Orthopedics

Feature Article 

Shorter Time to Surgery Is Associated With Better Outcomes for Spondylolisthesis in the Workers' Compensation Population

Bryan O. Ren, BS; Christopher A. Rothfusz, BS; Mhamad Faour, MD; Joshua T. Anderson, MD; Jeffrey A. O'Donnell, MD; Arnold R. Haas, BS, BA; Rick Percy, PhD; Stephen T. Woods, MD; Uri M. Ahn, MD; Nicholas U. Ahn, MD

Abstract

This study sought to determine the impact of time to surgery on clinical outcomes in patients with spondylolisthesis in the workers' compensation (WC) population. There is conflicting evidence regarding the effect of time to surgery on patients with spondylolisthesis. Patients receiving WC are known to have worse outcomes following spine surgery compared with the general population. A total of 791 patients from the Ohio Bureau of Workers' Compensation were identified who underwent lumbar fusion for spondylolisthesis between 1993 and 2013. The patients were divided into those who had surgery within 2 years of injury date and after 2 years. Confounding factors were corrected for in a multivariate logistic regression to determine predictors of return to work (RTW) status. Multivariate logistic regression determined that longer time to surgery (P=.003; odds ratio, 0.89 per year), age at index fusion (P=.003; odds ratio, 0.98 per year), and use of physical therapy before fusion (P=.008; odds ratio, 0.54) were negative predictors of RTW status. Patients who had surgery within 2 years were more likely to RTW and have fewer days absent from work, lower medical costs, and fewer sessions of psychotherapy, physical therapy, and chiropractor care. The authors demonstrated that for WC patients with spondylolisthesis, longer time to surgery was a negative predictor of RTW status. Patients who had surgery within 2 years of injury date were significantly more likely to RTW compared with after 2 years. [Orthopedics. 2020;43(3):154–160.]

Abstract

This study sought to determine the impact of time to surgery on clinical outcomes in patients with spondylolisthesis in the workers' compensation (WC) population. There is conflicting evidence regarding the effect of time to surgery on patients with spondylolisthesis. Patients receiving WC are known to have worse outcomes following spine surgery compared with the general population. A total of 791 patients from the Ohio Bureau of Workers' Compensation were identified who underwent lumbar fusion for spondylolisthesis between 1993 and 2013. The patients were divided into those who had surgery within 2 years of injury date and after 2 years. Confounding factors were corrected for in a multivariate logistic regression to determine predictors of return to work (RTW) status. Multivariate logistic regression determined that longer time to surgery (P=.003; odds ratio, 0.89 per year), age at index fusion (P=.003; odds ratio, 0.98 per year), and use of physical therapy before fusion (P=.008; odds ratio, 0.54) were negative predictors of RTW status. Patients who had surgery within 2 years were more likely to RTW and have fewer days absent from work, lower medical costs, and fewer sessions of psychotherapy, physical therapy, and chiropractor care. The authors demonstrated that for WC patients with spondylolisthesis, longer time to surgery was a negative predictor of RTW status. Patients who had surgery within 2 years of injury date were significantly more likely to RTW compared with after 2 years. [Orthopedics. 2020;43(3):154–160.]

Surgical treatment for lumbar spondylolisthesis is considered when conservative measures of symptom management have failed. The standard surgical procedure is a lumbar decompression with fusion.1,2 When conducted, surgery has been shown to improve symptoms and function in patients with spondylolisthesis.3–6 Similarly, the notable Spine Patient Outcomes Research Trial demonstrated that patients undergoing standard decompressive laminectomy (with or without fusion) for spondylolisthesis scored better on the Short Form-36 for bodily pain and physical function and the Oswestry Disability Index up to 4 years after surgery compared with patients treated nonoperatively.7

