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CME Article . 2021 Series . Number 4

Factors Associated With Symptomatic Rotator Cuff Tears

The Rotator Cuff Outcomes Workgroup Cohort Study

Grusky, Alan Z. BS; Song, Amos MD; Kim, Peter MS; Ayers, Gregory D. MS; Higgins, Laurence D. MD, MBA; Kuhn, John E. MD, MS; Baumgarten, Keith M. MD; Matzkin, Elizabeth MD; Jain, Nitin B. MD, MSPH

Author Information
American Journal of Physical Medicine & Rehabilitation: April 2021 - Volume 100 - Issue 4 - p 331-336
doi: 10.1097/PHM.0000000000001684

Abstract

What Is Known

  • Current evidence suggests that older age is associated with rotator cuff tears, but other factors have not been clearly elucidated.

What Is New

  • In a cohort of patients with shoulder pain, we identified older age, involvement of the dominant shoulder, and a higher body mass index as independent factors for rotator cuff tear.

Rotator cuff tears are a common etiology of shoulder pain.1 Particularly in the elderly population, rotator cuff tears represent one of the most common causes of disability related to shoulder issues.2 Prevalence of rotator cuff tears in the general population has been estimated to range from 5%3 to 39%.4 Several studies have reported that the prevalence of rotator cuff tears increases with older age.5–7 Over the past two decades, the number of clinical visits and the number of surgical procedures to manage rotator cuff pathology have increased in the United States.8 With an aging and increasingly active US population, it is expected that there will be a continued increase in patients with rotator cuff–related issues. Other possible factors, such as smoking and hypercholesterolemia, have been implicated in previous studies,9 but the overall evidence is limited.

Because of its enormous public health impact, it is important to understand the underlying factors that are associated with rotator cuff tears. Assessment of factors associated with rotator cuff tears can improve our understanding of the mechanisms of this disorder and encourage investigations on potential prevention strategies. Hence, in a cohort of patients with shoulder pain, we assessed factors associated with symptomatic rotator cuff tears.

MATERIALS AND METHODS

Patient Population

We used data from a multicenter longitudinal cohort study named the Rotator Cuff Outcomes Workgroup.10–14 Patients in this cohort were recruited from sports medicine/shoulder clinics (from three academic settings and one community setting) from February 2011 to July 2016. Recruited patients were 45 yrs or older and had been experiencing shoulder pain and/or loss of range of motion. The age cutoff was determined based on our goal to recruit patients with degenerative rotator cuff tears. Exclusion criteria for the study included the following: current shoulder fracture on the same side, history of shoulder surgery on the same side, and findings of cervical pain radiating to the ipsilateral shoulder/arm/hand (active cervical radiculopathy). All inclusion and exclusion criteria were applied to the symptomatic shoulder. Patients who had a shoulder magnetic resonance imaging (MRI) and those who completed a baseline questionnaire on enrollment were eligible for this analysis (N = 266). Patients included in the study provided written informed consent. The study was approved by our institutional review boards. This study conforms to all Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines and reports the required information accordingly (see Supplemental Checklist, Supplemental Digital Content 1, http://links.lww.com/PHM/B205).

Structured History Questionnaire and Outcome Measures

Upon enrollment in the study, patients completed a structured history questionnaire. An abridged version of this questionnaire (excluding questions on comorbidities and social history) was subsequently mailed to patients at follow-up time points. The questionnaire elicited basic demographic information, alcohol and tobacco use, medical comorbidities, level of shoulder use at work, onset and characterization of symptoms, and patient expectation for improvement.

Daily shoulder use at work was evaluated by asking patients to assess the level of manual labor at their current job. If patients were not working at the time, they were instructed to answer the question with reference to their past job. Body mass index (BMI) was calculated from the height and weight of the patient using information from the electronic medical record and self-reported data. Duration of symptoms, shoulder instability, steroid medication use, and medications per day were self-reported on the baseline questionnaire.

Patients completed a modified Fear-Avoidance Beliefs Questionnaire,15 assessing fear-avoidance beliefs about physical activity and work due to their shoulder pain. In addition, patients completed the Mental Health Inventory,16 assessing mental health status. A score of 68 or lower on the Mental Health Inventory indicates a possible mood disorder, such as depression.17,18 The Shoulder Pain and Disability Index19 and the American Shoulder and Elbow Surgeons Standardized Shoulder20 form were also used to measure shoulder pain and functional outcomes.

