The Persian Version of the SIGAM Mobility Scale Was Cross-Culturally Adapted and Validated in Adults with Lower Limb Amputation

Abstract

Background: Mobility assessment is a crucial aspect of rehabilitation for individuals with lower limb amputation, as it directly influences their independence and quality of life. The objective of this study was to translate and cross-culturally adapt the Special Interest Group in Amputee Medicine (SIGAM) mobility grades questionnaire in the Persian language and to investigate its psychometric properties. Methods: The SIGAM mobility scale was translated into Persian according to international guidelines for cross-cultural adaptation of self-reported measures and was administered to forty Persian-speaking people with lower limb amputations. Measurement properties were evaluated following COSMIN (COnsensus-based Standards for the Selection of Health Measurement INstruments) recommendations and included internal consistency, test–retest reliability, and hypotheses testing for construct validity by comparing SIGAM mobility grades to the Locomotor Capabilities Index-5 (LCI-5), Houghton scale, Activities-specific Balance Confidence (ABC) scale, the 2-Minute Walk Test (2-MWT), and the Timed Up and Go (TUG). Results: SIGAM mobility scale demonstrated acceptable internal consistency (Kuder-Richardson 20 coefficient = 0.72) and excellent test–retest reliability (Cohen Kappa coefficient = 0.85). Hypothesis testing for construct validity confirmed the good to very good correlations of the Persian SIGAM mobility scale with the LCI-5 (r = 0.63, 0.55, and 0.63 for the general, basic, and advanced activities components, respectively), Houghton scale (r = 0.63), ABC scale (r = 0.73), 2-MWT (r = 0.50), and TUG test (r = −0.51). Conclusion: The Persian version of the SIGAM mobility scale demonstrated preliminary evidence of acceptable psychometric properties, supporting its clinical applicability.

1. Introduction

Lower limb loss profoundly alters daily life, affecting not only physical abilities but also psychological, social, and vocational domains [1]. Globally, it is estimated that more than one million people undergo lower limb amputation each year, with vascular disease, diabetes, trauma, and malignancy as the leading causes [2]. In low- and middle-income countries, trauma and untreated infections remain prevalent causes, whereas in higher-income nations, peripheral vascular disease and diabetes dominate [3]. Beyond the loss of a limb, lower limb amputation often results in chronic pain, reduced independence, depression, and social isolation [4]. Individuals with lower limb loss often face reduced independence, increased risk of depression, and limitations in community participation and employment opportunities [5]. The economic burden is also substantial, including costs related to surgical care, prosthetic fitting, rehabilitation services, and long-term healthcare utilization [6]. Successful rehabilitation therefore requires addressing not only physical restoration but also psychosocial adaptation, with mobility recognized as a cornerstone of functional recovery [7].

Mobility is essential for daily activities like personal care, socializing, work, and recreation [8,9]. Lower limb amputation impairs mobility and subsequently lowers quality of life (QOL) [9,10]. Consequently, improving mobility outcomes is a central goal of rehabilitation programs [10,11]. Mobility also affects physical activity, social participation, and emotional well-being [10,12]. Conversely, limited mobility is associated with physical deconditioning, increased fall risk, and poorer psychological well-being [13]. Thus, assessing mobility is critical not only for clinical decision-making but also for identifying those at risk of adverse outcomes and for evaluating rehabilitation interventions [14]. This likely explains why regaining and optimizing functional mobility has been considered a primary goal of rehabilitation for individuals with lower limb amputation [11,15]. Moreover, quality of life is often closely associated with the ability to walk in this population [16,17]. Therefore, assessing mobility outcomes is crucial for informing treatment decisions, selecting appropriate prosthetic components, and evaluating the effectiveness of rehabilitation interventions in individuals with lower limb amputation [18]. Accurate and culturally adapted tools are necessary for assessing these outcomes in diverse populations. Cross-cultural adaptation ensures that measurement tools retain their validity and reliability in different linguistic and cultural contexts.

