Materials and methods

This cross-sectional, observational study was performed to evaluate gender-based variations in the Q-angle and ICD of the femur in an adult Indian population, including 600 participants, 300 male participants and 300 female participants, aged 20-50 years, of North Indian origin. This study was done in the Department of Anatomy, MMIMSR, Ambala, Haryana, following approval from the Institutional Ethics Committee (IEC NO 3511).

This study included adult participants aged 20-50 years without lower-limb deformities. Informed consent was obtained before the study in both vernacular and English languages. The study excluded participants with a history of trauma, surgery in the lower limbs, musculoskeletal or neurological disorders, or any gait abnormalities.

The height of participants was measured using a standard stadiometer (PrimeSurgicals height measuring scale; PrimeSurgicals, New Delhi, India). Participants stood barefoot in an erect posture with heels slightly apart, back straight, and head in the Frankfurt plane. The measurement was recorded to the nearest 0.1 cm.

Body weight was measured using a calibrated digital weighing scale (Thermomate Deluxe product CAMRY, digital weighing scale, CAMRY Electronic Co., Ltd., Zhongshan, Guangdong, China), with participants wearing light clothing and no footwear. Values were recorded to the nearest 0.1 kg.

The Q-angle was measured using a universal manual goniometer (goniometer degree protector angle scale, LISAMED, Coimbatore, India), whose intraclass correlation coefficient consistently exceeded 0.90 [14], following standardized anatomical procedures. The participant was positioned in a standing, weight-bearing posture, with hips and knees fully extended, quadriceps relaxed, and feet placed in a neutral position. Anatomical landmarks were identified and marked as (i) anterior superior iliac spine (ASIS), (ii) center of the patella, defined as the point of intersection of the longest vertical line and transverse diameter of the patella, and (iii) the highest bony prominence of the tibial tuberosity. The axis of the goniometer was placed over the center of the patella. One limb of the goniometer was aligned with the line joining the ASIS to the patella. The other was aligned with the line joining the tibial tuberosity to the patella. The angle formed between these two lines was recorded as the Q-angle (Q°), as shown in Figures 1a, 1b.

Figure 1: a) Measurement of the Q-angle in standing position by a universal 360° goniometer, and b) line diagram for measuring the Q-angle (Q°), showing the following reference points: (A) Anterior superior iliac spine (ASIS); (B) midpoint of the patella; (C) tibial tuberosity.(b) Image credit: Rahul Sharma (first author), and software used for marking the illustration was Paint software, 11.2603.251.0, Microsoft 2026 (Microsoft Corporation, Redmond, USA).

The ICD of the femur was measured using a digital Vernier caliper scaled from 0 cm to 20 cm and with a marginal error of ±1mm (Zhart Vernier Caliper Digital 150mm/6 inch Video Display measurement tool; Zhart, Shenzhen, Guangdong, China) in accordance with standard anthropometric procedures. The participant was seated with the knees flexed to 90° and feet flat, facing forward. The medial and lateral femoral condyles were carefully palpated and identified. The immovable jaw of the caliper was positioned on the lateral condyle, while the moving jaw was positioned on the medial condyle. The distance between the two condyles was then recorded in millimeters (mm), converted into centimeters (cm), as shown in Figure 2. A single trained investigator performed all measurements to ensure consistency and reduce inter-observer variability. Three measurements were recorded for each side, and the average value was noted.

Figure 2: Measurement of the bicondylar distance (ICD) by using a digital vernier caliper.

Data were recorded and incorporated into Microsoft Excel and analyzed using IBM SPSS Statistics for Windows, Version 27 (Released 2019; IBM Corp., Armonk, New York, United States).

Statistical analysis

Descriptive statistics were used to calculate the mean ± standard deviation (SD) for age, height, and weight. Normality of the sample was evaluated using the Shapiro-Wilk W-statistic for male and female participants (p>0.05), which revealed that the ICD was normally distributed, while the Q-angle deviated from normality.

Non-parametric tests were employed to draw statistical inferences regarding the Q-angle, as the data were not normally distributed. The Mann-Whitney U test was conducted to compare the male and female groups, and the Wilcoxon signed-rank test was applied to determine the difference between paired variables on the right and left sides in male participants and female participants.

Parametric tests were applied to draw statistical inferences regarding the ICD, as data were normally distributed. A paired-sample t-test was used to assess the difference between the right and left side variables in male participants and female participants. An independent-samples t-test was used for comparison of normally distributed male and female groups. Spearman's correlation coefficient (r) was used to evaluate the relationships between the Q-angle and ICD for all participants. A significance level of p < 0.05 was adopted.