Notably, both classic SD and atypical SD are associated with back pain.14,16,17,19–22 Although Scheuermann kyphosis is uncommon, SD radiological signs have been observed in 18% to 40% of the general population,23 suggesting that SD, or more precisely, “SD-like” spine, may be a variant of normal spine morphology rather than a disease. A genetic role in the cause of SD has been proposed, with a suspected autosomal dominant pattern of inheritance.20,24 The Trp3 allele, a variant of the COL9A3 gene, has been associated with SD.20
We speculated whether an SD-like spine is associated with LBP in the general population. However, previous studies on the relationship between SD and LBP have primarily focused on patients with Scheuermann kyphosis, back pain, or sciatica. Therefore, we conducted this study to investigate the relationship between SD-like spines and LBP in a local population of hospital staff members.
MATERIALS AND METHODS
This retrospective cohort study involved 188 staff members from Peking University Third Hospital. A database was established in 2007 with the original purpose to investigate potential LBP risk factors among hospital employees, which contained lumbar MR images and self-administered questionnaires concerning participants' LBP issues. This primary information formed the basis of this study 6 years later. Participants were classified into 2 groups, SD-like and “non–SD-like,” according to whether their lumbar MR images met SD diagnostic criteria, and LBP rates were compared between the groups based on questionnaire data. Among LBP sufferers (participants who ever had LBP), LBP consequences, and functional limitations were compared between SD-like participants and non–SD-like participants. We also conducted follow-up interviews to compare LBP progression during a 6-year period between the 2 groups. The study protocols were approved by the hospital ethic committee. All participants provided written informed consent.
The database inclusion criterion was full-time employment at our hospital. Exclusion criteria included a history of spinal fracture or violent back trauma, spinal surgery, ankylosing spondylitis, spinal tuberculosis, and tumor. Pregnant females and employees committed to long-term analgesic use for reasons other than back pain were also excluded. Participants were sampled from all 66 departments of our hospital using stratified cluster sampling with unequal probabilities. The departments were stratified according to function: clinical services (36) and administrative and logistical affairs (30). In each stratum, we randomly sampled 2 departments using the method of sampling with unequal probabilities, according to the number of staff members in each department. The corresponding author of this study visited the directors of the sampled departments and invited all departmental staff members to participate. Qualified participants were offered a free lumbar MR examination and multiple clinical visits at the spine service. Initially, 198 participants from the departments of orthopedics (29 physicians, 51 nurses), respiratory disorders (13 physicians, 30 nurses), finance (30 administrative/clerical/accounting staffs), and department of general services (30 drivers, 15 engineers/plumbers) were enrolled. Each department had more than 85% enrolment. After reviewing the data, 1 case of ankylosing spondylitis, 1 previous spinal fracture, and 8 participants who did not take the scheduled lumbar MR examinations were excluded. Finally, 188 participants were included in this study.
The LBP Questionnaire
At the time of enrolment, each participant completed a questionnaire on their demographic information, LBP status, consequences, and functional limitations. An indicative anatomical drawing showing the low back area (between the lowest ribs and lower gluteal folds) was printed on the questionnaire, and 9 questions (Table 2) were used to evaluate LBP status and consequences. Functional limitations were assessed with the Oswestry Disability Index (version 2.0). Although participants completed the questionnaire, a spine surgeon was present for instruction and technical checking of missing data and logical errors. Then, the retrieved questionnaires were relayed to the medical assistants' office, and the data were double entered and corrected for entry errors using EpiData software version 3.0 (EpiData Association, Odense, Denmark). The questionnaires were completed, and all data entered and verified, during 2 months from June to August 2007.
Lumbar MR Classification
The participants underwent lumbar MR examination within 6 months after completing the questionnaire. Lumbar MR image covered the T10–T11 disc level in 156 of 188 participants (83.0%). Participants were classified as SD-like or non–SD-like according to lumbar MR image manifestations. SD-like participants were identified using SD diagnostic criteria, either by the classical Sorenson criterion of at least 3 consecutive wedge-shaped vertebrae showing more than 5° of anterior wedging,15 or by a modified Heithoff criterion for SD. In the original study by Heithoff et al,17 3 of the 5 signs on MR image, including WV, SN, IE, disc space narrowing, and disc dehydration, were necessary for SD diagnosis. However, because disc space narrowing and disc dehydration are highly nonspecific in adults, we modified Heithoff criterion to “simultaneous presence of WV, SN, and IE” to identify SD-like participants (Figure 2). Two spine surgeons blinded to participants' LBP status independently reviewed and classified the MR images. The inter-rater consistency between these evaluators demonstrated good consistency (κ= 0.931, P < 0.0001). The classification results presented in this study are from the senior physician of the 2 evaluators.