Mobility can be assessed through clinician-administered, performance-based tests such as the Timed Up and Go (TUG) and Two-Minute Walk Test (2-MWT) [19,20,21,22]. While informative, these timed assessments capture only certain dimensions of mobility and may not fully reflect patients’ lived experiences. Many patient-reported outcome measures (PROMs) have been developed as a result of this point, and as the patient answers them, they can provide unique insights into the respondent’s thoughts, feelings, and experiences without being influenced by the interpretation of the assessor [19]. These PROMs provide more holistic insights by capturing patients’ autonomy, participation, and quality of life, which timed tests often miss. Along with clinical and laboratory mobility measures, patient-reported outcomes can be used for screening, monitoring health outcomes, and evaluating the success of rehabilitation programs in people with LOWER LIMB AMPUTATION [23].

Several self-report tools have been created to assess mobility outcomes in individuals with lower limb loss, but only the Locomotor Capabilities Index-5 (LCI-5) has been validated in the Persian language to date [24]. The LCI-5 is a part of the Prosthetic Profile of the Amputee (PPA) questionnaire that evaluates the capability to perform various walking tasks with a prosthesis; however, its high ceiling effect restricts its sensitivity to changes in higher-functioning individuals [24,25,26]. The Special Interest Group in Amputee Medicine (SIGAM) mobility grades questionnaire, developed by the British Society of Rehabilitation Medicine in 2003, is another assessment tool that is recommended for monitoring the effectiveness of prosthetic interventions in routine clinical practice [27]. This scale features 21 dichotomous (yes/no) items that evaluate amputees’ walking ability across multiple dimensions, including use of walking aids, walking distance, and the ability to navigate different terrain and weather conditions. Responses are processed through a defined algorithm to assign a single global mobility grade from A (lowest mobility) to F (highest mobility), with grades C and D further subdivided by type of walking aid [27]. The SIGAM has been translated and validated in multiple languages, including French, Dutch, and Turkish, where it has demonstrated reliability, validity, and ease of use [27,28,29,30]. Importantly, the scale is quick to administer and sensitive to changes following rehabilitation, making it attractive for both clinical practice and research.

Given the questionnaire’s potential for rapid and comprehensive assessment of walking abilities in individuals with lower limb amputation, along with its high sensitivity to change [27], we translated the measure into Persian and assessed its psychometric properties (internal consistency, test–retest reliability, and hypothesis testing for construct validity) in individuals with lower limb amputations.

2. Materials and Methods

2.1. Study Design

This cross-sectional study had two phases: first, translating the SIGAM mobility scale into the Persian language, and second, assessing the psychometric properties of the translated questionnaire. A convenient sample of forty people with lower limb amputation was recruited from a single center (The Rehabilitation Center of the Iranian Red Crescent Society, Isfahan, Iran) from November 2022 to March 2024. Inclusion criteria included individuals aged 18 or older with unilateral or bilateral amputations at or above the ankle disarticulation level. Exclusion criteria included a history of receiving a prosthesis less than six months prior, modifications made to the prosthesis less than four months ago, inability to read or understand the Persian language, cognitive disorders preventing questionnaire completion, and concurrent neurological or orthopedic deficits that further impaired mobility. A sample size of 40 was deemed acceptable for this preliminary validation study. Although general recommendations for correlation analyses suggest >50 participants (e.g., Green’s formula) [31], recruitment was limited by the strict eligibility criteria and the relatively small pool of eligible participants at a single center. This sample size, however, is comparable to or larger than those used in other cultural adaptations of the SIGAM scale (e.g., n = 50 in French, n = 43 in Turkish). The study protocol was approved by the Medical Ethics Committee of Isfahan University of Medical Sciences. All patients completed a written informed consent form prior to the study.

