1 Introduction

Total knee arthroplasty (TKA) is a well-established treatment for advanced knee osteoarthritis, effectively reducing pain and improving function for most patients. However, dissatisfaction remains a critical concern, with up to 20 % of patients reporting residual pain, suboptimal function, and unmet expectations postoperatively [1,2]. Persistent anterior knee pain, affecting up to 50 % of patients after TKA, further compromises patient satisfaction [2,3]. Continuous innovation in TKA implant design aims to address these challenges by improving biomechanics, patellofemoral tracking, and joint kinematics [4].

The Traditional Multi-Radius implant design, introduced over 30 years ago, has demonstrated excellent long-term survivorship and clinical outcomes [5]. Nevertheless, the Traditional Multi-Radius has been associated with persistent anterior knee pain and patellar crepitus, limiting patient satisfaction at mid-term follow-up [3,6]. The Modern Anatomic system, launched in 2013, introduced design modifications to enhance clinical outcomes. These included an anatomic trochlear groove, refined femoral profiles, and a medialized patellar component designed to optimize patellofemoral mechanics and reduce anterior knee pain (Fig. 1) [3,6]. Comparative studies have reported mixed outcomes regarding these innovations. Ranawat et al. 3 reported a significantly lower incidence of anterior knee pain with the Modern Anatomic implant design with enhanced trochlear geometry compared to the Traditional Multi-Radius implant. Interestingly, the incidence of painful crepitation was low in both groups, with no significant difference. Both groups also had comparable high satisfaction scores of 8.6 and 8.4 for the Modern Anatomic and the Traditional Multi-Radius implant groups, respectively [3]. Similarly, Carey and Harty demonstrated significant short-term improvements in Oxford Knee Scores favoring the Modern Anatomic implants over Traditional Multi-Radius implants. [5] However, multiple randomized and multicenter studies found no clinically significant differences in overall patient satisfaction, functional recovery, knee stability, or long-term survivorship between Modern Anatomic implants and the Traditional Multi-Radius implants [4,6–8]. Radiostereometric analyses have shown similar implant migration and fixation stability between Modern Anatomic implants and Traditional Multi-Radius implants, challenging whether newer designs substantially enhance long-term outcomes [7].

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Fig. 1 Modified design features of the Modern Anatomic compared to the Traditional Multi-Radius implant design. (A) The trochlear groove of the Modern Anatomic implant design is extended more distally than Traditional Multi-Radius implant design, resulting in a reduced intercondylar box ratio. (B) Reduced width and thickness of the Modern Anatomic implant design (inner dimension; solid line) compared to the Traditional Multi-Radius implant design (outer dimension; dotted line). (C) The Modern Anatomic prosthesis has a medialized dome patellar component for optimizing patellofemoral conformity. Image courtesy of: Song, Sang Jun & Kang, Se & Park, Cheol & Bae, Dae. (2018). Comparison of Clinical Results and Risk of Patellar Injury between Attune and PFC Sigma Knee Systems. Knee Surgery and Related Research. 30. 10.5792/ksrr.18.020.

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The Next-Generation Cementless implant design with 3D-printed porous surface system was introduced in late 2021, utilizing advanced 3D-printed cementless technology designed to enhance biological fixation, particularly beneficial for active patients. This innovation features a porous, lattice structure closely resembling natural bone architecture, aimed at improving immediate stability and long-term implant integration (Fig. 2) [9]. Despite the technological advancements of the Next-Generation Cementless implant, including optimized component positioning, improved surgical precision, and enhanced biological fixation, robust comparative clinical evidence supporting meaningful improvements in patient outcomes and satisfaction compared to earlier Modern Anatomic implants remains limited.

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Fig. 2 Illustrated schematic of the Next-Generation Cementless Total Knee Arthroplasty implant highlighting key design features intended to optimize kinematic performance and promote biological fixation. The Modern Anatomic implant design GRADIUS™ Curve (purple) transitions smoothly throughout flexion, aiming to reduce paradoxical anterior translation and improve patellofemoral kinematics. The femoral and tibial components are coated with a 3D-printed porous titanium surface to support osseointegration. Four tibial pegs with scalloped geometry and a central cruciform keel are strategically positioned to enhance initial implant stability and long-term biological fixation.

