Surgical treatment is often considered when patients with lumbar disk herniation and radiculopathy fail to improve with conservative treatment within 6 to 12 weeks. Lumbar decompression and diskectomy is recommended in such cases to relieve neural compression and to improve radicular symptoms and neurologic deficits.
The optimal timing of surgery in patients with lumbar disk herniation and radiculopathy is indeterminate. Several studies have determined that longer symptom duration has an adverse impact on surgical results for lumbar diskectomy.1–5 A point beyond which surgical outcomes become compromised has been estimated to be approximately 6 months.4 However, a prospective randomized clinical trial of 283 patients with severe radiculopathy showed that 1-year outcomes were comparable in patients receiving early lumbar disk surgery vs those assigned to conservative treatment and eventual lumbar disk surgery. It was determined that pain relief and recovery rates were faster for the group with early surgical intervention.6
Individuals receiving workers' compensation (WC) comprise a distinct patient population, with majority consensus that these patients have poorer clinical outcomes with surgical treatment.7 Spine disorders in particular impose an enormous stress on the WC system because of extensive costs and lengthy disability. A 2015 meta-analysis involving 31 studies of compensation status and outcomes in spine surgery found that WC patients have a 2-fold increased risk of unsatisfactory outcome compared with noncompensated patients following surgery.8 The Spine Patient Outcomes Research Trial found that receiving WC and having symptoms for more than 6 weeks were both independently associated with worse patient-reported outcomes following surgery for lumbar disk herniations.9
This study was performed to determine the effect that time to surgery has on outcomes in WC patients with single-level lumbar disk herniation. Specifically, the authors sought to determine whether there is an upper limit duration of conservative treatment for WC patients with single-level lumbar disk herniation and radiculopathy before proceeding with surgery. To the authors' knowledge, no other studies have explicitly studied surgical outcomes or the effect of time to surgery on surgical outcomes in WC patients with single-level lumbar disk herniation.
Materials and Methods
The authors identified 10,592 patients receiving lost-work compensation from the Ohio Bureau of Workers' Compensation who were diagnosed with lumbar disk herniation after sustaining a workplace injury between 2005 and 2012 using International Classification of Diseases, Ninth Revision (ICD-9) diagnosis codes. Patients with spondylolisthesis, spinal deformity, vertebral fractures, epidural hematomas, epidural abscesses, and spinal tumors were excluded from this study. Smoking is a known risk factor for worse outcomes, so patients with a positive smoking history were excluded, as identified with ICD-9 codes or the use of prescription smoking deterrents. Patients treated surgically for lumbar disk herniation were identified. Only patients receiving a single-level diskectomy and a minimum of 3 years of follow- up were included in this study. This left 1287 patients. Patients were placed into one of several groups depending on the duration between injury date and surgical intervention (Figure 1).
Subject selection flow diagram. The authors used a combination of International Classification of Diseases, Ninth Revision, diagnosis and Current Procedural Terminology procedural codes to identify all subjects under study.
The primary outcome measure was whether a patient made a successful return to work (RTW). Successful RTW was defined by criteria outlined in prior studies that evaluated spine surgical outcomes in the WC population.10,11 These prior authors defined successful RTW as a patient's ability to return within 2 years and work for at least 6 months within 3 years.
Secondary outcomes measured included permanent disability, perioperative mortality, postoperative infection, development of psychological illness, additional lumbar surgery, physical therapy use, chiropractic care use, and psychotherapy sessions. Psychological illness included depression, anxiety, adjustment disorder, posttraumatic stress disorder, bipolar disorder, and schizoaffective disorder. Use of physical therapy, chiropractic care, and psychotherapy was defined as attending at least 1 session. The numbers of sessions used for each service were also analyzed. All secondary outcomes were tabulated within 3 years of index diskectomy.
The authors computed the ranking of each outcome using the analysis of variance method. The subgroups for this study were divided into time periods representing duration between claim diagnosis and surgery. These subgroups were defined as 0 to 6 weeks, 6 to 12 weeks, 3 to 6 months, 6 to 12 months, 1 to 2 years, and greater than 2 years of duration. To determine the impact that preoperative characteristics had on the primary outcome of RTW, the authors used multivariate logistic regression analysis.
