Chronic subscapularis tendon tear (SBT) is a degenerative disease and a common pathologic cause of shoulder pain. Several potential risk factors for chronic SBT have been reported. Although metabolic abnormalities are common risk factors for degenerative disease, their potential etiological roles in chronic SBT remains unclear. The purpose of this study was to investigate potential risk factors for chronic SBT, with particular attention to metabolic factors.
This study evaluated single shoulders of 939 rural residents. Each subject undertook a questionnaire, physical examinations, blood tests, and simple radiographs and magnetic resonance imaging (MRI) evaluations of bilateral shoulders. Subscapularis tendon integrity was determined by MRI findings based on the thickness of the involved tendons. The association strengths of demographic, physical, social, and radiologic factors, comorbidities, severity of rotator cuff tear (RCT), and serologic parameters for SBT were evaluated using logistic regression analyses. The significance of those analyses was set at p<0.05.
The prevalence of SBT was 32.2% (302/939). The prevalence of partial- and full-thickness tears was 23.5% (221/939) and 8.6% (81/939), respectively. The prevalence of isolated SBT was 20.2% (190/939), SBT combined with supraspinatus or infraspinatus tendon tear was 11.9% (112/939). In multivariable logistic regression analysis, dominant side involvement (p<0.001), manual labor (p=0.002), diabetes (p<0.001), metabolic syndrome (p<0.001), retraction degree of Patte tendon (p<0.001), posterosuperior RCT (p=0.010), and biceps tendon injury (p<0.001) were significantly associated with SBT.
Metabolic syndrome is a potential risk factor for SBT, as are these factors: overuse activity, diabetes, posterosuperior RCT, increased retraction of posterosuperior rotator cuff tendon, and biceps tendon injury.
The function of the subscapularis muscle and the integrity of the subscapularis tendon are of great importance to shoulder function. Providing approximately 50% of rotator cuff force, the subscapularis is the largest and most powerful of the rotator cuff muscles and its importance in arm elevation outweighs that of both the supraspinatus and infraspinatus [
Chronic SBT is a common pathologic cause of shoulder pain. However, the etiology of chronic SBT remains incompletely understood. Several previous studies that focused mostly on anatomical or radiological parameters have investigated potential SBT risk factors, including subcoracoid stenosis [
This study was approved by the Institutional Review Board of Gyeongsang National University Hospital (No. GNUH 2015-02-001). Informed consent was obtained from the volunteers included in this study.
A survey of upper extremity morbidity was conducted with support from public health officers. The study cohort was comprised of 1,149 uncompensated volunteers from the studied rural region. One of those recruited volunteers had an amputated shoulder; therefore, 2,297 shoulders were included in the study cohort. Of these volunteers, study subjects were enrolled according to the following inclusion and exclusion criteria. The inclusion criteria were the completion of a written consent and of a questionnaire, physical examinations, fasting blood tests, and simple radiographs (true anteroposterior, axillary lateral, and outlet views) and MRI evaluations of bilateral shoulders. The exclusion criteria were a lack of participation in shoulder MRI studies (n=17), a relevant history of trauma (n=26), previous shoulder surgery (n=13), glenohumeral joint osteoarthritis (n=12), calcific tendinitis (n=15), frozen shoulder (n=9), and/or use of medications that could affect serum lipid profiles (n=118). After exclusion, a total of 939 enrolled subjects, of whom 462 were male and 477 were female with a mean age of 59.2±8.4 years, were included in the study. Because several non-systemic variables are shoulder-related factors that would not affect both bilateral shoulders similarly, only one shoulder per subject was included in the analysis as the studied side to evaluate the strength of associations among variables. For subjects with either bilateral SBT or no SBT, one shoulder was randomly included (using random number generation by Excel). For each subject with unilateral SBT, only the involved shoulder was included as the studied side (