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Given the substantial resources invested in new implant technologies, rigorous clinical evaluations are essential to objectively determine whether design innovations genuinely yield tangible clinical benefits and improved patient outcomes. In the United States, the average cost for knee implants in 2022 was approximately $4563 for cementless knee designs featuring coated femoral and tibial components, such as the newer Next-Generation Cementless implant design system, compared to slightly lower costs for traditional cemented models (approximately $4033) [10]. This study critically compared patient-reported outcome measures among the Modern Anatomic implants, Next-Generation Cementless implants, and Traditional Multi-Radius implants at short-term and mid-term follow-up. Clarifying whether recent implant innovations provide measurable clinical benefits beyond established designs can significantly impact decision-making regarding implant selection, patient counseling, and the future direction of innovation in TKA.

2 Materials and methods

3 Results

4 Discussion

Despite advancements in TKA, approximately 15–20 % of patients remain dissatisfied postoperatively, often due to persistent pain, functional limitations, and unmet expectations [^1,2,11]. In response, modern implant systems such as the Modern Anatomic and, more recently, the Next-Generation Cementless implant have been introduced with the promise of improving patellofemoral tracking, reducing mid-flexion instability, and better restoring native kinematics through design features such as the GRADIUS™ curve and 3D-printed cementless fixation (Fig. 3) [^3,9,12,13]. However, an increase in implant complexity and associated costs necessitates objective evidence to determine whether such innovations confer clinical benefit. This study aimed to compare PROMs and functional outcomes between patients receiving the Modern Anatomic, Next-Generation Cementless, and Traditional Multi-Radius implants to evaluate whether newer designs provide meaningful advantages in the short-term to mid-term postoperative period.

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Fig. 3 Schematic comparison of femoral component geometries in Total Knee Arthroplasty demonstrating the evolution from traditional multi-radius designs to the Modern Anatomic implant design GRADIUS™ curve. Left: Multi-radius designs utilize abrupt changes in curvature throughout the flexion arc, potentially resulting in mid-flexion instability and unnatural kinematic transitions. Middle: Single-radius designs aim to maintain a consistent flexion-extension axis but may limit posterior femoral rollback. Right: The Modern Anatomic implant design GRADIUS™ curve incorporates a gradually evolving radius to reduce paradoxical anterior sliding and improve kinematic fidelity, facilitating smoother femoral rollback and potentially enhancing patient-perceived stability and quadriceps function during deep flexion. Image courtesy of: Ng, J. W. G., Bloch, B. V., & James, P. J. (2019). Sagittal radius of curvature, trochlea design and ultracongruent insert in total knee arthroplasty. EFORT Open Reviews, 4(8), 519–524. Retrieved May 27, 2025, from https://doi.org/10.1302/2058-5241.4.180083.

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All 3 implant groups in our study, the Modern Anatomic, Next-Generation Cementless, and Traditional Multi-Radius group, demonstrated meaningful improvements from baseline in KOOS subscales for ADL, PAIN, and QoL, with no statistically significant differences between groups at both 3 and 12 months postoperatively. Suggesting that, at least in the short-term to mid-term period, patients experience comparable functional recovery and symptom relief regardless of implant design. These findings are consistent with prospective matched cohort studies reporting similar PROMs between the Modern Anatomic and Traditional Multi-Radius implants [^5,8,14,15]. While isolated studies have shown modest early differences in range of motion favoring newer designs, these advantages often diminish by 1 year and may not consistently translate into improved global functional scores [^14,16]. A recent cross-sectional study comparing cruciate-retaining, fixed-bearing Modern Anatomic and Traditional Multi-Radius implants without patellar resurfacing found that patients who underwent TKA with the Traditional Multi-Radius implants reported higher postoperative physical function and vitality scores. While these findings appear to challenge the clinical advantage of newer designs, the limited sample size and unequal follow-up durations (mean 45 vs. 24 months) introduce confounding 17.

