Personalized Alignment Strategies and the Need for Customization in Total Knee Arthroplasty: The Role of MISSO Joint Robotic System

Introduction Total knee arthroplasty (TKA) has witnessed remarkable advancements over the past two decades, from refined implant designs to improved surgical workflows. Yet, the pursuit of optimal alignment and true kinematic restoration remains elusive. Restoring each patient’s unique anatomy and joint mechanics continues to challenge conventional approaches. This ongoing dilemma has shifted attention toward more personalized strategies in TKA [1]. The traditional mechanical alignment (MA) approach positions components perpendicular to the mechanical axis, achieving symmetrical gaps through ligament releases. Historically favored for its potential to enhance implant longevity, this standardized methodology may compromise the restoration of natural knee kinematics [2]. This realization has spurred the development of personalized alignment strategies, including kinematic, inverse kinematic, restricted kinematic, and functional alignment (FA) approaches [3]. These patient-specific techniques aim to recreate the individual’s pre-arthritic anatomy by precisely restoring native limb alignment, joint line orientation, and physiological soft-tissue tension while minimizing ligamentous disruption [4]. Implementing such customized alignment protocols presents considerable technical challenges with conventional instrumentation, particularly regarding precise intraoperative decision-making and the lack of real-time feedback on tissue balance and resection accuracy. This paradigm shift toward anatomical restoration highlights the essential role of robotic-assisted systems, such as MISSO Robotics, which offer the precision and reproducibility required to execute these advanced alignment concepts while maintaining implant stability and longevity. Personalized Alignment Strategies in TKA Anatomic alignment (AA) First proposed by Hungerford and Krackow in the 1980s, AA aims to achieve a joint line oriented in 2–3 of valgus relative to the mechanical axis [5]. Modern prostheses now incorporate this principle through built-in three degrees coronal obliquities. The surgical technique for AA closely follows that of MA, differing primarily in the intentional deviation from neutral alignment [5]. Kinematic alignment (KA): Restoring native anatomy First described by Howell et al. (2008), KA restores native knee anatomy by replicating pre-arthritic joint surfaces, unlike MA, which enforces neutral positioning [6]. Using calipered instrumentation (“true KA”), it involves articular-parallel bone cuts, wear compensation, and minimal soft-tissue release. While KA better preserves natural kinematics, concerns remain about mechanical axis deviations and stability in extreme anatomies, representing a shift from standardized to patient-specific reconstruction [7]. Inverse kinematic alignment (iKA) This alignment strategy prioritizes the restoration of the pre-arthritic tibial joint line while adjusting the femoral distal/posterior cuts for ligament balance. In practice, iKA involves the following key steps: Preserves tibial anatomy Prevents over-resection Independently balances flexion/extension gaps [8]. Robotic assistance enhances precision by enabling real-time intraoperative adjustments, overcoming limitations of conventional instrumentation. By maintaining native tibial obliquity and optimizing femoral component positioning, iKA reduces post-operative complications while achieving physiological joint kinematics [3]. Restricted kinematic alignment Unrestricted KA remains controversial due to elevated implant stresses (24.8–32.2% increase in moderate/severe varus knees) [3] and potential polyethylene wear [8]. Vendittoli’s restricted KA protocol establishes safe zones (±5° femoral/tibial cuts, ±3° HKA angle) as a hybrid approach between MA and KA [9]. This technique preserves KA’s anatomical principles while mitigating excessive stresses by primarily adjusting tibial component positioning to control coronal alignment and joint line obliquity [3]. FA: A hybrid approach FA integrates kinematic principles with dynamic soft-tissue balancing through robotic assistance. This approach: Restores pre-arthritic alignment Achieves precisely balanced flexion-extension gaps (±1–2° accuracy) Optimizes mediolateral tension [8]. Robotic systems facilitate this process by enabling real-time, quantifiable adjustments in all anatomical planes, ensuring reproducible non-neutral alignments (±2° precision) and minimizing limb alignment outliers. FA preserves native knee kinematics, reduces soft-tissue releases, and maintains physiological joint mechanics [3]. While FA represents a promising shift toward personalized TKA, it is important to note that not all studies have shown substantial clinical differences between kinematic and MA strategies. Although early trends favor improved kinematic restoration and joint function, definitive long-term superiority of FA in terms of