MRIs were performed using a 1.5-T scanner (Siemens Medical Systems, Erlangen, Germany). Four sequences, each with a slice thickness of 3 mm, a field of view from 15.9 to 18.0 cm, and one excitation, were obtained as follows: (1) oblique sagittal T1-weighted spin echo, (2) oblique sagittal T2-weighted turbo-spin-echo (TSE) with fat saturation, (3) oblique coronal T2-weighted TSE with fat saturation, and (4) axial T2-weighted TSE with fat saturation. All MRIs were interpreted by one experienced musculoskeletal radiologist who was blind to the clinical findings (JBN). Full thickness RCTs were diagnosed based on a discontinuity or gap in the tendon or an increased signal intensity on T2-weighted images, extending from the articular to the bursal surfaces. Partial thickness RCTs were diagnosed based on partial high intensity in the rotator cuff tendon or on a slight increase in signal intensity in the cuff tendon, without a definite defect on either the intra-articular or the bursal side. Biceps tendon injuries were determined by MRI, then classified as partial or complete tear, or subluxation. Partial biceps tendon tear was identified by increased intra-tendinous T2-weighted signal intensity. A complete tear was identified by absence of the LHBT intra-articularly or within the bicipital groove. Subluxation was identified by displacement of the LHBT from the bicipital groove [
The studied variables were as follows. The demographic or general physical factors included age, sex, waist circumference, and dominant side involvement. The social factors included tobacco smoking, alcohol use, and manual labor and the comorbidities included diabetes, hypertension, metabolic syndrome, and dyslipidemia. Previous diagnoses of diabetes and hypertension were accepted. New diagnoses were made during the study using current standards for blood test and blood pressure findings as follows: diabetes, by serum levels of glycated hemoglobin (HbA1c) ≥6.5% or of fasting glucose ≥126 mg/dL [
Factors related to tear chronicity detected on MRI were Patte retraction degree [
The prevalence and 95% confidence intervals (CIs) of SBTs were analyzed. Using univariate logistic regression analyses, the odds ratios and 95% CIs were calculated to identify any association between SBT and the studied variables. Then, multivariable logistic regression analyses, using only the significant variables identified in the univariate analyses, were performed. Multivariable logistic regression analysis was performed after assessment of multicollinearity using factors with both a variance inflation factor and a condition index <10, indicating no multicollinearity [
The prevalence of SBT among enrolled subjects was 32.2% (302/939); among subjects with overall RCT, it was 74.6% (302/405). The prevalence of SBT when isolated, when combined with PSRCT, and in relation to tear thicknesses is summarized in
In multivariable analysis, dominant side involvement, manual labor, diabetes, metabolic syndrome, Patte retraction degree, PSRCT, and biceps tendon injury were significantly associated with SBT (p≤0.041) (
A notable finding of this study is that metabolic syndrome is a significantly associated factor for SBT, as are the following previously-reported significantly associated factors: dominant side involvement, manual labor, diabetes, Patte retraction degree, PSRCT, and biceps tendon injury. Metabolic syndrome is a well-known risk factor for various degenerative diseases, among which are cardiovascular disease, stroke, diabetes, osteoarthritis, and Achilles enthesopathy [
The prevalence of SBT was found by one cadaveric study to be 37% and also found that all tears were articular side partial tears [
The current study found dominant-side involvement to be a significantly associated factor of SBT. Most previous relevant studies reported the greater prevalence of RCT on the dominant side [
The main finding of this study that diabetes is strongly associated with SBT is consistent with the findings of several previous studies that noted diabetes as a risk factor for RCT and for retear after rotator cuff repair [
In this study, Patte retraction degree was significantly associated with SBT. The retraction degree has been reported to be significantly associated with supraspinatus muscle atrophy, which could explain the tear severity and/or tear chronicity of supraspinatus tear that is associated with SBT [
Several studies reported that lesions of the LHBT are significantly associated with SBT [
This cross-sectional study has some limitations. Subjects included volunteers only, and they may not have been representative of the entire local population. Agricultural workers made up a major portion of this cohort, and their characteristics may not be generalizable to other populations in other locations. This study did not evaluate differences in ethnic backgrounds, family histories, educational attainments, or activity levels. SBT and biceps tendon injury were diagnosed by 1.5-T MRI, which has been reported to have less diagnostic accuracy than arthroscopy or 3.0-T MRI [
A grant from the Farmers’ Musculoskeletal Disease Investigation of the Korean Rural Development Administration supported this work.
None.
Supplementary materials can be found via
Flowchart for inclusion and exclusion criteria for this study. All 939 subjects met the authors’ inclusion and exclusion criteria. MRI: magnetic resonance imaging.
