Authors: Juhyung K An, Daniel Berman, Jacob Schulz
Categories: Spine disorders, Scoliosis, adolescent idiopathic scoliosis, back pain, biochemistry, biomechanics, scoliosis epidemiology
Source: Journal of Children's Orthopaedics
review
Adolescent idiopathic scoliosis (AIS) is a common spinal deformity that affects millions of children worldwide. A variety of treatment algorithms exist for patients based on radiographic parameters such as the Cobb angle and the Risser stage. However, there has been a growing focus on nonradiographic outcomes such as back pain, which can cause functional disability and reduced quality of life for patients. In spite of this, back pain in AIS is poorly characterized in the literature. We aimed to summarize various factors that may influence back pain in AIS and the impact of different treatment methods on pain reduction.
A comprehensive systematic review was undertaken using the PubMed and Cochrane database. Keywords that were utilized and combined with “Adolescent Idiopathic Scoliosis” included, “back pain,” “treatment,” “biomechanics,” “biochemistry,” “epidemiology,” and “biopsychosocial.” The literature was subsequently evaluated and deemed relevant or not relevant for inclusion.
A total of 93 articles were ultimately included in this review. A variety of contradictory literature was present for all sections related to epidemiology, underlying biomechanics and biochemistry, biopsychosocial factors, and treatment methodologies.
Back pain in AIS is common but remains difficult to predict and treat. The literature pertaining to causative factors and treatment options is heterogeneous and inconclusive. Longer-term prospective studies combining biopsychosocial intervention in conjunction with existing curve correction techniques would be meaningful.
Keywords: Scoliosis, back pain, adolescent idiopathic scoliosis, biomechanics, biochemistry, scoliosis epidemiology
Adolescent idiopathic scoliosis (AIS) is a common spinal deformity that affects 1%–3% of children aged 10–16 years.^1,2^ It is characterized by a structural curvature of the spine with a coronal Cobb angle of at least 10° and vertebral rotation. Treatment approach varies with the severity of the deformity and the patient’s stage of skeletal growth, with mild curves less than 25° in skeletally immature patients (Risser 0–2) and curves less than 40° in skeletally mature patients managed with observation. Moderate curves between 25° and 45° in skeletally immature patients are often treated with bracing.^ 3 ^ Surgery is considered for AIS patients with severe curves greater than 45°, which have a high rate of progression even after skeletal maturity. The main goal of treatment is to minimize risk of progression and create structural balance. There has also been a growing focus on nonradiographic outcomes such as back pain. Back pain is a common symptom of AIS patients. Some studies suggest twice the prevalence in AIS patients compared to healthy controls,^4,5^ but there is little understanding of the causative relationship between AIS and back pain. This can be attributed to a high background prevalence of back pain in the general adolescent population, a lack of association between curve severity and pain, and limited and contradictory evidence indicating benefit of curve-reducing treatment methods on pain reduction.^ 6 ^ Despite this, back pain is an important consideration in treatment. AIS patients can experience moderate functional disability and reduced quality of life (QoL) attributed to their back pain.^ 7 ^ Data also show AIS patients with chronic back pain can have greater rates of depression and sleep disorders.^ 8 ^ We aimed to summarize the various factors that may influence back pain in AIS and the impact of treatment methods on pain reduction, to better understand how back pain can be managed.
