1 Introduction

As the number of shoulder surgeries continues to rise annually,^1–3 understanding the factors that influence pain in this population is increasingly important. Postoperative pain control can impact the path to restoring shoulder function and mobility as well as patient satisfaction.⁴ However, pain control is often balanced with the risks associated with narcotic medications.⁵ Opioids are commonly used as a means of postoperative orthopaedic pain management and orthopaedic surgeons are third highest prescribers of opioids in the United States.^4,6–8 Therefore, determining patient characteristics associated with increased pain after shoulder surgery may help orthopaedic surgeons anticipate outcomes and better understand this patient population.⁹

Pain can be influenced by multiple psychosocial factors including anxiety and/or depression, age, severity of preoperative pain, smoking, alcohol use, and socioeconomic status.^10–14 Classically, pain has been rated on a numerical scale, which gives little perspective into the degree of impact on an individual's function and quality of life.¹⁵ A more insightful measure may be Pain Interference (PI), known as “pain impact,” which is the degree that pain interferes with an individual's physical, mental, and social activities.¹⁶ PI has become increasingly important to understand patient experiences and is a key outcome in pain clinical trials.¹⁷

Multiple validated pain interference measurements exist, each with their respective strengths and weaknesses.^18–21 The National Institutes of Health developed the Patient-Reported Outcomes Measurement Information System (PROMIS) to standardize patient reported outcome assessments, including pain interference.²² Furthermore, PROMIS is comparable to traditional orthopaedic patient reported outcome tools,^23–26 but with reduced administration time.²⁷ Although PI has been explored in other orthopaedic subspecialties, there is currently a paucity of literature investigating pain interference in shoulder surgery patients.

The purpose of this study was to identify preoperative characteristics associated with worse PROMIS pain interference scores two years after shoulder surgery. We hypothesized that worse pain interference after shoulder surgery would be associated with older age, greater comorbidities, mental health impairment, and lower socioeconomic status.

2 Methods

This was a retrospective review of prospectively acquired data. From May 2015 to June 2018, patients undergoing elective shoulder surgery by seven surgeons at a single urban institution were enrolled into an institutional review board approved orthopaedic registry.²⁸ Survey questionnaires were electronically collected within one week of surgery and then two years postoperatively.

Demographic information, social history and surgical history were self-reported. Medical records were reviewed for pertinent data including preoperative medications, smoking status, comorbidities, American Society of Anesthesiologists (ASA) score and Current Procedure Terminology (CPT) codes.²⁹ CPT codes were confirmed by reviewing operative notes. Pre-treatment patient expectations were assessed with the Musculoskeletal Outcomes Data Evaluation and Management System (MODEMS) questionnaire.³⁰ Participants were also administered the PROMIS Computer Adaptive Test consisting of six domains: Pain Interference (PI) v1.1, Physical Function (PF) v1.2, Social Satisfaction (SS) v1.0, Fatigue v1.0, Anxiety v1.0, and Depression v1.0. For each PROMIS domain, the average score in the general population is 50 ± 10. PROMIS PI is an inverted scale and indicates the degree to which pain interferes with physical, mental, and social activities; a higher score indicates a greater level of hindrance in these disciplines. The Numeric Pain Scale (NPS) was used to evaluate pain in the operative shoulder (NPS shoulder) and the whole body (NPS whole body) on a standard Likert scale.³¹ Physical activity level was assessed with the International Physical Activity Questionnaire (IPAQ) to report Metabolic Equivalent Task minutes per week (MET-min/wk),³² the Tegner Activity Scale (TAS),³³ and the Marx Shoulder Activity Rating Scale (MARS).³⁴ The American Shoulder and Elbow Surgeons (ASES) assessment form was used to evaluate shoulder function.³⁵

Continuous data was presented as mean and standard deviation, while categorical data were reported as frequencies and percentages. Change in patient scores from baseline to two years postoperatively was calculated by subtracting the baseline score from the two-year score. When scales were inverted (i.e. PROMIS pain interference where a higher score indicates “worse” PI), a negative change value indicated outcome improvement. Spearman rank correlation coefficient (rho, ρ) was used to assess correlations between two continuous variables. The Wilcoxon rank-sum test was used to compare means between two groups and the Kruskal-Wallis test was utilized to compare means among three or more groups. CPT codes were analyzed both by primary CPT code (first procedure listed in the operative note) and by all CPT codes to account for concomitant procedures. Preoperative predictors of two-year and change in PROMIS PI scores were determined by backwards stepwise multivariable regression. All significant categorical and continuous variables from bivariate analysis were selected to be incorporated into the model. All statistical tests were two-sided, and a significance level of P < 0.05 was used. All analyses were performed using JMP Pro, Version 13 software (JMP®, Version 13. SAS Institute Inc., Cary, North Carolina).

