INTRAOPERATIVE ASSESSMENT OF COMPONENTS IN NAVIGATED KNEE ARTHROPLASTY IN THE ELDERLY

ABSTRACT

Objective:

This study aims to evaluate the sizing and positioning of femoral and tibial components in Primary Total Knee Arthroplasty (TKA) procedures conducted at the Instituto Ortopédico de Goiânia (IOG), Goiânia, Goiás Brazil.

Methodology:

Elderly patients undergoing primary TKA with the use of SCORE® prostheses and the Amplivision Navigation System were included in the study. The size and positioning of the femoral and tibial components were analyzed. Data collection was performed using the Amplivision system and statistical analysis was conducted using Minitab21 software. The study was approved by the Ethics Committee and is in accordance with the Brazilian General Data Protection Law (LGPD).

Results:

All patients received the SCORE® prosthesis, with a higher prevalence of procedures on the right knee (60%). No statistically significant differences were observed in the positioning of femoral and tibial components.

Conclusion:

Surgical navigation proved to be effective in optimizing the sizing and positioning of implants, contributing to the technical quality of the procedure and the durability of prosthetic components. Level of Evidence: III, Cross-Sectional Observational Study.

INTRODUCTION

Total knee arthroplasty (TKA) is one of the most frequently performed orthopedic procedures worldwide, primarily indicated for the management of end-stage knee osteoarthritis. With the progressive aging of the population and increasing life expectancy, the demand for TKA continues to rise. Despite its high success rates, the procedure's long-term outcomes are closely dependent on the accurate restoration of limb alignment, joint line positioning, and soft tissue balance. Failures in achieving these parameters have been associated with accelerated wear, aseptic loosening, instability, persistent pain, and early revision surgery. ^1,2

Traditional mechanical alignment techniques in TKA aim to place components perpendicular to the mechanical axis of the lower limb. While this approach has been the gold standard for decades, recent evidence suggests that a one-size-fits-all alignment philosophy may neglect patient-specific variations in joint anatomy and kinematics, potentially compromising postoperative satisfaction and functionality ^3,4 . This has led to the emergence of personalized alignment strategies, such as kinematic and functional alignment, which attempt to restore the native pre-arthritic alignment of the knee ⁵ .

The advent of computer-assisted surgery (CAS), and more specifically, navigation systems, has revolutionized the technical execution of TKA. Navigation technologies employ infrared tracking, 3D mapping, and real-time visual feedback to guide bone cuts and component placement with sub-millimetric precision. These systems register anatomical landmarks and construct a virtual model of the joint, allowing surgeons to assess and modify surgical parameters intraoperatively without reliance on intramedullary guides ^6,7 .

Among the many benefits of navigation-assisted TKA are the increased accuracy of component alignment, reduction in outliers, elimination of intramedullary instrumentation (which may reduce embolic complications), and adaptability to different alignment philosophies. Studies have demonstrated that navigation can lead to improved load distribution, better joint mechanics, and more natural gait patterns when compared to conventional techniques ^8–10 . Moreover, by providing objective intraoperative data, navigation systems contribute to standardizing the surgical procedure and may serve as valuable tools for training and quality control.

Despite these advantages, the incorporation of navigation systems into routine clinical practice remains uneven globally, particularly in developing countries. Barriers such as cost, learning curve, lack of training infrastructure, and limited high-quality local data have restricted its widespread adoption. In Brazil, few institutions systematically apply navigation in primary TKA, and even fewer have documented their clinical experiences using implant-specific protocols.

To address this gap, the present study was conducted at the Instituto Ortopédico de Goiânia (IOG), a high-complexity orthopedic center. The main objective is to evaluate the sizing and positioning of femoral and tibial components in primary TKA procedures performed using the Amplivision® navigation system in conjunction with the SCORE® prosthesis. These data are essential to determine the reliability and reproducibility of navigated TKA in the Brazilian clinical setting, with direct implications for surgical training, patient safety, and implant durability.

The justification for this study rests on the growing body of international evidence supporting navigated TKA as a superior alternative in terms of technical precision and patient-specific customization ^11–14 . However, the extrapolation of these findings to the Brazilian population and local health systems requires regionally validated data. By documenting objective metrics of implant positioning, this research seeks to inform best practices, contribute to clinical guidelines, and encourage evidence-based integration of navigation technologies in orthopedic centers across the country.

Expected outcomes include confirmation of high levels of accuracy in component placement using navigation, with minimal variation in sizing and alignment parameters. The study also aims to reinforce the feasibility of navigation as a viable strategy for improving long-term outcomes and reducing the rate of technical complications in TKA.

