Early-onset scoliosis (EOS) is defined as an abnormal spine curve of >10° with an onset age of <10 years [1]. Congenital anomalies of the vertebrae, neuromuscular, and syndromic conditions, and unknown causes are common causal reasons. If left untreated, EOS may cause severe spinal deformities and cardiorespiratory problems, increasing the mortality risk [2–4]. Pediatric patients with EOS and their caregivers experience several challenges owing to progressive spine deformity and the possibility of lung dysfunction [5]. Thus, a comprehensive view of the condition of EOS patients and their families is important.

The most common treatments for pediatric EOS patients are serial casting [6], brace wearing [7], and surgery [8]. Complications that can be treated non-surgically are skin lesions, chest deformities, cardiorespiratory problems, and kidney dysfunction [9]. Complications related to surgical procedures include infection, instrumentation failure, long-term hospital stay, and neurodevelopmental issues caused by repeated anesthesia administration [10–12].

Generally, EOS patients with progressive curves need long-term treatment that is stressful and expensive; further, it may affect different life aspects of the patients and their parents. Therefore, as clinical and radiological parameters, the health-related quality of life (HRQoL) variables of EOS patients should also be considered to evaluate the outcomes of the disease and its treatment types.

The 24-item Early-Onset Scoliosis Questionnaire (EOSQ-24) is a parent-based instrument designed by Matsumoto et al. [13] for assessing the HRQoL of EOS patients and their caregivers. Previous research has demonstrated that EOSQ-24 is a valid outcome measure for evaluating the quality of life (QoL) of EOS patients [14–20].

Similar to other widely used questionnaires, the EOSQ-24 requires to be translated into other languages for use in populations from different cultures and societies. This increases the possibility of international communication and allows researchers to compare the results of their studies. Currently, the EOSQ-24 is available in Chinese [21], Arabic [17], Norwegian [18], Dutch [15], Turkish [20], Spanish [19], German [16], and Brazilian Portuguese [14] versions.

Thus, this study aimed to translate the EOSQ-24 into Persian and investigate its validity and reliability.

The ethics committee of Iran University of Medical Sciences approved the study protocol (no., IR.IUMS.REC.1398.791). Before initiating the study, we contacted the EOSQ-24 developers via email and obtained their approval for translation.

The study was performed in the following two phases: (1) the translation and cross-cultural adaptation of the EOSQ-24 into the Persian version (P-EOSQ-24) (development phase), and (2) the validity and reliability analysis of the P-EOSQ-24 (validation phase).

This study investigated the psychometric properties of the P-EOSQ-24 in EOS patients. As per our findings, the P-EOSQ-24 has very good internal consistency and satisfactory convergent and known groups validity.

The results of the Cronbach’s α coefficient revealed that the P-EOSQ-24 has very good internal consistency (Cronbach’s α=0.88). Therefore, the P-EOSQ-24 has a homogeneous internal structure for measuring the HRQoL of EOS patients. In the other versions of the EOSQ-24, the Cronbach’s α value was 0.88–0.95 [14–21], consistent with that in the P-EOSQ-24. With respect to the sub-domains of the EOSQ-24, the Cronbach’s α value was >0.7 in the pain, physical functioning, fatigue, parental status, and emotion sub-domains. However, the value of the Cronbach’s α was <0.7 for general health, pulmonary function, daily living, and satisfaction sub-domains.

In the Chinese [21], Brazilian Portuguese [14], and Dutch [15] versions, Cronbach’s α was <0.7 in general health and pulmonary function sub-domains, consistent with our results. In the daily living sub-domain, our results were consistent with those in the Brazilian Portuguese version [14]. However, in the satisfaction domain, our results were different from the results of the other versions of the EOSQ-24. This might be because of the different perspectives of the parents with respect to certain questions in this domain. In our study, most parents (87%) stated that their child did not have a particular problem in dressing and did it without any challenges (Q11). In Q12, 51% of the parents reported that their child required the same amount of time to eat the same amount of food as a healthy child. In Q23 from the satisfaction domain, the parents are required to answer a question about their child’s satisfaction with his/her ability to perform tasks. However, Q24 seeks to know the parents’ satisfaction with their child’s ability to perform tasks. In Q23, parents answered this question based on their point of view on behalf of their child. In fact, the patients’ perceptions about their child’s functional limitations and his/her ability to perform tasks can be different from the child’s perspective.