Back pain is common in adolescents as a whole. Up to 40% of adolescents aged 9–18 years across high-, medium-, and low-income countries have reported lifetime prevalence of low back pain.^ 9 ^ Recently, Fabricant et al.^ 10 ^ conducted a cross-sectional study of 3669 American adolescents aged 10–18 years old. A professional market research company surveyed participants aged 13–18 years and parents of participants aged 10–13 years who then asked their children to complete the survey. Participants were weighted by demographic data representative of the 2010 US census. 33.7% of participants reported back pain at any time within the last year, of which 26.3% was severe pain and 35.4% was moderate pain. 46.9% reported pain duration of less than 1 month and 23.1% reported pain of 1–3 months duration suggesting that back pain in the general adolescent population is not chronic. High prevalence of back pain in the general adolescent population can make it difficult to elucidate back pain resulting from AIS. However, AIS is considered a risk factor for back pain, and epidemiological and natural history studies indicate that there is more frequent, severe, and longer duration of back pain in AIS than in controls.^5,6,11,12^ Sato et al.^ 5 ^ surveyed a large cross-sectional study in 43,630 school-aged children aged 9–15 years and found a 58.8% prevalence of back pain in AIS participants compared to a 33% prevalence in non-AIS participants. When adjusted for sex and school grade, AIS participants still had twice greater prevalence. The back pain reported by AIS participants was longer and more frequent than that reported by non-AIS participants. Joncas et al.^ 13 ^ found that among 239 AIS patients, 54% experienced back pain which was most common in the lumbar region. Makino et al.^ 14 ^ found that 22.5% of AIS patients who had not undergone surgical correction experienced chronic back pain lasting at least 6 months. The Iowa natural history study showed both chronic and acute back pain were more prevalent in the AIS population over a 50-year time period.^ 4 ^ The meaning of and numerical changes in pain scores are still being evaluated. A systematic review that included 21 patient cohorts from 15 different studies reported that although 81% of those cohorts reported statistically significant worse pain in AIS patients, only 5% met the minimal clinically important difference (MCID).^ 15 ^
The underlying etiology of back pain in AIS can be discussed from three different perspectives: biochemical, biomechanical, and neuropsychological. Much of our knowledge about the biochemistry of back pain comes from discogenic models in the adult degenerative population. Crean et al.^ 16 ^ took representative samples during surgery for low back pain associated with both scoliosis and disk degeneration and found a correlation between increasing levels of matrix metalloproteinases 2 and 9 and grade of degeneration. In scoliotic patients, there was a differential level of expression of these enzymes across the disk, with the highest levels found on the convexity of the curve. This shows that asymmetric forces across the disk may lead to an altered inflammatory environment.^ 16 ^ In addition, Gruber et al. analyzed pro-inflammatory cytokines such as bradykinin-receptor C1, calcitonin gene-related peptide, and catechol-0-methyltransferase, and demonstrated increased levels through immunohistochemistry in degenerative disks. They theorized that due to the avascular nature of the intervertebral disk, inflammatory cytokines cannot be cleared effectively over time and lead to an increased nociceptive response.^ 17 ^ Dongfeng et al.^ 18 ^ continued to explore the pro-inflammatory cytokine environment by demonstrating increases levels of tumor necrosis factor (TNF)-alpha positive cells, small round blue cells, and fibroblasts in degenerative disks. Unfortunately, many of these biochemical associations are theoretical when it comes to the etiology of pain in AIS. In the majority of AIS patients, there is insignificant disk degeneration, and due to the lack of discectomy in most AIS procedures, tissue analysis is not generally obtainable in the surgical setting.
There is also a major theoretical contribution of biomechanical factors contributing to the etiology of back pain in AIS. In the adult population, one of the most significant pain generators is facet arthropathy. Until recently, this has not been evaluated to a complete degree in the AIS population. In 2018, Bisson et al. performed a study comparing the articular cartilage from facets in AIS patients undergoing corrective surgery with nonscoliotic articular facet cartilage in cadaveric organ donors. Alterations in articular cartilage structure were evaluated histologically with Safranin O/fast green and modified Osteoarthritis Research Society International (OARSI) grading scale. Pro-inflammatory cytokines, matrix metalloproteinases (MMPs), and fragmented matrix molecules were evaluated with immunohistochemistry and western blotting. Analysis showed that young scoliotic facets had clear signs of degeneration with substantial proteoglycan loss, increased cell density, increased pro-inflammatory markers, and expression and fragmentation of small leucine-rich proteins such as chondroadherin, decorin, biglycan, and fibromodulin.^ 19 ^ This study demonstrates degenerative changes in AIS facet cartilage similar to adult osteoarthritis and suggests this could be a major contributor to pain perceived in these individuals. In another prospective study, Samaan et al. proposed a theory that pain has an association with paraspinal muscle inflammation and fibrosis. Secondary to asymmetric loading, they believe various chemokine gradients in the paraspinal musculature lead to increased concentrations of macrophages and pro-inflammatory cells and increased muscle fibrosis, leading to pain and worsening deformity.^ 20 ^ Their prospective research is ongoing at this time.
Finally, Teles et al. evaluated the possibility of impaired pain modulation pathways in patients with AIS. They performed quantitative sensory testing in 94 patients with AIS using validated tests such as mechanical detection thresholds, pain pressure thresholds, and heat tolerance threshold. They were able to observe a significant correlation between deformity severity and pain pressure thresholds, neuropathic pain scores, and temporal summation of pain.^ 21 ^ These findings of impaired pain modulation and its relation to deformity severity may suggest that spinal deformity can be a trigger for neuroplastic changes in the AIS population.