Diagnostic Imaging

Shoulder experts (LDH and NBJ or JEK and NBJ) read shoulder MRIs in a blinded fashion. The methodology of MRI reviews in this study has been described in a previous study, in which good interrater and intrarater reliability was shown compared with readings by a musculoskeletal radiologist.13

Diagnosis of Rotator Cuff Tear

The diagnosis of a rotator cuff tear in this study was based on (1) MRI findings that indicated a rotator cuff tear and (2) clinical diagnosis of a rotator cuff tear by an attending-level sports medicine or shoulder fellowship-trained physician.10–14 Patients in whom there was a suspicion of a rotator cuff tear based on clinical impression (assessment made before MRI was ordered) but without evidence of a structural defect on MRI (n = 33) were deemed to not have a rotator cuff tear. Similarly, patients in whom it was clinically determined that their symptoms were not attributable to a tear but had structural evidence of a tear on MRI were deemed not to have a tear in our study (n = 20).

Selection of Factors

The primary objective of this analysis was to estimate the association of factors with the probability of a rotator cuff tear. Potential factors were selected a priori based on expert knowledge and the existing literature.6,21–24 These included the following: patient demographics (sex, age, race, and ethnicity), social factors (smoking, alcohol use, education, marital status), shoulder-related factors (dominant arm, contralateral shoulder problems, duration of symptoms, shoulder use at work, shoulder osteoarthritis, and shoulder instability), medical comorbidities (hypertension, diabetes, rheumatoid arthritis, osteoporosis, depression), BMI, and medication use (oral steroid medication use and duration, total number of medications used per day). Variables that had low prevalence (shoulder instability, contralateral shoulder problems, osteoporosis, rheumatoid arthritis) or had very few patients in one category (race, ethnicity, oral steroid medication duration) were excluded from the analysis. The American Shoulder and Elbow Surgeons Standardized Shoulder and the Shoulder Pain and Disability Index were not analyzed as potential factors because these were used as outcome scores in our cohort.

Statistical Analysis

Redundancy analysis was performed and variables with a R2 value of greater than 0.9 were deleted. Hierarchical clustering using the Spearman correlation metric was estimated to assess whether a set of variables provided similar information. Subsequently, clinical expertise was used to select a set of variables that were meaningful and had potential association with rotator cuff tear. The final set of variables that were assessed for potential association with rotator cuff tear from the previously mentioned process included the following: age, depression, smoking status, BMI, shoulder use at work, hypertension, diabetes, steroid medication usage, and involvement of the dominant arm. To adjust for missing data, 20 imputation data sets were analyzed using predictive mean matching. Estimates of standard errors among these data sets were calculated using Rubin’s rules.25 Logistic regression, with and without imputed data, was used to estimate the association between predictor variables and the probability of a rotator cuff tear. All analyses were conducted using R 3.4.1.26

RESULTS

Among the 266 patients in this analysis, 163 (61.3%) had a rotator cuff tear and 103 (38.7%) did not have a rotator cuff tear (Table 1). The patients who had rotator cuff tears were older (median age of 63 yrs [interquartile range {IQR} = 55–67] for those with rotator cuff tear vs. 59 yrs [IQR = 52–67] for those without rotator cuff tear, P = 0.05). The patients with rotator cuff tears had a shorter duration of symptoms (median duration of 6 months [IQR = 4–18] for those with rotator cuff tear vs. 10 months [IQR = 5–19] for those without rotator cuff tear, P = 0.04) and were more likely to have their dominant shoulder affected (71% for those with rotator cuff tear vs. 56% for those without rotator cuff tear, P = 0.01).

