Keywords
arthroplasty, replacement, knee - osteoarthritis, knee - prostheses and implants -
robot surgery
Palavras-chave
artroplastia do joelho - cirurgia robótica - osteoartrite do joelho - próteses e implantes
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 physiology and balance of each
patient's ligaments to improve three-dimensional surgical planning, increasing the
accuracy 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]
[9]
[10]
[11]
[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]
[9]
[10]
[11]
[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 biomechanics[14]
[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 hyper- or 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]
[18]
[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) macro- and 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 extra- and 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
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 CA-TKA 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]
[33]
[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 three-dimensional 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 literature[35]
[36]
[37]
[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.
Bibliographical Record
Marcus Vinicius Malheiros Luzo, Marcio de Castro Ferreira, Alexandre Barbieri Mestriner,
Idemar Monteiro de Palma, Carlos Eduardo da Silveira Franciozi, Marcelo Seiji Kubota.
Technological Innovation in Total Knee Arthroplasty: Navigation, Robotics, and Customization.
Rev Bras Ortop (Sao Paulo) 2025; 60: s00451810044.
DOI: 10.1055/s-0045-1810044