METHODOLOGY

Study Design and Participants

This study employed a quantitative, observational, and descriptive research design, conducted at the Instituto Ortopédico de Goiânia (IOG), a high-complexity orthopedic referral center located in Goiânia, Brazil. The institution is recognized for its expertise in joint reconstruction procedures and the implementation of advanced surgical technologies. The investigation specifically targeted elderly patients undergoing primary total knee arthroplasty (TKA), with all procedures performed using computer-assisted navigation systems to ensure precision in component sizing and positioning.

The sample included 83 elderly individuals (mean age: 70.10 years), composed of 62 females (75.29%) and 21 males (24.71%). With respect to laterality, 51 procedures (60%) were performed on the right knee and 34 procedures (40%) on the left.

Ethical Considerations

This study was approved by the Research Ethics Committee UFG under protocol number 3.845.175 and conducted in full accordance with the ethical principles established by the Declaration of Helsinki (2013 revision), which governs research involving human subjects. In addition, the study complied with Brazilian national ethical regulations, particularly Resolution No. 466/2012 of the National Health Council, which outlines guidelines for research involving human beings, and Law No. 13.709/2018 – the General Data Protection Law (Lei Geral de Proteção de Dados – LGPD), ensuring the confidentiality, privacy, and protection of personal data.

All participants were informed about the objectives, procedures, potential risks, and benefits of the study, and voluntarily signed a written informed consent form prior to their inclusion in the research. The confidentiality of all collected data was guaranteed throughout the study, with secure storage and restricted access in accordance with data protection protocols.

Inclusion and Exclusion Criteria

The inclusion criteria established for this study encompassed patients aged 60 years or older, with a confirmed clinical and radiographic diagnosis of primary knee osteoarthritis, and a clear indication for primary total knee arthroplasty (TKA). Eligible participants were those who underwent the procedure using the SCORE® prosthesis in combination with the AMPLIVISION® computer-assisted navigation system, and who had voluntarily signed a written informed consent form, authorizing their participation and the use of their data for research purposes.

Conversely, individuals were excluded from the study if they had undergone revision TKA procedures or if they received implants other than the SCORE® system. Patients diagnosed with inflammatory joint diseases (e.g., rheumatoid arthritis) or secondary osteoarthritis (due to trauma or metabolic conditions) were also excluded, as were those presenting with significant extra-articular deformities that could interfere with the reliability of navigation-based alignment assessments. Additional exclusion criteria included the presence of cognitive or neurological impairments that might compromise the ability to provide informed consent or adhere to postoperative evaluations, as well as cases with incomplete or invalid intraoperative data generated by the navigation system.

Surgical System and Prosthesis

All surgical procedures included in this study were performed using the SCORE® total knee arthroplasty system, manufactured by Amplitude Surgical (Valence, France). This prosthesis features a high congruity rotating platform design, which promotes greater articular stability, reduces polyethylene wear, and accommodates the anatomical variability commonly observed in elderly patients. Its biomechanical characteristics aim to optimize joint function and increase implant longevity.

Intraoperative guidance was provided by the AMPLIVISION® navigation system, an advanced, wireless, real-time 3D optical tracking platform that enhances surgical precision. The system uses infrared technology and reflective markers to register key anatomical landmarks and track the spatial positioning of instruments and bone structures throughout the procedure. This allows for accurate measurement of implant size and component positioning, without requiring the use of intramedullary alignment guides.

Data generated by the system are digitally processed and stored, enabling standardized, objective documentation of the surgical procedure. The integration of the SCORE® prosthesis with the AMPLIVISION® system provides a reliable platform for performing total knee arthroplasty with high technical accuracy and reproducibility.

Data Collection Protocol

The intraoperative data were systematically obtained using the AMPLIVISION® navigation system, a wireless optical tracking platform that provides high-resolution, real-time 3D modeling of anatomical structures during total knee arthroplasty (TKA). This system enables precise spatial orientation of the surgical instruments and prosthetic components throughout the procedure, eliminating the need for traditional intramedullary guides and enhancing both the safety and accuracy of the intervention.

The data collection process commenced with the digital registration of anatomical landmarks, including the medial and lateral femoral condyles, the proximal tibial plateaus, the Whiteside line, and the centers of the hip, knee, and ankle. These reference points were captured through reflective markers and processed by the system to construct a patient-specific three-dimensional virtual model of the knee. This step also enabled the definition of mechanical axes for both the femur and tibia, which served as intraoperative references for alignment and measurement.

