The Short Form-36 (SF-36) questionnaire is a multidimensional survey that focuses on the eight most important quality-of-life constructs from the Medical Outcomes Survey (MOS) [41, 54]. The MOS assesses 40 different physical and mental health constructs. The SF-36 is considered to be a generic measure of HRQL that is not age, treatment, or disease specific. SF-36 measures scores for the following eight domains: Physical Functioning, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional, and Mental Health. In addition, two composite scores can be calculated: a physical composite summary score (PCS) and a mental composite summary score (MCS) can also be calculated.

In patients with adult scoliosis, the average SF-36 domain scores were much lower than the scores for the general US population for all eight domains. In people aged 55–64, SF-36 scores were much lower in 7 out of 8 domains in patients with adult scoliosis (all except General Health scale) compared to the general population. Loss of lumbar lordosis was associated with significantly diminished SF-36 Social Functioning, Role Emotional, and General Health domain scores [46]. However, in a healthy volunteer elderly population, subjects with Cobb angles between 10° and 20° had higher SF-36 Physical Function but lower Vitality and Mental Health scores in comparison with US benchmark data.

More recent reports have utilized the Short Form-12 (SF-12) in spinal deformity surgery. The SF-12 is a subset of 12 items from the SF-36 that has been found to be as reliable, valid, and highly similar to the SF-36 [12, 47, 53]. The shorter questionnaire has been used in conjunction with ODI and SRS-22R. The value of the SF-36 or SF-12 is that each permits evaluation of the health effect of spinal deformity surgery compared to the health effect of other interventions such as total joint arthroplasty or cardiac bypass surgery. Previous work has identified a minimal clinically important difference (MCID) of 5.2 points in SF-12v2 physical component scores (PCS) as a threshold for improvement at 1-year postoperative follow-up [53]. Another group reported a MCID of 4.9 points for PCS in lumbar spine surgery [19]. Substantial clinical benefit (SCB) thresholds for the SF-36 PCS have been defined as a 6.2-point net improvement, a 19.4 % improvement, or a final raw score of greater than 35.1 points at 1-year follow-up [27].

The EuroQOL-5D (EQ-5D) is an indirect measure of health state utility value that consists of a descriptive system and a visual analog scale (EQ VAS) [52]. The descriptive system has five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Each has three possible levels of problems: none, moderate, or severe. Respondents mark the box with the most appropriate statement in each of the five dimensions. A utility index score can be calculated, and the score ranges from 1 (perfect health) to 0 (death), with the possibility of a negative score for a worse than death status [17]. The EQ VAS records the respondent’s self-rated health on a vertical, visual analog scale that ranges from “best imaginable health state” to “worst imaginable health state.”

While SRS-22R scores were reproducible for AIS patients in one report, poor correlations with EQ-5D were seen, especially with self-image and satisfaction [1]. In older spinal deformity patients, those who underwent surgery had improved EQ-5D compared with patients that had nonoperative treatment [39]. Data regarding use of EQ-5D in ASD patients is limited, but may be more prevalent with pressures to demonstrate cost-effectiveness of operative treatment.

The Oswestry Disability Index (ODI) has been established as the current standard to measure HRQL in patients with low-back disability. It has been found to be valid, reliable, and responsive to change [23]. It consists of ten sections. Six statements comprise each section; with the first statement marked a score of 0, and the last statement marked a score of 5. Intervening statements are scored according to rank. The sum of scores from the ten sections are added and then divided by the total possible score. The score is then multiplied by 100 to give a percentage score out of 100. Patients with scores between 0 and 20 have minimal disability, between 21 and 40 have moderate disability, 41–60 have severe disability, 61–80 are crippled, and 81–100 are bed-bound or exaggerating their symptoms. Patients with positive sagittal balance have reported worse ODI scores than those with normal sagittal balance [25, 26, 40]. The U.S. Food and Drug Administration has considered a 15-point change in ODI as a criterion to determine success for patients who undergo spinal fusion. MCID in one report was determined to be 12.8-point improvement [19]. Identified SCB thresholds in ODI are a net improvement of 18.8 points, a 36.8 % improvement, or a final raw score of less than 31.3 points in patients at 1-year follow-up after lumbar spine arthrodesis [27].