Recognizing factors beyond implant design contextualizes our findings. Patient satisfaction after TKA primarily hinges upon achieving meaningful pain relief, managing expectations, and avoiding complications [1,2]. Edwards et al. demonstrated that demographic and social factors, while statistically significant, account for less than 1 % of outcome variation, reinforcing the importance of clinical and surgical factors over demographic considerations 11. Interestingly, our analysis identified a statistically significant difference in the MCS improvement at 12 months, favoring the Next-Generation Cementless implant design group over the Modern Anatomic and Traditional Multi-Radius implant design groups (P = 0.02). However, the absolute differences observed in MCS between these groups were minimal, rendering its clinical relevance uncertain. Additionally, the mean MCS score of the US population is 50, and despite some decline, all three groups in our study maintained MCS scores above this threshold 18. Although mental well-being is an important dimension of recovery, these findings more likely reflect subtle variations in patient expectations, subjective perception of recovery, or psychosocial factors, rather than definitive implant-related differences. Halawi et al. and others have argued that PROMs are not surrogate markers for meaningful success in patients with high expectations or specific lifestyle demands 19. This is relevant when evaluating newer implant designs, which may offer kinematic or durability improvements not readily reflected in standard outcome tools. Thus, reinforcing that metrics such as the KOOS or SF-12 may fail to detect nuanced benefits that matter most to patients, such as knee confidence, stability during demanding activities, or return to recreational function [^20,21].

Furthermore, improvements in patellofemoral function warrant careful consideration. Previous studies have documented higher rates of anterior knee pain and patellofemoral crepitus with older prostheses, prompting iterative design changes aimed at improving patellar tracking and reducing mechanical instability during flexion. In a prospective matched-pair analysis, Ranawat et al. reported significantly lower rates of anterior knee pain (12.5 vs. 25.8 %; P = 0.02) and audible or palpable crepitus (17.7 vs. 30.9 %; P = 0.02) in the Modern Anatomic implant group compared to the Traditional Multi-Radius implant group at 2-year follow-up despite comparable Knee Society Scores and global satisfaction ratings [3]. Similarly, a recent systematic review by Choudhury et al. further supported the Modern Anatomic implant's modest superiority in managing patellar complications 4. Martin et al. observed a substantial reduction in symptomatic patellofemoral crepitus at both 1 and 2 years (0.33 and 0.83 %, respectively, in the Modern Anatomic implants vs. 3.9 and 9.4 % in the Traditional Multi-Radius implants; P < 0.001), attributing these improvements to femoral component design changes such as a lower intercondylar box ratio and a narrower anterior flange 22. The Modern Anatomic GRADIUS™ Curve has been designed to reduce abrupt kinematic transitions seen in traditional multi-radius (“J Curve”) designs, minimizing paradoxical anterior sliding, and promoting more natural posterior femoral rollback throughout flexion (Fig. 3). However, direct evidence supporting enhanced quadriceps efficiency remains limited. In a pilot kinematic study comparing the Modern Anatomic implant design to another Contemporary System using motion analysis and surface electromyography, the Modern Anatomic implant was associated with better preservation of quadriceps strength postoperatively. Yet, the authors did not assess moment arms or torque output, precluding definitive conclusions about true quadriceps efficiency 23. Therefore, while the Modern Anatomic implant may theoretically enhance the mechanical environment for quadriceps function, high-quality comparative data substantiating a functional advantage over earlier designs, such as the Traditional Multi-Radius implant design or alternative modern implants, is lacking.