Following this, the navigation system performed real-time calibration of the limb's anatomical orientation. The spatial relationships among bones and surgical tools were updated continuously, ensuring accurate visualization and execution of bone resections. With these calibrations in place, the surgeon proceeded with navigation-assisted bone cuts, where the system provided dynamic feedback for each resection plane, minimizing variability and increasing precision.

Based on the registered anatomical data, the system generated automatic implant size suggestions, estimating the optimal dimensions for the femoral and tibial components to ensure proper cortical coverage and joint congruence. After the prosthetic trial and final component placement, the AMPLIVISION® system recorded the definitive values regarding the size and position of each component.

The collected variables included the numerical size (in mm) of both the femoral and tibial components, selected from the standardized options available in the SCORE® prosthesis system. In addition to dimensional sizing, several parameters related to component positioning were analyzed in angular measurements (degrees). For the femoral component, coronal alignment was recorded as the angle of deviation from the mechanical axis, indicating varus (< 0°) or valgus (> 0°) positioning, while sagittal alignment referred to the flexion (> 0°) or extension (< 0°) inclination of the component in relation to the femoral shaft.

For the tibial component, the variables included coronal alignment (varus or valgus) in degrees (°), axial rotation (internal or external), measured relative to the tibial tuberosity and the second metatarsal line, also expressed in degrees, and posterior slope, which was quantified as the angle (°) between the horizontal plane and the inclination of the tibial tray in the sagittal plane. These values were captured directly and automatically by the navigation system, minimizing subjectivity in the assessment process.

All collected data were digitally stored in the AMPLIVISION® database and subsequently exported in tabular format for statistical processing. The precision and standardization ensured by this method provided a robust and objective foundation for the analysis of implant configuration and surgical reproducibility.

Statistical Analysis

All intraoperative data collected through the AMPLIVISION® navigation system were exported to a dedicated database and subsequently analyzed using the Minitab21® statistical software (Minitab Inc., State College, PA, USA). Prior to statistical testing, data integrity and consistency were verified, and all variables were assessed for completeness and validity. The dataset included both continuous and categorical variables related to patient demographics, component sizing, and implant positioning.

A descriptive statistical analysis was conducted to characterize the study sample and summarize the distribution of the surgical variables. Measures of central tendency, such as the mean, and measures of dispersion, including the standard deviation (SD), were calculated for continuous variables (e.g., age, angles of alignment, and posterior slope in degrees). Categorical variables, such as operated side (right or left knee) and prosthetic component size classifications, were expressed in terms of absolute frequencies and percentages.

To assess potential differences between subgroups, particularly between right and left knee procedures, inferential statistical tests were applied. The Student's t-test for independent samples was used to compare the means of continuous variables between these groups, under the assumption of normal distribution and homogeneity of variance. The test evaluated whether statistically significant differences existed in component alignment angles or prosthetic sizes based on surgical laterality or other stratifying factors.

The level of statistical significance was set at p < 0.05, meaning that any p-value below this threshold was interpreted as indicative of a significant difference between groups. All statistical tests were two-tailed. The analysis aimed to identify not only the central tendencies of the variables studied, but also to verify the consistency and reproducibility of implant sizing and positioning in surgeries performed with the aid of computer-assisted navigation. This statistical approach provided a robust foundation for interpreting the precision and uniformity of navigated total knee arthroplasty in the sample studied, supporting evidence-based conclusions regarding surgical standardization.

RESULTS

All participants in this study underwent primary total knee arthroplasty (TKA) with the implantation of the SCORE® cemented prosthesis, developed by Amplitude Surgical (Valence, France). Surgical laterality revealed a predominance of procedures on the right knee, corresponding to 60% of cases, while 40% were performed on the left knee.

Regarding the dimensional distribution of prosthetic components, Size 3 was the most frequently selected for both femoral and tibial components, representing 31.32% of the implants used. Component size selection followed the intraoperative recommendations of the AMPLIVISION® system, which proposed optimal sizing based on anatomical calibration. Figure 1 illustrates the distribution of component sizes used in the study population.

Figure 1. Distribution of Femoral and Tibial Component Sizes Used (SCORE® Prosthesis).

Analysis of the femoral component positioning revealed no statistically significant differences for most angular measurements. The mean values were 4.90° (±2.35) for flexion (p = 0.003), 1.92° (±1.62) for rotation, 0.62° (±0.90) for varus alignment, and 0.61° (±1.61) for valgus alignment (p = 0.70 for all except flexion).