The dependent variable was whether RTW criteria were met. The authors adjusted for the following categorical variables: sex, heavy labor occupation, permanent disability, chiropractic care, legal representation, psychological comorbidity, and degenerative disk disease. They adjusted for the following continuous variables: age, mean household income, and duration of time to surgery. Variables not shown to predict RTW status after reoperation were removed from the regression model in a stepwise manner. Values were reported as odds ratios (ORs) with 95% CIs. A P value less than .05 was considered statistically significant. For all analyses, Statgraphics Centurion XVI, version 16.2.04, software (Stat-point Technologies, Inc) was used.
A total of 1287 patients met the inclusion criteria, with 976 (75.8%) men and 311 (24.2%) women. Mean patient age was 40.0 years (range, 18–80 years), and 755 (58.7%) patients were married. A total of 434 (33.2%) patients held labor-intensive occupations. Average household income was estimated to be $58,364. No cases of perioperative mortality were observed. Of all patients, 1028 (79.9%) had legal representation. Average latency time from injury to surgery was 364 days (range, 2–2710 days). Patients were separated into cohorts based on the time from injury to surgery.
There were 102 patients in the 0 to 6 week cohort; 168 in the 6 to 12 week cohort; 263 in the 3 to 6 month cohort; 354 in the 6 to 12 month cohort; 221 in the 1 to 2 year cohort; and 179 in the greater than 2 years from injury date cohort. Demographics of these groups are summarized in Table 1.
Preoperative Population Characteristics
Overall, 712 (55.3%) patients returned to work. Notably, duration of radiculopathy prior to surgery was a strong negative, independent predictor of postoperative RTW status in the regression model (OR, 0.97 per month; 95% CI, 0.91–1.00; P<.01). Additional negative predictors of RTW were legal representation and psychological comorbidity before diskectomy. Mean household income was the only covariate positively associated with RTW. Table 2 contains data on all variables significantly associated with RTW status from the regression model. A chi-square goodness of fit test determined that there was no reason to reject the fitted logistic regression model at the 95% CI level. No serious multicollinearity was observed in the regression model because no correlation coefficient absolute value was greater than 0.5. Permanent disability benefits and degenerative disk disease were not found to predict RTW status (with P>.5) and were thus removed from the regression model.
Predictors of Return to Work Status
All outcomes are reported in Table 3. Undergoing lumbar diskectomy within 6 months of a workplace injury was associated with a significantly higher rate of RTW compared with longer than 6 months (P<.01). Permanent disability after index surgery was significantly higher for patients waiting more than 2 years for surgery (P=.01). Permanent disability after index surgery was also higher for those having surgery within 6 weeks of their injury, although this difference was not significant.
Those who had a shorter duration to surgery were less likely to develop a psychological illness (P<.01). Patients were less likely to use psychotherapy sessions after diskectomy when surgery occurred prior to 6 months from injury (P<.01). Of the patients who had psychotherapy care, those who had surgery before 6 months went to fewer sessions (P=.02).
Patients were less likely to go to physical therapy if they had surgery within 12 months (P<.01) and to go to chiropractic care if they had surgery within 6 months (P<.01). Patients having surgery between 6 weeks and 6 months after their injury went to significantly fewer physical therapy sessions (P=.01).
A decrease in RTW rates was observed among the different time to surgery groups (Figure 2). When patients were operated on within 12 weeks, a successful RTW was achieved 70.0% (95% CI, 65.9%–74.1%) of the time. On the other hand, if a patient waited more than 2 years to have surgery for radiculopathy, rates decreased as low as 31.3% (95% CI, 26.3%–36.3%).
Return to work status. Duration of radiculopathy prior to diskectomy was negatively associated with return to work status (odds ratio, 0.97 per month; 95% CI, 0.91–1.00; P<.01).
Five (0.4%) postoperative infections were observed. This was not statistically different among the groups (P=.53). A total of 342 (26.6%) patients had additional lumbar surgery with no difference among the cohorts (P=.42).
Back injuries are the most commonly occurring and most expensive single injury type receiving WC, accounting for 10.5% of claims, with an average of $11,643 of total compensation and $18,715 of total indemnity per nonzero claim.12 This combination of high frequency and cost puts a tremendous stress on the compensation system.
The authors designed a retrospective study of 1287 WC patients who underwent surgery for single-level lumbar disk herniation to determine whether time to surgery from diagnosis would affect RTW outcomes. Patients were placed into 6 groups: less than 6 weeks, 6 to 12 weeks, 3 to 6 months, 6 to 12 months, 1 to 2 years, and greater than 2 years of duration of preoperative radiculopathy due to single-level disk herniation. Return to work is an important factor in evaluating clinical improvement in WC patients and was the primary outcome measure of this study.