functional outcomes and implant longevity remains under investigation [10]. This balanced perspective acknowledges the potential of FA while underscoring the need for continued high-quality research. The Role of Coronal Plane Alignment of the Knee (CPAK) Classification in Personalized TKA The CPAK classification provides a systematic framework for categorizing knee phenotypes based on the native alignment and joint line obliquity. Developed by MacDessi et al. [11], CPAK is instrumental in identifying the pre-arthritic anatomical configuration of the knee, which is essential for implementing patient-specific alignment strategies. In the context of robotic-assisted TKA, the CPAK classification aids in accurately assessing the native knee phenotype, enabling surgeons to plan precise, individualized bone cuts that restore the original kinematic profile. Robotic systems, such as MISSO Robotics, may enhance this process by providing real-time feedback and adaptive intraoperative adjustments, which might ensure that the restored alignment closely matches the patient’s original anatomy. By incorporating CPAK-guided planning, robotic-assisted TKA facilitates the preservation of native knee mechanics, potentially leading to improved functional outcomes and patient satisfaction. The Case for Customization in TKA The significant anatomical variability among individuals necessitates a paradigm shift from standardized techniques to personalized alignment strategies in TKA. The key scientific rationale for this approach includes: Improved patient satisfaction: Advanced navigation systems provide intraoperative guidance to accurately restore native joint alignment and physiological soft-tissue balance. This preservation of natural kinematics improves joint functionality, potentially leading to superior patient-reported outcomes and increased rates of post-operative satisfaction [10]. Optimized biomechanical performance: Personalized alignment techniques demonstrate superior replication of native knee biomechanics compared to MA. By maintaining physiological joint line orientation during weight-bearing activities, this approach reduces shear forces at articulating surfaces and implant-bone interfaces, thereby decreasing stress concentrations that may compromise long-term implant performance [12]. Physiological soft-tissue preservation: The personalized alignment methodology precisely restores constitutional joint line orientation while maintaining native ligamentous laxity patterns. This anatomical approach eliminates the need for soft-tissue releases, preserving the knee’s natural stabilizing structures and proprioceptive feedback mechanisms [12]. Robotic-Assisted TKA: Benefits and Limitations bullet points are: Robotic-assisted TKA utilization has grown substantially in recent years. These systems were specifically engineered to enhance alignment precision and prosthetic positioning through three key technological features: (1) real-time intraoperative navigation, (2) dynamic calibration, and (3) haptic feedback mechanisms [13]. By improving bone resection accuracy and minimizing alignment outliers, robotic TKA aims to extend implant longevity. Clinical evidence confirms that proper mechanical axis restoration is correlated with reduced polyethylene wear rates and a decrease in revision surgery incidence [14]. Several robotic platforms have achieved widespread clinical adoption, including: MAKO (Stryker), ROSA (Zimmer Biomet), NAVIO/CORI (Smith and Nephew), and CUVIS (Curexo, South Korea,). These systems demonstrate superior performance compared to conventional instrumentation, offering: Enhanced implant positioning accuracy, reduced soft-tissue disruption, more precise bone resection, and improved gap balancing [13]. However, limitations remain: Limited haptic feedback Some semi-active systems provide limited tactile feedback, potentially affecting bone preparation precision compared to fully active systems [15]. Bulky hardware and setup complexity Some platforms require large operating room footprints and complex setups, which limit maneuverability and increase turnover time between cases [16]. Compatibility issues Not all systems are universally compatible with all implant designs or manufacturers, reducing flexibility for surgeons [15]. Procedural risks Potential need for intraoperative conversion to conventional technique [14] These limitations highlight the need for next-generation systems that optimize cost efficiency, workflow integration, adaptive surgical planning, and user-friendly interfaces. MISSO Robotics: A Theoretical Advancement in Personalized Alignment The MISSO Joint Robotic System (Meril Healthcare Pvt. Ltd., India) represents a transformative innovation in computer-assisted orthopedic surgery, establishing new standards for precision in joint replacement procedures. As a fully autonomous robotic platform, MISSO is designed to achieve submillimeter accuracy (≤0.5 mm) in bone resection [17]. According to early testing, the system can potentially adjust