3 Results

Of the 389 patients that completed preoperative surveys, 293 patients completed the two-year follow-up surveys providing a 75.3% completion rate. In our cohort, the mean age was 49.1 ± 16.4 years, and 164 (56%) were male. In this population of shoulder patients, average preoperative PROMIS PI was 61.4 ± 7.3. Two-years after shoulder surgery, average PROMIS PI improved to 50.9 ± 10.3 (P < 0.0001). From baseline to two-years after surgery, the mean change in PI was −10.7 ± 9.4. No significant differences were observed between CPT codes for two-year and change in PROMIS PI for primary CPT codes (Table 1) or for all CPT codes (Table 2).

Two-year and change in PROMIS PI scores and their correlations to preoperative continuous variables can be seen in Table 3. Worse two-year PROMIS PI was significantly correlated with older age, higher BMI, greater comorbidities, and more previous surgeries. Less improvement in PROMIS PI was significantly correlated with greater comorbidities and more previous surgeries.

Two-year and change in PROMIS PI scores were also associated with multiple preoperative categorical variables (Table 4). Worse two-year PROMIS PI was associated with female gender, non-Hispanic/Latino ethnicity, high school education level, unemployment, lower income, a Workers’ Compensation claim, and a prior legal claim. Worse two-year PROMIS PI was also associated with clinical factors such as smoking, preoperative opioid use, history of depression or anxiety, history of back pain, higher ASA score, and a prior orthopaedic surgery on the operative side. No differences in two-year PROMIS PI were found between the various anesthetic techniques. Less improvement in PI from baseline to two-year follow up was associated with unemployment, prior orthopaedic surgery on the operative joint, and a higher ASA score.

Preoperative patient-reported outcome scores and their correlations with two-year and change in PROMIS PI are listed in Table 5. Better scores on all preoperative measures correlated with better two-year PROMIS PI. Greater improvement in PROMIS PI was significantly correlated with worse preoperative PROMIS PI and PROMIS SS, and better MODEMS and NPS whole body.

Multivariate linear regression demonstrated that independent predictors for worse two-year PROMIS PI included a Workers' Compensation claim, preoperative opioid use, greater NPS whole body score, and greater preoperative PROMIS PI (Table 6). This model accounted for 34% of the variance in two-year PROMIS PI scores. Less improvement in two-year PROMIS PI was predicted by a Workers’ Compensation claim, preoperative opioid use, greater NPS whole body score, and lower preoperative PROMIS PI. This model accounted for 22% of the variance in change in PROMIS PI scores (Table 7).

4 Discussion

Pain assessment is a crucial component of the patient recovery experience and PROMIS PI provides a more comprehensive assessment of pain in comparison to legacy patient reported outcome measures such as the NPS. The results of this study supported our hypothesis that worse pain interference two years after shoulder surgery is associated with older age, greater number of comorbidities, worse mental health, and lower socioeconomic status. Additionally, our findings demonstrated that preoperative Workers’ Compensation, opioid use, NPS whole body score, and PROMIS PI are independent predictors of worse two-year postoperative PROMIS PI and change in PROMIS PI scores. To our knowledge, this is the first study to investigate preoperative predictors of PROMIS PI two years after shoulder surgery.

Past literature has demonstrated that preoperative pain and psychosocial factors can be predictive of shoulder pain after surgery,^36–39 but the utilization of PROMIS PI in orthopaedic literature, particularly in shoulder surgery, is limited.⁴⁰ Chen et al. demonstrated that patients undergoing total shoulder arthroplasty with a preoperative PROMIS PI score greater than 66.9 were 90% likely to achieve a meaningful clinically important difference in PI.⁴¹ Our results support this finding, showing that worse preoperative pain interference was an independent predictor of improvement in PROMIS PI two years after shoulder surgery. However, our analysis also suggests that worse preoperative PROMIS PI is associated with worse absolute pain interference two years postoperatively. Although patients with worse preoperative PROMIS PI demonstrate the greatest potential for reduction in pain interference, these patients may also have greater pain interference two years postoperatively. Furthermore, a study by Forlenza et al. assessed PROMIS PI in patients undergoing isolated biceps tendonesis. They determined the absolute substantial clinical benefit and the patient acceptable asymptomatic state to be a pain interference score of 52.4.⁴² Interestingly, we report a mean two-year pain interference score of 52.5 for this procedure.