Duration of radicular symptoms due to a single-level lumbar disk herniation was associated with several secondary outcome measures as well. Patients operated on prior to 6 months had a 7.7% rate of developing a psychiatric diagnosis after diskectomy, whereas those operated on after 6 months had more than double the risk, with a rate of 17.6%. Patients waiting 2 years before surgical treatment had the highest rates of newly awarded permanent disability benefits at 5.0%. Patients received more physical therapy and chiropractic care post-diskectomy the longer they had preoperative radiculopathy before surgery. These results suggest that patients either did not improve at all or took longer to improve postoperatively, necessitating relatively more conservative treatment.
Psychological comorbidities are higher in patients with chronic pain symptoms and in patients who are unemployed,13–15 and they have been shown to lead to poor clinical outcomes in spinal care.16,17 Mathew et al18 showed that patients score significantly higher on scales for depression, anxiety, and stress after chronic low back pain onset. In the current study, patients with a longer duration of symptoms had higher rates of preoperative psychological comorbidity, in line with what other authors have found. Psychological comorbidities were negatively associated with RTW status in the logistic regression model (OR, 0.32; 95% CI, 0.13–0.81; P=.01). Higher incidence of new-onset psychological illnesses in patients who have later diskectomy may be a contributing factor to the poor clinical results seen. By the same token, lower incidence of preoperative psychological comorbidity in early surgical groups could partially explain the better outcomes detected. Despite these preoperative differences, the logistic regression showed that time to surgery was still an independent predictor of RTW status after adjusting for confounders such as psychological illness.
The authors found that WC patients treated surgically for radiculopathy secondary to single-level lumbar disk herniation had markedly improved RTW rates when operated on within 6 months of their injury. Prolonged conservative treatment greater than 6 months was shown to have significantly worse outcomes, with those waiting more than 2 years before surgery doing the worst. Other studies involving non-WC subjects have come to similar conclusions as the current study.1–5 In the current cohort, better post-diskectomy outcomes in WC patients with radiculopathy caused by single-level disk herniation were achieved if surgery was performed within 6 months from time of injury.
Lumbosacral spinal stenosis has been shown to result in ischemia and demyelination of the spinal nerve root.19 Nerve compression leads to Wallerian degeneration of the nerve fibers and breakdown of the blood–nerve barrier, both ultimately leading to conduction disturbances and/or ectopic discharges, which are responsible for the symptoms of neurogenic claudication.20 Therefore, a longer duration of neural compression may devitalize the nerve and compromise its ability to heal and for the patient to have a successful result.
These findings are not meant to show that early diskectomy is appropriate for all WC patients with lumbar disk herniation. Many patients with lumbar disk herniation will improve without operative management. However, in the current cohort, significantly better RTW outcomes were noted in patients undergoing surgery within 6 months of symptom onset. In patients with chronic, unacceptable radicular symptoms from a single-level lumbar disk herniation with failure of conservative options, earlier surgery should be considered.
The limitations of this study are well recognized. First, it was limited by its observational and retrospective design. The authors adjusted for many potentially confounding covariates in their logistic regression model, but the subgroups may have varied in unobserved ways. The baseline characteristics of the cohorts were different. This was to be expected with varying durations of radiculopathy, and this heterogeneity was useful for explaining the results. The completeness of the data could have been limited by the use of administrative information. However, Oleinick et al21 found that statewide WC administrative databases have utility for studying work injuries because of their size and sensitivity. In addition, this is a captured group of patients, with low patient dropout from the compensation system.
A study found that Current Procedural Terminology and ICD-9 coding data from a Veterans Affairs database, when compared with medical records, were sensitive and specific, indicating that large ICD-9 and Current Procedural Terminology coding databases can provide accurate information.22 Next, the severity of radiculopathy was unable to be determined. The authors knew that subjects were diagnosed with this condition based on billing codes. This study included the entire population of subjects in the Ohio Bureau of Workers' Compensation fitting the study design and undergoing diskectomy between 2005 and 2012. This helped eliminate bias and increased the likelihood of having a distribution of disease severity present in other populations of such cases.
Although RTW rates provide an objective clinical outcome measure, RTW is not a functional outcome. These results cannot lead to conclusions about successes or failures from an operational standpoint because there are other factors that impact the ability of a patient to RTW, such as psychosocial issues. The stepwise regression was limited in that P values and estimates of variance are biased toward 0. Finally, the type of diskectomy performed was not known.