While the strength of the SF-36 as an outcomes instrument is its generalizability to permit comparisons of treatment effectiveness between interventions, disease-specific measures are more sensitive to change in specific conditions, such as spinal deformity. The need for deformity-specific outcomes instrument for scoliosis patients led to the development of the Scoliosis Research Society-22R (SRS-22R) [30]. The SRS questionnaire includes domains of pain, self-image, mental health, function, and satisfaction; a total score is also calculated [13]. The development of the SRS-22 has undergone several iterations, including the SRS-30, SRS-29, SRS-24, SRS-23, and SRS-22 and the SRS-22R [2–4]. Modifications improved the scope and the internal consistency of the instrument.

The SRS instrument has been validated for use in adolescent idiopathic scoliosis (AIS) [3, 4]. In the AIS population, the SRS-22 mental health and pain domain scores can be accurately calculated from correlating SF-36 scores. SRS-22 function scores can be fairly well predicted from the SF-36 PCS domain. However, self-image could not be correlated with SF-36 scores [38]. The established MCID in AIS for SRS pain is 0.2 points, SRS appearance is 0.98 points, and SRS activity is 0.08 points [18]. MCID for mental health, satisfaction, or total scores have not been determined due to lack of baseline comparisons [18].

Subsequent studies have shown the SRS-22R questionnaire to be reliable and valid in patients with ASD [6, 12, 13, 29]. Compared with normal adult volunteers in age–gender matched groups, ASD patients had SRS-22R scores that were significantly worse for pain, self-image, and function. Only the mental health domain scores of older deformity male patients were not statistically lower than their normal counterparts [5]. Furthermore, the SRS questionnaire has concurrent validity with SF-36. Comparisons of pain with pain index, function with physical functioning, self-image with social function and mental with mental health index of the SRS and SF-36, respectively, demonstrate high correlation between the two instruments in the adult scoliosis population [6, 13]. Similarly, SRS-22R correlated well with ODI (functional component) [13]. SRS-22R has been shown to be more responsive to change than ODI, which was more responsive than SF-12 to changes due to primary surgical treatment of ASD patients [12]. The MCID value that has been used for SRS Pain is 0.587 points, SRS Appearance is 0.8 points, SRS Activity is 0.375 points, and SRS Mental is 0.42 points [8].

Prospective analysis of a cohort of patients with ASD, using the Schwab–SRS Classification subtype and sagittal modifiers, demonstrated that operative patients were older, had more comorbidities, greater disability, and worse sagittal spinopelvic alignment than patients treated nonoperatively. The Schwab–SRS classification correlates with HRQL scores, including ODI, SRS, and SF-36 [48]. Change in SVA modifier at 1 year was associated with changes in ODI, SF-36 PCS, as well as SRS-22 total and all subscores. Change in PI-LL modifier at 1 year was associated with changes in SF-36 PCS, SRS-22 Total score and four of the SRS-22 subscores. Changes in SVA and PI-LL modifiers were associated with achieving MCID for ODI and SRS subscores [50].

HRQL measures, in conjunction with radiographs and clinical presentation, can be used to guide treatment decisions in patients with spinal deformity, help provide information to the patient and physician regarding expectations after treatment as well as provide a measure of treatment effectiveness. Multiple centers have collaborated recently in the Spinal Deformity Study Group/Adult Deformity Outcomes (SDSG/ADO) section to prospectively study and to quantify problems facing ASD patients [11]. Several studies, including those of the SDSG, have reviewed patient cohorts that were divided into surgical and nonsurgical groups and their associated scores for SF-36 or SF-12, ODI, and SRS instrument scales [7, 24, 28, 43, 51].

SF-12 PCS and MCS have been utilized in patients with spinal deformity. In one report, SF-12v2 PCS of below 35 were over six times more likely to improve by 5.2 points or more on the same scale as those with a baseline score of 35 or greater [47]. Another report showed that those patients who chose surgery over nonoperative treatment had worse SF-12 PCS scores [43].

ODI, specifically the Walking domain, was found to be worse for patients requiring surgery, compared to those who did not undergo surgery [7, 24, 43, 51]. Correlations were present between increased positive sagittal balance and the ODI Standing domain, as well as between increased PT and the ODI Walking domain. This correlation indicates that high PT limits effective ambulation, and thus the goal of treatment is to achieve pelvic realignment to a PT within the normal range [37]. Patients who underwent surgery demonstrated significant improvement of ODI [10, 51], which was maintained for a minimum of 5 years in follow-up [10, 34]. Patients who had complications including instrumentation failure, pseudoarthrosis, deep-wound infections, and reoperations demonstrated worse ODI scores at two- and five-year follow-up than those who did not have complications [10].