Defining “successful” treatment outcomes in adolescent idiopathic scoliosis: a scoping review

Adolescent idiopathic scoliosis (AIS) is the most common type of scoliosis that affects children aged 10–18 years old, manifesting in a three-dimensional spinal deformity. This study aimed to explore outcome measures used in defining AIS treatment success. Particularly, analyzing the extent of qualitative and quantitative (radiographic and quality of life domains) measures to evaluate AIS and whether AIS treatment approaches (surgical, bracing and physiotherapy) influences outcomes used as proxies of treatment success. EMBASE and MEDLINE databases were used to conduct a systematic scoping review with 654 search queries. 158 papers met the inclusion criteria and were screened for data extraction. Extractable variables included: study characteristics, study participant characteristics, type of study, type of intervention approach and outcome measures. All 158 studies measured quantitative outcomes. 61.38% of papers used radiographic outcomes whilst 38.62% of papers used quantitative quality of life outcomes to evaluate treatment success. Irrespective of treatment intervention utilized, the type of quantitative outcome measure recorded were similar in proportion. Moreover, of the radiographic outcome measures, the subcategory Cobb angle was predominantly used across all intervention approaches. For quantitative quality of life measures, questionnaires investigating multiple domains such as SRS were primarily used as proxies of AIS treatment success across all intervention approaches. This study identified that no articles employed qualitative measures of describing the psychosocial implications of AIS in defining treatment success. Although quantitative measures have merit in clinical diagnoses and management, there is increasing value in using qualitative methods such as thematic analysis in guiding clinicians to develop a biopsychosocial approach for patient care.


Introduction
Adolescent idiopathic scoliosis (AIS) is a three-dimensional spinal deformity involving sagittal, frontal and axial planes [1]. Mild AIS is defined as a lateral curvature (Cobb angle) greater than 10° with vertebral rotation in the absence of congenital or neuromuscular abnormalities. It is the most common spinal deformity affecting 1-3% of the pediatric population [2], with peak prevalence in 1.2% of females aged 12 [3]. The incidence of AIS is equal amongst females and males, but females have a tenfold increased likelihood of disease progression to a Cobb angle exceeding 30° [2]. The extent of curve progression reflects major periods of growth spurts and pubertal changes [4]. Exact etiology of AIS remains undefined, but it is believed to be a multifactorial, polygenic disorder [5].
Mild to moderate AIS is often asymptomatic; however, due to apparent visual deformities, it can induce significant emotional distress for some patients. Thus, the aim of treatment is to reverse or halt progression of curvature and improve quality of life. Current treatment options are split 1 3 based on curve severity: conservative options (bracing or scoliosis-specific physical therapy) for mild to moderate AIS, whilst more invasive surgery is reserved for severe AIS.
Presently, there is a substantial body of evidence evaluating AIS treatment outcomes through quantitative radiographic and quality of life scales. However, to date, the literature lacks an approach that collates these various measures to appreciate the complexity of AIS and its biopsychosocial impacts on patients. Biopsychosocial impacts refer to the interplay between physical, psychological and social outcomes that are affected by AIS.
The aim of this review is three-fold: 1. Gather and examine, in a single review, the variety of outcome measures employed to determine AIS treatment success. 2. Explore whether different schools of treatments (surgical, bracing, physiotherapy etc.) employ different means of measuring successful treatment. 3. Investigate the extent to which quantitative or qualitative measurements for radiographic and quality of life domains are used in defining treatment success.
This scoping review is not intended to discredit the validity or accuracy of either radiographic or quantitative quality of life means to measure AIS treatment success. Rather, this study aims to synthesize a knowledge of current outcome measures used in defining treatment success and thus identify potential gaps in the holistic evaluation of a patient's treatment outcome.

Protocol design
In conducting this scoping review, we followed the preferred reporting items for systematic reviews and meta-analysis extension for scoping reviews (PRISMA-ScR) checklist [6].

Search strategy
A comprehensive literature search was performed using the bibliographic databases MEDLINE and EMBASE. The literature search was last updated on April 27th, 2022. All records were imported into Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia) for primary screening and data extraction.