Patients receiving WC with shorter duration of radiculopathy before diskectomy had higher RTW rates; fewer physical therapy, chiropractic, and psychotherapy sessions; and fewer postoperative diagnoses of psychological illnesses. A multivariate logistic regression model showed that time to surgery was an independent, negative predictor of RTW (OR, 0.97 per month; 95% CI, 0.91–1.00; P<.01). The model also showed that legal representation (OR, 0.56; 95% CI, 0.43–0.72; P<.01), psychological comorbidity (OR, 0.32; 95% CI, 0.13–0.81; P=.01), and mean household income (OR, 1.01 per $1000; 95% CI, 1.00–1.02; P<.01) significantly affected RTW status.
Within 12 weeks of injury, post-diskectomy patients do reasonably well, with a 70.0% (95% CI, 65.9%–74.1%) rate of RTW. On the other hand, if a patient waited more than 2 years to have surgery for radiculopathy, RTW rates decreased as low as 31.3% (95% CI, 26.3%–36.3%). These results confirm that duration of radiculopathy due to single-level lumbar disk herniation has predictive value for the WC population undergoing diskectomy. Few WC patients with chronic radiculopathy greater than 2 years improved with diskectomy.
- Quon JA, Sobolev BG, Levy AR, et al. The effect of waiting time on pain intensity after elective surgical lumbar discectomy. Spine J. 2013;13(12):1736–1748. doi:10.1016/j.spinee.2013.05.038 [CrossRef] PMID:23850131
- Sabnis AB, Diwan AD. The timing of surgery in lumbar disc prolapse: a systematic review. Indian J Orthop. 2014;48(2):127–135. doi:10.4103/0019-5413.128740 [CrossRef] PMID:24741132
- Rahmathulla G, Kamian K. Lumbar disc herniations ‘to operate or not’ patient selection and timing of surgery. Korean J Spine. 2014;11(4):255–257. doi:10.14245/kjs.2014.11.4.255 [CrossRef] PMID:25620990
- Schoenfeld AJ, Bono CM. Does surgical timing influence functional recovery after lumbar discectomy? A systematic review. Clin Orthop Relat Res. 2015;473(6):1963–1970. doi:10.1007/s11999-014-3505-1 [CrossRef] PMID:24526298
- Alentado VJ, Lubelski D, Steinmetz MP, Benzel EC, Mroz TE. Optimal duration of conservative management prior to surgery for cervical and lumbar radiculopathy: a literature review. Global Spine J. 2014;4(4):279–286. doi:10.1055/s-0034-1387807 [CrossRef] PMID:25396110
- Peul WC, van Houwelingen HC, van den Hout WB, et al. Leiden-The Hague Spine Intervention Prognostic Study Group. Surgery versus prolonged conservative treatment for sciatica. N Engl J Med. 2007; 356(22):2245–2256. doi:10.1056/NEJMoa064039 [CrossRef] PMID:17538084
- Kilgour E, Kosny A, McKenzie D, Collie A. Interactions between injured workers and insurers in workers' compensation systems: a systematic review of qualitative research literature. J Occup Rehabil. 2015;25(1):160–181. doi:10.1007/s10926-014-9513-x [CrossRef] PMID:24832892
- Cheriyan T, Harris B, Cheriyan J, et al. Association between compensation status and outcomes in spine surgery: a meta-analysis of 31 studies. Spine J. 2015;15(12):2564–2573. doi:10.1016/j.spinee.2015.09.033 [CrossRef] PMID:26431997
- Koerner JD, Glaser J, Radcliff K. Which variables are associated with patient-reported outcomes after discectomy? Review of SPORT disc herniation studies. Clin Orthop Relat Res. 2015;473(6):2000–2006. doi:10.1007/s11999-014-3671-1 [CrossRef] PMID:24818737