In order to evaluate the convergent validity of the P-EOSQ-24, we compared the corresponding sub-domains of this questionnaire with the P-SRS-22r. The results showed a significant correlation between these two questionnaires (r range, 0.23–0.78). In the report on the Dutch version [15], the researchers first used the parent form of the SRS-22 to evaluate the convergent validity of the EOSQ-24, wherein a strong correlation was obtained between the two questionnaires (r range, 0.61–0.76). The original version of the SRS-22 was developed for adolescents who had idiopathic scoliosis [23]. However, recently, Li et al. [28] conducted a study on patients with congenital scoliosis and found that except for the satisfaction domain, there was a strong correlation between all the sub-domains of the SRS-22 and EOSQ-24. Therefore, SRS-22 is a good instrument for investigating the convergent validity of the EOSQ-24.

The total score of the P-EOSQ-24 showed that it could discriminate patients with different curve magnitudes. As expected, we found that patients with a lower curve magnitude had superior QoL than those with a higher curve magnitude. This result is in keeping with the results obtained from the Spanish [19], Dutch [15], Norwegian [18], and Arabic [17] versions. However, the P-EOSQ-24 could not discriminate between the patient’s sex and treatment type. This may be attributable to the heterogeneity of the patients receiving different surgical and non-surgical treatments. Similar results were also obtained in the Dutch version [15].

The P-EOSQ-24 had a low percentage of missing response (<1%), indicating that it offered sufficient clarity and can be well understood by the parents. There were no floor effects in our population in keeping with the results obtained in the Dutch [15], Spanish [19], Norwegian [18], Turkish [20], and Chinese [21] versions. However, in the Arabic version [17], Q17 had a significant floor effect (36.2%). In the Brazilian Portuguese version [14], Q10 and Q11 showed a significant floor effect (43.4% and 32.9%, respectively). Similar to previous studies, the ceiling effect was observed in some items of the P-EOSQ-24 [14–17,19–21]. The highest ceiling effect was related to Q2 (general health). The reason might be that the child’s health was very important to the parents or because most parents do not consider their children as being unwell. Further, Q5 and Q6 (pulmonary function) and Q7 (transfer) had high ceiling effects, in agreement with the results obtained from the Dutch [15], Spanish [19], Norwegian [18], Brazilian Portuguese [14], and Arabic [17] versions.

There were some limitations to this study. First, most study subjects had idiopathic scoliosis and were ambulatory. Therefore, it was not possible to compare their EOSQ-24 scores with those of non-ambulatory patients and patients with syndromic, congenital, and neuromuscular scoliosis. Second, we did not assess the changes in the EOSQ-24 scores over time and during the treatment periods. Third, we performed this study at only two referral centers for EOS; therefore, its generalizability to the entire Persian-speaking population is unclear. However, about 50% of the patients came from different regions of Iran for treatment.

Finally, Persian is one of the oldest languages of the world that is still spoken. At the present time, this language is spoken in many regions of the world, including but not limited to several modern Middle-Eastern and Central Asian countries. These countries or many of their regions were once parts of Iran (Persia), a much larger country, including Afghanistan, Pakistan, Uzbekistan, Turkmenistan, Tajikistan, Armenia, Azerbaijan, etc. In all these countries, Persian (Farsi) remains the mother tongue or second language of people residing in certain areas. Currently, there are three standard forms of the Persian language, Tehrani or Farsi (used formally in Iran), Dari Persian (used formally in Afghanistan), and Tajiki Persian (used formally in Tajikistan and myriad people in Uzbekistan) [29]. We performed this study in Iran; all the included participants spoke the Tehrani dialect. Although Persian speakers in Iran, Afghanistan, and Tajikistan can communicate with each other, there might be instances of different understandings of a word or phrase in some dialects or vernaculars owing to geographical and cultural differences (the same problem that is apparent in all English or French language questionnaires that are only provided in the standard dialects, including the original English version of the EOSQ-24). Therefore, the applicability of the EOSQ-24 in the other forms of the Persian language and regions of the world requires further investigation.

The P-EOSQ-24 can serve as a disease-specific instrument that possesses strong validity and reliability for the evaluation of patients with EOS.