An appropriate measure such as the FAOS is essential for monitoring patient outcomes and the efficacy of treatment in CLAI patients. Results of this study demonstrated that all five subscales of the Indonesian version of the FAOS displayed nearly symmetrical score distributions, low floor and ceiling values, acceptable internal consistency and test-retest reliability, satisfactory responsiveness, and fair construct validity, although certain items in the pain and OSs subscales showed lower factor loadings.
Among the five subscales of the FAOS, the ADLs and FAQL had the highest proportions of ceiling values, indicating that a substantial proportion of participants might not have experienced any restriction in their daily activities, and they may also have a satisfactory social life. Previous studies showed that young adults with CLAI maintained sufficient performance of their daily activities and an adequate quality of life , whereas older CLAI patients had poorer daily activities and quality of life compared to healthy older people . Our study sample may have contributed to the high ceiling values in the FAOS’s ADL and FAQL in that young patients have faster physical and mental recovery from neuromuscular dysfunction, as well as a faster return to routine ADLs and sports, compared to older patients .
A low correlation unexpectedly existed between the pain subscale of the FAOS and the NPRS. A study even found a negative correlation (r=-0.74) between FAOS’s pain and the NPRS . One possible explanation for this result is that the FAOS and NPRS use different time periods to assess pain. The FAOS measures pain based on multiple activities during the previous week, and the NPRS evaluates the intensity of pain in the past 24 h. Since pain is a multidimensional construct , the underlying constructs between the FAOS’s pain and NPRS might considerably differ. Future research might consider using other pain instruments, instead of the NPRS, with a construct similar to the FAOS’s pain subscale.
Item P1 (pain frequency) had a low loading on the latent pain subscale (Factor 4) but had a higher loading on the latent FAQL (Factor 5). This low loading might have been due to P1 evaluating the pain frequency, while the other items of the subscale evaluate the pain intensity for a specific ankle function. Another possible explanation for this finding is that participants may have misperceived P1, which asks about the extent to which the foot and ankle problem affects their daily life, like FAQL1, since other items of the pain subscale ask about the pain intensity in specific ADLs . Items P3 (pain during ankle straightening), P4 (pain during ankle bending), and P5 (pain on walking on a flat surface) had low loadings onto their latent pain subscale but had higher loadings onto the latent ADLs or OSs factors from the PCA. Since young athletes usually have high expectations for returning to their preinjury sport and overcoming setbacks following an injury , the characteristics of our young participants may have played a role in that result. Furthermore, individuals with a higher athletic identity also had more-positive attitudes and reported a higher level of willingness to play through pain than did those with a lower athletic identity, and young athletes commonly have a strong athletic identity . Since young Indonesian patients are more likely than older patients to undertake self-treatment with anti-inflammatory drugs to reduce musculoskeletal pain , those with a CLAI might use over-the-counter pain medications to keep physically and socially active in their daily lives or sport activities .
Items OS6 (morning stiffness) and OS7 (resting stiffness) were not moderately or highly correlated with OSs but were with ADLs. We noted that both OS6 and OS7 assess the severity of an ankle’s symptoms during a specific time, while the other items of the OSs assess the severity in a particular function. In addition, it seems that the type of rating scale anchors of OS6 and OS7 were the same as those of the FADL’s items (intensity type) but different from the other items of OSs (frequency type). Nonetheless, associations of morning stiffness with functional disability and pain were found to be stronger than the association of swelling and the erythrocyte sedimentation rate in patients with early rheumatoid arthritis given that morning stiffness is a symptom used as a measurement of rheumatoid arthritis . As such, our participants might have perceived foot/ankle stiffness in the morning as a functional disability during daily living rather than as a biomarker of CLAI. Furthermore, since resting stiffness may result from a long period of immobilization and muscle positions , our participants may have perceived ankle resting stiffness during sedentary activities, such as studying, working, and watching movies.
Both the distribution-based and anchor-based responsiveness statistics indicated that the FAOS is a responsive HRQOL measure for CLAI patients. Among the five FAOS subscales, pain was the most responsive, possibly because pain is the most common problem of CLAI patients and often is the main reason for a clinical visit . Moreover, most effect sizes of the FAOS subscales in improvement of the SF-36’s “change” were larger than those in deterioration of the SF-36’s “change”, indicating that FAOS items were more sensitive to positive changes in the health status . Anchor-based responsiveness depends on external measures, and here, it was determined by the strength of the association of the FAOS subscale with the SF-36’s “change”. Furthermore, a lower responsiveness in the distribution-based approach vs. the anchor-based approach could have resulted to some extent from positive changes occurring over a 1-month period, which were adjusted in anchor-based responsiveness, because those who perceived no change in the SF-36’s “change” item still displayed considerable positive changes in all five FAOS subscales.
There are some limitations to the study. First, the results possibly cannot be generalized to older populations with CLAI since the ages of our participants ranged 17 ~ 35 years, and they still maintained moderate to high levels of physical activity in their daily lives. It would be intriguing to further investigate whether the FAOS has age-related differential item functioning for CLAI patients. Second, examination of the construct validity was dependent on the selected measures, and some of those measures, such as the NPRS, might not be very appropriate, although the NPRS is one of the most commonly used tools to measure pain. It seems that the NPRS could not capture the complexity and idiosyncratic nature of the pain experiences of CLAI patients. Third, we did not measure intra-articular lesions of the ankle or physical functions of the hip and knee. Intra-articular lesions (synovitis, cartilage defects, tendinitis, and ligament tears) were suggested to be the cause of persistent symptoms of CLAI and were associated with clinical outcomes , while hip and knee problems might also affect ankle functions .