There can be variability in the time to surgery among patients because they may fail conservative measures at different time points during their treatment. There is conflicting evidence on the timing of surgery for patients with spondylolisthesis. Villavicencio et al8 reported shorter duration of symptoms in patients with degenerative disk disease (DDD) and stenosis with spondylolisthesis receiving fusion resulted in improved radicular symptoms. However, duration of symptoms had no impact on back pain or Oswestry Disability Index and Short Form-36 physical component summary scores. In a study of lumbar fusion for chronic low back pain in the workers' compensation (WC) population, total number of days off work before surgery was a predictor of return to work (RTW) status, although time between date of injury and date of surgery was not.9 An analysis of the Spine Patient Outcomes Research Trial found no difference in surgical outcomes based on symptom duration for lumbar degenerative spondylolisthesis.10

Patients who are receiving WC are known to have worse outcomes following lumbar fusion than the general population.11–14 The ability to RTW is of critical importance in the WC population, particularly given the financial consequences to the state and the individual as well as the psychological impact that being out of work can have on the individual. A study determined that low back pain cases accounted for 16% of the claims but 33% of all costs in a WC population.15 Tao et al16 confirmed this relationship, showing spinal surgery, and especially fusion, to be associated with higher claim costs. Lumbar fusion in WC patients is linked with poor RTW rates.9,17 For this reason, understanding what affects RTW rates is valuable in terms of providing the appropriate medical care to this clinically distinct population and reducing costs.

Prior studies with WC patients either did not take into account time to surgery or did not isolate spondylolisthesis as the diagnosis being studied.9,11–17 Therefore, the purpose of this study was to examine the impact that time to surgery has on RTW rates for spondylolisthesis specifically in the WC population.

Materials and Methods

Using Current Procedural Terminology codes, the authors identified 6392 WC patients from the Ohio Bureau of Workers' Compensation who received a lumbar fusion between 1993 and 2013. Anterior, posterior, and 360° fusion types as well as single and multilevel fusions were included. The authors then identified patients diagnosed with spondylolisthesis using International Classification of Diseases, Ninth Revision, diagnosis codes. From this subset, they excluded patients who had a prior history of lumbar surgery before their fusion and those who did not have at least 3 years of follow-up after fusion. Smoking is known to negatively impact outcomes, so patients with a positive smoking history were excluded using International Classification of Diseases, Ninth Revision, codes and those using prescription smoking deterrents were also excluded. The final spondylolisthesis cohort consisted of 791 patients. This cohort was then divided into having surgery within 2 years of injury date (n=363) and after 2 years (n=428). Figure 1 illustrates the selection process.

Subject selection flow diagram. A combination of Current Procedural Terminology procedural and International Classification of Diseases, Ninth Revision, diagnosis codes were used to identify the patients in this study.

Figure 1:

Subject selection flow diagram. A combination of Current Procedural Terminology procedural and International Classification of Diseases, Ninth Revision, diagnosis codes were used to identify the patients in this study.

Several preoperative population characteristics were collected, including age at index fusion, sex, mean household income, legal representation, single vs multilevel fusion, lumbar comorbidities, psychiatric history, and use of psychotherapy, physical therapy (PT), and chiropractor care. Mean household income was estimated by matching each patient's zip code to the mean per capita income from 2010 US Census data. Lumbar comorbidities included DDD, disk herniation, spinal stenosis, radiculopathy, spondylolysis, and spondylosis. Psychiatric history included diagnoses of depression, anxiety, and post-traumatic stress disorder.

The primary outcome for this study was whether patients met the RTW criteria after their fusion. The criteria used to evaluate RTW status have been outlined in previous studies of spinal surgery outcomes in the WC population.18,19 These authors defined RTW criteria as returning to work within 2 years after surgery and remaining working for at least 6 months. The addition of the 6 months was to ensure that workers were able to make a meaningful, sustained RTW.

Postoperative secondary outcomes were also collected and included days absent from work, additional fusion and decompression procedures, new psychiatric diagnosis (including depression, anxiety, or post-traumatic stress disorder), and use of psychotherapy, PT, and chiropractor care. The authors also obtained information regarding medical costs and use of opioid analgesics. Medical costs were given as monthly sums, while other secondary outcomes were calculated within 3 years of index fusion. Opioid analgesic use was calculated using oral prescriptions and converted to milligrams of total morphine equivalent units and average daily morphine equivalents.