Given the role of nutrients, particularly calcium and vitamin D, in bone health, overall nutritional status in AIS patients has been studied. Studies^22–26^ have found higher rates of osteopenia in AIS than in healthy controls. Cheung et al.^ 22 ^ concluded that there may be an abnormally high rate of bone growth in AIS patients, and inadequate calcium intake can exacerbate insufficient bone mineralization. Their cross-sectional study of 621 AIS females matched with 300 healthy controls showed longer anthropometric measurements, but lower bone mass and higher bone alkaline phosphatase (ALP) levels in AIS. Lee et al.^ 25 ^ found that although calcium intake was similar for both AIS and matched healthy controls, bone mass was 6.5% lower in AIS patients. In the AIS group only, calcium intake and weight-bearing physical activity were significantly correlated with bone mass, and these two factors were independent predictors of bone mass in AIS. The authors concluded that prevention of generalized osteopenia may be important in controlling AIS progression.
In contrast, a cross-sectional study of 2431 Japanese females aged 12–15 years who underwent a school screening for scoliosis were identified into an AIS group (Cobb angle at least 15°) or a healthy control group.^ 27 ^ Participants were administered a validated diet history questionnaire for school children and adolescents, which assessed dietary habits for the prior month. There were no associations found between any of the analyzed nutrients or food groups, and the authors concluded that dietary habits may not be associated with AIS. There was no significant association found between any specific nutrient or food group and AIS.
Although this study indicated no relationship between dietary habit and AIS in Japanese girls, there may be other defects in the biochemical pathway related to bone health in AIS. A Korean study of 198 female AIS patients matched with healthy controls showed overall lumbar spine and femoral neck bone mineral densities in AIS patients were lower than healthy controls.^ 28 ^ The BsmI polymorphism of the vitamin D receptor had a statistically significant association with lower lumbar spine bone mineral density. Lower levels of 25-OH-D3, the active form of vitamin D, have also been repeatedly shown in AIS. A study of 100 pre- and postmenarcheal Polish girls by Goździalska et al.^ 29 ^ found 23.5% and 36.2% lower levels of serum 25-OH-D3, respectively, compared to controls. Balioglu et al. assessed 25-OH-D3 levels in 229 AIS patients and 389 age-matched healthy controls. In the AIS group, mean 25-OH-D3 was lower and classified as deficient.^ 30 ^ Silva et al.^ 31 ^ found that 97% of patients in their 42 AIS patient study had insufficient levels of serum 25-OH-D3.
A direct relationship between vitamin D status and back pain, however, is still not clear. Silva et al.^ 31 ^’s study found no relationship between 25-OH-D3 levels and the Scoliosis Research Society (SRS-30) QoL scores in AIS patients. Al-Taiar et al.^ 32 ^ found no association between vitamin D levels and low back pain in the adolescent population at large, and there was no difference in mean 25-OH-D3 levels between those with low back pain and those without. A Norwegian case–control study of individuals aged 19–55 years found no association between vitamin D status and risk of chronic low back pain.^ 33 ^
Sleep and other biopsychosocial factors may modulate back pain. Wong et al.^ 8 ^ cross-sectionally assessed sleep quality in 987 nonsurgically treated AIS patients from Hong Kong. Analyses revealed AIS patients with current back pain had more severe insomnia (odds ratio (OR) = 1.80; p = 0.02, 95% confidence interval (CI) = 1.10–2.93) and greater daytime sleepiness (OR = 2.41; p < 0.001, 95% CI = 1.43–4.07) than those without back pain. Episodic and/or chronic back pain were also associated with greater daytime sleepiness and insomnia. In addition, moderate depression independently predicted a greater than three times likelihood of chronic back pain. Teles et al.^ 21 ^ assessed sleep quality in 94 AIS patients with chronic back pain in a cross-sectional study. 76.6% had back pain lasting more than 1 year and 55.3% experienced daily back pain. In this study population, 75.5% reported poor sleep quality as measured by the Pittsburgh Sleep Quality Index (PSQI). Mean PSQI score was 6.71 (2.94), where a score 5 or higher indicates the poor sleep quality.
The relationship between back pain and poor sleep has been implicated in the adolescent population at large. A two-year follow-up survey on a cohort of adolescents with musculoskeletal back pain from the 1986 Northern Finland Birth Cohort found that insufficient quantity or quality of sleep at age 16 years predicted a nearly three times greater likelihood of low back pain in girls and twice as greater likelihood in boys.^ 34 ^ Wirth and Humphreys^ 35 ^ showed that sleep disorder was a significant predictor for pain in more than one spinal area and trended for more frequent pain in more than one spinal area. Based on the assessment of electronic sleep diaries, Gerhart et al.^ 36 ^ found poor sleep quality was significantly associated with higher pain scores, higher negative effect, lower positive effect, poorer physical function, and higher pain catastrophizing.
