial sections;
- The height of the joint interline;
- The equalization of the flexion and extension gaps; and
- Polyethylene dimensioning.
The literature35–38 presents favorable and promising outcomes regarding the ability of this technology to result in greater precision of the components, soft tissue protection, greater patient satisfaction, short learning curve, ideal ergonomic design, and lower levels of fatigue for the surgeon and surgical team. Other studies have demonstrated clinical outcomes similar to those of the conventional techniques. In a systematic review analyzing more than 6 thousand patients, Onggo et al.32 concluded that rTKA and conventional TKA are reliable, safe, and yield good outcomes, even though the final limb alignment is more accurate with robotics. A review by Mancino et al.39 found an advantage for the rTKA group in terms of the initial functional outcomes and radiolucency lines compared to the group submitted to the conventional procedure. They reported no significant differences between the two groups in terms of overall survival, revision rate, and operative time. In their systematic review and meta-analysis of 12 randomized clinical studies involving more than 2 thousand patients, Ruangsomboon et al.40 concluded that, although rTKA probably results in better radiological accuracy than the conventional technique, this outcome may not have clinical significance.
A recent systematic review by Nogalo et al.41 explored complications in robotic arthroplasties. The main complications observed were metaphyseal fractures in the fixation holes of the navigation reflector pins, with ~ 1.4% occurring around the twelfth postoperative week. The incidence rate of infection at the reflection pin and accessory incision sites was of 0.47%.42 It is worth emphasizing that robotic surgery is safe. Nonetheless, complications may occur and are more related to the surgical technique than a direct consequence of the technology.43
Final Considerations
Given the considerations addressed in the current study regarding the purposes of incorporating new technologies and technical concepts into TKA, the advances are promising. Still, further studies with higher-quality methodologies and longer follow-up periods are required to understand the medium and long-term technical advantages regarding the clinical outcomes and, consequently, to enable the development of better techniques and practices for knee arthroplasties.