Regarding socio-demographic and clinical factors, Meldau et al. showed nonsignificant associations between preoperative PROMIS PI and age, BMI, and median household income.⁴³ Our results contradict these findings, suggesting that worse two-year PROMIS PI is associated with older age, higher BMI, and lower median household income. This could be partially explained by the larger sample size in our study and analysis of shoulder patients only, whereas Meldau et al. included both shoulder and elbow patients. These discrepancies could also be attributed to our study analyzing two-year PROMIS PI, while Meldau et al. examined only preoperative PROMIS PI.⁴³ Additionally, multiple studies have reported younger age to be predictive of worse postoperative pain,^44,45 but our analysis demonstrated a relationship between older age and worse two-year PROMIS PI. Previous studies typically focus on individual surgical procedures and measured postoperative pain with traditional pain indicators, such as the visual analog scale. In contrast, our study assessed a variety of procedures and utilized PROMIS PI. It is important to note that PROMIS PI assesses the degree that pain interferes with an individual's physical, mental, and social activities, which may reflect a different component of pain when compared to traditional pain scales.

Prior literature has suggested that patients with medical comorbidities are at an increased risk for increased pain and,⁴⁶ correspondingly, our study observed that more prior surgeries and more comorbidities were associated with worse two-year PROMIS PI. Furthermore, Frank et al. previously demonstrated that patients with prior ipsilateral surgeries experienced less pain control after undergoing total shoulder arthroplasty.⁴⁷ Our results support this relationship as they pertain to two-year postoperative PROMIS PI, but are generalized to any type of prior surgery. These findings could be due to the medical complexity of these patients, where a multitude of confounding medical factors and comorbid conditions impact pain control. Our findings also found preoperative NPS whole body score to be a predictor of worse PROMIS PI two years after shoulder surgery. Various comorbidities and psychosocial determinants of health, including chronic pain, have been identified to affect patient pain.^48,49 Thus, higher NPS whole body score at baseline could be an indicator of chronic pain in patients, which may serve as a surrogate for a patients comorbidity status.

Workers' Compensation and preoperative opioid use were also predictors of worse two-year postoperative pain interference. It has been established that preoperative opioid use is a predictor of worse pain after shoulder surgery,⁵⁰ however, most of these studies analyze a single procedure such as total shoulder arthroplasty.^38,49 Our results suggest that these findings also apply to a broad spectrum of shoulder surgeries. In regard to worse pain interference and Workers' Compensation, similar results have been observed after shoulder arthroplasty and rotator cuff repair.^51,52 The role of Workers’ Compensation in postoperative pain may be due to compensatory incentives associated with worse pain, but it is likely multifactorial in nature and warrants further investigation.

Although our study did not find PROMIS Anxiety or Depression to be predictors of two-year pain interference, mental health impairment is being recognized as a contributor to postoperative pain after shoulder surgery.³⁶ Worse preoperative PROMIS PI has been associated with worse preoperative PROMIS Depression in patients undergoing shoulder and elbow surgery.⁴³ Similarly, our study showed an association between worse preoperative PROMIS Depression and Anxiety to worse PROMIS PI two years after surgery.

Our study is not without limitations. First, due to the retrospective study design, we are unable to infer causality. Second, it is well known that survey utilization is prone to loss to follow-up, which can inadvertently bias results. Third, our study population was derived from a single urban medical center, which may limit the generalizability of our results. Despite these limitations, our study had a 75% two-year follow-up rate, included a diverse patient population, and presents the largest cohort of patients studying PROMIS PI after shoulder surgery.

5 Conclusion

As hypothesized, worse pain interference after shoulder surgery was associated with older age, greater comorbidities, mental health impairment, and lower socioeconomic status. Predictors of worse pain interference two years after shoulder surgery included preoperative Workers’ Compensation, opioid use, NPS whole body score, and PROMIS PI. These findings may help orthopaedic surgeons screen patients and provide appropriate preoperative counseling.

Credit author statement

Matthew Chrencik: Conceptualization, Writing-Original Draft, Writing-Review & Editing.Dominic Ventimiglia: Conceptualization, Writing-Original Draft, Writing-Review & Editing.Matheus B. Schneider: Writing- Original Draft, Writing- Review & Editing, Methodology, Data Curation; Formal Analysis.Tina Zhang: Writing- Original Draft, Writing- Review & Editing, Methodology, Data Curation; Formal Analysis.Kalin Fisher: Writing- Original Draft, Writing- Review & Editing.Alexander Hahn: Writing- Original Draft, Writing- Review & Editing.Mohit N. Gilotra: Writing- Original Draft, Writing- Review & Editing, Supervision.S. Ashfaq Hasan: Writing- Original Draft, Writing- Review & Editing, Supervision.R Frank Henn III: Original Draft, Writing- Review & Editing, Methodology, Data Curation, Formal Analysis, Project Administration, Supervision, Funding Acquisition, Validation.

Funding

This work was supported by a grant from The James Lawrence Kernan Hospital Endowment Fund, Incorporated.

Institutional review board (IRB)

University of Maryland, Baltimore IRB approval was obtained for this project. HP-00062261-5.

Disclaimers

None.