Introduction

The quadriceps angle (Q-angle) and bicondylar distance (ICD) are critical biomechanical parameters that reflect lower limb alignment and functional loading of the knee joint [1]. Brattstrom (1964) represents the Q-angle as a resultant line of pull of the quadriceps muscle compared to the patellar tendon and is commonly used to assess patellofemoral joint mechanics. An increase in value mainly results in anterior knee pain, patellofemoral syndrome, and knee instability [2]. The ICD, measured between the medial and lateral femoral condyles of knees, serves as a secondary indicator of frontal plane knee alignment and genu varum-valgum characteristics [3].

The lower limb alignment differs with gender, as adult women show an increased Q angle compared to adult men. The difference occurs due to an increased pelvic width, an increase in femoral anteversion, valgus at the tibiofemoral joint, and laxation of ligaments [4,5]. Changes in the anatomical and postural alignment can result in alteration of force distribution along the patellofemoral joint, potentially causing an increase in lateral patellar tracking and increasing the stress load on the lateral femoral condyle. Compared to that, men show a smaller Q-angle and a larger ICD, showing relatively neutral and varus knee alignment [6]. Such examination of the gender-specific Q-angle and ICD together is more informative for understanding alignment [5].

Beyond gender differences, the Q-angle and ICD show bilateral similarity, although a smaller left vs. right difference can be seen or arise due to limb dominance, habitual loading patterns, or occupational need and past limb injury [7]. In existing literature, it has been seen that there is a bilateral Q-angle difference in both asymptomatic and symptomatic populations, suggesting that there is a greater mechanical stress on the predisposed limb during different functional activities such as walking, stair climbing, or prolonged standing over a dominant limb [8-10].

Anthropometric factors such as age, weight, height, and body mass index have also been measured in relation to the Q-angle and ICD and show a positive correlation between weight and age with the Q-angle, particularly in women [11,12]. An increase in weight results in increased stress on the lower limb, which may result in lower limb alignment deviations, thereby amplifying biomechanical stress on the knee joint [10]. In the adult population, this parameter becomes more important as this group falls in transition periods wherein an increase in mechanical load may induce early degenerative or overuse conditions [13].

Despite numerous studies done on the Q-angle, comparatively fewer studies have been conducted for the ICD in the adult population, particularly with respect to gender and bilateral baseline comparison. The ICD is a simple, cost-effective physical clinical measurement that provides linear information about the knee alignment in the frontal plane, in contrast to angular assessment [1]. When measured together, the Q-angle and ICD are said to provide a more comprehensive representation of lower limb alignment, measuring both angular and spatial characteristics of the knee joint. The present study aims to evaluate gender-based and bilateral variation in the Q-angle and ICD and to determine the correlation between these parameters among healthy North Indian adults aged 20-50 years to help establish the normative value and clarify the extent of right-to-left variations with age, height, and body weight. Such normative values are required for ergonomic assessment, injury prevention, and early identification of individuals at risk of developing patellofemoral disorder and degenerative knee conditions.