Statistical Analysis

Chi-square and t tests were performed to analyze preoperative and postoperative differences between the two groups. Significant preoperative differences between the groups were corrected for in a multivariate logistic regression to determine predictors of RTW status. The dependent variable was whether RTW criteria were met. The authors adjusted for the following categorical covariates: sex, legal representation, single vs multilevel fusion, DDD, spondylosis, depression, and use of psychotherapy, PT, and chiropractor care. They adjusted for the following continuous covariates: time to surgery, age at index fusion, and number of psychotherapy, PT, and chiropractor care sessions. Time to surgery was defined as the time from injury date to surgery date measured in years. P<.05 was considered statistically significant. All statistical analyses were performed with the Statistical Package for the Social Sciences software for Mac version 25.0 (IBM Corp, Armonk, New York).

Results

A total of 791 patients met the inclusion criteria for the spondylolisthesis cohort. Of these, 363 patients had surgery within 2 years and 428 had surgery after 2 years. Table 1 highlights the preoperative population characteristics. The patients who had surgery after 2 years were more likely to be older, be female, have legal representation, have multilevel fusion, have DDD, have spondylosis, have depression, and use more psychotherapy, PT, and chiropractor care compared with those who had surgery within 2 years. There was no significant difference between the groups regarding mean household income, disk herniation, spinal stenosis, radiculopathy, spondylolysis, anxiety, or post-traumatic stress disorder.

Preoperative Population Characteristics

Table 1:

Preoperative Population Characteristics

The multivariate logistic regression determined that time to surgery was a significant and independent negative predictor of RTW status (P=.003; odds ratio, 0.89 per year). Additional significant and independent negative predictors of RTW status were age at index fusion (P=.003; odds ratio, 0.98 per year) and PT use (P=.008; odds ratio, 0.54). These results are displayed in Table 2. The authors also adjusted for the following covariates in the logistic regression model: sex, legal representation, single vs multilevel fusion, DDD, spondylosis, depression, psychotherapy use, number of psychotherapy sessions, number of PT sessions, chiropractor care use, and number of chiropractor sessions. A chi-square goodness of fit test determined that there was no reason to reject the fitted logistic regression model at the 95% confidence level. No serious multicollinearity existed as there was no significant correlation between the predictor values and the correlation coefficient absolute values were greater than 0.5.

Predictors of Return to Work Status

Table 2:

Predictors of Return to Work Status

Table 3 outlines the postoperative outcomes from the study. Those who had surgery within 2 years were more likely to RTW compared with those having surgery after 2 years (36.1% vs 24.3%; P<.001). Surgery within 2 years was associated with fewer days absent from work (547.0 vs 732.5; P<.001), fewer psychotherapy sessions (22.2 vs 26.4; P=.011), fewer PT sessions (57.6 vs 76.7; P=.002), fewer chiropractor care sessions (27.5 vs 32.6; P=.020), and lower medical costs ($67,069 vs $75,791; P=.001). There was no difference between the two groups in terms of additional fusion rates (P=.880), additional decompression rates (P=.253), new depression diagnosis (P=.889), new anxiety diagnosis (P=.441), new post-traumatic stress disorder diagnosis (P=.907), psychotherapy use (P=.497), PT use (P=.233), chiropractor care use (P=.631), milligrams of total morphine equivalent units prescribed (P=.068), or average daily morphine equivalents (P=.561).

Postoperative Secondary Outcomes

Table 3:

Postoperative Secondary Outcomes

Discussion

There is conflicting evidence regarding the effect of time to surgery on patients with spondylolisthesis.8–10 Low back pain and spinal surgery are especially costly in the WC population.15,16 This population is also known to have poor outcomes following lumbar surgery.9,11–14,17 Therefore, the current authors aimed to examine the impact of time to surgery on RTW status for spondylolisthesis patients in the WC population. Return to work is an objective measure of clinical improvement that has been used in previous studies of WC patients.18,19

In the current cohort, time to surgery was divided into two groups: surgery within 2 years of injury date and after 2 years. Two years was used as a cutoff time point because evidence has shown that delaying surgery past 2 years negatively impacts RTW rates for WC patients undergoing multilevel cervical fusion.20 The groups differed in preoperative population characteristics (Table 1). Those who had surgery after 2 years were more likely to be older, be female, have legal representation, have multilevel fusion, have DDD, have spondylosis, have depression, and use more psychotherapy, PT, and chiropractor care compared with those who had surgery within 2 years.

