Simplified Chinese Version of the Spinal Instability Neoplastic Score in Evaluating Patients with Spinal Metastatic Tumor: A Cross-Cultural Adaptation and Validation


 Background: The Spinal Instability Neoplastic Score (SINS) in simplified Chinese has not been developed so far. This study aimed to translate the SINS into simplified Chinese, adapt it cross-culturally and to validate its psychometric properties in measuring spinal instability in patients with spinal metastatic tumors in the Chinese mainland. Methods: The original version of SINS (in English) was translated and cross-culturally adapted into simplified Chinese according to the internationally recognized guidelines. Internal consistency was evaluated with Cronbach’s alpha. Test-retest reliability was examined among the patients with a 4-week interval. The validity of the Chinese version of SINS (SC-SINS) was assessed by examining its relationship with Kostuik classification. In addition, floor and ceiling effects were considered present if more than 15% of respondents achieved the lowest or highest possible total score. Principal component analysis was conducted to confirm the factor structure of each subscale.Results: No major problems occurred in the forward and back translations of SINS. The internal consistency of SC-SINS was excellent (Cronbach’s a =0.857, ranging from 0.68 to 0.85). Test-retest reliability was also excellent with a value of 0.89, ranging from 0.86 to 0.95. Validity analyses indicated that the SC-SINS was positively and significantly correlated with Kostuik classification. All items showed principal component coefficients of over 0.4. No floor or ceiling effects was found in the SC-SINS.Conclusion: The results indicate that the SC-SINS is reliable and valid in measuring the spinal stability in patients with spinal metastatic tumor.


Background
For patients with metastatic bone disease, the spine is the most commonly affected site (1,2). Spinal metastasis may lead to spinal cord compression, secondary paralysis and dysfunction, which can bring signi cantly negative impacts on the patients' quality of life and survival (3). Spinal cord compression from epidural tumor is often considered as an indication for operation. In most spinal metastatic cases, the goal of surgery is not to cure, but to palliatively relieve pain, and to reduce the risk of spinal cord injury.
For spinal tumor surgery, apart from a thorough understanding of the tumor nature and prognosis, evaluating the stability of the lesion segment is also necessary for detailed surgical planning and outcome assessment. In 2010, the Spinal Oncology Study Group (SOSG) de ned spinal instability as the "loss of spinal integrity as a result of a neoplastic process that is associated with movement-related pain, symptomatic or progressive deformity, and/or neural compromise under physiological loads" (4). At present, two systems are widely used to assess the spinal instability: the Kostuik classi cation and Spine Stability Neoplastic Score (SINS). Kostuik classi cation, which was developed in 1991, divides each vertebra into six columns to determine which lesion may cause mechanical instability and thus require surgical treatment. The six columns include the four columns of the cross section of the vertebral body and two columns at the back. It is suggested that spinal instability occurs when the tumor occupies three or more columns, and will be more severe when the tumor involves ve or more columns.
The evidence-based Spine Instability Neoplastic Score (SINS) was developed based on the best available literature and expert-opinion consensus (5)(6)(7). As an adequate instrument to determine spinal instability, SINS allows easier consultation and communication among specialists treating spinal metastases.
However, SINS, which is in the English language, cannot be accurately understood and accepted by the population in the Chinese mainland. To the best of our knowledge, no reliable and valid simpli ed Chinese version of the SINS is available at present. Therefore, developing SINS in simpli ed Chinese can greatly bene t surgical strategy planning and assessment of clinical outcomes for doctors or physicians.
The objective of this study was to translate and cross-culturally adapt the original English version of SINS into simpli ed Chinese, and to assess the psychometric properties of SC-SINS in patients with metastasis spinal disease. The reliability and validity of SINS in simpli ed Chinese (SC-SINS) were also examined to demonstrate its accuracy and applicability in clinical practice.

Participants
Patients diagnosed with metastatic spinal disease between January 2016 and January 2020 were recruited. The participant population was advised to be at least 50 for appropriate analysis of reliability, construct validity, as well as ceiling or oor effects, and 100 patients are needed for internal consistency analysis (8). Patients participating in the study were all diagnosed with metastatic spinal disease con rmed by pathology or PET-CT. Eight spine evaluators are at least 6 years of education and ability to read and speak Chinese. Patients excluded were those who reported a history of spinal surgery or whose spinal disease was caused by infection, ankylosing spondylitis, or systemic rheumatologic disease. Complete imaging results and available clinical data were required for all patients. Complete imaging results included sagittal view, axial view and coronal view of magnetic resonance imaging (MRI). Clinical data included demographic characteristics, neurological function, tumor levels, pathology report, complications and surgical treatment. The study was approved by the Ethics Committee of our institution, and all patients signed a written informed consent.
Instruments SINS SINS, a comprehensive classi cation to diagnose neoplastic spinal instability, comprises six individual component scores: spine location, pain, lesion bone quality, radiographic alignment, vertebral body collapse, and posterolateral involvement of the spinal elements. The maximum score is 18, and the minimum is 0. The total score is divided into three categories in terms of stability: stable (0-6 points), potentially unstable (7-12 points), and unstable (13-18 points). In addition, the SINS score can also be analyzed as a binary indicator of surgical referral status: 'stable' (0-6 points) or 'current or possible instability' (7-18 points). A surgical consultation is recommended for patients with SINS scores greater than 7.

