Sex-based differences and relationship with the restricted knee flexion angle due to aging: a comparative study

BACKGROUND: The relationship between inferior patellar mobility (IPM) and knee flexion angle has yet to be elucidated. This study aimed to develop quantitative IPM measurement methods and clarify the relationship between IPM and knee flexion angle in community-dwelling older females. METHODS: This was a cross-sectional study. Overall, 128 healthy older women (age 65–79 years) were recruited from the community to evaluate the relationship between IPM and knee flexion angle. This study was performed between May 2015 and December 2017. The reference value of and sex differences in IPM were evaluated in 205 healthy young adults aged between 19 and 21 years. IPM was compared between healthy older and young women and was objectively measured using our specially designed patellofemoral arthrometer (PFA). Patellar mobility was calculated by normalization to body height. IPM reliability was assessed before all measurements. RESULTS: Intraclass correlation coefficients for intratester and intertester reliabilities varied from 0.87 to 0.99. The normal range based on two standard deviations of inferior patellar displacement/body height was 5.9–13.5% (young men), 5.1–14.3% (young women), and 1.2–8.8% (older women). IPM was significantly lower in older than young women (P < 0.001). There was a significant positive correlation (r = 0.72 and P < 0.01) between IPM and knee flexion angle in healthy older women unable to flex the knee joint fully. CONCLUSIONS: Our PFA has good intratester and intertester reliability. The results suggest that IPM decreases with aging in women. IPM and knee flexion angle are correlated among older women unable to flex the knee joint fully. CLINICAL TRIAL REGISTRATION: Not applicable. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-023-06367-0.