Exclusion/inclusion criteria and article selection
Title and abstracts were individually screened by two independent reviewers (IJ and ST), with disagreements resolved through consultation between the two reviewers. For primary abstract and title screening, articles were excluded if one or more of the following criteria were met: (1) non-English primary literature; (2) not peer-reviewed; (3) systematic review or meta-analysis; (4) population of study below 7 years of age; (5) study participants diagnosed with functional scoliosis, de novo scoliosis or secondary scoliosis; (6) full text not available; (7) pilot study; (8) conference abstract; (9) no treatment/intervention investigated in study (Fig. 1).
The remaining articles were subsequently subjected to full-text screening conducted by two-independent reviewers (IJ and ST); any disagreements were resolved through consultation. Studies that contained the following criteria were used to determine eligibility of the full-text articles: (1) primary literature; (2) involved a treatment/intervention (surgical, bracing, physiotherapy, etc.), with a specific outcome (Cobb angle, SRS-22 etc.) measured; (3) study population limited to true AIS patients, not secondary scoliosis or other forms of spinal deformity; (4) presence of a defined intervention with direct effects on outcome measures (Fig. 1).

Data collection and extraction
Following full-text screening, data extraction was conducted for the screened articles. A comprehensive inventory spreadsheet was created to extract data. Extractable variables were jointly developed by all the authors, which included: study characteristics (author, year of publication, country, doi, type of study), study participant characteristics (age range, income levels, gender, place of residence and ethnic backgrounds of study participants), type of study (qualitative vs. quantitative vs. mixed methods research approach), type of intervention approach (e.g., surgical, bracing, physiotherapy), and outcome measurements (radiographic or healthrelated quality of life outcomes (HRQoL). Quantitative measures were defined as outcomes that had any numeric value or attribute. Qualitative measures in contrast were defined as outcomes without numeric values, but employed descriptive statements, themes or ideas of outcomes. Two reviewers (IJ and ST) independently extracted data, resolving any discrepancies through discussion (Fig. 1).

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participants at the time of study was stratified into 3 categories: (1) under 18 years of age, (2) over 18 years of age, and (3) included participants whose ages spanned across both categories. 97 papers included only participants under the age of 18, 11 papers had participants whose age ranges were greater than 18, and 47 papers included participants both below and above 18 years of age; 3 did not report age ranges of participants. With regards to gender, 141 papers included both male and female participants, whilst 11 papers only had female AIS participants included in their study. No papers looked at only male AIS participants and 6 papers did not specify the gender of the participants included in the  Table 1 Studies identified in the scoping review to determine outcome measured after treatment/intervention for adolescent idiopathic scoliosis Author

Study outcome measures
Outcome measures from all 158 papers were broadly categorized into radiographic or health related quality of life (HRQoL) outcomes. Radiographic measures were then subcategorized into "Cobb angle", "trunk shape/alignment" and "flexibility/movement". HRQoL measures were subcategorized into the following: "questionnaires investigating multiple domains", "disability specific questionnaires", "visual appearance specific questionnaires", "pain specific questionnaires", and "mental health specific questionnaires". The subcategory of "questionnaires investigating multiple domains" refers to measures that assess multiple domains of outcomes (e.g., scoliosis research society (SRS), Short form survey (SF-36), Global rating of change (GRC), quality of recovery score (QOR-9), EuroQol-5 dimension (EQ-5D), bracing questionnaires). Amongst the studies selected for the scoping review, radiographic outcomes were reported a total of 275 (61.38%) times whilst quantitative HRQoL measurements were reported 173 (38.62%) times, as measures to evaluate intervention success. No papers reported qualitative HRQoL measurements ( Table 2).