TABLE 1 - Baseline patient characteristics
Risk Factor n Rotator Cuff Tear
Present (n = 163) Absent (n = 103)
Age, a median (IQR), yr 266 63 (55–67) 59 (52–67)
Sex
 Male 148 93 (57) 55 (53)
 Female 118 70 (43) 48 (47)
Race/ethnicity
 White (non-Hispanic) 226 133 (87) 93 (92)
 Other 28 20 (13) 8 (8)
Level of education
 College or above 178 107 (67) 71 (70)
 Less than college 82 30 (30) 52 (33)
Marital status
 Married 184 115 (71) 69 (68)
 Single, married, or divorced 78 32 (32) 46 (29)
Duration of symptoms, a median (IQR), mo 252 6 (4–18) 10 (5–19)
BMI, median (IQR), kg/m2 245 28 (25–33) 28 (25–32)
Dominant shoulder affected a
 Yes 167 112 (71) 55 (56)
 No 88 45 (29) 43 (44)
Daily shoulder use at work
 Heavy/moderate manual labor 63 42 (26) 21 (21)
 Light/no manual labor 200 119 (74) 81 (79)
Social history
 Alcohol use
  1–2 times per week or more 130 79 (50) 51 (51)
  2–3 times per month or less 129 80 (50) 49 (49)
 Smoking
  Current/past 134 87 (53) 47 (46)
  Never 125 72 (45) 53 (53)
 Steroid use 263 59 (37) 34 (33)
Comorbidities
 Arthritis 45 28 (17) 17 (16)
 Hypertension 95 60 (37) 35 (34)
 Diabetes 29 19 (12) 10 (10)
 Depression, median (IQR) 264 85 (75–90) 80 (75–90)
Data are shown as n (%), unless otherwise indicated. Depression measured by points on the Mental Health Inventory Scale. Missing values: race/ethnicity, n = 12; level of education, n = 6; marital status, n = 4; duration of symptoms, n = 14; BMI, n = 21; dominant shoulder, n = 11; daily shoulder use at work, n = 3; alcohol use, n = 7; smoking, n = 7; and steroid use, n = 3.
aSignificant differences between groups were seen for age (P = 0.05), duration of symptoms (P = 0.04), and dominant shoulder affected (P = 0.01).

Our multivariate logistic regression model demonstrated that the odds of having a rotator cuff tear increased with older age (per 1 yr: odds ratio [OR] = 1.03, 95% confidence interval [CI] = 1.02–1.07), if the dominant shoulder was affected (OR = 2.02, 95% CI = 1.16–3.52), and with a higher BMI (per 1 kg/m2: OR = 1.06, 95% CI = 1.03–1.12; Table 2). For ease of clinical interpretation, we also present ORs comparing the 75th percentile versus the 25th percentile of values for continuous variables in our data set, including age (67 yrs vs. 54 yrs: OR = 1.57, 95% CI = 1.03–2.39) and BMI (32.3 kg/m2 vs. 25 kg/m2: OR = 1.54, 95% CI = 1.02–2.31; Fig. 1).

TABLE 2 - Odds ratios and 95% CI of risk factors associated with the diagnosis of rotator cuff tears
95% CI
Risk Factor OR Lower Upper
Age, per 1-yr increment, yr 1.03 1.02 1.07
Sex, male a 0.98 0.59 1.72
Dominant shoulder affected a 2.02 1.16 3.52
Heavy/moderate daily shoulder use at work a 1.39 0.73 2.65
Smoking, past or current a 1.31 0.44 1.29
BMI, per 1-kg/m2 increment, kg/m2 1.06 1.03 1.12
Steroid use a 1.02 0.59 1.77
Diabetes 0.87 0.35 2.14
Hypertension 0.77 0.42 1.39
Depression 1.00 0.80 1.39
aReference variable is sex (female), nondominant shoulder affected, light/no daily shoulder use at work, never smoking, and no steroid use.

FIGURE 1
FIGURE 1:
Selected factors associated with the diagnosis of rotator cuff tears (N = 266). Strength of association is shown with ORs and 95% CIs. A 95% CI that excludes 1 denotes a statistically significant effect at P < 0.05.

A calibration curve for our final model displayed good overlap of predicted versus actual values (Appendix A, Supplemental Digital Content 2, http://links.lww.com/PHM/B206). The variables that most influenced our predictive model were age, dominant shoulder, and BMI (Fig. 2).

FIGURE 2
FIGURE 2:
Relative strength of contribution of factors to the model. A higher χ2-df represents a relatively higher contribution of the respective variable.

DISCUSSION

We assessed factors associated with the presence of rotator cuff tears in a cross-sectional analysis of our cohort of patients with shoulder pain. Overall, we identified older age, involvement of the dominant shoulder, and a higher BMI as independent factors associated with an increased likelihood of rotator cuff tear.

Previous epidemiological studies have recognized older age to be associated with rotator cuff tears.9 Yamamoto et al.6 studied 683 people from a mountain village in Japan and found the presence of rotator cuff tears in 20.7% of these subjects. They identified age, dominant arm, and a history of trauma as factors for rotator cuff tears in their cohort.6 Yamaguchi et al.7 found that prevalence of rotator cuff tears increases with age in a group of patients presenting with shoulder pain, with an average age of 58.7 yrs for those with a unilateral tear compared with an average age of 48.7 yrs in those without a tear. Tempelhof et al.27 used ultrasound to assess 400 patients with asymptomatic shoulders and found a significant positive correlation between age and rotator cuff tears.