For the tibial component, the mean values were 2.10° (±0.14) for posterior slope, 6.32° (±0.62) for rotation (p = 0.001), 0.36° (±0.06) for varus alignment, and 0.31° (±0.06) for valgus alignment (p = 0.81 for all except rotation). These results are summarized in Table 1.

Table 1. Angular Positioning of Femoral and Tibial Components.

Component	Movement	Mean (°) ± SD	p-value
Femoral	Flexion	4.90 ± 2.35	0.003*
	Rotation	1.92 ± 1.62	0.70
	Varus	0.62 ± 0.90	0.70
	Valgus	0.61 ± 1.61	0.70
Tibial	Posterior Slope	2.10 ± 0.14	0.81
	Rotation	6.32 ± 0.62	0.001*
	Varus	0.36 ± 0.06	0.81
	Valgus	0.31 ± 0.06	0.81

^*Statistically significant according to Student's t-test (p ≤ 0.05). Values are expressed in degrees (°) as mean ± standard deviation.

The analysis of component sizing and alignment demonstrated a high degree of consistency in surgical execution when using the AMPLIVISION® navigation system in conjunction with the SCORE® prosthesis. The predominance of intermediate sizes-particularly size 3-suggests a common anatomical profile among the elderly population studied, while the balanced distribution of other sizes confirms the system's adaptability to interindividual anatomical variability. The ability to tailor component selection intraoperatively based on real-time 3D mapping reinforces the accuracy and reproducibility of navigation-assisted total knee arthroplasty.

Furthermore, the absence of statistically significant deviations in most alignment parameters-except for femoral flexion and tibial rotation-indicates that the navigation protocol contributed to maintaining neutral and physiologically appropriate implant positioning across the sample. These findings suggest that computer-assisted navigation can support surgical standardization and improve component placement without excessive variability, thereby contributing to optimized joint biomechanics and potentially enhancing long-term clinical outcomes.

DICUSSION

The findings of this study provide robust evidence supporting the importance of accurate implant sizing and positioning in total knee arthroplasty (TKA), particularly when using computer-assisted navigation systems such as AMPLIVISION® and high-performance implants like the SCORE® rotating platform prosthesis. In the context of an aging population, where biomechanical integrity and early postoperative recovery are essential for preserving autonomy and functional independence, surgical precision plays a decisive role.

The predominance of size 3 for both femoral and tibial components (31.32%) reflect the anatomical consistency of the sample, as well as the system's ability to suggest prosthetic dimensions based on patient-specific 3D mapping. This feature reduces the risk of intraoperative estimation errors and reinforces what Morcos et al. ¹ and Yamamoto et al. ² describe as a pivotal benefit of real-time digital planning in elderly patients, who often present morphological changes associated with degenerative disease. Avoiding oversizing helps minimize soft tissue over-tensioning, while undersizing prevention avoids instability and early loosening.

Notably, femoral component flexion averaged 4.90°, a value within clinically favorable thresholds. As discussed by Almaawi et al. ³ and Gao et al. ⁵ , this slight anterior tilt of the component contributes to maintaining the posterior femoral offset, supporting a natural flexion pattern that benefits quadriceps efficiency and reduces anterior impingement during daily activities. For elderly patients, who often demonstrate reduced muscle mass and proprioceptive capacity, maintaining biomechanical synergy between the implant and the extensor mechanism is fundamental for pain-free ambulation and functional range.

The external rotation of the tibial component (mean: 6.32°) found in this study is equally relevant. This alignment improves patellar tracking, reducing lateral retinacular tension, and has been correlated with reduced anterior knee pain - a persistent challenge in TKA recovery ^7,8 . Navigation appears essential for achieving such precision, particularly in osteoarthritic knees where bony landmarks may be obscured. Patellar maltracking, a common source of functional dissatisfaction, can thus be mitigated with accurate rotational alignment, enhancing patient comfort and mobility.

Additionally, the lack of statistically significant deviations in varus/valgus alignment for both components reinforces the mechanical consistency afforded by the navigation system. As Schiraldi et al. ⁶ and Srivastava et al. ⁹ highlight, deviations beyond ±3° from the neutral axis are associated with asymmetric distribution, increased polyethylene wear, and long-term implant failure. The ability to maintain alignment within this safety window contributes not only to prosthetic survival but also to more stable gait and reduced fatigue during weight-bearing tasks.

