Apex Angle and Lateral Facet Ratio in Dry Human Patellae: Surgical and Morphological Implications

Abstract

Background: The patella is a key determinant of patellofemoral congruence, tracking, and contact stress. Small variations in its shape can influence patellofemoral pain, instability, and postoperative anterior knee symptoms. Among patellar morphologic indices, the apex angle reflects inferior pole geometry, while the lateral facet ratio quantifies lateral facet dominance; both parameters may affect trochlear engagement and patellar tilt. This study aimed to assess sex-related differences in apex angle, lateral facet ratio, and major patellar morphometric parameters in dry adult human left patellae, highlighting their potential surgical and morphological implications.

Materials & Methods: This cross-sectional analytical study was conducted at the Department of Anatomy, Dhaka Medical College, from January 2018 to June 2019. A total of 150 dry adult human left patellae of unknown sex were examined. Sex was assigned using linear discriminant function analysis based on maximum patellar height and width, classifying 92 specimens as male and 58 as female. Morphometric measurements were recorded using a digital slide caliper, a flexible wire for curved surfaces, and a protractor for apex angle. Weight and volume were measured using an electronic balance and a graduated glass cylinder, respectively.

 Results: Among the 150 dry left patellae, 92 (61.33%) were classified as male and 58 (38.67%) as female. Male patellae were significantly larger in major dimensions and mass, including height (42.10 ± 1.99 vs 36.16 ± 2.31 mm), width (42.87 ± 1.80 vs 36.94 ± 1.58 mm), thickness (20.73 ± 1.25 vs 18.69 ± 1.39 mm), weight (10.59 ± 2.13 vs 6.79 ± 1.45 g), and volume (10.88 ± 1.98 vs 7.10 ± 1.34 cm³), all p < 0.01. Males also exhibited greater ridge height and facet widths (all p < 0.01), with small but significant differences in facet thickness (p = 0.001-0.002). In contrast, females showed a significantly higher apex angle (110.17 ± 10.80° vs 104.65 ± 6.80°, p < 0.01) and a higher lateral facet ratio (0.61 ± 0.04 vs 0.58 ± 0.03, p < 0.01), corresponding to mean differences of 5.52° (95% CI: 2.37-8.67; g = 0.64) and 0.03 (95% CI: 0.018-0.042; g = 0.87), respectively. Patellar index and median ridge position did not differ significantly between the sexes (p = 0.599 and p = 0.127). Correlation analysis showed a weak, non-significant association between apex angle and lateral facet ratio (r = 0.11, p = 0.167), whereas lateral facet ratio correlated moderately and negatively with facet widths (r = -0.36, p < 0.01).

Conclusion: Male patellae were significantly larger in overall size and facet dimensions. Conversely, female patellae exhibited a higher apex angle and lateral facet ratio. No sex-based differences were observed in patellar index or ridge position.

Bangladesh Journal of Anatomy July 2023, Vol. 21, No. 2, pp. 50-56