1 Introduction

Understanding the expected timing of postoperative complications facilitates early diagnosis of potential adverse events and is important for optimizing postoperative care. Information on timing is also important for informed negotiating of payments in the era of bundled care.¹,2

Two recent investigations evaluated the timing of complications after spine surgery.²,3 De la Garza Ramos et al. studied ten complications after spinal deformity surgery, including myocardial infarction (MI), pulmonary embolism (PE), reintubation, pneumonia, urinary tract infection (UTI), sepsis, deep vein thrombosis (DVT), and deep, superficial, and organ space surgical site infection (SSI).³ Similarly, Bohl et al. examined the timing of eight complications following anterior cervical decompression and fusion (ACDF) and posterior lumbar fusion (PLF); a division was identified between “early” complications, such as transfusion, MI, and PE, and “late” complications (after postoperative day 7), such as UTI, DVT, and SSI². Importantly, the timing of complications differed between all three groups of patients (spinal deformity, ACDF and PLF). For example, UTI was diagnosed earlier in PLF patients than ACDF or deformity patients, and SSI was diagnosed earlier in ACDF patients.²,3

Though multiple studies have investigated the incidence and type of complications after posterior cervical fusion (PCF),^4–8 no study has described the timing of complications after posterior cervical spine surgery. In the current study the timing of ten complications after PCF was characterized in order to define the periods of highest risk for each complication in this patient population.

2 Methods

3 Results

A total of 2517 patients who underwent PCF met inclusion criteria. Mean age was 59.3 ± 12.5, and 54.6% of the patients were female. Mean BMI was 29.3 ± 6.5. The most common preoperative comorbidity was smoking status; 710 (28.2%) patients were current smokers. More than one level was fused in 65.0% of patients. Patient demographic and clinical characteristics are shown in Table 1.

The most common complications occurring within 30 days of surgery were anemia requiring blood transfusion (5.3% of patients), SSI (2.8%), and UTI (1.7%) (Table 2). The median day of diagnosis and interquartile range for each complication was: blood transfusion (0.0, 0-0), MI (3, 2–7), reintubation (3, 1–9), pneumonia (4, 3–10), DVT (7, 5–16), UTI (11.5, 5–17.5), sepsis (14, 7–20), PE (14, 8–21), SSI (15, 9–21), and wound dehiscence (15.5, 9–25) (Fig. 1). Table 2 provides the complication frequency and timing in all patients within 30 days of PCF.

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Fig. 1 Complication Timing within 30 days of PCF. The light blue boxes represent the second quartile, the dark blue boxes represent the third quartile, and the line separating them represents the median number of days to diagnosis of the complication. The error bars represent the range.

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Early complications including MI, reintubation, and pneumonia were diagnosed before discharge in over 80% of occurrences; later complications such as wound dehiscence and SSI were diagnosed before discharge in less than 10% of cases. Fig. 2 shows the percentage of complications diagnosed before discharge.

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Fig. 2 Complications Diagnosed before Discharge.

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A total 313 (12.4%) of patients had complications within 30 days of surgery; 238 (9.5%) had one complication, and 75 (3.0%) had more than one complication. Correlation analysis of the 10 studied complications revealed several significant associations. The strongest associations were between DVT and PE (r = 0.39), reintubation and pneumonia (r = 0.32), and reintubation and MI (r = 0.28) (Table 3). The covariance matrix for complications is shown in Table 3.

Univariate analysis results are shown in Table 4. Increasing age, decreased functional status, and fusion of more than one level were associated with increased complications (p < .002). Among comorbidities, current smoker status, diabetes, and CHF were also associated with a higher frequency of complications (p < .04). A sub-analysis comparing the frequency of specific complications between patients who had one level fused and patients who had more than one level fused revealed a significantly higher rate of blood transfusion (p = .007) in patients who had more than one level fused. There were no differences in the frequencies of any other complication.

4 Discussion

Utilizing the ACS NSQIP dataset, this study characterized the timing of ten complications after posterior cervical fusion. Early complications included blood transfusion, MI, reintubation, and pneumonia. These complications most commonly occurred before postoperative day 5 and over 70% were diagnosed before discharge. In contrast, the late complications of DVT, UTI, sepsis, PE, SSI, and wound dehiscence most often occurred on or after postoperative day 7. Less than 50% of these were diagnosed before discharge highlighting the importance of close patient follow-up. A higher risk of complications was identified in older patients, less functionally independent patients, smokers, diabetics, patients with heart failure, and patients who had more than one level fused.