The association of age with rotator cuff tears is likely the result of a natural degenerative process. This degeneration is mediated by several factors such as age-related compromise of the microvascular system,28 loss of cellularity and fibrocartilage mass at the rotator cuff insertion site,29 and collagen fiber disorientation.30 It is possible that a confluence of these factors places older individuals at a higher risk of sustaining rotator cuff tears. However, the exact mechanisms associated with the natural history of rotator cuff tears and whether they become symptomatic are not currently known.31

Other etiologies such as impingement, tensile overload, and repetitive stress that leads to microtrauma6 have been implicated in the pathogenesis of nontraumatic rotator cuff tears. These mechanisms may explain the reason for dominant shoulder as a factor for rotator cuff tears. A systematic review by Sayampanathan and Andrew32 concluded that, aside from older age, shoulder dominance was the other major factor associated with a greater chance of developing a rotator cuff tear. Consistent with our study, this analysis found that the dominant shoulder had more than double the odds of sustaining a rotator cuff tear compared with the nondominant shoulder.

There is substantial evidence that obesity and BMI play a role in the pathogenesis of musculoskeletal disorders,33 particularly in osteoarthritis.34–36 However, few studies have looked specifically at the relationship between BMI and rotator cuff tears. Wendelboe et al.37 performed a case-control study that showed increasing BMI to be a factor for rotator cuff tendonitis and related conditions. Gumina et al.24 showed that obesity (measured as BMI and body fat percentage) was a significant factor for both occurrence and severity of rotator cuff tears.

Given that the shoulder is not a weight-bearing joint, it is possible that the association between BMI and rotator cuff tears is due to metabolic factors as opposed to increased mechanical stress caused by obesity. The pathophysiology is still poorly understood, but tendon hypovascularity38 may be a plausible explanation. Most rotator cuff tears occur in an area of relative hypovascularity located within the distal 10 mm of the tendon near its insertion into the greater tuberosity of the humerus.39 Obesity, as modulated by other comorbidities such as diabetes,40 hypertension,23 and hyperlipidemia,21 may exacerbate the natural vascular deficiency in this area.24 This is hypothesized to be due to a pathway initiating with an increase in production of adipokines, inducing oxidative stress, inflammation, and cell apoptosis.41 This process eventually causes degeneration of the rotator cuff tendon that predisposes it to injury.42

The association of cigarette smoking with rotator cuff tears is debated in the literature. A retrospective case-control study by Baumgarten et al.22 suggests a strong association between smoking and rotator cuff tears. However, in our study, smoking was not associated with the presence of rotator cuff tears. It is possible that our sample size (especially of smokers) was not sufficient to detect the association between smoking and rotator cuff tears. Similarly, other factors such as shoulder use at work were not associated with rotator cuff tears in our study. It is possible that self-report of this variable does not accurately describe the microtrauma associated with heavy labor or that our sample size was not sufficient to detect this relationship.

Limitations of our study include exclusion of patients younger than 45 yrs, the use of a binary definition of rotator cuff tear (present vs. absent) instead of degree or size of tears, the absence of ultrasound examination, and the recruitment of patients from specialty clinics, which may have increased the overall prevalence of rotator cuff tears and may limit the generalizability of our findings to primary care settings. All patients in our cohort (including our control population) presented with shoulder pain. Hence, our controls were patients with shoulder pain and not those in the general population. Although this is a limitation, a study that uses the general population as controls would not be feasible because a shoulder MRI would be needed in these persons to avoid inclusion of asymptomatic tears. Although comprehensive information was collected on patients in our cohort, it is possible that unknown confounding variables were not accounted for in our analysis. Our study had minimal (<10% for all variables) missing data, but this also represents a limitation.

CONCLUSIONS

In a cohort of patients with shoulder pain, we identified older age, involvement of the dominant shoulder, and a higher BMI as independent factors associated with an increased likelihood of rotator cuff tear. The mechanism of how these factors are possibly associated with rotator cuff tears needs further research.

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Keywords:

Rotator Cuff Tear; Risk Factors; Shoulder Pain; Cohort

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