Related to sleep quality, sleep breathing patterns were assessed using wrist sleep
monitors by Li et al.^
37
^ in 57 patients with scoliosis (43 AIS, 14 congenital scoliosis), compared to
25 healthy controls. Patients with scoliosis had statistically significantly higher
Respiratory Disorders Index, which includes respiratory events like apnea, hypoxia,
and respiratory effort–related arousal per hour of sleep, than controls
(median = 10.10 vs 8.65). The Apnea and Hypopnea Index, measuring number of apnea
and hypopnea events per hour of sleep, was also higher in patients with scoliosis
(median = 1.60 vs 0.72). Apnea and Hypopnea Effort scores were higher when lying on
the convex side of the thoracic curve compared with the concave side (2.34 vs 2.28).
Minimal SaO2 value in patients with scoliosis was lower than controls
(median = 93% vs 94%), but no difference was found in the mean SaO2 value
during sleep.
A patient’s pain catastrophizing status may also play a role in pain intensity. Teles et al.^ 7 ^ conducted a cross-sectional single-center study of 124 AIS patients who had not undergone surgical treatment. Pain catastrophizing was an independent risk factor for back pain, and pain reported in the last 24 h was significantly associated with pain catastrophizing. In addition, there was a significant relationship between pain intensity and greater deformity, measured by the Cobb angle, torsion index, and axial intervertebral rotation of the upper half of the main curve in low catastrophizers. This relationship did not exist for moderate or high catastrophizers. This suggests negative effect, more so than curve morphology, is more important in modulating back pain in moderate to high-level catastrophizers. Similarly, anxiety and mood may be modifiable influences on back pain. Hwang et al.^ 38 ^ conducted a retrospective review of 2585 AIS patients and divided patients into two groups based on SRS pain scores. 83% of patients were categorized into the No Pain group (SRS score 4 or 5) and 17% of patients were categorized into the Pain group (SRS 3 or lower). Multivariate analyses showed lower mental health SRS scores contributed most to greater preoperative pain scores, with survey questions on anxiety followed by mood/depression having the most impact.
To our knowledge, socioeconomic status (SES) has not been studied in AIS, but the relationship between lower SES and greater prevalence of back pain has been shown. Lallukka et al.^ 39 ^ assessed back pain data from the prospective Young Finns Study. After evaluation by parents’ education and family income and adjusting for age, participants from high-income families were less likely to report back pain at follow-up. A stable lower SES and downward mobility were associated with a greater prevalence of radiating low back pain.
There is a paucity of evidence in regard to curve-specific factors and their influence on subjective pain outcome scores in both nonoperative and operative AIS candidates. Smorgick et al. analyzed predictors of back pain in surgical candidates and demonstrated a correlation between back pain and a more rigid lumbar curve based on coronal modifier. No difference was found in regard to back pain when comparing curve type or sagittal modifiers.^ 40 ^ The remainder of available studies analyzing curve type were in operative AIS patients. In an analysis of 85 fusion patients with AIS, Fekete et al. found no significant differences in pain with respect to coronal Cobb angle of the main curve.^ 41 ^ In a similar prospective study by Djurasovic et al., patients were evaluated for preoperative and postoperative SRS-22R pain scores. The “painful” and “nonpainful” outcome groups analyzed in this study had no difference in preoperative coronal curve magnitude.^ 42 ^ However, Hwang et al. performed a retrospective analysis of 1744 patients attempting to identify risk factors for postop pain in AIS. On multivariate analysis, patients with thoracic curves had significantly more pain than those with lumbar curves.^ 43 ^ The above studies demonstrate a lack of clear consensus on whether curve magnitude or location has a direct influence on preoperative and postoperative subjective pain scores.
The SRS currently recommends bracing for curves 25–40° in skeletally immature patients at the Risser stages 0–2.^ 44 ^ The results from the multicenter Bracing in Adolescent Idiopathic Scoliosis Trial (BrAIST) trial showed no significant differences in Pediatric Quality of Life Inventory (PedsQL) scores between braced and observed patients at baseline and at final follow-up in primary and intent-to-treat (ITT) analyses.^ 45 ^ Back pain was the most common adverse event reported. However, the two groups showed similar rates of pain. These data suggest that bracing does not meaningfully change frequency of back pain in AIS patients with moderate curves, but the extent to which back pain impacts PedsQL scores is unclear. Other aspects like poor body image can negatively influence QoL as shown by Schwieger et al.^ 46 ^ in a follow-up analysis of the BrAIST trial.