Kostuik classi cation
The Kostuik classi cation was used to classify the degree of tumor involvement of the spinal column. The vertebral body is divided into 6 components, and three categories of stability are considered: stable (1-2 partial damages), relatively unsteady (3-4 partial damages) and absolutely unsteady (5-6 partial damages).

Procedure
The study was conducted in two phases: rst, the SINS was translated into simpli ed Chinese; second, the factor structure, internal consistency, test-retest reliability, validity, and oor and ceiling effects of the SC-SINS were assessed. The procedures followed the cross-cultural adaptation guidelines issued by the American Association of Orthopedic Surgeons Outcome Committee.

Stage I: Forward translation into simpli ed Chinese
The 6-component SINS was translated into simpli ed Chinese independently by 2 bilingual translators who spoke Chinese as the rst language. One translator was a medical professional who knew the concepts related to the index well; the other translator was a professional translator with no medical background and was blind for the objective of the study.

Stage II: Synthesis of the translations
The expert committee, consisting of translators, radiologist and spinal surgeons specialized in metastatic spinal disease discussed the translations and compared them with the original English version SINS. After reaching a consensus, the forward translations were formulated into one single simpli ed Chinese version.

Stage III: Backward translation into English
Then backward translation was undertaken independently by another professional bilingual translator, a radiologist and a spinal orthopedist. All lacked medical backgrounds and were not aware of the prior translation procedures. They independently and blindly translated the simpli ed Chinese version back into English. Each English translation was then compared with the original English version and checked for inconsistencies.

Stage IV: Expert committee
The expert committee consolidated all the translations and discussed with all the translators, bilingual experts and spinal surgeons. A consensus was reached on all discrepancies. Then the committee came into an agreement on the equivalence between the original version and the target version. Finally, the SC-SINS was created.

Stage V: Evaluation of the pre-nal version
The data of 28 patients were collected for pilot test by evaluators. Each subsequently pointed out their di culties in completing the classi cation or understanding the purpose and meaning of each question.
The expert committee discussed all the ndings and then developed the nal version of SC-SINS which was used for further psychometric testing.
Stage VI: Evaluation of the nal version A booklet that included the nal SC-SINS and informed consent form was given to all participating patients who met the inclusion/exclusion criteria. We evaluated the internal consistency, test-retest reliability, and oor and ceiling effects of the nal version. Each patient's demographic characteristics were recorded.

Statistical analysis
SPSS18.0 (Chicago, IL, USA) was used for statistical analysis. Data were expressed as the mean ± standard deviation (SD). Values were reported with 95% con dence intervals (CIs) and P-values <0.05 indicated statistical signi cance.

Internal consistency
Internal consistency reliability was evaluated using Cronbach's a coe cient for each domain (9). High Cronbach's a indicated high correlations among the items. Cronbach's a of ≥0.70 was considered satisfactory. In addition, the item-total correlations of each item were calculated. Levels of agreement for a were graded according to the recommendations of Landis and Koch, with a value of 0.00 to 0.20 considered slight agreement; 0.21 to 0.40, fair agreement; 0.41 to 0.60, moderate agreement; 0.61 to 0.80, substantial agreement; and 0.81 to 1.00, almost perfect agreement (10).

Test-retest reliability
The test-retest reliability was assessed by comparing the results of the rst and nal SC-SINS scales. Two-way ANOVA random-effects intra-class correlation coe cient (ICC) was calculated to quantify the test-retest reliability (11,12). We assessed 60 patients for a second time after the rst completion. The sequence of SC-SINS was rearranged to reduce the memory error. A 4-week interval was designed between the two tests. ICC values ranged from 0 to 1, and a higher value indicated higher repeatability. An ICC above 0.7 could be accepted as good and below 0.4 as poor reliability (13). To assess criterion-related validity, we examined construct validity. We evaluated the relationship between the SC-SINS and Kostuik classi cation using the Pearson correlation coe cients. Correlation values of 0.81-1.0 was considered excellent, 0.61-0.80 very good, 0.41-0.60 good, 0.21-0.40 fair, and 0-0.20 poor.

Structural factor analysis
We used factor analysis to evaluate the factor structure of the SC-SINS, and to con rm the subscales. Since the original SC-SINS indicated that the items were distributed across six subscales, we used principal component analysis rotation to con rm the factor structure of each subscale, rather than exploratory factor analysis. Item loadings on each factor equal to or greater than 0.4 were considered satisfactory. In addition, oor and ceiling effects (de ned as the percentage of participants displaying the minimum and maximum possible scores, respectively) were calculated and those with over 15% of respondents achieving the lowest or highest possible total scores were considered signi cant (11).