Intervention Type and Specific outcome measure subcategories
Interventions described in the 158 papers were categorized into 4 broad treatments: (1) surgery, (2) bracing, (3) physiotherapy or physical activity, and (4) a combination of physiotherapy and bracing. A combination of surgery with other treatment interventions was not present in any of the papers. Amongst papers that explored surgical intervention in AIS patients, 50.48% of treatment outcomes were measured by radiographic means, whilst 49.52% were measured by HRQoL. For studies investigating bracing as an intervention, 57.14% of treatment outcomes were measured by radiographic means whilst 42.86% by HRQoL. Moreover, for physiotherapy or physical activity, radiographic measures accounted for 58.82% of outcomes whilst HRQoL measures accounted for 41.18% of outcomes. While only 12 interventions used a combination of physiotherapy and bracing, 50% of treatment outcomes were measured by radiographic means, and the remaining 50% by HRQoL. Note that if both radiographic and HRQoL measures were used in the same study, a tally was given to each category (Table 3).
An analysis of intervention versus specific radiographic outcome subcategories was also conducted. "Cobb angle" was the most investigated subcategory of radiographic outcomes  (Table 4).

Discussion
Based on the results, many individual studies each define and investigate a distinct outcome measure for successful AIS treatment. However, there is a lack of reviews that collate and analyze these various definitions. This scoping review seeks to create a more broad and inclusive definition of successful AIS treatment that identifies shortcomings of existing measures to better capture the psychosocial impacts on patient outcomes.

Evaluating the clinical utility of quantitative radiographic outcomes in defining successful AIS treatment
Based on the analysis, quantitative radiographic outcomes (61.38%) were the most frequently used measure in evaluating scoliosis treatment success, followed by quantitative    HRQoL measurements (38.62%). Notably, no qualitative HRQoL measurements were recorded (Table 2). In line with this, the literature indicates that radiographic measurements are the gold-standard for AIS diagnosis by excluding alternate underlying causes, characterizing the type of spinal curvature, determining the flexibility of curvature, and following disease progression [165]. In fact, a definitive diagnosis and the subsequent monitoring of patients with AIS cannot be made without imaging [166]. While a variety of radiographic information is available, our analysis indicated that regardless of the intervention used (surgery, bracing, physiotherapy/physical therapy or combination of physiotherapy and bracing), the Cobb angle was the most common proxy of success, in comparison to the measures of trunk shape/alignment and flexibility/movement ( Table 4). The Cobb angle is arguably the most important radiographic measure, with its primary clinical utility in determining curve progression risk, diagnosis establishment, treatment selection and monitoring change over time [166][167][168]. The Society on Scoliosis Orthopaedic and Rehabilitation Treatment (SOSORT) consensus defines conservative modes of scoliosis treatment success as a curve progression (stabilization) of ≤ 5° or a curve decrease (correction) of ≥ 6° at the end of treatment [122,169,170]. On the other hand, surgical interventions aim to terminate the progression of AIS, achieve maximum permanent correction of the 3D deformity, promote appearance by balancing the trunk, and keep lower incidence rate of short-term and long-term complications [171]. While the Cobb angle is a necessary measurement for diagnosing and monitoring AIS, it is important not to be over reliant on this single measure, as it has its own limitations. Studies investigating inter-and intra-observer reliability indicate the measurement error of the Cobb angle approximates to 3°-5° [172]. This degree of variation may interfere with the diagnosis and type of treatment pursued, which may ultimately have an impact on patient outcomes. Alternate radiographic measurements such as vertebral rotation, when used in conjunction with the Cobb angle, may enhance clinical utility by playing an integral role in AIS evaluation by predicting curve correction, decompensation, and progression [173,174]. However, there is still a lack of conclusive evidence that other long-term patient outcomes (such as function, quality of life, self-image, pain, etc.) in those with AIS are affected by improvements in radiographic outcomes [174]. In fact, research has indicated that the Cobb angle has limited prognostic value and is poorly related to overall quality of life, degree of morbidity, and pain experienced by the patient [122,172].