2.2. Transcultural Translation

We obtained permission from the SIGAM mobility scale’s developer to translate it into Persian, a language spoken in Iran, Afghanistan, and Tajikistan, and carried out the translation in consultation with the same developer (N.R.), as an expert. We adhered to the cross-cultural adaptation guideline recommended by Beaton et al. [32]. The first phase involved the questionnaire being independently translated into Persian by two bilingual native Persian speakers. A Ph.D. in physiotherapy was held by one of these translators, whereas the other was not in the healthcare profession. In the second step, a panel of experts, including the two translators and the first author, reviewed the discrepancies between the translations and created a synthesized version of the questionnaire. In the third step, two independent bilingual native English translators, unaware of the original questionnaire and not affiliated with the healthcare profession, translated it back into Persian. In the fourth step, a committee of experts (a methodologist, four translators, two physical therapists, and four prosthetists) reviewed all translations for semantic, idiomatic, experiential, and conceptual equivalence, finalizing a consensus version. The developer received the back-translation to assess its conceptual equivalence to the original version. The SIGAM’s pre-final Persian version was then pilot-tested on a small sample (n = 10) to evaluate its face validity and identify any items that were unclear, challenging, or culturally inappropriate.

2.3. Variables Measured

Each participant’s demographic and amputation-related data were recorded, including age, sex, the level and side of the amputation, the length of time since the amputation, and the reason for the amputation. We documented the outcomes of the four patient-reported questionnaires, which included the Locomotor Capabilities Index-5 (LCI-5), Houghton scale, Activities-specific Balance Confidence (ABC) scale, and SIGAM mobility scale (Supplementary File S1), in addition to the results of the two performance-based outcomes, the Timed Up and Go (TUG) test and the Two-Minute Walk Test (2-MWT). The participants were asked to complete the SIGAM mobility scale a second time at a two-week interval in order to evaluate test–retest reliability.

2.4. Instruments

• SIGAM Mobility Scale

There are 21 items on the SIGAM mobility scale, each having a yes/no response choice. These questions evaluate the amputee’s walking ability across various surfaces, climatic conditions, distances, and with the use of walking aids. The SIGAM has a simple algorithm for assigning mobility grades (A to F), with grade A representing the worst status and grade F the best. Grade C is further divided into C/a, C/b, C/c, and C/d based on the use of different walking aids, while Grade D is subdivided into D/a, D/b, and D/c according to whether one stick, two sticks, or no walking aids are used, respectively [27].

• Houghton Scale

This scale is a self-report outcome measure that includes four questions assessing daily prosthetic use and walking ability [33]. The first three questions use a four-point ordinal scale. The fourth question consists of three subcomponents, each with dichotomous response options. The total score ranges from 0 to 12. This scale has been used in Persian studies but lacks formal validation; its reported test–retest reliability (ICC) in the original version is 0.97 [34].

• Locomotor Capabilities Index-5

It is a self-report measure to evaluate patients with prostheses on their perceived ability to perform various ambulatory tasks [35,36]. The questionnaire comprises 14 items on a five-point ordinal scale, divided into two subscales: basic activities and advanced activities. Each subscale score ranges from 0 to 28. The Persian version of the LCI-5 has demonstrated good test–retest reliability (Interclass Correlation Coefficient = 0.94) [24].

• Activities-specific Balance Confidence Scale

This 16-item self-report questionnaire asks patients to rate their confidence in performing various ambulatory activities on a numerical scale [37]. A score of zero reflects no confidence, while a score of 100 represents maximum confidence. Although the ABC scale is used in Persian clinical practice, it lacks formal validation. Its original version showed excellent test–retest reliability (Spearman rho = 0.92) [38].

• Two Minutes’ Walk Test

It involves measuring the distance (in meters) a patient walks with a prosthesis in two minutes [21].

• Timed Up and Go Test

This performance test assesses mobility through actions such as standing from a chair, walking three meters, turning, and walking back to sit down again [39].