In the BrAIST trial, braced patients wore the brace for a mean 12.1 (6.5) h for the first 6 months of the trial and were followed up for a mean 24.2 months. QoL and pain data evaluating bracing during the treatment period have been conflicting (Table 1). This is an important consideration because longer daily usage of the brace is correlated with reduced risk of curve progression.^ 45 ^ Andersen et al. found no statistically significant difference in visual analog scale (VAS) score for back pain and 36-Item Short Form Health Survey (SF-36) scores on health-related QoL. Similarly, Ugwonali et al. found no significant differences in the Child Health Questionnaire (CHQ) and the American Academy of Orthopaedic Surgeons Pediatric Outcomes Data Collection Instrument (PODCI) scores between braced and observed patients. Observed patients did have a higher Global Function and Symptoms domain within the PODCI scores, which includes pain and comfort dimensions. In contrast, a cross-sectional study from Piantoni et al.^ 47 ^ showed that among 43 AIS patients, whom averaged 17.6 h of daily brace usage, nearly half of the patients expressed a deterioration of their QoL due to pain. 55% of patients experienced pain nightly. Patients should thus be counseled on the potential negative physical and mental effects of bracing.
Back pain in AIS patients who are braced appear to resemble natural history over the long-term.^50,73–77^ A meta-analysis by Meng et al.^ 48 ^ analyzed SRS-22 pain scores in AIS patients who received bracing or were managed by observation. Of the five studies eligible for pain analyses, there was no significant difference in pain between the two groups. A long-term case–control study by Danielsson and Nachemson^ 49 ^ followed 109 brace-treated patients for a mean 22.2 years. At the follow-up, there was greater prevalence of lumbar and thoracic back pain during the past year in AIS patients compared to an age- and sex-matched control group. The pain was considered mild (2.7 VAS score), and most patients had mild Oswestry Low Back Pain Disability Scores. The authors therefore concluded there were minimal differences in pain and function compared to the healthy control group. These findings corroborate with a later study by Danielsson et al.^ 50 ^ that found similar SRS-22 pain and SF-36 bodily pain scores at a mean 16-year follow-up period after skeletal maturity.
Conversely, a study of 30 female AIS patients who completed Milwaukee bracing treatment with mean 27.7 years follow-up^ 51 ^ showed these patients had higher levels of neck and lower back pain–related disability compared to age- and sex-matched controls. 53% and 20% of the AIS group experienced moderate and severe disability, respectively, from low back pain. Most severe limitations from back pain were related to moving and leaning/squatting. Lange et al.^ 52 ^ evaluated the long-term outcome in AIS patients 12 years or more after treatment with the Boston brace. Although 95% of patients had excellent, good, or fair back function, 12% of patients reported that they had consulted a physician for back complaints during the last year, and 28% had physiotherapy. Danielsson et al.^ 53 ^’s case–control study including 127 braced AIS patients found that reduced lumbar spinal mobility correlated with greater lumbar pain intensity and greater pain all over the body compared to healthy controls, at least 20 years after the completion of treatment.
The Schroth method is a scoliosis-specific physical therapy focused on sensorimotor, postural, and breathing exercises tailored to the type and severity of curvature.^54–57,78–80^ It aims to correct spinal imbalances and improve neuromuscular control of posture. AIS curves between 10° and 45° have responded well to treatment, and the data have shown improvement in back strength, breathing function, and psychological outcomes.^54–57,78–80^ A typical Schroth program consists of 45–60 min sessions over 12–24 weeks, although the number of sessions and length of program vary among patients. Continuation of an at-home program is critical to potential long-term benefits.
A prospective single-center study of 69 AIS patients with the Cobb angle between 10° and 45° (64% female) analyzed the effects of a 24-week combined Schroth and Pilates exercise program.^ 54 ^ The program regimen consisted of two different 10 week stages, consisting of combinations of daily exercises tailored to the patient’s specific curvature. Patients who had been wearing a brace prior to the study continued to wear the brace throughout the study period, and time out of the brace remained within acceptable limits. At the end of the 24-week treatment period, pain measured by SRS-22R showed mean improvement in patients regardless of bracing status.
Schreiber et al.^ 79 ^ conducted a randomized controlled single-center study of 50 AIS patients undergoing either a 6-month Schroth intervention added to standard of care or standard of care alone. The standard of care arm included observation or bracing consistent with SRS recommendations. Patient-rated change in improvements was measured via the Global Rating of Change scale, rated from −7 (“great deal worse”) to +7 (“great deal better”). GRC improved by +4.4 (2.2) in the Schroth treatment arm and decreased by −0.1 (0.6) in the standard of care arm at the end of the treatment period.^ 55 ^ The authors concluded that perceived improvements may not be solely due to changes in the Cobb angle, as those who reported a 2-point or greater increase in GRC experienced a mean 1.3° largest curve decrease. Through SRS-22R, pain scores did not significantly improve from baseline to 3 months, they did significantly improve from 3 to 6 months in the Schroth group compared to the control group.