Both Bohl et al. and De la Garza Ramos et al. also reported on “early” and “late” complications after spine surgery.²,3 For both anterior cervical fusions and posterior lumbar fusions, Bohl et al. found that transfusion, MI, pneumonia, and PE were “early,” while DVT, sepsis, SSI, and UTI were “late”.² Similarly, De la Garza Ramos found that “early” complications (defined as those diagnosed before day 6 after surgery for adult spinal deformity) were MI, reintubation, pneumonia, and PE.³ Late complications in their study included UTI, sepsis, DVT, and superficial/deep/organ space SSI.³ The largest differences in the timing of complications for the patient populations in these two studies were for UTI, which had a median day of diagnosis on day 17 in ACDF patients, day 11 in spinal deformity patients, and day 7 in PLF patients, and for DVT, which had a median day of 12 in spinal deformity patients, 10.5 in ACDF patients, and 8 in PLF patients.²,3 These differences were attributed to the differences in patient populations, including urinary tract catheterization practices.²,3

In our study, the median day of diagnosis for UTI was 11.5 which falls in the middle of the other two studies and is most similar to the timing for spinal deformity patients. In contrast, our patient population differs from the other three with regard to timing of DVT and PE. The median day of diagnosis for DVT was 7, which is similar to the PLF patients. The median day of diagnosis for PE was 14 compared to day 5 for the ACDF and PLF patients and day 4 for the adult spinal deformity patients.²,3 The 0.4% rate of PE is similar to the other groups: 0.1% for ACDF patients, 0.5% for PLF patients, and 1.2% for spinal deformity patients.²,3 It is unclear why PE is diagnosed much later in PCF patients. It is possible that the respiratory effects of the other procedures are more profound and lead to earlier advanced imaging investigation.

The complication rate for posterior cervical surgery has been reported in recent studies. Leckie et al. reported an overall rate of 22.9% for both primary and revision posterior cervical spine surgeries in 262 patients.⁴ Medvedev et al. reported a rate of 35.6%, for all posterior cervical surgeries in 5627 patients.⁵ In the current study the overall complication rate was 12.4%. This difference can be partially attributed to rates of blood transfusion. Medvedev et al. reported a 26.3% rate of blood transfusion,⁵ while only 5.3% of patients in our study required transfusion. This difference is potentially related to our exclusion of trauma cases and fusion incorporating the occiput, C1 and C2 levels.

SSI occurred in 2.82% of patients in our study. This infection rate is similar to the 2.6% of patients in Medvedev et al. and the 2.9% of patients in Sebastian et al., a study of 5441 patients who underwent posterior cervical surgery.⁵,9 Our infection rate is greater than the rate in either the ACDF group (0.4%) or the PLF group (1.8%) in the study by Bohl et al.² but similar to the spinal deformity group (2.8%) in the study by De la Garza Ramos et al.³

In our study, increasing age, increasing levels fused, decreasing functional status, smoking status, diabetes, and CHF were associated with increased complications. This correlates with the findings of Medvedev et al. who identified increasing age, increasing frailty, diabetes, and smoking to be associated with increased complications after PCF⁵. Of note, both Medvedev et al. and Buerba et al. found no association between BMI and complications after posterior cervical surgery⁵,8; obesity does not appear to increase the risk of infection at the cervical level.

This study has several potential limitations. The ACS NSQIP database is not specific to spine surgery, and it lacks spine-surgery specific complications such as incidental durotomy and functional outcomes. It also includes only complications that were diagnosed within the first 30 postoperative days. As such, our reported complication rates will be slightly lower than the actual rates, particularly for late-occurring complications. The database, however, is sufficient to characterize the timing of complications in the immediate postoperative period after PCF.

This data is useful to the practicing spine surgeon as it provides a guide for when to expect and investigate for specific complications after posterior cervical procedures. This data is useful in the early diagnosis of complications and may facilitate healthcare reimbursement negotiations by providing information on the rate and timing of complications following posterior cervical fusion.

Funding

No funding was obtained in support of this work.

Conflict of interest

None.