To our knowledge, this is the first study to investigate the relationship between Achilles tendon elastography and frailty. We observed a significant difference in AT-SWE between frail and non-frail individuals. Although AT-SWE measurements was found to be significantly lower in the frail group and there was a significant negative correlation with FFP score, we could not find a significant relationship between AT thickness and frailty; suggesting that SWE may provide unique information beyond structural changes. Moreover, regression analysis demonstrated that AT-SWE maintained a significant relationship with frailty even after adjusting for age, gender, and chronic diseases or the number of medicines used.
Shear wave elastography, showed a high level of agreement between operators, making it a reproducible technique for quantitatively assessing the mechanical properties of the AT. Using a longitudinal plane and a relaxed foot position, measures were shown to be even more reliable[17]. In this context, we also conducted measurements, using a longitudinal plane and a relaxed position.
The body's largest and strongest tendon AT, connects the calf muscles to the heel bone [4], and is susceptible to degenerative changes and altered stiffness due to its frequent use and strain during physical activities. Age and gender-related changes in AT stiffness have been previously examined, revealing a decrease in stiffness with age [13, 18–20]. Consistent with previous findings, we also found a negative correlation between age and AT SWE measurements.
Previous studies conducted with young adults examining the relationship between gender and AT flexibility have yielded conflicting results. In some studies it is claimed that men tend to have stiffer tendons compared to women in young [21] and older adults [22], and this difference attributed to changes in estrogen levels and force production abilities [21]. However, another study also found differences in the AT in terms of stiffness, tendon elongation, and strain between adult men and women, but statistical analysis revealed that the difference, was correlated to the difference in muscle strength rather than gender [23]. We did not observe a statistically significant difference in tendon stiffness between genders. This discrepancy may be due to differences in the studied populations. To address the confounding effect of the increasing incidence of frailty with age [11] and gender-related tendon stiffness in older adults previously reported in the literature, we performed regression analyzes adjusting for age and gender. It was observed that the significant relationship between frailty and AT-SWE persisted.
Tendon stiffness, which describes the relationship between applied force and tendon’s length change, significantly influences tendon kinematics during movement and enhances motion [23]. Age-related changes in AT stiffness have been shown to affect walking speed in older adults, which is a parameter of FFP[14]. We observed a weak but significant positive correlation with gait speed (0.230, p = 0.005), indicating that walking speed increases as the AT stiffness increases.
Although several studies have implicated the change of AT stiffness in various populations, including individuals with gout[24], hypothyroidism [25], DM [26], and cardiovascular disease [27], the significance of AT-SWE persists even after adjusting for CVD, DM, HT, hypothyroidism treatment, and the number of medicines used in different models of regression analyses. These results therefore strengthen our hypothesis by showing that the association between AT and frailty is independent of common parameters shared with low AT stiffness, such as gait speed decline, and the multimorbidity associated with frailty.
Our study has several strengths. Primarily it is the first study in the literature to examine the relationship between AT and frailty. Secondly, we try to carefully exclude the factors espically diseases with physical consequences that could influence the investigation of the relationship between AT and frailty. However, the study has some limitations. One of these is the cross-sectional design of the study. Longitudinal, prospective studies are the ideal approach, but they would be impractical for understanding the effects of aging and other confounding factors on AT stiffness. In this context, we were unable to assess changes in patients' weight, the severity and chronic course of diseases until their current age, exercise habits throughout their lives, and variations in biomechanical load on the AT due to working conditions. Additionally, medications such as corticosteroids, quinolone antibiotics, aromatase inhibitors, and HMG-CoA reductase inhibitors used in comorbid diseases throughout life can affect the AT, often causing tendinopathy [28] and the other muscles and tendons may also be affected by one or a combination of these drug classes. Although the current results include chronic diseases and laboratory values that could affect tendon structure, we could not analyze recent and past drug use histories. Given the challenges of long-term monitoring of all these factors, cross-sectional designs with larger sample sizes covering a wide age range would be valuable.
In conclusion, our findings suggest that reduced AT stiffness is associated with frailty and may serve as a valuable marker for identifying individuals at risk of adverse health outcomes. Further research is needed to elucidate the underlying mechanisms and clinical implications of this relationship. AT SWE may offer a novel perspective on frailty and develop interventions to prevent or mitigate frailty-related functional decline in older adults.