After correcting for such differences between the groups, the logistic regression model determined that time to surgery was an independent negative predictor of RTW status (odds ratio, 0.89 per year). Age at index fusion and PT use before surgery were also negative predictors of RTW status. Postoperatively, those who had surgery within 2 years of injury date were significantly more likely to RTW. Surgery within 2 years also led to fewer days absent from work, lower medical costs, and fewer psychotherapy, PT, and chiropractor care sessions.

The current data suggest that prolonging time to surgery can yield poorer outcomes. Patients with spondylolisthesis will generally have associated neural compression at the level, which is the primary pain generator.21 It would therefore stand to reason that if the neural compression is relieved within an earlier time frame, there may be an improved chance of neurologic recovery after the decompression procedure is completed. This may be due to the decreased time that the nerve is subject to ischemia as well as exposed to various chemical mediators due to the breakdown of the blood–nerve barrier.22 This principle of prolonged neural compression resulting in inferior outcomes has been linked to other lumbar spine conditions as well. Longer duration of symptoms before surgery has been associated with worse leg and back pain, function, and quality of life in lumbar spinal stenosis.23 Furthermore, delaying time to surgery for patients undergoing either lumbar fusion or decompression led to higher medical costs and more time lost from work among Louisiana WC patients.24 Such results support the notion that in spondylolisthesis, and other conditions involving nerve compression, there may be better restoration of function if the compression is relieved at an earlier time.

Patients who have had surgery delayed for an extended period may have been administered opioid medications for a longer period. Prolonged preoperative opioid use has been associated with worse RTW outcomes for WC patients with lumbar disk herniations25 and lumbar stenosis.26 The current authors believe that the same relationship may apply for spondylolisthesis, given that all of these conditions involve nerve compression. Hypotheses for this phenomenon include opioid-induced hyperalgesia and withdrawal pain.25 Another factor that could explain the current results is that patients with long-standing symptoms prior to surgery may have been off work for a longer period, decreasing the likelihood that work retraining would be successful postoperatively. These patients also may have received PT for an extended period and become deconditioned, making it less likely to be able to RTW. This is supported by the current data, which determined that PT use was a negative predictor of RTW status.

Longer periods with chronic pain and disability have also been associated with psychosocial issues.24 Depression is a predictor of poor lumbar fusion outcomes for WC patients.18 The current data provide evidence of this claim, demonstrating use of more psychotherapy sessions for those having surgery after 2 years of injury date. It is important to consider these issues, in combination with possible medical explanations, for the outcomes of WC patients due to the complexity of this clinically distinct population. A biopsychosocial predictive model of low back disability was outlined in a WC population.27 In this study, cognition, such as perceptions of one's health and expectations for recovery, and emotional distress, such as fear of losing one's job, were determined to be meaningful predictors of RTW status. With an increasing time to surgery, likely related to an increasing time with low back pain and being out of work, there can be an increased cognitive and emotional burden. Thus, the biopsychosocial issues of these patients should also be considered in the treatment process.

Limitations

The limitations of this study were primarily due to its observational and retrospective design. Although the authors adjusted for several covariates on multivariate logistic regression, the two groups studied could have varied in unobserved ways. The authors were unable to analyze differences in disease severity or pain because they included patients via Current Procedural Terminology and International Classification of Diseases, Ninth Revision, codes. More specifically, they could not determine the grade of spondylolisthesis. Nevertheless, the authors believe that their inclusion of the entire Ohio WC population from 1993 to 2013 meeting their inclusion criteria helped reduce the impact of unaccounted confounding variables and variations in disease severity.