Translation and cross-cultural adaptation
No major problems occurred in the forward and back translations of SINS. The minor differences caused by cultural differences in some items were then adapted cross-culturally and some modi cations were also made. In section 2 (Pain), "occasionally, not consistently. No severe pain, and it was tolerable" was added as the explanation.
In pilot trial, 28 classi cations that included suggestions about the pre-nal SC-SINS were asked. Among the 28 participants (12 males and 16 females), 17 received surgical treatment and 11 received nonsurgical treatment. Table 1 summarized the patients' characteristics. Among the 28 patients, 13 mistakenly considered that the items were asking about the severity of pain before or after surgery. After consulting the expert committee, we revised the pre-nal SC-SINS and emphasized "pain" referred to the preoperative pain for patients undergoing surgical treatment. Finally, the simpli ed Chinese version of the SINS was produced.
Demographic and clinical characteristics of the sample A total of 160 participants (88males and 72 females) were enrolled in the nal test. The mean age, gender, duration and BMI of the pre-nal, test-retest, and validity groups were similar. The number of participants with Frankel Score (A-C) were 16, 17, 73 in the three group respectively. Pathologically, the primary tumors were mostly lung, breast, liver, renal, gastric, intestinal tumors. The demographic data of the participants in each group and descriptive statistics were shown in Table 1. Internal consistency The internal consistency of SC-SINS was excellent (Cronbach's a =0.857). All the item-total score correlations were moderate to high, ranging from 0.68 (Pain, item 2) to 0.85 (Location, item2). The Cronbach's a with elimination of one item did not increase by more than 0.1 for each item, indicating that all items were relevant to this population.  Validity Validity analyses indicated that the SC-SINS was positively and signi cantly correlated with Kostuik classi cation (P<0.0001). The six components of the SC-SINS were also signi cantly associated with the three components of the Kostuik classi cation (all P values <0.0001). Table 3 showed that the correlations between "Posterolateral Involvement of Spinal Elements" and "1-2 Partial Damage" was the highest with a correlation value of 0.792. The correlations between "Pain" and "1-2 Partial Damage" was the lowest with a value of 0.341.    there is no "gold standard" for the use of the scoring system should be used, and the doctors' views on spinal stability vary greatly. SINS is a valuable tool to quantify the patients' spinal stability and conduct data analysis. This study described the process of cross-cultural adaptation, structural validity, reliability and construct validity of SINS in Chinese-speaking subjects. The unidimensional scale displayed satisfactory reliability and construct validity in patients with spinal metastatic tumor.
Following the recommended guidelines, the translation and cross-cultural adaptation was successfully conducted. The comprehensibility of the translated items was then con rmed, thus leading to a valid measure of spinal stability, allowing comparability of the data and cross-national studies. The SC-SINS was easy to understand and simple to use. After minor modi cations, no item was hard for participants to understand, and all items were answered in pretest and formal study, which revealed good acceptability of SC-SINS. No signi cant oor or ceiling effects were found in of SC-SINS.  (17). The item-total score correlations were moderate to high (ranging from 0.68 to 0.85), and when a single item was deleted, the deletion did not increase the Cronbach's a by more than 0.1. Those ndings suggested greater homogeneity of all sections and that each section was well correlated to the SC-SINS. Item 1, a question based on objective fact, had the highest ICC value (Location, ICC = 0.85), which indirectly revealed the success of cross-cultural adaptation. However, item 2 presented the lowest ICC value (Pain, ICC = 0.68). One possible explanation might be that the feeling of pain is subjective, which may change with the different treatment. The test-retest reliability was excellent in this study. The ICC value of our study reached 0.89, which is higher than that in the abovementioned studies.
Item 3, another subjective item, presented the lowest ICC value (Radiographic spinal alignment, ICC = 0.86), which could be attributed to the change caused by different body positions or other situations.
The correlation between the components of SC-SINS and Kostuik classi cation was in accordance with our hypothesis that SC-SINS was positively and signi cantly correlated with Kostuik classi cation.
According to the results of our study, the association between "Location" and "Posterolateral Involvement of Spinal Elements" of SC-SINS and "1-2 Partial Damage" of Kostuik Classi cation was the strongest (r = 0.741 and 0.792, respectively). One possible reason might be that these two components are both designed to evaluating tumor involvement, and both of them are important for developing surgical strategies.
The limitations of our study must be noted. First, the participants in this study could not represent the entire Chinese population with spinal metastatic tumor. The patients were recruited from only four institutions, so enrollment of participants from multiple institutions would provide better sampling and improve the generalizability. However, the variability of this study was enough to demonstrate responsiveness. Second, the clinical experience of evaluators can affect the accuracy. Different understanding on systems may lead to a deviation in the results. Skilled spinal tumor surgeons should have been invited as evaluators to minimize bias, because they can make an agreement more easily than unskilled surgeons(18).

Conclusions
The cross-cultural adaption of SINS into simpli ed Chinese was successful. The SC-SINS demonstrated high internal consistency and test-retest reliability. The SC-SINS has been proven valid and reliable to measure spinal stability of patients with spinal metastatic tumor in the population who uses simpli ed Chinese.
Abbreviations SINS: Spinal Instability Neoplastic Score Declarations