Follow-up interviews were conducted to compare LBP progression during a 6-year period between SD-like participants and non–SD-like participants. Participants completed a 3-question follow-up questionnaire concerning change in LBP status during the follow-up period (Table 2). A surgical resident who was blinded to the study protocol and had completed an orthopedics rotation conducted the follow-up. We prepared gifts for each interviewee (hand mirror for females and mobile phone portable charger for males) to encourage their participation.
The objective of this study was to investigate the relationship between SD-like spine and LBP in this series of hospital employees. The study items and outcome measures are listed in Table 3.
The independent-samples t test was used to compare normally distributed data. For data that were not normally distributed, the rank sum test was used. The χ2 test was used to compare rates. SPSS version 21.0 (SPSS, Chicago, IL) was used for statistical analysis. The α value was set at 0.05.
SD-Like and Non–SD-Like Participants' Demographic Information
Among the 188 study participants, 34 had SD-like spine, and the remaining 154 had non–SD-like spine. Among the 34 SD-like participants, 24 met Sorensen criterion, 21 met modified Heithoff criteria, and 11 met both. A higher proportion of males were included in the SD-like group (67.6% vs. 39.6%; χ2 = 8.857, P = 0.003). Therefore, the majority of the following study items were examined overall and according to sex. No significant differences in age, occupation, height, weight, body mass index, or smoking status were observed between groups (Table 4).
Radiological Features of SD-Like Participants
Scheuermann signs, including WV, SN, and IE, were clustered in the thoracolumbar region between T11–T12 and L2–L3 (Figure 3). The median thoracolumbar kyphotic angle of SD-like participants (12.1°; interquartile range, 10.8°–12.8°) was significantly higher than that of non–SD-like participants (7.3°; interquartile range, 5.7°–8.5°; Z =−7.635; P < 0.0001).
LBP Issues in SD-Like and Non–SD-Like Participants
Rates of lifetime LBP, previous 1-year LBP, and point LBP did not significantly differ between the 2 groups (Table 4). When stratified by sex, SD-like males had a higher rate of lifetime LBP and previous 1-year LBP than non–SD-like males (Table 4).
SD-like and non-SD-like LBP sufferers demonstrated no significant difference in pain type (chronic vs. acute), point VAS score, or Oswestry Disability Index score. However, SD-like LBP sufferers had higher rates of work absence and sought medical care due to LBP than non-SD-like LBP sufferers (Table 5). The intensity (VAS score) of the most severe LBP episode in the past 2 years was also significantly higher among SD-like LBP sufferers.
The most frequent causes of LBP were heavy workload, awkward working postures, and cold environment in both groups (Figure 4), with the exception of SD-like females, in whom the third most frequent cause was minor body movement. A significantly higher proportion of SD-like participants than non–SD-like participants listed “heavy workload” (94.7% [18/19] vs. 61.4% [48/74], χ2 = 6.548, P = 0.011).
LBP Progression in SD-Like and Non–SD-Like Participants
We successfully followed 159 of the 188 participants (84.6%), including 29 SD-like participants and 130 non–SD-like participants. The follow-up rates did not significantly differ between groups (SD-like: 85.3% [29/34], non–SD-like: 84.4% [130/154]; χ2 = 0.016, P = 0.898). The reasons for loss to follow-up were death in 3 participants, resignation in 23 participants, and retirement in 3 participants. The follow-up period was 6 years (from August 2007 to August 2013). During the follow-up period, 21 new cases of LBP occurred in 6 SD-like participants and 15 non–SD-like participants.
LBP incidence during the follow-up period did not significantly differ between SD-like participants and non–SD-like participants (20.7% [6/29] vs. 11.5% [15/130], χ2 = 1.026, P = 0.311). However, the rate of LBP aggravation during the follow-up period was significantly higher among SD-like participants than non–SD-like participants (55.2% [16/29] vs. 26.9% [35/130], χ2 = 8.685, P = 0.003). The difference remained significant for both sexes (males, 47.4% [9/19] vs. 18.8% [9/48], χ2 = 5.647, P = 0.017; females, 70.0% [7/10] vs. 31.7% [26/82], χ2 = 4.139, P = 0.042). Aggravation in pain intensity was noted by 93.7% (15/16) of SD-like participants whose LBP progressed, with or without an increase in frequency, whereas 6.3% (1/16) only reported increased frequency. In non–SD-like participants whose LBP progressed, the corresponding rates were 68.6% (24/35) and 31.4% (9/35) (χ2 = 2.596, P = 0.107).
In this series of hospital employees, 18.1% of the participants met radiological criteria of SD, and 55.9% of these SD-like participants had a history of LBP. SD-like LBP sufferers were more likely to experience work absence and seek medical care due to LBP than non-SD-like LBP sufferers, and a higher proportion of SD-like participants demonstrated LBP progression over time. Moreover, when sex was considered, SD-like males were more likely to experience LBP than non–SD-like males. However, LBP incidence during the follow-up period was not significantly different between groups, which does not support that an SD-like spine is a risk factor for LBP.