The posterior tibial slope, averaging 2.10°, was consistent across the cohort and remained within recommended values. This parameter is essential in posterior-stabilized or rotating platform implants like SCORE®, as excessive inclination may increase posterior translation and compromise implant congruence. On the other hand, insufficient slope may impede flexion and lead to abnormal loading. Giurazza et al. ⁴ and Gao et al. ⁵ emphasize that controlled slope contributes to flexion mechanics and supports a functional range of motion without overstressing ligaments or posterior structures.

Functionally, this degree of precision in implant positioning is strongly associated with improved patient-reported outcomes. Studies by Hadi et al. ¹⁰ , Nisar et al. ¹¹ , and Gousopoulos et al. ¹⁵ demonstrate that when alignment and sizing are accurately controlled, patients report reduced pain, better function, and greater satisfaction. These outcomes are especially significant in elderly populations, where prolonged recovery is associated with increased risks of deconditioning, falls, and dependence.

Patients in this study benefited from a streamlined intraoperative protocol that avoided the use of intramedullary guides, thereby reducing surgical invasiveness - a key consideration in geriatric orthopedic care. As Schnurr et al. ¹⁶ and Li et al. ¹⁷ point out, the avoidance of medullary canal instrumentation reduces intraoperative bleeding, lowers embolic risk, and supports safer anesthesia management, which collectively translate to fewer complications and faster postoperative mobilization.

These findings align with large-scale evidence. de Steiger et al. ¹⁸ and Lei et al. ¹⁹ found that computer-assisted navigation in TKA leads to fewer malpositioned implants and lower revision rates. In a broader context, where health systems face increasing demands from aging populations, technologies that enhance procedural consistency while reducing failure rates contribute not only to better outcomes but also to cost-effectiveness and surgical sustainability.

Moreover, the SCORE® prosthesis used in this study integrates high-congruity surfaces and a rotating platform that allows for controlled axial rotation. This mechanical behavior accommodates minor physiological variances and provides a "self-aligning" capacity, especially useful in elderly patients with asymmetric loading or soft tissue imbalances. Winnock de Grave et al. ¹³ , Bigoni et al. ²⁰ , and Elbuluk et al. ²¹ note that such implants reduce anterior knee discomfort and promote greater confidence in movement, contributing to improved performance in mobility tests such as the Timed Up and Go (TUG) and six-minute walk test (6MWT).

In the context of the current study, the integration of a navigation system and a biomechanically adaptive implant design resulted in highly reproducible and physiologically favorable component positioning, which likely underpins improved functional trajectories for the sample. Although this analysis did not directly measure clinical outcomes such as range of motion, gait parameters, or patient satisfaction, the literature consistently supports the conclusion that precision in intraoperative execution - as demonstrated here - is closely linked to functional recovery, reduced complication rates, and greater prosthesis longevity ^18,19,22 .

The results of this investigation reinforce the understanding that accurate positioning and sizing of components, enabled by surgical navigation, are critical to achieving optimal functional outcomes in TKA. Particularly for elderly patients, who may be more vulnerable to biomechanical deviations, technological adjuncts such as AMPLIVISION® allow surgeons to deliver highly standardized care, supporting early mobilization, autonomy preservation, and ultimately, an improved quality of life.

CONCLUSION

This study aimed to evaluate the precision of component sizing and positioning in primary total knee arthroplasty (TKA) procedures performed with the aid of the AMPLIVISION® navigation system and the SCORE® cemented rotating platform prosthesis. The results demonstrated a high level of intraoperative accuracy in implant alignment and dimensioning, with minimal variability in key parameters such as femoral flexion, tibial rotation, coronal alignment, and posterior slope.

The consistent selection of prosthetic sizes, particularly the predominance of size 3, reflects anatomical compatibility within the studied elderly population and reinforces the reliability of the navigation system in facilitating patient-specific surgical planning. Furthermore, the precise placement of femoral and tibial components within biomechanically favorable ranges supports the notion that real-time, computer-assisted techniques contribute directly to improved joint function and enhanced postoperative recovery.

In conclusion, the integration of the AMPLIVISION® system with the SCORE® prosthesis proved to be an effective strategy for optimizing the surgical execution of TKA. By ensuring accurate implant positioning without the use of intramedullary guides, this approach not only improves procedural safety but also lays a foundation for better long-term functional outcomes in elderly patients undergoing knee arthroplasty.

DATA AVAILABILITY DECLARATION

The authors confirm that the data supporting the findings of this study are available within the article.