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Achilles tendinopathy is a clinical condition characterized by localized pain and impaired function of the Achilles tendon, particularly during mechanical loading . Achilles Tendinopathy is prevalent among runners, with up to 60 % of active runners being affected over their lifetime . While it is most commonly associated with overuse, it may also occur in the general population in sedentary, middle-aged, and overweight individuals . The condition substantially impairs the functionality of the tendon and is known to cause disability in athletes who consistently load the Achilles tendon . As a result, appropriate treatment and rehabilitation are critical, with exercise being the most frequently utilized therapeutic approach . However, there is a lack of adequate patient-reported outcome measures (PROMs) to assess the effectiveness of these interventions, particularly regarding tendon-related disability ^,, .

The most frequently used self-reported scale in the evaluation of Achilles Tendinopathy is the Victorian Institute of Sport Assessment-Achilles (VISA-A) . It was used in 46 % of the studies on Achilles Tendinopathy in 2021 . However, VISA-A has substantial flaws in its measurement properties, including inadequate content validity (VISA-A development did not involve patient input ^,,,, ), and inadequate structural validity. Further, methodological testing using Rasch analysis has shown that VISA-A scale lacks sufficient structural validity and is significantly influenced by irrelevant factors, such as age and body mass index ^, . In clinical practice, tendon-related disability measures are rarely utilized with concerns related to the relevance, comprehensiveness and comprehensibility ^, . As a result, reviews have highlighted the need to move beyond VISA-A for both research and clinical purposes ^,, .

In response to these limitations, the TENDINopathy Severity Assessment–Achilles (TENDINS-A) scale was developed and its content validity confirmed (Myles C ). Co-designed by patients, clinicians, and researchers, the TENDINS-A addresses the need for a more reliable and valid measure of disability in Achilles Tendinopathy. The scale is focused on assessing the severity of tendon-related disability, covering subdomains of pain, symptoms, and physical function (Myles C ). Initial evaluations of TENDINS-A demonstrate that it has construct validity and excellent reliability (Myles Calder ). Further Rasch analysis has also demonstrated its structural validity and measurement invariance . Given its excellent measurement properties, TENDINS-A has been recommended for use in both clinical practice and research to evaluate the severity of disability associated with Achilles Tendinopathy . To date, TENDINS-A has not been cross-culturally adapted in any languages and its measurement properties have only been evaluated in English. Therefore, the aim of this study was to test the construct validity, reliability (test–retest, internal consistency and standard error of measurement) and interpretability of the Turkish version of TENDINS-A (TENDINS-A-TR) scale. Additionally, the study aimed to test and determine the measurement properties of the scale, including cutoff score, sensitivity, specificity, minimal detectable change, minimal important change and ceiling or floor effects. The introduction of the Turkish version of the scale will provide a comprehensive tool for improving the assessment and management of Achilles Tendinopathy in Turkish-speaking populations.

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This observational cross-sectional was approved on 23.11.2023 by XXX University Non-Interventional Clinical Research Ethics Committee (2023/957). Data were collected online between December 2023 and December 2024. Individuals with Achilles Tendinopathy and healthy individuals who agreed to participate signed the informed, electronic consent form. They then completed an online questionnaire containing socio-demographic information and outcome measures. Pain intensity was evaluated using the Numeric Pain Rating Scale (NPRS) at rest, activity, and night , physical activity level with the Tegner Activity Scale , and tendon symptoms with TENDINS-A, VISA-A, and the Foot and Ankle Outcome Score (FAOS).

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People with Achilles Tendinopathy and healthy controls were recruited. Inclusion criteria were: age between 18 and 65 years, local pain using a pain map and tenderness on Achilles tendon palpation, pain and morning stiffness occurring with or after loading of the Achilles tendon (e.g., running, sprinting, jumping activities), pain in the tendon with a single-leg hopping test (NPRS>1/10, where 0 represents “no pain” and 10 represents “the worst possible pain”), symptoms of pain, swelling, tenderness, and morning stiffness in the Achilles tendon in the last 3 months. People with a history of any foot or ankle surgery and/or fracture in the past year, previous Achilles tendon rupture on the affected side, who had injection therapy for the affected Achilles tendon in the past 3 months or have existing symptomatic lower back and other lower extremity musculoskeletal issues or neurological diseases were excluded. The flowchart of the study was shown in Fig. 1 .

Flowchart of the study.

