Anatomically, the knee joint, being the largest and most intricate joint in the body, comprises the femur, tibia, patella, and surrounding soft tissues, all working in concert to ensure knee stability within physiological limits (Zhao et al., 2021). Under normal physiological conditions, the knee joint capably fulfills its essential biomechanical functions. However, deviations in bone or soft tissue anatomy can lead to undesirable mechanical load distribution and persistent knee instability (Campos et al., 2022), ultimately paving the way for the development of knee osteoarthritis (KOA).

With the global population aging, the prevalence of KOA is estimated to be 22.9% in individuals aged 40 years and older, making it one of the leading contributors to chronic disability (Cui et al., 2020). Recognized risk factors encompass gender, genetic predisposition, obesity, aberrant gait biomechanics, joint laxity, and meniscal injuries (Heidari, 2011). Among these factors, the role of biomechanics in KOA development has consistently come to the forefront and been substantiated (Lee, 2014; Aljehani et al., 2022; Spierings et al., 2023).

Knee joint kinematics results from the intricate roto-translation movements characteristic of the tibiofemoral and patellofemoral articulations (Vasso et al., 2017). The patella functions as an articulating fulcrum, enhancing the moment arm of the extensor mechanism. Additionally, it enhances quadriceps muscle efficiency by elevating the extensor mechanisms away from the axis of rotation of the knee, thus increasing torque (Wheatley et al., 2021). Moreover, it assists in reducing frictional wear that could otherwise damage the extensor mechanism tendon. When the knee is fully flexed, the patella serves as a connection between the quadriceps and the patellar ligament. Daily activities subject the patellofemoral joint to compressive forces of 3.3 times body weight during stair climbing and 7.6 times body weight during squatting (Reilly and Martens, 1972). From 45° flexion to full extension, the patella articulates with the femur, displacing the extensor mechanism from the knee’s mechanical axis, thereby enhancing torque generation for terminal extension (LeBrun et al., 2012). Gait patterns vary based on the position and orientation of the patella relative to the trochlear groove and the alignment of the tibia in relation to the femur. Within the knee joint complex, the patella, the largest sesamoid bone in the body, plays a crucial role in knee biomechanics (Suzuki et al., 2013). Early intervention is believed to facilitate timely stabilization and restoration of knee biomechanics, thereby reducing the risk of concurrent knee pathology (Bornes et al., 2014). Consequently, a comprehensive investigation into the factors influencing knee joint biomechanics, early identification of biomechanical irregularities, and prompt intervention become crucial components in slowing the progression of KOA.

Currently, the assessment of KOA involves patient-reported outcome measures (PROMs) as well as various imaging techniques, including X-ray, computed tomography, magnetic resonance imaging, and gait analysis. While PROMs provide clinical insights, their subjective nature, potential ceiling effects, and reliance on pain rather than daily life activities limit their clinical value (Bolink et al., 2015). Imaging evaluation, on the other hand, is constrained by factors such as cost, time, accessibility, and the static nature of images (Vomer et al., 2023). Fortunately, recent advancements in three-dimensional motion analysis have enabled objective, quantitative, reproducible, and standardized evaluation of knee joint kinematics (Piriyaprasarth and Morris, 2007). Prior studies (Clark et al., 2016; Hösl et al., 2018; Murakami et al., 2018) have already established the influence of patellar sagittal and coronal alignment, as well as the mechanical axis, on knee joint kinematics.

As such, this study’s primary focus is to evaluate how patellar morphology and transverse alignment impact the kinetics and kinematics of the knee joint in individuals without pre-existing knee conditions. The secondary objective involves assessing the influence of femoral and tibial morphology, femoral-tibial angle (FTA), and Q angle on knee kinetics and kinematics within this specific population.

The knee, a pivotal component of the locomotor system, serves as a weight-bearing joint susceptible to degenerative changes primarily driven by abnormal mechanical loads (Zhao et al., 2021; Campos et al., 2022). Therefore, it is imperative to acquire a comprehensive understanding of the multifaceted factors influencing the mechanical load conditions experienced by the knee joint. Such insights can inform the tailoring of prevention strategies to mitigate inherent risks. The geometric characteristics of the knee’s articular components play a pivotal role in predicting joint contact mechanics. There is a prevailing consensus that the biological function of the patella is intricately linked to the compatibility of the patellofemoral joint (PFJ), which, in turn, depends significantly on PFJ morphology and biological performance (Fox et al., 2012). Previous studies (Clark et al., 2016; Hösl et al., 2018; Murakami et al., 2018) have predominantly focused on the substantial roles played by sagittal and coronal alignments of the PFJ and the mechanical axis of the lower limbs in mediating knee joint mechanics. However, the impact of patellar morphology and transverse alignment remains an area that warrants more extensive investigation. Building on existing literature, this study is thus well justified.