Evaluating the clinical utility of quantitative HRQoL outcomes in defining successful AIS treatment
In light of increasing emphasis and recognition of patientreported outcomes, quantitative HRQoL measures that  explore the psychosocial impacts of AIS have become mainstay in evaluating treatment success amongst clinicians [175]. Our analysis corroborates this, showing approximately equal radiographic and quantitative HRQoL measures amongst the different schools of treatment (Table 3). Moreover, within each treatment approach, "Questionnaires investigating multiple domains" was the primary quantitative HRQoL outcome measure (Table 4). Particularly, the Scoliosis Research Society questionnaire (SRS) was the most extensively used questionnaire in this category, likely due to its high reliability, internal consistency, and reproducibility that is supported by the literature [176]. The most recent version, SRS-22, measures 5 domains: pain, function/activity, self-image/appearance, mental health, and satisfaction with management. Each domain is rated using a Likert-type scale of 1-5 where a score of 1 denotes "none" and 5 denotes "severe", for a total score of 25. Although the SRS is a widely validated measurement tool, being a Likert-type scale, it is not without limitations. Particularly, there is a high degree of subjectivity, where perceived distances between the response categories and the interpretation of the values may vary by respondent [176]. Additionally, extremes of Likert-type responses are frequently avoided in favor of neutral or central choices, thereby artificially narrowing the range of responses [177]potentially misrepresenting true patient experiences.
In this paper, we also identified other quantitative HRQoL measures investigating specific isolated domains such as disability, visual appearance, pain, and mental health. While the questionnaires investigating multiple domains captured a large portion of an AIS patient's subjective experiences, some aspects present within these specific questionnaires were missed. Thus, a combination of these questionnaires may be of greater clinical utility in evaluating AIS patient experiences.

The value of thematic analysis in capturing AIS patient biopsychosocial experiences
Above all, by categorizing the HRQoL into 5 distinct domains, the SRS may fail to appreciate the true complex psychosocial experiences of AIS patients. HrQoL questionnaires are strictly a quantitative measure of the biopsychosocial outcomes of AIS and thus are limited in capturing the nuances of AIS patients' lived experiences.
In contrast, thematic analysis is a qualitative measure that has been increasingly used to address this limitation. This approach involves systematically coding and identifying patterns in a data set (written or verbal discussions) to develop overarching themes. It is particularly suited in the analysis of interview transcripts and when used with an inductive approach, lends to a more accurate and in depth account of AIS patient biopsychosocial experiences.
The call for a biopsychosocial approach emerged out of dissatisfaction with historic biomedical models that neglected to appreciate health and illness as a result of a complex interaction between biological, psychological and social factors. At the heart of the biopsychosocial model is the emphasis of patient-centered framework and a collaborative approach to care amongst healthcare professionals. The model underpins that disease can affect social, personal, physical health and emotional contexts for an individual, with each domain heavily influencing the other. It predicts that some consequences of disease can be addressed beyond physical management; moreover, it suggests that addressing social challenges, psychological attitudes or behavior can alter illness pathology and transform the quality of life for patients. With chronic diseases accounting for a great proportion of morbidity, there is an increase in health care resources directed to address patient quality of life and disease management. However, studies have demonstrated that improvements in patient-reported outcomes and reduction of healthcare cost have not advanced despite increasing disease burden under a biomedical approach strictly. Consequently, there is a need for greater understanding and utilization of the biopsychosocial model to improve patient outcomes [178].
A recent qualitative study by Motyer and colleagues attempted to address this gap amongst adolescent pre-surgical AIS patients through thematic analysis of qualitative interviews with AIS patients. Thematic analysis allows for the development of detailed psychosocial experiences of AIS patients through systematic coding of interview transcripts [179].
Whilst the SRS does assess the degree of visual appearance dissatisfaction, it overlooks the link between AIS patients' own visual dissatisfaction and its implications on social relations and fears of being different. Motyer and colleagues describe that visual dissatisfaction in AIS patients are more pronounced in social situations as opposed to when they are alone. Particularly, AIS patients described apprehension and challenges in disclosing their diagnosis, which seemed to further exacerbate visual dissatisfaction [179]. Likewise, although the SRS domain "Mental health" attempts to assess self-confidence and self-esteem, it fails to capture the dynamic feelings of social isolation, desire for reassurance, and fear due to limited knowledge of their condition as described in Motyer's study.
These key themes explored in Motyer and colleagues' study underline the limitations of quantitative HRQoL measures in fully capturing the dynamic psychosocial experience and concerns of AIS patients-to what extent can a numerical value capture the diverse and rich AIS patient narratives? Whilst these questionnaires are undoubtedly useful, it is apparent that thematic analysis can create deeper connections and narratives that appreciate the full patient biopsychosocial experience and concerns. It is paramount then, that clinicians consider and inquire into the patient's perspective regarding concerns, feelings, and goals from treatment to provide optimized care.
A lack of the use of the biopsychosocial approach in AIS treatment is evident and underlines the importance of considering the intersectionalities of biological, psychological and social factors in treating patients. Current AIS treatment approaches often place spine surgeons as the primary care providers for patients in the pre-and postoperative stages.
While several studies have documented the adverse impact that patient psychosocial distress has on treatment outcomes [180][181][182], few spinal surgeons have been shown to evaluate these measures [183].
A recent prospective study conducted by Daubs and colleagues evaluated the clinicians' ability to categorize their patients' psychological distress level. They identified that large proportions of patients that presented for spinal evaluation had some levels of psychological distress. Moreover, spine surgeons were found to often underestimate and demonstrate low sensitivity rates in detecting their patients' distress. The study underlines the adverse relationship of psychological distress and spinal conditions, and the importance for spine surgeons to be more aware of psychological distress in patients [184].
Taken together, the invaluable role of interviews in eliciting biopsychosocial experiences of AIS patient demonstrated by Motyer and colleagues, along with the findings that spine surgeons have low sensitivity rates for detecting patient distress, indicate a role for qualitative methods such as interviews in defining a patient perspective of AIS treatment success. This suggests that thematic analysis has great clinical utility in providing health care providers invaluable insight into the biopsychosocial challenges and limitations of living with AIS, thereby eliciting a direct means of addressing the concerns to foster true patient-centered care. Strategies could include fine tuning healthcare resource allocation that reflect the shortcomings of existing AIS treatment paths. Moreover, thematic analysis can also reveal the positive experiences and unique biopsychosocial adaptations that can be protective factors that clinicians can incorporate in caring for AIS patients.
In light of this, we believe that more conversations and discussions need to occur with AIS patients to learn about the positive and negative biopsychosocial impacts of living with the condition. Moreover, the approach to research should be done in a joint collaborative fashion placing the stakeholders, AIS patients, at the true center in creating reforms in the standard of care. By incorporating a thematic analysis approach, we strongly believe that a greater appreciation of AIS patient concerns and desires can be gained for clinical utility.