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Permission to use and translate TENDINS-A scale was obtained from the scale’s creators (MCM). The translation and cross-cultural adaptation procedure followed the international guidelines recommended by Beaton et al. . The first step in this process is the translation from the original language to Turkish. This translation was performed by two independent translators proficient in both languages and familiar with their structures. Then, both translations were compared by the authors who are fluent in both English and Turkish, and inconsistencies in the translations were emphasized. Next, authors reached on an agreed version of the translations. Following this, two other independent translators performed backward translation to the original language in order to compare with the original version by a committee consisting of a linguist, and the research team, which includes experts in Achilles Tendinopathy. This committee evaluated and checked the inconsistencies and appropriateness of the translations, and made any necessary cultural adaptations. The committee then finalized and approved the Turkish version of TENDINS-A (TENDINS-A-TR) which is available in Supplement 1.

We created a readily available online version as online use of PROMs are preferable to paper versions due to their accessibility, lower cost, faster completion, and efficient data management ^, . Thus, remote data collection is crucial for reducing patient burden and research costs while ensuring valid and reliable outcomes. Studies in musculoskeletal conditions have confirmed the feasibility and reliability of electronic PROMs ^,,, .

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All outcome measures were completed by participants in a single questionnaire, which forced responses, ensuring no missing data. For the test-retest reliability, TENDINS-A-TR was re-administered within 3–14 days .

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TENDINS-A scale consists of 5 unscored and 10 scored items, 15 in total, assessing situations that increase pain or symptoms, their duration and timepoints (unscored items), pain itself (3 items), symptoms (4 items), and physical function (3 items) (Myles Calder ). Responses vary across items, with each item having its own scoring provided in Supplement 1. Specifically for the physical function subscale, if participants were unable to complete a load-dependent pain test (e.g., single-leg hop), they were instructed to skip it, and a score of ‘10’ was assigned. The total score ranges from 0 to 100, with higher scores indicating a higher level of disability (Myles C ).

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The VISA-A, developed in 2001, consists of eight questions that assess pain (item 1–3), functionality (item 4–6), and activity levels (item 7–8) . Responses to the first six questions are scored from 0 to 10, reflecting the severity of symptoms, while the seventh and eighth questions are categorized into five sections based on the activity-pain relationship and activity duration. An individual participating in asymptomatic sports can score up to 100, while someone not participating in sports can score a maximum of 70. Lower scores indicate greater disability, and scores below 80 suggest the presence of Achilles Tendinopathy. The Turkish validity and reliability of the scale were studied in 2011 .

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The FAOS was developed in 2001 consisted of 42 questions under five subscales to assess pain (9 items), symptoms (7 items), daily life activities (17 items), sport functionality (5 items), and quality of life (4 items) related to the foot and ankle . For each subscale, 0 represents the worst condition, and 100 represents the best condition. The Turkish version of FAOS was validated in 2009 .

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Sample size calculation for the validity was based on minimum 10 events per variable as it is one of the most common methods to estimate sample size in observational studies . Each item of TENDINS-A was considered as a variable. Therefore, minimum required sample size was 130 participants (10 ×13 item) in total. This was based on the development study of 13-item TENDINS-A (Myles C ). Sample size calculation for the reliability was based on COSMIN guidelines, which suggest that a sample of > 50 participants is considered adequate .

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Descriptive statistics were reported as mean±standard deviation for continuous variables and n (%) for categorical variables. Construct validity of TENDINS-A-TR was assessed with VISA-A and FAOS scales in all participants (n = 130). Construct validity was analyzed using Pearson’s correlation coefficients and classified as < 0.3, 0.3–0.5 and > 0.50 being weak, moderate and strong, respectively . For the discriminative validity, Receiver Operating Characteristic (ROC) analysis of TENDINS-A-TR was examined (participants with Achilles Tendinopathy vs healthy participants). With ROC analysis, the best cut-off point for TENDINS-A-TR was determined, and sensitivity and specificity values were calculated for this cut-off point to evaluate the classification success of the scale . Area under the ROC curve was interpreted as acceptable (>0.7) and excellent (>0.8) . To determine the relative reliability of TENDINS-A-TR, test-retest reliability (n = 50) was analysed using the Intraclass Correlation Coefficient (ICC, two-way random, absolute agreement). The ICC values were classified as < 0.5, 0.5–0.75, 0.75–0.9, and > 0.90 being poor, moderate, good, and excellent, respectively . Internal consistency (n = 50) was analysed by calculating Cronbach’s alpha coefficient, and a score of > 0.70 was considered high internal consistency . For the absolute reliability (n = 50), the standard error of measurement (SEM) and the minimal detectable change (MDC) were calculated. The SEM was calculated as SD × √(1-ICC), where SD is the standard deviation of all test and retest scores. Minimal detectable change at the 95 % confidence level (MDC ₉₅ ) was calculated as MDC ₉₅ =SEM × 1.96 × √2. For the interpretability, the minimal important change at the 95 % confidence level (MIC ₉₅ ) was estimated using a distribution-based method as SD × 0.5 , where SD is the standard deviation of the test scores from participants with AT (n = 60). This approach provides a distribution-based estimate of the smallest detectable change likely to be meaningful but does not reflect an anchor-based, patient-reported minimal clinically important difference. Because, MIC ₉₅ refers a meaningful change, it was analyzed in participants with AT only. Finally, the presence of ceiling or floor effects was reported only when more than 15 % of participants with AT obtain the maximum (ceiling effect) or minimum score (floor effect) . Statistical analyses were performed using the licensed IBM SPSS software (version 29.0, USA). A significance level of p < 0.05 was considered statistically significant for all analyses.

