Fibromyalgia increases 90-day complications and cost following primary total hip arthroplasty

Introduction

Total hip arthroplasty (THA) has been shown to be a cost effective and safe procedure with minimal outcomes (1). Recent studies have shown that there has been an increase in the number of THA procedures performed in the United States and is expected to grow exponentially (1). Kurtz et al. predict the number of primary THA procedures being performed will increase 174% to 572,000 annually (2). With the increasing number of THAs being performed, Orthopedic Surgeons continue to stay cognizant on patient reported outcome measurements (PROMs) as a method to track patient recovery and improvement (3). Identifying risk factors associated with adverse events and worse clinical outcomes prior to surgery, may mitigate postoperative complications and improve PROMs (3).

Currently, 2.1% of females and 1.8% of males are affected with fibromyalgia (FM), with the incidence of the disease continuing to increase (4). FM is characterized by chronic pain, fatigue, sleep disruption, and joint stiffness. Low et al. have identified painful experiences during infant development, physical and psychological trauma during childhood, maternal deprivation, and premature birth as being potential risk factors for developing FM; in addition to rheumatoid arthritis, female gender, family history and obesity (5-7). With the increasing prevalence of FM and number of primary THA procedures being performed, the impact of FM on postoperative outcomes and economic burden on THA has not been well established (2,7).

The purpose of this study was to determine whether patients undergoing primary THA with FM had poor postoperative outcomes compared to patients without FM, with the use of an administrative database. The researchers of this study hypothesize that patients with FM undergoing THA will have greater postoperative and implant related complications, 90-day readmissions, day of surgery costs and total global 90-day episode of care cost following the index procedure.

Methods

A retrospective, Level III, analysis was performed from 2005–2014 using the Medicare Standard Analytical Files from the PearlDiver supercomputer (PearlDiver Technologies, Fort Wayne, IN). PearlDiver is a commercially available database used extensively for orthopedic-related research and is compliant with the Health Information Portability and Affordability Act (HIPAA) (8). The database contains records of over 100 million patients providing information such as diagnosis, complications, procedures, length of stay (LOS), cost, and reimbursements; in addition to other information. Since PearlDiver contains de-identified information the study was exempt from International Review Board (IRB) approval. Patients in the study were queried using the International Classification of Disease, ninth revision (ICD-9) codes.

The inclusion criteria of the study included all patients in the database who underwent primary THA and were queried using ICD-9 procedure code 81.51. All patients with a diagnosis of FM were queried using ICD-9 diagnosis code 729.1. Using Boolean command operations, the study group consisted of all patients in the database with a diagnosis of FM 90 days prior to their index procedure and a diagnosis on the day of their procedure. Patients undergoing primary THA without FM served as the control group. Study group patients were matched to controls according to age, gender, and Charlson-Comorbidity Index (CCI). CCI is a measurement of morbidity and mortality and predicts worse outcomes with a higher score, and was used as a marker to ensure that the two groups were matched appropriately and no statistical significance existed (9). After the matching process, two mutually exclusive cohorts were formed. Medial and implant related complications were analyzed and compared through ICD-9 coding, using previously described techniques (9) (Table S1).

Additionally, 90-day readmission rates and cost were also analyzed and compared. 90-day was chosen as the time period for medical complications, readmission rates, and reimbursements as that is the time frame in accordance with the bundled payment care initiative (BPCI) set forth by the Center of Medicare and Medicaid Services (CMS) for joint arthroplasty (9). Reimbursements were used as a marker for cost, since it provides accurate information as to what providers were paid through insurance companies (9).

Statistical analysis was performed using the programming language R (University of Auckland, New Zealand) to calculator odds-ratios (OR) along with their respective 95% confidence interval (95% CI) and P value. A P value of <0.05 was considered statistically significant.

Results

After the matching process, a total of 152,206 patients (female =113,152; male =37,238; unknown =1,816) with (n=76,103) and without (n=76,103) FM underwent primary THA between 2005–2014 (Table 1). Comparison of CCI scores of both cohorts was 5.68±2.31, with a P value of 1.00 indicating the study and control group were matched (Table 1). The calculated annual growth rate (CAGR) of patients with FM undergoing primary THA in the Medicare population was 31.54% (Figure 1).

Table 1 Demographics of patients with and without fibromyalgia undergoing primary total hip arthroplasty within the Medicare population
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Figure 1 Annual trends of patients with fibromyalgia undergoing primary total hip arthroplasty within the Medicare population from 2005–2014.

90-day medical complications

Patients with FM undergoing primary THA were at greater odds and incidence of developing 90-day medical complications (2.88% vs. 1.43%; OR: 2.05, 95% CI: 1.91–2.21, P<0.001) such as shortness of breath (OR: 3.38, 95% CI: 2.64–4.32, P<0.001), cerebrovascular accidents (OR: 3.27, 95% CI: 1.66–6.43, P<0.001), pneumonia (OR: 2.67, 95% CI: 1.86–3.85, P<0.001), non-healing surgical wound (OR: 2.27, 95% CI: 1.11–4.62, P<0.001), urinary tract infections (OR: 2.10, 95% CI: 1.82–2.43, P<0.001), acute post-hemorrhagic anemia (OR: 1.95, 95% CI: 1.70–2.25, P<0.001), thrombocytopenia (OR: 1.84, 95% CI: 1.05–3.22, P=0.032), requiring transfusions (OR: 1.69, 95% CI: 1.36–2.10, P<0.001), and acute kidney failure (OR: 1.58, 95% CI: 1.14–2.20, P=0.005) compared to patients without FM undergoing primary THA.