A prospective, historical cohort-matched study assessed 24 braced AIS patients undergoing an 8-week Schroth exercise program consisting of training sessions once every 2 weeks followed by a home exercise program with follow-up every 2 months versus a 1 historical cohort.^ 56 ^ A group of braced AIS patients were treated at the same center matched for age, gender, skeletal maturity, and curve magnitude. There were statistically significant improvements in SRS-22 function and total scores in the experimental group, but changes in other domains did not reach significance. The control group did not reach significance in any individual domain or total score.
A systematic review analyzed 10 studies (total n = 494; inclusion criteria of AIS, interventions included any Schroth methods in either study or control group with a comparator group or standard of care, no treatment, or other non-Schroth exercise).^ 57 ^ Two randomized controlled trails (RCTs) and two controlled trials suggested Schroth alone and with bracing or traditional exercise reduced Cobb angle >5°. One RCT specifically implicated no difference between bracing and scoliosis-specific exercise (SSE) in preventing curve progression for moderate scoliosis. However, there was insufficient evidence to support the positive effects of SSE on improving truck asymmetry and QoL.
Another systemic review analyzed nine RCTs including studies that compared Schroth with other nonoperative interventions for AIS.^ 58 ^ Three studies compared Schroth to non-Schroth exercises or standard of care. Two of these studies demonstrated those who received Schroth intervention had better SRS-22 pain scores than those who received standard of care (mean difference = 0.5, 95% CI = 0.4–0.7). A third study showed small but significant improvements in pain. One study indicated a difference in pain scores between individuals who received the Schroth intervention and those who received bracing at 6-month follow-up (mean difference = 0.0, 95% CI = −0.1 to 0.0) and 12-month follow-up (mean difference = 0.0, 95% CI = −0.1 to 0.1).
Whether SSEs render greater improvement in pain than traditional physical therapy warrants further study. A study by Monticone et al.^ 59 ^ compared scoliosis-specific, active self-corrective, and task-oriented spinal exercises against traditional spinal exercises in an RCT (110 mild AIS patients with Cobb angle <25° and Risser sign 0–1). Intervention continued until patients reached skeletal maturity (Risser sign 5). Both groups saw improvements in SRS-22 domains by the end of the treatment period, but the experimental group experienced further improvements of >0.75. The authors concluded pain diminished as a result of patients’ abilities to better understand and modify risk factors in lifestyle, physical, and school-related aspects of their lives. Another study by Yagci and Yakut^ 60 ^ compared core stabilization exercises and SSEs, both in addition to bracing in moderate AIS patients with curves 20°–45°. Patients attended 40 min individual sessions once a week for 4 months. In contrast to findings by Monticone et al., this study showed no improvements in QoL in either group, and the SRS-22 pain score improved only in the core stabilization exercise group. However, the differences in frequency of treatment sessions and patient characteristics between this study (moderate curves and braced) and that of Monticone et al. (mild curves) are notable. Gür et al.^ 81 ^ compared core stabilization exercises focused on respiratory control, neural spinal position, rib cage placement, and neck–head placement against traditional exercises in 25 AIS patients who additionally received bracing. SRS-22 pain score improved by 0.27 in the core stabilization group and decreased by 0.05 in the control group. The SRS-22 pain scores post-treatment in Gür et al. and Monticone et al. were comparable, but mean baseline pain score was already greater by approximately 0.6 in the former.
Maintenance of the benefits of Schroth exercises is dependent upon the patient’s compliance to an at-home program after the formal sessions are completed. Schreiber et al. had an at-home compliance rate of 82.5%, similar to the 85% attendance rate of the prior exercise sessions. The authors attributed the high compliance rates to daily or weekly logbooks completed by the parents and physiotherapists. In Kwan et al.’s historical cohort-matched study, compliance to treatment (defined as >80% attendance of therapy and completion of 5 of 7 days/week of at-home treatment) was associated with curve improvement. 31% of compliant patients improved spinal deformity while 0% of noncompliant patients improved spinal deformity. Kuru et al.^ 82 ^ emphasized the importance of caregivers’ education to proper Schroth technique to ensure compliance. AIS patients whose at-home exercises were unsupervised had progression in the Cobb angle similar to patients who did not practice Schroth exercises. Although the relationship between compliance and pain data has not been directly studied to our knowledge, improvement in pain could follow a similar trend as curve improvement.
Fusion surgery is considered for AIS patients with severe curves greater than 45°, which have a high rate of progression even after skeletal maturity. Pain data have been conflicting. Aghdasi et al.^ 61 ^ conducted a meta-analysis of studies that prospectively reported SRS-22 questionnaire data for AIS patients who underwent spinal fusion using posterior pedicle screw instrumentation. The seven studies that were included reported preoperative data and 24-month or >50-month postoperative data. At 24 months, three of seven studies indicated worse SRS pain scores after surgery. At
60 months, two of three studies indicated worse SRS pain scores after surgery. MCID was met only at the 24-month time point.