2.5. Statistical Analysis

Descriptive statistics were calculated for the study variables. The normal distribution of continuous variables was assessed using Shapiro–Wilk’s test. The measurement properties were evaluated following the COSMIN (COnsensus-based Standards for the selection of health Measurement INstruments) recommendations [40]. The Kuder-Richardson Formula 20 (KR-20), a special case of Cronbach’s alpha for dichotomous items, was applied to evaluate the internal consistency of the SIGAM mobility scale scores during its initial administration. A value of 0.7 to 0.9 is considered acceptable [41]. The Cohen’s Kappa Coefficient was used to evaluate the test–retest reliability between the SIGAM mobility scale scores from the first and second administrations. A Kappa coefficient of >0.81 indicates almost perfect agreement, 0.80–0.61 signifies strong agreement, 0.60–0.41 reflects moderate agreement, 0.40–0.21 demonstrates weak agreement, and <0.21 represents very weak agreement [42]. Hypothesis testing for construct validity, specifically to evaluate convergent validity, was performed by analyzing the correlation between SIGAM mobility grades and the 2-MWT, TUG, ABC scale score, Houghton scale score, and LCI-5 subscale scores using Spearman’s rank correlation. A correlation coefficient of ≥0.4 is satisfactory, 0.4–0.6 is good, 0.61–0.80 is very good, and 0.81–1.00 is excellent [43]. It was hypothesized a priori that there would be a good correlation between the SIGAM mobility grade, the 2-MWT score, and the TUG score. A good correlation was also expected between the SIGAM mobility grades and the Houghton scale scores, ABC scale, and subscale scores of LCI-5. For the statistical analyses, which were conducted using SPSS software (V.18; IBM, Armonk, NY, USA), the significance level was set at 0.05.

3. Results

Forty people with lower limb amputation (31 males and 9 females) participated in the validity study. The mean age of participants was 48.4 ± 14.8 years. Amputation was caused by trauma in 52.5% of patients and diabetes in 20%. Demographic characteristics of the participants are presented in

Table 1. Demographic and amputation-related characteristics of participants (n = 40).

Variable		Value*
Age (year)		48.4 ± 14.8 (18–78)
Height (cm)		172.13 ± 10.06 (150–190)
Weight (kg)		76.85 ± 13.25 (50–106)
Time since amputation (year)		15.35 ± 14.95 (1–49)
Gender	Male	31 (77.5%)
	Female	9 (22.5%)
Level of amputation	Below knee	39 (97.5%)
	Above knee	1 (2.5%)
Amputation side	Left	20 (50%)
	Right	17 (42.5%)
	Double sides	3 (7.5%)
Cause of amputation	Trauma	21 (52.5%)
	Avascular necrosis	1 (2.5%)
	Diabetes	8 (20%)
	Cancer	3 (7.5%)
	Congenital limb deficiency	2 (5%)
	Burnt	5 (12.5%)
Activity levels	K1: limited mobility, indoor walking	2 (5%)
	K2: community walking, basic obstacles	12 (30%)
	K3: active mobility, variable pace	24 (60%)
	K4: high-energetic activities	2 (5%)

* Values are presented in mean ± SD and range (Minimum–Maximum) unless indicated in another form.

.

3.1. Translation

No major changes were made during the forward and backward translation process. Only the challenges in selecting a more suitable translation for “false leg” and “indoors” were discussed. The term “false leg” used in many items in the SIGAM mobility scale questionnaire was translated as “Pa (Paha) Masnoei” (artificial limb). “Indoors” was translated as “Fazaye Mosaghaf” by one translation and as “Dakhele Khaneh” by another. In the end, we chose to translate “indoors” as “Dakhele Manzel” since the patient will comprehend it better. The pilot study did not provide any challenges for the participants. Less than five minutes was needed to finish the questionnaire.

3.2. Reliability

Since items 1, 2, 5, 14, and 17 had zero variance and were therefore not regarded as variables, they were not included in the internal consistency analysis. Items 9, 13, 15, and 21 were negatively correlated with the total score, prompting their reversal. The KR-20 coefficient was 0.71. All patients participated in test–retest reliability, yielding a Cohen Kappa Coefficient of 0.85.