Isthmic and degenerative spondylolisthesis diagnoses were both included, but not differentiated, in the current spondylolisthesis cohort, so the authors cannot make distinctions in outcomes between the two. The use of an administrative database also comes with limitations in the completeness of data. However, a prior study supported the validity of database use by showing sensitivities and specificities of 95% or greater with Current Procedural Terminology and International Classification of Diseases, Ninth Revision, codes in a large Veterans Affairs database.28 The use of statewide WC databases has also been supported due to their size and sensitivitiy.29 Finally, the authors' use of the Ohio WC population may limit how well the results can be generalized to other populations given variability in state geography, treatment guidelines, and legislation. Despite these limitations, this study provides information regarding clinical outcomes for WC patients and a baseline for future prospective studies.

Conclusion

This study produced several findings related to the WC population diagnosed with spondylolisthesis. A multivariate logistic regression revealed that time to surgery, age, and PT use were negative predictors of RTW. Surgery within 2 years of injury diagnosis was associated with better RTW rates, fewer days absent from work, lower medical costs, and less use of psychotherapy, PT, and chiropractor care.

References

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  23. Sigmundsson FG, Kang XP, Jönsson B, Strömqvist B. Prognostic factors in lumbar spinal stenosis surgery. Acta Orthop. 2012;83(5):536–542. doi:10.3109/17453674.2012.733915 [CrossRef] PMID:23083437
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  25. O'Donnell JA, Anderson JT, Haas AR, et al. Preoperative opioid use is a predictor of poor return to work in workers' compensation patients after lumbar diskectomy. Spine. 2018;43(8):594–602. doi:10.1097/BRS.0000000000002385 [CrossRef] PMID:28837531
  26. Tye EY, Anderson JT, Faour M, et al. Prolonged preoperative opioid therapy in patients with degenerative lumbar stenosis in a workers' compensation setting. Spine. 2017;42(19):E1140–E1146. doi:10.1097/BRS.0000000000002112 [CrossRef] PMID:28187073
  27. Schultz IZ, Crook JM, Berkowitz J, et al. Biopsychosocial multivariate predictive model of occupational low back disability. Spine. 2002;27(23):2720–2725. doi:10.1097/00007632-200212010-00012 [CrossRef] PMID:12461399
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  29. Oleinick A, Zaidman B. Methodologic issues in the use of workers' compensation databases for the study of work injuries with days away from work: I. Sensitivity of case ascertainment. Am J Ind Med. 2004;45(3):260–274. doi:10.1002/ajim.10333 [CrossRef] PMID:14991853

Preoperative Population Characteristics

CharacteristicSurgery ≤2 ySurgery >2 yP
Patients, No.363428
Age at index fusion, mean±SD, y42.9±10.147.8±10.3<.001a
Sex, No.
  Male266 (73.3%)271 (63.3%).003a
  Female97 (26.7%)157 (36.7%).003a
Household income, mean±SD, $24,117±366424,428±4053.262
Legal representation, No.b223 (61.4%)306 (71.5%).003a
Levels fused, No.
  Single262 (72.2%)270 (63.1%).007a
  Multi101 (27.8%)158 (36.9%).007a
Lumbar comorbidities, No.b
  Degenerative disk disease46 (12.7%)126 (29.4%)<.001a
  Disk herniation112 (30.9%)148 (34.6%).266
  Spinal stenosis60 (16.5%)84 (19.6%).261
  Radiculopathy56 (15.4%)77 (18.0%).337
  Spondylolysis17 (4.7%)15 (3.5%).402
  Spondylosis33 (9.1%)63 (14.7%).016a
Depression diagnosis, No.b8 (2.2%)37 (8.6%)<.001a
Anxiety diagnosis, No.b1 (0.3%)7 (1.6%).057
Post-traumatic stress disorder diagnosis, No.b2 (0.6%)3 (0.7%).791
Psychotherapy use, No.b7 (1.9%)45 (10.5%)<.001a
Psychotherapy sessions, mean±SD, No.b5.86±3.738.7±67.2<.001a
Physical therapy use, No.b291 (80.2%)392 (91.6%)<.001a
Physical therapy sessions, mean±SD, No.b47.7±58.6111.1±137.6<.001a
Chiropractor care use, No.b83 (22.9%)177 (41.4%)<.001a
Chiropractor sessions, mean±SD, No.b43.5±35.869.4±75.3<.001a