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A total of 130 participants including 60 people with Achilles Tendinopathy (Mean±SD age=34.7 ± 11.7 years, n = 34 males) and 70 healthy participants (Mean±SD age=27.8 ± 8.9 years, n = 39 males) were recruited. People with Achilles Tendinopathy were older (p < 0.001) and had lower physical activity levels (p = 0.02) compared to healthy participants. There was a significant difference between people with Achilles Tendinopathy and healthy participants in all PROMs. Demographics and PROM scores were provided in Table 1 .

Table 1

Participants’ descriptive features.

Demographics	All participants (n = 130)	People with AT (n = 60)	Healthy participants (n = 70)	P value
Age, years	30.9 ± 10.8	34.7 ± 11.7	27.8 ± 8.9	< 0.001
Height, cm	172.7 ± 9.3	171.8 ± 7.8	173.6 ± 10.4	0.27
Mass, kg	72.8 ± 13.6	72.5 ± 12.9	73.11 ± 14.4	0.79
Body mass index, kg/m 2	26.6 ± 4.3	24.5 ± 3.8	24.1 ± 3.5	0.54
Tegner Activity Scale	5.60 ± 2.7	5.0 ± 2.4	6.11 ± 2.9	0.02
Male: Female	73 (56 %): 57 (44 %)	34 (57 %): 26 (43 %)	39 (56 %): 31 (44 %)	0.91
Dominant side (Right:Left)	109 (84 %): 21 (16 %)	50 (83 %): 10 (17 %)	59 (84 %): 11 (16 %)	0.88
Injured side
Right Left Bilateral	NA	33 (55 %) 12 (20 %) 15 (25 %)	NA	NA
Education
Primary School Secondary School High School Pre-registration Undergraduate Postgraduate	1 (1 %) 2 (2 %) 35 (27 %) 10 (8 %) 54 (41 %) 28 (21 %)	1 (2 %) 2 (3 %) 11 (18 %) 4 (7 %) 28 (47 %) 14 (23 %)	0 (0 %) 0 (0 %) 24 (34 %) 6 (9 %) 26 (37 %) 14 (20 %)	0.18
Semptom Duration, months	NA	8.2 ± 11.9	NA	NA
Numeric Pain Rating Scale
Rest Activity Night	1.0 ± 1.8 1.9 ± 2.7 0.9 ± 1.8	2.15 ± 2.1 4.1 ± 2.6 1.9 ± 2.3	0.6 ± 0.5 0.1 ± 0.6 0.0 ± 0.3	< 0.001 < 0.001 < 0.001
TENDINS-A-TR score (test)	20.9 ± 21.9	38.2 ± 20.2	5.9 ± 7.7	< 0.001
VISA-A	68.9 ± 26.3	45.1 ± 19.3	89.3 ± 7.7	< 0.001
FAOS score
Symptom Pain Activity daily living Sports Quality of life	85.4 ± 17.4 86.3 ± 16.9 89.2 ± 16.8 80.9 ± 22.3 74.6 ± 29.0	75.4 ± 18.4 73.9 ± 17.3 78.8 ± 19.3 63.2 ± 20.2 51.9 ± 26.8	94.0 ± 10.8 96.9 ± 5.8 98.1 ± 5.8 96.1 ± 8.3 94.1 ± 11	< 0.001 < 0.001 < 0.001 < 0.001 < 0.001

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