Several studies^62–65,83–87^ suggest pain may improve initially but may recur over time, even to baseline levels. Upasani et al.^ 62 ^ found a statistically significant decrease in the SRS-22 pain score from the 2- to 5-year postoperative mark, although the 5-year pain score was still an improvement from baseline. A retrospective review from Bennett et al.^ 63 ^ showed SRS pain scores trended toward improvement from baseline at 5 years. Helenius et al.^ 64 ^ conducted a prospective single-center study of AIS patients who underwent surgical treatment with bilateral segmental pedicle screw instrumentation. Preoperatively, 31% of patients who underwent surgical correction reported moderate to severe pain. Pain scores significantly improved from 4.0 to 4.3 and were greater compared to an untreated AIS group. Compared to a matched healthy control group, pain scores were similar, although surgically treated patients performed significantly worse in function scores. Newton et al.^ 65 ^ collected prospective data on 174 AIS patients. SRS-22 pain score significantly improved at 2-year follow-up, but returned to baseline level at the 10-year mark. The mean thoracic curve was 22° (57% correction) at the latest follow-up. This suggests curve correction does not necessarily lead to improved pain scores.
The precise relationship between pain scores and clinical significance has been proxied by the minimal clinical important difference (MCID). Rushton and Grevitt^ 66 ^ conducted a systematic review of 16 cohorts of patients of which >85% were AIS patients. The cohorts mainly involved patients with Cobb angle between 50° and 60° and mixed curve types. 81% showed statistically significant improvement in SRS pain scores at 2 years postoperatively, yet only 1 of 12 cohorts met MCID for pain. In a prospective multicenter study from Djurasovic et al.,^ 42 ^ patients were grouped based on their baseline SRS-22R pain scores into a painful group and a nonpainful group. In the painful group, there was significant improvement at 2 years, and 81% of patients reached MCID improvement. However, patients in the nonpainful group still had better scores in all domains than those in the Painful Group at that time point.
Preoperative pain score—modulated by psychological factors like mental health, mood, and anxiety—appears to be a meaningful predictor of postoperative pain score.^38,43,67,88,89^ Hwang et al.^ 38 ^ conducted a retrospective review of 2585 AIS patients who underwent surgical correction with minimum 2-year follow-up. 82.8% were classified into the No Pain group (SRS-22 pain score 4–5) and 17.2% into the Pain Group (SRS-22 pain score ≤ 3). Multivariate Classification and Regression Tree (CART) analysis indicated low preoperative SRS mental health score and older age were associated with lower preoperative SRS pain score. 89.1% of patients who scored >3.25 in the mental health component of the SRS-22 were in the no pain group. 52.2% of patients who scored <3.25 on the SRS-22 mental health score were in pain group. Questions on mood and anxiety had the greatest associations with low preoperative SRS pain score. Connelly et al.^ 67 ^ conducted a prospective single-center study that utilized VAS score to assess pain. Greater baseline pain and anxiety predicted slower daily improvement in the typical and highest pain level. Similarly, greater confidence in ability to control pain predicted more rapid declines in the typical and highest pain level. Voepel-Lewis et al.^ 88 ^ found that AIS patients with a high symptom profile also had higher levels of depression, fatigue, pain interference, neuropathic pain, and pain catastrophizing. Girls were nearly six times more likely to have a high symptom profile. Gender disparities were also observed by McKean and Tsirikos,^ 90 ^ who found males fared better in pain and function 2 years after surgery. Anxiety and pain catastrophizing behavior between parent and child can parallel each other too, although this relationship was weak.^ 68 ^
Of clinical concern could be those who develop chronic pain (CP) in the long term without shorter-term pain. These patients may not have an identifiable risk factor for long-term pain. Chidambaran et al.^ 68 ^ conducted a prospective single-center study of adolescent with idiopathic scoliosis and/or kyphosis undergoing posterior spinal surgery. 38% were considered to have CP (persistence of pain 2–3 months after surgery), and 42% were considered to have persistent pain (PP; persistence of pain 1 year after surgery). CP and acute pain were significant predictors for the development of PP. Pain trajectories revealed 65% of patients who developed PP reported CP and high pain trends. Patients who reported PP but not CP represent those who do not present an obvious risk factor for developing longer term pain, particularly if they are only followed up for up to 1 year after surgery.