Limitations of this scoping review
Despite efforts in undertaking a comprehensive investigation and analysis of the current literature regarding outcome measures used as proxies of successful AIS treatment, this scoping review is not without limitations. Although 2 large databases (EMBASE and MEDLINE) were searched, we recognize that relevant studies may still have been missed in this scoping review. Only primary literature written in English and published in peer-reviewed journals were included in our search. In this study, only articles that explored a specific treatment or intervention to AIS were included. Therefore, papers that discussed potential treatment success measures may have been missed.

Conclusion
In this scoping review, we identified that to date, the literature predominantly attempts to stratify AIS treatment success via either radiographic or quantitative HRQoL means. Notably, no papers employed qualitative measures of describing the psychosocial implications of AIS in determining what successful AIS treatment is. Moreover, it was found that the Cobb angle was the most predominantly used quantitative radiographic measure, whilst "Questionnaires with multiple domains", was the most favored outcome measure within quantitative HRQoL measurements. Although quantitative measures undoubtedly play an important role in the clinical diagnosis, management, and evaluation of how AIS impacts patients, it is apparent that numerical values alone cannot describe and integrate the full extent of biopsychosocial experiences. There is increasing value to using qualitative methods, such as thematic analysis, to deliver a more thorough patient narrative, aligning with the biopsychosocial model. Future research should seek to investigate qualitative interpretations of treatment success from the patient perspective in order to aid clinicians in developing a more patientoriented care approach.