3.3. Validity

There was a strong association between the LCI-5 basic activities (r = 0.55), 2-MWT (r = 0.50), TUG scores (r = −0.51), and the SIGAM mobility grade.

Table 2. Summary measures of questionnaires and correlation between the different questionnaires and SIGAM.

Questionnaire/Test	Value	r	p-Value
SIGAM grades		NA	NA
A	0 (0%)
B	0 (0%)
C	3 (7.5%)
D	2 (5%)
E	13 (32.5%)
F	22 (55%)
2-MWT (meter)	96.5 ± 36.24 (7.12–150)	0.50	0.001 *
TUG (sec.)	15.97 ± 21.87 (5.62–144)	−0.51	0.001 *
Houghton scale	10.55 ± 1.43 (6–12)	0.63	<0.001 *
ABC scale	80.78 ± 23.47 (11.25–100)	0.73	<0.001 *
LCI-5 general	49.48 ± 12.25 (14–56)	0.63	<0.001 *
LCI-5 basic activities	26.2 ± 4.51 (11–28)	0.55	<0.001 *
LCI-5 advanced activities	23.28 ± 8.23 (1–28)	0.63	<0.001 *

* Indicates a significant correlation; r indicates Spearman’s correlation coefficient. NA: not applicable; Values are presented in mean ± SD and range (Minimum–Maximum) unless indicated in another form.

presents the results of hypotheses testing for the construct validity results. The ABC score (r = 0.73), the Houghton score (r = 0.63), the LCI-5 total index (r = 0.63), and the LCI-5 advanced activities subscales (r = 0.63) all show very strong associations with the SIGAM mobility grades.

4. Discussion

This study translated the SIGAM mobility scale from English to Persian and evaluated its psychometric properties in individuals with lower limb amputation. Forty participants with lower limb amputation participated in the validation phase, and all of them completed the SIGAM mobility scale again two weeks after its initial administration to assess test–retest reliability. The correlation between SIGAM grades and scores from similar questionnaires like the ABC scale, LCI-5, and Houghton scale was evaluated as part of hypothesis testing for the construct validity of the SIGAM mobility scale. Furthermore, the TUG and 2-MWT tests were used to assess construct validity, as they measure various mobility-related aspects relevant to evaluating the physical functioning of people with lower limb amputation. The lack of a gold standard made it impossible to verify the criterion validity of the Persian version of the SIGAM mobility scale.

The mean 2-MWT distance in our study sample was 96.5 m. Walking distance is widely known to be altered by functional levels, with reference values of 138.4 m and 81.7 m recorded for K3 and K2 levels, respectively [44]. The study found a positive correlation between SIGAM mobility grades and the 2-MWT. Contrary to our findings, Joussain et al. [30] reported no correlation between the French version of the SIGAM mobility grades and the 2-MWT. However, they noted a strong correlation when excluding patients who could walk 50 m without stopping. The mean score on the ABC scale for our participants was 80.78, suggesting a good level of balance confidence during various ambulatory activities. In this study, where over half of the participants were classified as near-normal ambulators (grade F), it is not surprising to find a strong positive correlation between the SIGAM mobility grades and the ABC scale, as balance plays a vital role in developing and regaining walking ability [45]. Previous studies have demonstrated a strong link between balance and walking ability in individuals with lower limb amputation [18]. Additionally, the SIGAM mobility grades exhibited a significant negative correlation with the time taken to complete the TUG test. This implies that as patients’ mobility increases, the time required to complete the TUG test is reduced. In our study, approximately 55% of participants received a grade of F (near normal), and roughly 62% were able to accomplish TUG tasks such as getting out of a chair, walking three meters, turning, and returning to a sitting position in 10 s or fewer. Similar to our findings, Yilmaz et al. [28] found a considerable negative connection between the TUG score and the Turkish version of the SIGAM mobility grades.