FM patients were found to be at greater odds of delirium (OR: 1.90, 95% CI: 0.92–3.96, P=0.082), acute pancreatitis (OR: 1.76, 95% CI: 0.89–3.49, P=0.100), deep vein thrombosis (OR: 1.22, 95% CI: 0.91–1.63, P=0.183), postoperative wound infections (OR: 1.12, 95% CI: 0.78–1.58, P=0.531), paralytic ileus (OR: 1.11, 95% CI: 0.78–2.15, P=0.739), and pulmonary embolism (OR: 1.04, 95% CI: 0.59–1.82, P=0.886) compared to controls however no statistical difference was found (Table 2).

Table 2 90-day medical complications amongst patients with and without fibromyalgia undergoing primary total hip arthroplasty within the Medicare population
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Two-year implant related complications

FM patients were found to have greater odds and incidence of 2-year short-term implant related complications (5.94% vs. 3.74%; OR: 1.60, 95% CI: 1.52–1.68, P<0.001) such as articular bearing surface wear of prosthetic joint (OR: 3.20, 95% CI: 1.93–5.29, P<0.001), broken prosthetic joint implant (OR: 2.00, 95% CI: 1.56–2.56, P<0.001), THA revisions (OR: 1.85, 95% CI: 1.45–2.36, P<0.001), mechanical loosening of prosthetic joint (OR: 1.71, 95% CI: 1.50–1.94, P<0.001), dislocation of prosthetic joint (OR: 1.63, 95% CI: 1.51–1.75, P<0.001), periprosthetic fracture around prosthetic joint (OR: 1.44, 95% CI: 1.26–1.64, P<0.001), and prosthetic joint infection (PJI) (OR: 1.38, 95% CI: 1.26–1.52, P<0.001) compared to match controls (Table 3).

Table 3 Two-year implant related complications amongst patients with and without fibromyalgia undergoing primary total hip arthroplasty within the Medicare population
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90-day readmission rate and episode-of-care

Patients with FM undergoing THA were found to have a greater incidence and risk of (12.5% vs. 11.6%; OR: 1.71, 95% CI: 1.50–1.94, P<0.001) of 90-day readmission rates compared to patients without FM. Total global 90-day episode of care mean reimbursements were higher in FM patients undergoing THA ($71,081.10 vs. $70,969.65, P<0.001) compared to matched controls.

Discussion

As the prevalence of FM continues to increase; the number of primary THA procedures is also increasing (2,7). The study illustrates FM to be a risk factor for postoperative complications following primary THA. Patients with FM were found to have greater odds of developing medical complications, implant related complications, readmission rates, which overall was associated with increased episode of care costs following primary THA. Predominantly known to effect the musculoskeletal system, the study illustrates FM being associated with pulmonary, neurovascular, and immune-related complications.

In a retrospective study performed by Çetin et al., 57.1% of patients with FM (n=35) complained of having dyspnea (10). According to the World Health Organization’s dyspnea classification, nine patients were classified as grade 1, six had grade 2, four patients had grade 3, and one had grade 4 dyspnea; whereas none of the matched cohorts suffered from dyspnea (10). Forti et al., found that patients with FM had reduced respiratory muscle endurance, inspiratory muscle strength, and thoracic mobility compared to healthy patients (11). Reduction in these parameters have been shown to lead to shortness of breath, atelectasis, pneumonia, and other respiratory complications; whereas respiratory muscle training has shown to reduce the relative risk of respiratory related complications (12,13). These pulmonary changes would help to explain why patients with FM were at greater odds of developing respiratory complications such as dyspnea and pneumonia. Additionally, the findings in the study are consistent with the literature on FM increasing the odds of developing cerebrovascular accidents (CVA) (14,15). In a population based study by Tseng et al., multivariate analysis illustrated that patients with FM were found to be at greater risk of developing an ischemic stroke compared to patients without FM (14). The pathophysiology behind this mechanism is endothelial dysfunction caused by chronic pain. Arterial flow mediated dilatation and vascular response to sublingual nitroglycerine were found to be diminished in patients with FM (15). These vascular imbalances could help explain the increased risk of CVA in patients with FM.

Furthermore, patients with FM incurred greater total episode of care costs compared to controls. While FM is not considered to be an independent risk factor for increasing cost following THA, the complications from FM are associated with increased costs. Phillips et al. found that the cost for treating periprosthetic fractures increased in patients with an in-hospital LOS more than 30 days, operating time, type of implants used and in those patients with concomitant deep infections (16). Similarly, pneumonia and CVA which were complications seen in this study, have been shown to increase the cost of care by an average of $7,154 and $3,890–$28,451, respectively (17,18). The economic burden of this condition is the reason why providers continually seek to optimize patients prior to surgery. Presurgical optimization may not only minimize postoperative complications, but may potentially decrease cost of care in patients (9).

The study is not present without limitations. The use of a database analysis study, the validity of the study and results are reliant on accurate procedural and diagnostic coding within the database (19). This translates to the fact that miscoding and noncoding by providers is a potential source of error. It is estimated that 1.3% of coding errors are currently present in the Medicare population (20). Additionally, this study only analyzed a single insurer’s data and may not be a true cross-sectional depiction of FM in the United States (20). Lastly, patients with FM are prone to having other comorbid conditions and adverse events which may be underreported (19).

Conclusions

The study illustrates that patients with FM undergoing primary THA are at a greater risk for medical complications and early implant failure along with greater odds of 90-day readmission rates, and incurring a higher episode of care costs. The results of this study may improve a providers’ ability to counsel patients regarding specific adverse events associated with FM and THA. The study necessitates further research on comparing preoperative optimization methods which can help to minimize postoperative complications.

Table S1 International Classification of Disease (ICD-9) ninth revision codes
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Acknowledgments

Funding: None.

Footnote

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/aoj.2018.08.04).The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Since PearlDiver contains de-identified information the study was exempt from International Review Board (IRB) approval.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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