The current study provided nationwide data regarding the comparison of reoperation rate in patients undergoing lumbar spine fusion based on RA as a comorbidity. There have been multiple previous reports describing abnormal radiological findings in the lumbar spine of patients with RA compared to normal patients1,7. Since the introduction of biological agents in management of RA, the number of severe cervical lesions is expected to decrease with a main pathology of severe synovitis. However, the number of lumbar lesions with RA might increase because the main pathology is degeneration, not synovitis. Thus, life expectancy should increase, resulting in greater age-related degeneration8. The facets and vertebral end-plates are the most important areas affected in the lumbar spine6,7,9. Consequently, chronic facet arthritis and enthesopathy at the disco-vertebral junction are important findings in the lumbar spine and is present in up to 25% of patients with RA1,8. Common pathological findings in the lumbar spine that are encountered in patients with RA are degenerative spondylolisthesis, endplate erosions, disc space narrowing, facet erosion, facet cysts, and vertebral fractures secondary to osteoporosis2,10,11. There have also been reports of rheumatoid nodules causing spinal stenosis and radiculopathy.9,12
Important causes of revision surgery are implant malposition, inadequate decompression, epidural hematoma, iatrogenic neural injury, and infection. These are commonly encountered in the early post-operative period13,14. The causes for delayed reoperation are generally pseudoarthrosis, implant failure, adjacent segment disease (ASD), and uncommonly late-onset infection13,14. In a series assessing the problems of posterior lumbar interbody fusion in the lumbar spine of patients with RA, the authors reported a high rate of complications including collapse of adjacent vertebra, adjacent level instability, and infection2. Our study demonstrated increased overall risk of reoperation in RA patients undergoing lumbar fusion. This effect was more evident 12 months after index surgery. The Kaplan-Meier cumulative event analysis revealed that the reoperation rate was more evident at one year follow-up, and this difference gradually increased until 5 years after index surgery. The difference stabilized until the final follow-up two years later. ASD is one of the common causes of reoperation after lumbar spinal fusion, especially after 12 months from the index surgery. The rate of ASD in patients with RA has been infrequently described3,15. In a study by Crawford et al., the researchers reported similar clinical outcomes in patients with and without RA after lumbar spinal fusion6. However, that group studied a small sample of only 19 age-matched cases and controls. The group also reported that the rate of complications was significantly higher in the RA group (37%) than the controls (21%). Implant failure, osteopenia, and wound infections were frequent concerns in patients with RA undergoing spinal fusion. Most recent advancements in the treatment of RA have centered on the molecular understanding of the autoimmune mechanism and the subsequent development of biologic agents16,17. As a consequence, the number of patients reaching end stage joint destruction has decreased. There has been growing interest in the level of disease activity indicators such as the 28-joint Disease Activity Score (DAS28) including C-reactive protein (CRP) level (DAS28-CRP), matrix metalloproteinase 3 (MMP-3) level, and the presence of radiographic ASD. Seki et al. found elevated disease activity indicators (DAS28-CRP and MMP-3) to be associated with radiographic ASD, suggesting that control of disease activity is crucial in preventing ASD after index surgery5. Using multivariate logistic regression analysis, these researchers discovered that elevated DAS28-CRP showed the highest positive correlation with ASD incidence after surgery. Therefore, control of disease activity can lead to reduced ASD after surgery. The group recommended beginning biologic therapy before development of ASD, especially when the patient starts to show early structural changes in weight-bearing joints5,18. In their study, 21% of patients required revision surgery for ASD, and 50% patients showed radiographic changes consistent with ASD. This percentage was higher in patients undergoing fusion than in patients undergoing decompression alone. Overall, the rate of revisions in the patients undergoing fusion was 37% compared to 4% in patients undergoing decompression alone. Of all revision surgeries, 73% were indicated due to symptomatic ASD; ASD was the most frequent reason for revision surgery in their study. Kang et al. reported a significantly higher rate of complications after posterolateral lumbar fusion in RA patients (47.5%) compared to non-RA patients (17.1%). Patients with RA experienced significantly higher rates of ASD (p < 0.001). Similarly, in a study by Park et al., patients with RA were associated with 4.5 times higher risk of fusion-related ASD than patients without RA. Park et al. also concluded that long segment fusion (3 level) was associated with higher risk of ASD requiring surgery than was single or double level fusion.
Osteoporosis is an important cause of implant failures and vertebral fractures in RA patients undergoing lumbar fusion surgery and increases the likelihood of revision surgeries. Patients with RA have lower bone mineral density than controls19. This occurs for two reasons: a chronic inflammatory state and use of oral corticosteroids in management of the disease20. A few authors have suggested a positive correlation between oral corticosteroid use and risk of osteoporotic fractures, but others have found either no correlation or an inverse relationship19,21−23.In patients with osteoporosis, starting appropriate anti-resorptive or anabolic medications to prevent associated implant-related complications and vertebral fractures is of prime importance. Our study demonstrated a higher overall risk of reoperation in the RA group with osteoporosis, and this effect was more pronounced within 3 months of index surgery.
The major limitations of most previous studies on this topic are their small sample sizes and single-center experiences. There has been nationwide analysis of RA in cervical spine fusions but not lumbar spine fusions24. Our current study based on a nationwide database provided insight on this topic. There are some important limitations to our study. The most important is that the level of disease activity might not be uniform in all patients included in the study. It was also not possible to pinpoint to the exact causes of revision surgery in the patients undergoing reoperation. Another limitation being the surgical choice is generally dependent on each surgeon’s experience and it is difficult to control this factor in population-based study.
In conclusion, this population-based cohort study showed that patients with RA had a 1.31 times higher risk of reoperation than controls. Kaplan-Meier cumulative event analysis demonstrated that the higher risk of reoperation in the RA group occurred after 1 year post-surgically. This risk increased further until 5 years post-surgically and then was stable through the last follow-up at 7 years.