The SIGAM mobility scale showed strong and positive relationships with the Houghton score, the LCI-5 total index, and the advanced activities subscale, as well as a positive association with the LCI-5 basic activities subscale. The mean score on the Houghton scale for our participants was 10.55, indicating the participants were successful prosthetic ambulators. The LCI-5 and Houghton scale are appropriate for use in the initial rehabilitation stage, not for long-term follow-up [19], whereas the SIGAM mobility scale can be used for follow-up and can assess mobility levels of amputees, the need to use walking aids, and the ability to move various walking distances, on variable terrain, and even in different weather conditions. As a result, the SIGAM can provide healthcare practitioners with an accurate indicator of lower limb amputee mobility for clinical applications.

The Cohen Kappa coefficient was 0.85, indicating high test–retest reliability of the Persian SIGAM mobility scale. The current study’s reliability value was similar to the original SIGAM mobility scale (k = 0.86) and its adaptation into French and Turkish (k = 0.87 and 0.82, respectively) [27,28,30]. It should be noted that the time gap between test and retest administration for the Turkish version was 72 h, whereas the test–retest interval was considered two weeks in our study; therefore, the Persian reliability results could be more favorable for clinical use. The reliability of the Dutch SIGAM is higher than the value found in the current study. Although excellent test–retest reliability was recorded in the Dutch version (ICC = 0.90) for patients with steady walking ability, it was fair to good for non-stable patients [29].

The KR-20 coefficient was 0.71, suggesting acceptable internal consistency for the dichotomous items. It should be noted that when a questionnaire evaluates a large scope, internal consistency coefficients are low; when a questionnaire tests a restricted scope, they are higher. The SIGAM mobility scale incorporates numerous dimensions, including walking ability, esthetics, and weather circumstances; hence, its internal consistency is acceptable but not higher.

Our study has some limitations. None of the participants received grade A (amputees not wearing prostheses) or grade B (prostheses used only for therapy). Thus, our participants are functional ambulators; those using prostheses solely for esthetics or transfers were excluded. Additionally, three participants were grade C (walking less than 50 m on level ground), and two were grade D (walking over 50 m in good weather on level ground). While the study’s inclusion of diverse causes of lower limb amputation enhances representativeness, it also results in a less homogeneous sample. While trauma is the second leading cause of lower limb amputation after peripheral vascular disease [45], in our study population, the primary cause was trauma from gunshot wounds and traffic accidents. The superior SIGAM grades and mobility outcomes in our study can be partly attributed to the younger age of our participants. Participants’ mobility and balancing abilities could be considerably reduced if they had amputations from vascular insufficiency and other age-related systemic comorbidities. An additional limitation was the use of the Houghton and ABC scales, which, although commonly applied in Persian clinical settings, have not undergone formal validation in Persian. This may affect the interpretability of the correlations observed with these tools. Additionally, the limited sample size (n = 40), below the ideal threshold suggested by rules of thumb for correlation analyses, reflects recruitment challenges with this specific population. As a result, factor analysis could not be performed, and results should be interpreted with caution. Another limitation is that not all psychometric properties were evaluated. For example, responsiveness and structural validity (via factor analysis) were not assessed in this preliminary study. Future studies with larger samples are needed to address these measurement properties.

5. Conclusions

This study conducted a cross-cultural adaptation and preliminary psychometric evaluation of the Persian version of the SIGAM mobility scale in individuals with lower limb amputation. The findings demonstrated acceptable internal consistency, good test–retest reliability, and preliminary evidence based on hypothesis testing for construct validity, as assessed using COSMIN-recommended domains of measurement properties. While the results are encouraging, they must be interpreted with caution due to the small sample size and the lack of structural validity testing (e.g., factor analysis). Future studies with larger, more diverse samples are needed to confirm these findings and to assess additional measurement properties such as responsiveness and cross-cultural equivalence. Until then, the Persian SIGAM mobility scale may serve as a promising tool for assessing patient-reported mobility in clinical and rehabilitation settings.