- Anderson JT, Haas AR, Percy R, Woods ST, Ahn UM, Ahn NU. Return to work after disk-ogenic fusion in workers' compensation subjects. Orthopedics. 2015;38(12):e1065–e1072. doi:10.3928/01477447-20151120-02 [CrossRef] PMID:26652326
- Faour M, Anderson JT, Haas AR, Woods ST, Ahn UM, Ahn NU. Return-to-work rates after single level cervical fusion surgery for degenerative disc disease (DDD) compared to fusion for radiculopathy in workers' compensation (WC) setting. Spine J. 2015;15(10)(suppl):S106. doi:10.1016/j.spinee.2015.07.063 [CrossRef]
- Mroz TM, Carlini AR, Archer KR, et al. Frequency and cost of claims by injury type from a state workers' compensation fund from 1998 through 2008. Arch Phys Med Rehabil. 2014;95(6):1048–1054.e6. doi:10.1016/j.apmr.2013.11.025 [CrossRef] PMID:24480333
- Subramaniam M, Vaingankar JA, Abdin E, Chong SA. Psychiatric morbidity in pain conditions: results from the Singapore Mental Health Study. Pain Res Manag. 2013;18(4):185–190. doi:10.1155/2013/798205 [CrossRef] PMID:23936892
- Zieger M, Luppa M, Meisel HJ, et al. The impact of psychiatric comorbidity on the return to work in patients undergoing herniated disc surgery. J Occup Rehabil. 2011;21(1):54–65. doi:10.1007/s10926-010-9257-1 [CrossRef] PMID:20689982
- Menendez ME, Neuhaus V, Bot AG, Ring D, Cha TD. Psychiatric disorders and major spine surgery: epidemiology and perioperative outcomes. Spine. 2014;39(2):E111–E122. doi:10.1097/BRS.0000000000000064 [CrossRef] PMID:24108288
- Anderson JT, Haas AR, Percy R, Woods ST, Ahn UM, Ahn NU. Clinical depression is a strong predictor of poor lumbar fusion outcomes among workers' compensation subjects. Spine. 2015;40(10):748–756. doi:10.1097/BRS.0000000000000863 [CrossRef] PMID:25955092
- Sinikallio S, Aalto T, Airaksinen O, et al. Depression is associated with poorer outcome of lumbar spinal stenosis surgery. Eur Spine J.2007;16(7):905–912. doi:10.1007/s00586-007-0349-3 [CrossRef] PMID:17394027
- Mathew J, Singh SB, Garis S, Diwan AD. Backing up the stories: the psychological and social costs of chronic low-back pain. Int J Spine Surg. 2013;7(1):e29–e38. doi:10.1016/j.ijsp.2013.02.001 [CrossRef] PMID:25694901
- Watanabe R, Parke WW. Vascular and neural pathology of lumbosacral spinal stenosis. J Neurosurg. 1986;64(1):64–70. doi:10.3171/jns.1986.64.1.0064 [CrossRef] PMID:3941352
- Kobayashi S. Pathophysiology, diagnosis and treatment of intermittent claudication in patients with lumbar canal stenosis. World J Orthop. 2014;5(2):134–145. doi:10.5312/wjo.v5.i2.134 [CrossRef] PMID:24829876
- 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
- Singh JA, Ayub S. Accuracy of VA databases for diagnoses of knee replacement and hip replacement. Osteoarthritis Cartilage.2010;18(12):1639–1642. doi:10.1016/j.joca.2010.10.003 [CrossRef] PMID:20950694
Preoperative Population Characteristics
|Characteristic||Time from injury to surgery|
|0–6 weeks||6–12 weeks||3–6 months||6–12 months||1–2 years||>2 years|
|Age, mean±SD, y||43.1±9.5||41.4±10.4||40.0±9.9||39.6±9.9||39.7±9.7||38.2±9.9|