Our study’s findings indicated that there was no statistically significant correlation between PTA, a measure of transverse alignment in the PFJ, or the PI, an indicator of patellar morphology, and knee movement kinematics or kinetics (p > 0.05, respectively). Notably, an increase in PTA and PI, which play a critical role in assessing patellar stability, may suggest patellar malalignment. Such malalignment has been associated with conditions such as patellar instability, patellofemoral pain syndrome, and chondromalacia patellae. In contrast to metrics like the tibial tubercle trochlear groove distance in the coronal plane and the Insall-Salvati ratio or Caton-Deschamps index in the sagittal plane (Verhulst et al., 2020), our distinct results underscore two key observations. On the one hand, significant variability in patellofemoral alignment suggests that the observed patellar features in our study population may not accurately represent the broader trends across all populations (Hochreiter et al., 2020). On the other hand, while patellar alignment in individuals with osteoarthritis may lead to morphological changes, subsequently affecting muscle function and mechanical loading, it is important to acknowledge that this perspective has yet to be confirmed in the general population.

Our study provided evidence supporting the idea that FTA exerted a substantial and independent influence on KAM in individuals without underlying knee conditions, even after adjusting for potential confounding factors (p = 0.007). The KAM, a structural risk factor for KOA, is frequently used as an indicator of medial-to-lateral knee joint load distribution during gait (Zhao et al., 2007). Previous studies (Miyazaki et al., 2002; Barrios et al., 2009) have found associations between static frontal plane knee alignment and peak KAM magnitude. Increased varus malalignment is believed to augment the knee ground reaction force lever arm, thereby increasing the KAM during gait and the risk of various knee-related conditions (Bennell et al., 2011).

Our correlation analysis revealed that among demographic factors, age, BMI, and gender did not have a statistically significant impact on the velocity of the healthy population. However, we did observe that age was associated with adduction and internal rotation angles. Additionally, BMI showed a sole association with the abduction angle, while gender was related to the adduction angle, extension moment, and KAM (p < 0.05, respectively). Nonetheless, the multivariate regression model did not demonstrate any significant disparities between demographic independent variables and dependent variables related to the adduction angle, or KAM. This suggested that the absence of discernible differences in dependent variables may be attributed to the unique characteristics of the normal population under investigation. Furthermore, differences in demographic factors can be linked to the Q angle and the FTA. Q angle is frequently cited as a possible predictor of knee pathology and lower limb injury (Rauh et al., 2007). The varus-valgus angulation of the knee has been associated with mediolateral distribution of loads on the knee’s articular structures. Minor increases in varus alignment (approximately 5%) have the potential to greatly increase (approximately 20%) medial knee loading (Schipplein and Andriacchi, 1991). Previous research (Tran et al., 2022) has shown variations in gender, age, and BMI concerning the Q angle and FTA, which in turn affect mechanical distribution by influencing moments, ultimately increasing the likelihood of developing KOA.

The consideration and design of therapeutic interventions aimed at reducing peak KAM are of paramount importance in the effort to delay or prevent the development and/or progression of KOA in middle-aged adults. Correcting varus alignment disperses high-pressure zones, resulting in significant improvements in knee pain and other KOA symptoms. Interventions such as footwear, knee bracing, exercise, and gait retraining may be appropriate for reducing varus tibial malalignment in KOA and should be periodically evaluated (Hatfield et al., 2016).

This study provides the initial comprehensive analysis of the relationship between knee imaging evaluation and three-dimensional gait analysis, enriching our understanding of how the morphology and transverse alignment of the patella, femur, and tibia impact knee kinematics and kinetics. However, it is essential to interpret the findings considering certain limitations. Firstly, our study exclusively recruited healthy senior adults, indicating the necessity for further investigations across diverse age demographics to thoroughly validate our findings. Secondly, it is worth noting that, compared to the sagittal plane, the frontal and transversal planes exhibit smaller ranges of motion. This characteristic increases the susceptibility of skin markers to soft tissue artifacts, thereby limiting the reliability of our results. Nevertheless, it is important to acknowledge that skin markers provide a non-invasive and reproducible method for visual motion capture. Thirdly, our study did not incorporate surface electromyography of the lower limb to evaluate muscle activity. Although it is improbable for healthy individuals to display abnormal muscle co-contraction, this aspect should be considered in future studies involving individuals with KOA. Finally, this study did not explore the correlation between patellar shape, alignment, and the onset of articular cartilage degeneration and KOA. Subsequent studies should include populations with KOA for comparative analysis and subsequent conclusions.

In summary, this study found that the morphology and transverse alignment of the patella do not significantly impact knee gait characteristics in a sample of healthy Chinese adults aged 40 years and older. Notably, the FTA emerges as a pivotal determinant influencing the KAM, a crucial parameter for assessing normal mechanical knee function. Future investigations should focus on establishing threshold values for FTA, Q-angle, and PTVA that could indicate an increased risk of mechanical dysfunction in individuals. Furthermore, there is a pressing need for comprehensive studies that encompass structural, passive, and dynamic elements to formulate treatments aimed at reducing the incidence of KOA.