Nearly one-fifth of these hospital staff members had lumbar MR image manifestations that met SD diagnostic criteria. This rate is comparable with the reported 18% to 40% prevalence of SD radiological signs in the general population.23 They did share some traits with patients with SD. First, more males were classified as SD-like, consistent with previously reported sex ratios in patients with SD.16–19,21,22,24 Second, Scheuermann signs in SD-like participants were mainly aggregated at the thoracolumbar junction area between T11–T12 and L2–L3 and sparse in the lower lumbar region, consistent with previous radiological descriptions of “lumbar” or “atypical SD.”18,19,25,26 Third, thoracolumbar kyphosis of SD-like participants was significantly greater than that of non–SD-like participants, which, we postulate, was indicative of a mild form of Scheuermann kyphosis.
Although SD has been associated with back pain,14,16–22 our results indicate 3 characteristics of LBP in SD-like spine. First, LBP was more painful. Although point LBP intensity did not significantly differ between LBP sufferers in the 2 groups, the most severe episode of LBP in the past 2 years was significantly more painful among SD-like LBP sufferers. Follow-up assessment also indicated that aggravation of pain intensity was present in most SD-like participants whose LBP progressed. Second, LBP was more disabling. Significantly higher proportions of SD-like LBP sufferers required work absence or medical care, and selected “heavy workload” as a causative factor of LBP. Third, LBP was more progressive, with a significantly higher proportion of SD-like participants reporting LBP progression at follow-up. Statistically, these characteristics were more robust in males than in females, which may be because of the greater prevalence of males than females in the SD-like group. In contrast, female sex itself is a potential risk factor for LBP, which may weaken the difference in LBP status between SD-like females and non–SD-like females.5,6
These observed characteristics of LBP associated with SD-like spine may originate from a synergism of multiple pathologies, including DD, endplate lesions, and abnormal spinal curvature. SD has been shown to promote DD.17,18,25 Histological studies revealed developmental structural weakness in the disc and endplate of patients with SD,27 which may favor the development of both DD and endplate lesions. Endplate lesions, especially SN,28 are well associated with SD and may irritate local nerve endings that supply it, resulting in LBP.29 As for increased thoracolumbar kyphosis, as observed in SD-like participants, it may cause LBP via altered stresses or mechanisms of referred pain due to irritation of the T12 or L1 spinal nerve.30 Thus, LBP in people with SD-like spine seems more related to specific pathologies with a possible genetic background than to nonspecific functional disturbances.
Several possible confounding factors should be discussed. DD has long been suspected of playing a role in LBP development,2,12 but we did not evaluate DD or stratify results by the degree of DD in this study, because current evidence has not verified that DD is associated with LBP, and SD itself can promote DD.17,18,25 In addition, participants were enrolled and classified regardless of their DD status. Another possible confounder is occupation because the percentage of manual workers (drivers, engineers, and plumbers) was twice as high in the SD-like group (P = 0.075). However, several systematic reviews suggested that work-related mechanical factors were unlikely to independently cause LBP,2 and among athletes who typically handled heavy physical loads, those with SD were more likely to present back symptoms and radiological degeneration aggravated over time than those without SD.31 Therefore, in this study, occupation was unlikely independently causative of LBP. Nevertheless, mechanical factors were notably associated with SD development.31–34 Thus, we postulate that occupation-related mechanical factors and SD-related intrinsic factors may work together in causing LBP in some study participants with SD-like spines.
It is important to note that this study is more related to a preliminary investigation in an attempt to establish a justifiable hypothesis than late-stage research with results that could change current spinal practice. The limitations of this study include its retrospective design, single-hospital setting, and small sample size. Furthermore, the definition of atypical SD remains controversial. However, our results suggest a possible association between SD-like spine and LBP in the general adult population. This phenomenon definitely warrants further research, because additional verification may bring some social effects. For example, people with SD-like spine may want to know the risks if they develop LBP and make career and recreational choices accordingly. Future investigations in this field should involve lumbar MR in larger, prospective population-based cohorts.12,35
- In the general population, lumbar MR images of many people would meet the diagnostic criteria of SD.
- Among LBP sufferers, SD-like spine is associated with higher rates of work absence and seeking medical care due to LBP, as well as greater intensity of the most severe LBP episode in the past 2 years.
- When sex is considered, SD-like males are more likely to experience LBP than non–SD-like males.
- Having SD-like spine is likely to be associated with the severity and progressive nature of LBP in the general population.
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Keywords:© 2014 by Lippincott Williams & Wilkins
Scheuermann disease; atypical Scheuermann disease; lumbar Scheuermann disease; low back pain; lumbar spine; magnetic resonance imaging; Schmorl node; irregular endplate; wedged vertebra; hospital