The summary of demographic data, prevalence, mean or median for each of studied variables
Characteristics | Subscapularis tendon tear group (n=302) | Subscapularis tendon intact group (n=637) |
---|---|---|
Age (yr) | 60.53±8.43 | 58.63±8.30 |
Male | 174 (57.6) | 288 (45.2) |
Waist circumference (cm) | 84.82±8.80 | 83.94±8.39 |
Dominant side involvement | 172 (57.0) | 266 (41.8) |
Smoking | 119 (39.4) | 242 (38.0) |
Alcohol | 201 (66.6) | 417 (65.5) |
Manual labor | 228 (75.5) | 424 (66.6) |
Diabetes | 78 (25.8) | 91 (14.3) |
Hypertension | 73 (24.2) | 147 (23.1) |
Metabolic syndrome | 138 (45.7) | 178 (27.9) |
Serum lipid level (mg/dL) | ||
Cholesterol | 191.5±33.2 | 195.7±32.3 |
TG | 109 (81–150) | 107 (79–148) |
LDL | 133.10±28.7 | 131.8±31.1 |
HDL | 54.0 (45.0–62.0) | 56.0 (46.0– 66.0) |
Non-HDL | 145.1±30.5 | 141.3±28.9 |
Prevalence of dyslipidemia | ||
Hyper-cholesterolemia | 138 (45.7) | 263 (41.3) |
Hyper-TGmia | 109 (36.1) | 181 (28.4) |
Hyper-LDLemia | 246 (81.5) | 505 (79.3) |
Hypo-HDLemia | 83 (27.5) | 167 (26.2) |
Hyper-non-HDLemia | 195 (64.6) | 398 (62.5) |
TG/HDL ≥3.5 | 88 (29.1) | 126 (19.8) |
Patte grade | 1.1±1.0 | 0.7±1.1 |
Global fatty degeneration index | 0.33 (0.33–0.66) | 0.33 (0.33 to 0.66) |
Goutallier grade | 1.00 (0.00–1.10) | 1.00 (0.00–1.00) |
Tangent sign | 48 (15.9) | 87 (13.7) |
Occupation ratio grade | 0.00 (0.00–0.00) | 0.00 (0.00–0.00) |
Superior displacement of humeral head | 48 (15.9) | 90 (14.1) |
Posterosuperior cuff tear | 135 (44.7) | 167 (26.2) |
Biceps injury | 101 (33.4) | 106 (16.6) |
Values are presented as mean±standard deviation, number (%), or median (interquartile range).
TG: triglyceride, LDL: low-density lipoprotein, HDL: high-density lipoprotein.
Prevalences of SBT among enrolled subjects
Prevalence | Enrolled subject (n=939) | 95% CI |
---|---|---|
SBT | 32.2 (302/939) | 32.17–32.23 |
Partial-thickness SBT | 23.5 (221/939) | 23.47–23.53 |
Full-thickness SBT | 8.6 (81/939) | 8.58–8.62 |
Isolated SBT | 20.2 (190/939) | 20.17–20.23 |
SBT with PSRCT | 11.9 (112/939) | 11.88–11.92 |
Among SBT subjects (n=302) | ||
Partial-thickness SBT | 73.2 (221/302) | 73.17–73.23 |
Full-thickness SBT | 26.8 (81/302) | 26.77–26.83 |
Isolated SBT | 62.9 (190/302) | 62.86–62.93 |
SBT with PSRCT | 37.1 (112/302) | 37.07–37.12 |
Among over all RCT subjects (n=405) | ||
SBT | 74.6 (302/405) | 73.57–74.63 |
Values are presented as percent (number).
SBT: subscapularis tendon tear, CI: confidence interval, PSRCT: posterosuperior rotator cuff tear, RCT: rotator cuff tear.
Factors significantly associated with subscapularis tendon tear in univariate analyses
Studied variable | Odds ratio (95% CI) | p-value |
---|---|---|
Age (yr) | 1.03 (1.01–1.05) | 0.001 |
Male | 1.65 (1.25–2.17) | <0.001 |
Dominant side involvement | 1.85 (1.40–2.43) | <0.001 |
Manual labor | 1.55 (1.14–2.11) | 0.006 |
Diabetes | 2.09 (1.49–2.94) | <0.001 |
Metabolic syndrome | 2.17 (1.63–2.89) | <0.001 |
TG/HDL ≥3.5 | 1.67 (1.22–2.29) | 0.001 |
Retraction degree of Patte | 2.55 (1.91–3.39) | <0.001 |
Global fatty degeneration index | 2.01 (1.36–2.96) | <0.001 |
Goutallier grade | 1.32 (1.05–1.68) | 0.020 |
Occupation ratio | 1.70 (1.07–2.72) | 0.025 |
Posterosuperior RCT | 2.28 (1.71–3.03) | <0.001 |
Biceps tendon injury | 2.52 (1.83–3.46) | <0.001 |
CI: confidence interval, TG: triglyceride, HDL: high-density lipoprotein, RCT: rotator cuff tear.
Factors significantly associated with subscapularis tendon tear in multivariable analysis
Studied variable | Odds ratio (95% CI) | p-value |
---|---|---|
Dominant side involvement | 2.00 (1.45–2.76) | <0.001 |
Manual labor | 1.75 (1.24–2.48) | 0.002 |
Diabetes | 2.80 (1.90–4.12) | <0.001 |
Metabolic syndrome | 2.05 (1.50–2.84) | <0.001 |
Retraction degree of Patte | 2.03 (1.48–2.83) | <0.001 |
Posterosuperior RCT | 1.67 (1.15–2.71) | 0.010 |
Biceps tendon injury | 2.12 (1.36–2.93) | <0.001 |
Hosmer-Lemeshow test | - | 0.427 |
CI: confidence interval, RCT: rotator cuff tear.