Predictors of Return to Work Status

Independent VariableOdds Ratio95% Confidence IntervalP
Time to surgery (years)0.890.82–0.96.003a
Age at index fusion0.980.96–0.99.003a
Sex1.030.72–1.48.868
Legal representationb1.140.81–1.62.455
Levels fused0.880.62–1.26.488
Degenerative disk diseaseb0.810.53–1.24.340
Spondylosisb0.560.31–1.00.050
Depression diagnosisb0.250.05–1.14.074
Psychotherapy useb0.750.15–3.73.727
Number of psychotherapy sessionsb0.970.89–1.06.490
Physical therapy useb0.540.34–0.85.008a
Number of physical therapy sessionsb1.001.00-1.00.401
Chiropractor care useb1.010.68–1.71.741
Number of chiropractor sessionsb1.001.00-1.00.542

Postoperative Secondary Outcomes

CharacteristicSurgery ≤2 ySurgery >2 yP
Patients, No363428
Met return to work criteria, No.131 (36.1%)104 (24.3%)<.001a
Absent from work, mean±SD, db547.0±483.5732.5±460.4<.001a
Additional fusion, No.b42 (11.6%)51 (11.9%).880
Additional decompression, No.b28 (7.7%)43 (10.0%).253
New depression diagnosis, No.b53 (14.6%)64 (15.0%).889
New anxiety diagnosis, No.b5 (1.4%)9 (2.1%).441
New post-traumatic stress disorder diagnosis, No.b1 (0.3%)1 (0.2%).907
Psychotherapy use, No.b89 (24.5%)114 (26.6%).497
Psychotherapy sessions, mean±SD, No.b22.2±20.226.4±26.0.011a
Physical therapy use, No.b327 (90.1%)374 (87.4%).233
Physical therapy sessions, mean±SD, No.b57.6±55.876.7±109.8.002a
Chiropractor care use, No.b45 (12.4%)58 (13.6%).631
Chiropractor sessions, mean±SD, No.b27.5±28.632.6±32.8.020a
Medical costs at 36 mo after index fusion, mean±SD, $b67,069±36,49375,791±38,970.001a
Morphine equivalents at 3 y after fusion, mean±SD, mgb31,647±56,73645,270±141,094.068
Morphine equivalents per day, mean±SDb61.1±52.063.6±68.8.561
Authors

The authors are from the Department of Orthopaedics (BOR, CAR, MF, NUA), University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, Cleveland, the Ohio Bureau of Workers' Compensation (ARH, RP), Columbus, and Central Ohio Primary Care Sports, Spine & Joint (STW), Westerville, Ohio; the Department of Orthopaedics (JTA), University of Utah School of Medicine, Salt Lake City, Utah; the Department of Orthopaedic Surgery (JAO), Duke University School of Medicine, Durham, North Carolina; and the New Hampshire NeuroSpine Institute (UMA), Bedford, New Hampshire.

Mr Ren, Mr Rothfusz, Dr Faour, Dr Anderson, Dr O'Donnell, Mr Haas, Dr Percy, and Dr Woods have no relevant financial relationships to disclose. Dr U M Ahn has received payment for development of instrumentation and surgical tools from Osseus, Pinnacle, and Alphatec. Dr N U Ahn has received a grant from Osseus.

Correspondence should be addressed to: Bryan O. Ren, BS, Department of Orthopaedics, University Hospitals Cleveland Medical Center, Case Western Reserve University School of Medicine, 11100 Euclid Ave, Cleveland, OH 44106 ( bor5@case.edu).

Received: August 25, 2019
Accepted: December 23, 2019
Posted Online: March 20, 2020

10.3928/01477447-20200314-04

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