The effect of July admission on inpatient morbidity and mortality after adult spinal deformity surgery

Discussion

The so-called “July effect” has been widely examined in the medical literature.^{1–3, 6, 8, 11} Every July new residents and fellows start their training at teaching hospitals in the United States, and this phenomenon has been suggested as a potential source of increased error and complications for patients treated by the “new” staff.⁶ Though some studies have suggested the “July effect” does exist,^{2, 3} others have found no difference in outcomes for patients treated in July versus other months.^{1, 6, 8, 11}

In this study, we investigated whether patients undergoing surgery for ASD in July had different rates of inpatient morbidity and mortality when compared to patients treated in other months. After analysis of over 27,000 patients, it was found that crude overall complication rates, major complication rates, and mortality rates were not found to be significantly different between groups. Likewise, a multivariable analysis that controlled for patient characteristics, operative parameters, and comorbidities found no increased odds of adverse events for patients treated in July.

Similar to the present findings, McDonald et al. examined over 500,000 spinal procedures performed at teaching hospitals between 2001 and 2008, and found no evidence of increased complications for patients admitted in July.⁶ However, that study differed from the present one in various ways. First, McDonald et al. did not stratify patients based on preoperative diagnosis, and included patients with degenerative spine disease, spinal tumors, spinal infections, deformity, and others. Second, they included both elective and non-elective admissions. Lastly, they only examined mortality, discharge disposition, surgical site infection, wound dehiscence, and implant complications. Though results were similar to our findings, the present study specifically investigated whether the July effect exists for ASD patients, and 16 unique complications were examined.

In a similar study, Hoashi et al. performed a retrospective multicenter review of 575 patients who underwent surgery for adolescent idiopathic scoliosis.¹¹ The authors found no preoperative differences between patients based on the month of surgery, including preoperative Cobb angles and Scoliosis Research Society-22 scores. Following surgery, there were no significant differences in intraoperative blood loss, operative time, total complications, or major complications based on the month of admission. The authors of that study concluded: “our results support the finding that the participation of physicians-in-training in surgery for adolescent idiopathic scoliosis does not have a season-dependent impact on patient outcomes.”¹¹

In contrast to these previous findings, Dasenbrock et al. found that patients who underwent surgery for spinal metastatic disease in July had higher rates of inpatient morbidity and mortality compared to other months.² The authors examined 2,920 admissions, and found a 7.5% mortality rate in July compared to 4.3% in August and June.² Similarly, a multivariable analysis revealed increased odds of in-hospital death (OR 1.81; 95% CI, 1.13 – 2.91) and intraoperative complication development (OR 2.11; 95% CI, 1.41 – 3.17).² There are several possible explanations for the difference in findings between that study and ours. Patients with metastatic disease are usually sicker and may require more urgent care than patients undergoing elective ASD surgery, making them prone to medical errors and complications.

The overall inpatient morbidity rate in the present study was 44.7%, and the major complication rate was 12.5%, both of which did not significantly differ based on the month of admission. Generally speaking, ASD surgery is considered a highly morbid procedure, with overall complication rates ranging from 40% to 86% in the literature.^{13, 14} On the other hand, Schawb et al. conducted a multi-center review of 953 ASD patients, finding a “major” complication rate of 8.4%.¹⁵ The most common complications found in their study were excessive blood loss (over 4 liters), deep wound infection, and pulmonary embolism.¹⁵ Identified risk factors for complication occurrence were staged procedures and combined anterior-posterior procedures.

For the aforementioned reasons, it could be argued that performing such operations at the commencement of the academic year with new trainees (particularly upcoming senior residents and spine fellows) may put patients at higher risk for complications and mortality. Interestingly, no differences were found in relation to these outcomes, suggesting that undergoing ASD surgery at the beginning of the academic year in July has insignificant impact on inpatient morbidity and mortality. These findings were also true after performing a subanalysis on patients admitted in July-August and for patients undergoing “complex” procedures such as osteotomy, fusion of 8 or more levels, revision procedures, or patients with a comorbidity score of 3 or higher. The absence of a “July effect” for ASD surgery may have several explanations. First, ASD surgery typically involves an attending surgeon with one or two assistants.¹¹ Second, the steep learning curves of pedicle screw placement and correction maneuvers do not usually allow for a new senior resident or fellow to perform these procedures without adequate supervision.¹¹ Lastly, postoperative care is done by a multidisciplinary team of surgeons, internists, anesthesiologists, intensive care specialists, pain managers, and others; it is likely that this approach compensates for any potential shortcomings (i.e. lack of training or experience) occurring with the influx of new staff in July.

The NIS is the largest inpatient database in the United States, and allows for examination of thousands of admissions, something that is not usually possible with single institution case series or even multi-center collaborations. Additionally, the inclusion of data such as race, primary payer, and comorbidities allows for adequate multivariable regression analyses. Nonetheless, this study has various limitations. First, the NIS does not include information on presenting symptoms, neurological status, sagittal/coronal balance, and others that may potentially influence patient outcomes. Second, there is the risk of miscoded data, but numerous studies have used this database for spinal surgery research^{2, 6, 17} and it is also unlikely that if it were the case, that data miscoding would only affect a specific month. Third, outcomes beyond the inpatient period are not recorded in this database, and prospective studies with longer follow-up are encouraged. Lastly, though the NIS clearly distinguished between teaching and nonteaching hospitals, it is a sample of community hospitals, so capture of traditional academic setting may not be occurring. Additionally, there is no information regarding the presence of resident, fellow, or cosurgeons during the operative procedure.