Disk degeneration (DD) is a concerning long-term outcome,^ 91 ^ but it has not been associated with the presence of back pain. A cross-sectional study evaluated clinical outcomes via the Oswestry Disability Index (ODI) and VAS score in AIS patients who underwent posterior spinal fusion (PSF) surgery and followed for a mean 5.6 years.^ 92 ^ DD was observed in 16% of patients, but it was not associated with preoperative or postoperative vertebral tilt, VAS and ODI scores. Other residual deformities and their relationship to pain have been explored by various studies. In a study by St. Georges et al.,^ 69 ^ participants completed the SRS-30 questionnaire and a modified version of the Adolescent Pediatric Pain Tool (APPT) to characterize pain. Pain score showed statistically significant improvements at 6 weeks and 6 months. Pain intensity lessened in both thoracic and lumbar spine but worsened in the neck at 6 weeks and 6 months. Greater residual Cobb angle difference between main thoracic (MT) and thoracolumbar/lumbar (TL/L) curves was associated with greater pain severity at 6 weeks. Greater residual thoracic deformity was associated with significant pain severity at 6 months. Hwang et al. found curve type was significantly associated with postoperative pain. 16% of thoracic curves compared to 10% of lumbar curves were associated with having a postoperative SRS pain score of 3 or greater or reporting a complication of back pain. In a subgroup of thoracic curves, 9% of patients had pain when fused to T2, 13% had pain when fused to T3, and 18% had pain when fused to T4. The mean time from date of surgery to the first complaint of back pain was 25.6 (21.6) months. Patient age at time of surgery and use of bracing prior to surgical intervention may correlate with pain. Rodrigues et al.^ 70 ^ found a negative correlation between patient age at time of surgery and back pain, and patients who underwent surgical treatment after 15 years of age had worse outcomes. The use of bracing prior to surgical treatment led to smaller improvements in function and pain compared to no use of bracing.
Anterior Vertebral Body Tethering (AVBT) is a newer surgical procedure that aims to modulate spinal growth by applying a flexible tether to the convex side of the spinal curvature. By introducing a compressive force to the convex aspect, the concave side is allowed to grow further to correct the curvature. In a recent review article, Newton^ 93 ^ indicated consideration for AVBT on right thoracic curves 45°–65° in those with substantial growth remaining. Pain data on AVBT are limited due to the procedure’s novelty. A single-center, retrospective review by Newton et al.^ 71 ^ compared 23 AIS patients who underwent AVBT with 26 AIS patients who underwent PSF. Mean follow-up period was 3.4 years. At the time of final follow-up, the AVBT group had greater deformity with mean thoracic curve 33° compared to 16° in the PSF group. There were nine revision procedures conducted in the AVBT group versus none in the PSF group. Despite this, postoperative domain and total SRS-22 scores were similar. SRS-22 pain scores were 4.4 in both the AVBT and PSF groups. Preoperative pain data were not available. Thus, it was not possible to assess the effect of each therapeutic intervention. High SRS-22 pain scores at follow-up do suggest pain was largely mild regardless.
Wong et al.^ 72 ^ conducted a prospective single-center observational study of five female AIS patients treated with AVBT with minimum 4-year follow-up. Curve correction of tethered segments ranged from 0% to 133% at 4 years. Overcorrection occurred in three patients, and two of whom required corrective spinal fusion. Mean SRS-22 total score decreased from baseline to 36 months. SRS-22 pain data were not specified in the study, but mean SRS-22 satisfaction score decreased overall from baseline to 36 months. There was some improvement from the 12-month to 36-month time points.
Back pain in AIS is common but remains difficult to predict and treat. Existing treatment methods have produced mixed results on pain improvement. Braced patients appear to have back pain that resembles the natural history of pain in AIS, while back pain for patients who undergo fusion surgery may improve in the short-term but decline over time. Schroth exercises are promising at least in mild curves but require high level of compliance over the long-term. Pain data are limited with AVBT, and its effect on pain is unclear. Diet and nutrition do not clearly influence back pain, although genetic polymorphisms in Vitamin D metabolism can be considered. It is also challenging to interpret the clinical significance of various pain scores. This is particularly so with no consensus on the definitions of short-term or CP. A good course of action for AIS patients with significant back pain may be a focus on mental health and sleep counseling. Helping to manage depression, pain catastrophizing tendency, and fatigue could encourage AIS patients to take greater agency in their pain management and better navigate through risk factors of back pain at school, at home, or at work. Evidence from the Monticone study where they provided counseling to its participants to view AIS as a manageable condition rather than a serious disease with large negative impact on their personal and professional lives supports this hypothesis. Longer-term studies focusing on counseling and other biopsychosocial factors are critical to better understand and treat chronic back pain in AIS.