|Household income, mean±SD||$62,518±$16,287||$59,950±$15,283||$59,413±$15,786||$61,879±$16,428||$58,323±$16,494||$58,563±$14,786|
|Degenerative disk disease (95% CI)a||0.0%||0.6% (0.0%–2.8%)||0.8% (0.0%–2.5%)||5.4% (3.9%–6.9%)||4.5% (2.7%–6.4%)||14.0% (11.9%–16.1%)|
|Psychiatric diagnosis (95% CI)a||0.0%||0.0%||0.0%||0.9% (0.0%–2.0%)||4.1% (2.6%–5.6%)||14.0% (12.3%–15.6%)|
|Psychotherapy use (95% CI)a||0.0%||0.0%||0.0%||0.9% (0.0%–2.1%)||4.5% (2.9%–6.1%)||16.8% (15.0%–18.5%)|
|Psychotherapy sessions, mean (range), No.a||5.4 (0.0–17.7)||8.0 (1.5–14.5)||12.5 (8.0–17.0)||23.4 (20.3–26.5)||32.4 (29.1–35.8)||53.5 (50.1–57.0)|
|Physical therapy (95% CI)a||10.8% (4.6%–17.0%)||23.2% (18.4%–28.1%)||31.7% (27.8%–35.6%)||48.3% (45.0%–51.6%)||67.4% (63.2%–71.7%)||79.3% (74.6%–84.0%)|
|Physical therapy sessions, mean (range), No.a||5.4 (0.0–17.6)||8.0 (1.5–14.5)||12.5 (8.0–17.0)||24.0 (20.3–26.5)||32.4 (29.1–35.8)||53.5 (50.1–57.0)|
|Chiropractic care (95% CI)a||12.8% (6.8%–18.7%)||16.1% (11.4%–20.7%)||19.1% (15.4%–22.8%)||28.3% (25.0%–31.5%)||38.5% (34.4%–42.5%)||48.6% (44.1%–53.1%)|
|Chiropractic care sessions, mean (range), No.a||4.9 (0.0–16.6)||13.9 (5.7–22.0)||16.6 (10.7–22.6)||31.1 (26.9–35.3)||43.7 (39.1–49.3)||59.4 (54.9–63.9)|
Predictors of Return to Work Status
|Independent variable||Odds ratio||95% CI||Pa|
|Time to surgeryb,c||0.97||0.91–1.00||<.01|
|Mean household incomed||1.01||1.00–1.02||<.01|
|Characteristic||Time from injury to surgery|
|<6 weeks||6–12 weeks||3–6 months||6–12 months||1–2 years||>2 years||P|
|Return to work (95% CI)||71.6% (65.0%–78.2%)||69.0% (63.9%–74.2%)||65.6% (61.5%–69.8%)||56.5% (53.0%–60.0%)||43.0% (38.5%–47.5%)||31.3% (26.3%–36.3%)||<.01a|
|New permanent disability (95% CI)b||3.9% (2.0%–5.8%)||1.8% (0.3%–3.3%)||1.9% (0.7%–3.1%)||1.4% (0.4%–2.4%)||0.0%||5.0% (3.6%–6.5%)||.01a|
|New psychiatric diagnosis (95% CI)b||5.9% (1.2%–10.5%)||8.9% (5.3%–12.6%)||7.6% (4.7%–10.5%)||17.5% (15.0%–20.0%)||19.5% (16.3%–22.6%)||15.6% (12.1%–19.2%)||<.01a|
|Psychotherapy use (95% CI)b||11.8% (6.4%–17.2%)||11.9% (7.7%–16.1%)||11.1% (7.7%–14.4%)||22.3% (19.4%–25.2%)||28.5% (24.8%–32.2%)||31.8% (27.8%–35.9%)||<.01a|
|Psychotherapy sessions, mean (range), No.b||10.0 (0.0–20.1)||13.8 (5.9–21.6)||16.3 (9.9–22.8)||23.6 (19.7–27.6)||24.9 (20.5–29.3)||30.4 (25.8–35.0)||.02a|
|Physical therapy (95% CI)b||52.0% (45.2%–58.7%)||46.4% (41.2%–51.7%)||50.0% (45.8%–54.2%)||54.0% (50.3%–57.6%)||69.7% (65.1%–74.3%)||65.4% (60.3%–70.4%)||<.01a|
|Physical therapy sessions, mean (range), No.b||31.8 (25.1–38.5)||27.0 (21.4–32.5)||29.7 (25.5–34.0)||39.9 (36.3–43.4)||39.1 (35.2–43.0)||39.2 (34.7–43.7)||.01a|
|Postoperative infection (95% CI)b||1.0% (0.1%–1.8%)||0.6% (0.0%–1.3%)||0.8% (0.2%–1.3%)||0.0%||0.5% (0.0%–1.0%)||0.0%||.53|
|Additional lumbar surgery (95% CI)b||23.5% (17.5%–29.6%)||24.4% (19.7%–29.1%)||23.3% (19.5%–27.1%)||29.4% (26.1%–32.6%)||26.2% (22.1%–30.4%)||30.2% (25.6%–34.8%)||.42|
|Chiropractic care (95% CI)b||10.8% (5.5%–16.0%)||12.5% (8.4%–16.6%)||13.0% (9.7%–16.3%)||20.6% (17.8%–23.4%)||23.5% (20.0%–27.1%)||23.5% (19.5%–27.4%)||<.01a|
|Chiropractic sessions, mean (range), No.b||36.7 (23.7–49.8)||25.2 (15.7–34.7)||27.8 (20.3–35.2)||38.1 (33.0–43.1)||24.7 (18.7–30.7)||30.9 (24.2–37.6)||.20|