Although short-term clinical outcomes were comparable across implant types, long-term fixation and implant survivorship remain central to the decision-making process in TKA. Radiostereometric analyses provide early insights into implant micromotion and the potential for future loosening. A randomized controlled trial by Kaptein et al. comparing tibial migration in cemented Modern Anatomic implants and Traditional Multi-Radius cruciate-retaining implants demonstrated similar early fixation behavior at 2 years 24. However, other observational studies have raised concerns regarding radiographic lucencies associated with the Modern Anatomic implants. In a multicenter analysis, Giaretta et al. reported a 22.4 % incidence of tibial radiolucent lines at short-term follow-up, but the clinical implications of these findings remain uncertain and may reflect differences in implant interface geometry or cementation technique rather than true loosening 25. Importantly, the Traditional Multi-Radius implant has proven long-term durability, with survivorship rates exceeding 97 % at 12 years and documented success extending beyond 20 years in certain cohorts 26. In contrast, while the Modern Anatomic implant system has shown promising mid-term outcomes, long-term data remain limited, particularly for the Next-Generation Cementless implant due to its more recent introduction, which utilizes a 3D-printed porous structure designed for biological fixation but currently lacks robust migration and survivorship evidence. A recent randomized trial comparing two cementless rotating-platform designs, including the Next-Generation Cementless implant, showed no significant differences in component migration, though longer-term monitoring is needed to confirm the durability of fixation beyond 2 years 27. Given the proven reliability of the Traditional Multi-Radius implant and the limited longitudinal data for newer platforms in cementless applications, continued surveillance through prospective registries and radiographic studies is warranted 28.

Beyond clinical equivalence, economic considerations also inform implant selection. Given the absence of significant differences in patient-reported outcomes across cohorts in our study and similar findings reported in multicenter analyses, the higher cost of newer implants warrants thoughtful consideration [^7,8,14]. However, the value in arthroplasty extends beyond short-term PROMs. Newer designs may offer benefits that may not be fully reflected in conventional outcome measures or captured within the early follow-up window. Whether these theoretical advantages lead to improved long-term durability, reduced revision rates, or downstream cost savings remains to be determined. As healthcare systems continue to emphasize value-based care, implant selection must strike a balance between innovation and demonstrable clinical utility. While legacy systems like the Traditional Multi-Radius implant have established long-term reliability, emerging designs such as the Next-Generation Cementless implant hold potential in specific patient populations for improved biomechanical performance. Ongoing prospective studies and registry data will be essential to clarifying the long-term impact of these design evolutions on patient outcomes and healthcare resource optimization.

5 Conclusion

In this comparative analysis of three TKA systems, namely the Modern Anatomic, Next-Generation Cementless, and Traditional Multi-Radius implant designs, we observed no significant differences in PROMs at short-term to mid-term follow-up. While newer implants incorporate design innovations intended to improve patellofemoral tracking, mid-flexion stability, and fixation strategies, these refinements did not translate into measurable superiority in global PROMs within the study period. However, current PROMs may not fully capture functional nuances such as joint stability, confidence in motion, or biomechanical efficiency during demanding activities. This may hold value for select patients, even if not reflected in traditional outcome scores. As the field continues to evolve, design innovation must be matched by rigorous, long-term clinical validation. Until such data are available, the selection of TKA implants should remain individualized, balancing theoretical advantages with proven reliability, cost considerations, and the broader goals of value-based care.

Authors' contributions

NG, SJP, JL, MD, MAA, and MJM assisted in generating the manuscript. VA served as a supervisor, providing the resources to complete the project, and revised and edited the manuscript.

Ethical considerations and patient consent

This study was reviewed and approved by the Institutional Review Board at the Warren Alpert Medical School of Brown University and Brown University Health (IRB #2059622-6). All procedures performed were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments.

This study involved a retrospective review of de-identified patient records. No personal identifiers, photographs, or protected health information were collected or reported. Informed consent for retrospective review was waived by the IRB, as permitted under institutional policy for minimal risk studies using existing data.

All data were stored in secure, HIPAA-compliant systems, and only study personnel approved by the IRB had access. No identifying information (including names, initials, medical record numbers, dates of birth, or social security numbers) is included in the manuscript or supplementary materials. No patient images or videos are included in this publication.

Authors' contributions

SP, MD, JL, NG, JN, SN, and AP: Writing and Data collection.

MM, MA, VA: Review and Supervision.

Ethics

The Institutional IRB approval was granted before conducting this research.

Funding

None.