In a recent cross-sectional study, researchers from The Australian National University and The Canberra Hospital investigated sex differences in the shape of the patellar articular surface among healthy individuals and those with patellofemoral osteoarthritis. The study aimed to quantify differences in patellar morphology between male and female patients and to identify potential shape features that may contribute to the higher prevalence of patellofemoral osteoarthritis in female patients.
In the study, published in Osteoarthritis and Cartilage, the researchers analyzed 97 healthy knees (50 female patients and 47 male patients) and 67 knees with patellofemoral osteoarthritis (40 female patients and 27 male patients) from patients aged 18 to 90 years. All of the participants underwent computed tomography scanning, and three-dimensional models of the patella were created for analysis. The researchers then collected linear measurements and utilized geometric morphometrics to quantify shape differences in the medial and lateral patellar facets.
The researchers discovered that sex differences in patellar dimensions were more pronounced than differences between healthy patients and those with patellofemoral osteoarthritis. The medial facet exhibited greater shape variance than the lateral facet across both sexes and health statuses. Male patients displayed a posteriorly-curving, taller, and narrower medial facet compared with female patients. Lateral facet shape variance increased with higher patellofemoral osteoarthritis severity based on the Kellgren and Lawrence score.
Linear measurements revealed that the patellar dimensions were 5% to 17% larger in healthy male patients compared with healthy female patients and 8% to 21% larger in male patients with patellofemoral osteoarthritis compared with female patients with patellofemoral osteoarthritis. The greatest mean differences were observed in patellar width and height between male patients with patellofemoral osteoarthritis and healthy female patients. One-way analysis of variance (ANOVA) showed significant differences in mean values between groups for four out of six linear measurements: patellar width, medial facet width, lateral facet area, and medial facet area.
Geometric morphometric analysis showed that sex differences were primarily concentrated in size-related shape variations for the lateral facet. In contrast, the medial facet exhibited greater shape variance and sex-specific features, with males having a more posteriorly-curving, taller, and narrower facet compared with females. Procrustes ANOVA revealed significant effects of grouping (healthy female patients, healthy male patients, female patients with patellofemoral osteoarthritis, male patients with patellofemoral osteoarthritis) on both lateral and medial facet shapes. Pairwise comparisons of mean shapes showed significant differences between healthy female patientss and male patients with patellofemoral osteoarthritis for the lateral facet, and between healthy male patients and all other groups for the medial facet.
Disease severity, as measured by the Kellgren and Lawrence score, was not associated with unique shape features in either sex. However, lateral facet shape variance increased significantly with higher scores, indicating greater dispersion about the group mean in more advanced stages of patellofemoral osteoarthritis. Pairwise comparisons showed differences in lateral facet shape variance between all groups except healthy female patients and healthy male patients. Medial facet shape variance did not differ significantly between groups.
The researchers concluded that sex differences in patellar shape were more prominent than differences related to patellofemoral osteoarthritis status. The differing magnitudes of shape variance in the medial and lateral facets may reflect differences in joint loading and contact areas. Although the study did not identify female-specific shape features that could explain the higher prevalence of patellofemoral osteoarthritis in this patient population, the increased lateral facet shape variance associated with patellofemoral osteoarthritis severity warrants further investigation.
The study had some limitations, including its cross-sectional nature, which prevented the assessment of bone shape prior to patellofemoral osteoarthritis onset or symptom development. Additionally, the study did not capture cartilage thickness or patellofemoral joint congruency, limiting the understanding of the biomechanical significance of the findings. Finally, the study may have been underpowered to detect patellofemoral shape differences as a result of its initial design for detecting differences in knee kinematics.
Study authors had no conflicts of interest to declare that are relevant to the content of this article.