PD patients have been demonstrated to manifest more postoperative surgical complications due to various musculoskeletal problems. Studies have investigated high rates of perioperative and postoperative complications following hip and knee surgery in PD patients using a nationwide inpatient database [24, 25]. Furthermore, other surgical studies on the PD population have suggested higher rates of postoperative medical complications such as pneumonia, delirium, and sepsis [5]. However, there have been only a few case series which have examined the relationship between PD and complications following corrective surgery for ASD. Furthermore, few studies have compared PD patients with non-PD patients in terms of detailed radiographic parameters. Thus, we retrospectively analyzed both postoperative complications and radiographic parameters in this multicenter database of ASD patients, and compared PD patients with non-PD patients. The strengths of this study are 1) collecting detailed data of radiographic parameters and early/ late complications, 2) comparison of PD and non-PD in both crude analysis and propensity matching analysis, 3) at least 2-year follow-up, 4) number of samples with statistical power.
The results of this study demonstrated that the rate of delirium was significantly higher, and the rates of PE and DVT also tended to be higher in the PD(+) group. In accordance with our result, Watanabe et al. previously reported that postoperative delirium was more common in patients with PD (23.1%) than in the control group (3.4%) [26]. The patients who developed delirium were on at least one medication for PD, with a HY scale of more than 2 in our study. Thus, this higher rate of delirium is possibly due to the use of PD drugs as well as the neurodegenerative state in PD patients. Although delirium is thought to be a reversible condition, previous studies reported that postoperative delirium increased morbidity and mortality leading to prolonged hospitalization. Additional complications may also occur due to falls or movement beyond the limits of restriction. Thus, we need to pay extra attention to the modifiable risk factors including sedation management, deliriogenic medications, immobility, sleep disruption especially in patients with PD. For thrombotic events, the incidence was relatively high in PD patients, but we could not find statistically significant difference in this study. However, a previous study suggested the significantly increased risk for PE in PD patients using large national database[27]. PE is recognized as a possible adverse reaction to dopamine precursors, such as levodopa [28]. Yamane et al. reported a higher incidence (20%) of DVT in PD patients with a postural abnormality [29]. Since the corrective surgery for ASD itself has a higher risk of PE due to its long operation duration time and immobilization period after surgery, it is estimated that the risk of PE of this surgery in PD patients is high. Thus, surgeons should consider thrombotic events when patients develop chest pain and dyspnea after surgery especially in PD patients. Preoperative screening of D-dimer or ultrasound examination of DVT can be a viable option to prevent the complications.
In this study, we found significantly higher preoperative SVA and larger correction of SVA in the PD(+) group. We also found SVA at the final follow-up was higher in the PD (+) group. The loss of correction in SVA was slightly higher in PD patients, even though fusion of a greater number of vertebral segments was performed in the PD(+) group. This finding suggests that the deformities in the PD(+) group were severe but primarily flexible, and were largely corrected by the surgery. However, the improved SVA could not be well maintained in this group. The exact reasons of increased SVA after surgery in PD patients are unknown. However, the stooping posture related PD itself can deteriorate the overall sagittal balance, and this may be one of the causes for the poorer outcome in PD patients. Kawaguchi et al. reported that longer fusion, up to the T4 level, yielded a good clinical outcome in a PD patient after corrective surgery from L1 to S1 was unsuccessful [30]. Watanabe et al. reported that surgically treated ASD patients with PD demonstrated poor clinical outcomes, with a high non-union rate and adjacent segmental disease [31]. Thus, it is crucial to consider possible prevention strategies, including fusion of a greater number of segments.
This study demonstrated that the revision rate due to mechanical complications was 33.3%, which was almost double for the PD(+) group as compared with the PD(−) group. Similar to our study, Sheu et al. investigated 66 PD patients who underwent thoracolumbar or lumbar instrumented surgery due to degeneration or deformity; 29% of them required revision surgery due to mechanical complications [15]. Bouyer et al. reported a high revision rate of 42% in 48 ASD patients with PD, 89% of which were due to mechanical complications [18]. In terms of each complication, PJK has been reported to be significantly higher in PD patients[5]. In contrast, a history of PD had no significant impact on the PJK rate in this study. Alternatively, rates of radiological pseudarthrosis and rod failure were higher in the PD(+) group. Even after matching on fusion levels and preoperative SVA using propensity matched score analysis, the rate of radiological pseudarthrosis was higher in the PD (+) group. Pseudarthrosis can initiate pain and hardware issues, such as loosening of screws and rod fracture. Thus, for PD patients, the surgeon should consider prevention strategies, such as the administration of teriparatide.
Several studies have investigated the risk factors for revision surgery in PD patients. Schroeder et al. reported that an HY stage > 2, diabetes mellitus, treatment for osteoporosis, and a combined anterior and posterior surgical approach were risk factors for revision surgery in 94 lumbar spine surgeries [14]. According to Sheu et al., HY stage > 2, cancer history, osteoporosis, and a three-column osteotomy, were risk factors for revision surgery [15]. Evaluation of walking ability using the HY scale can be affected by symptoms of ASD, and thus the stage itself may not reflect the exact severity of PD in ASD patients. However, in our study, the HY stage tended to be higher in the revision subgroup. In addition, disease duration of PD was significantly longer in the revision subgroup. Thus, it is vital to consider disease duration of PD, as well as the severity of the PD, when performing surgical treatment in ASD patients.
There are several limitations to this study. First, there was a selection bias in which the surgeon could change the choice of surgical procedure based on the patient’s PD status. Second, as this is a multicenter study, we used simple criteria in order to identify mechanical complications using plain-film X-ray in this study. Thus, the diagnosis for mechanical complications by plain-film X-ray may underestimate the rate of nonunion. Third, the background of PD and non-PD patients were different. Thus, we conducted a matching analysis to compare the PD and non-PD patients. Fourth, our study was retrospective in nature, and the number of PD patients was relatively low. When considering the rate of radiological pseudarthrosis in the PD and non-PD groups in this study, the effect size (w) was 0.376. Then, a post hoc analysis revealed that the statistical power for the chi-square test was β = 0.99, when type I error rate (α) was set at 0.05 (G*power 3.1). Therefore, we consider that the sample size was of sufficient size regarding the main result of this study, and we actually found a significant difference in the rate of radiological pseudarthrosis. However, this does not necessarily mean that the sample size was large enough for all of the analyses. Studies with more appropriate designs and a larger sample size are needed.
Despite these limitations, this study demonstrated important findings: 1) Delirium was more frequent in the PD patients on the early postoperative days, 2) The rate of radiological pseudarthrosis and revision surgery was higher in the PD patients on the late postoperative days even after adjusting the background data.