As medical technology including medication, equipment and educational programs progresses, surgery will be indicated for a broader patient subset. Elderly patients often have several comorbidities, and younger patients often have cardiovascular disease, have previously undergone surgery or have renal disease that requires hemodialysis. For these reasons, identifying the preoperative risk factor is important and essential to not only spine surgery but to all surgeries in general. The stratification of comorbidities is helpful for comprehensively understanding the patient’s general condition.
Degenerative lumbar disease including spondylolisthesis and lumbar spinal canal stenosis is a common and well-known pathology. It presents with symptoms that can include low back pain, leg pain and neurologic deficits that affect daily life. Conservative therapy is usually the first choice for initial management, but if unsuccessful surgical intervention is considered. PLIF is a common general procedure for degenerative lumbar disease. The clinical outcome of PLIFs is widely recognized to be satisfactory [9–11]. Liu reported that a PLIF alone improved clinical satisfaction and decreased complications [9]. Degenerative spondylolisthesis is more common in patients over 60 years of age [13]. As the patients age they are more likely to develop this disease, and their likelihood of several comorbidities may also be higher.
The impact of comorbidities on spine surgery has been reported, but most prior studies described readmission, mortality and complications [1, 7, 8, 14, 15]. One of them reported that a higher CCI was associated with increased postoperative complication rates following a minimally invasive transforaminal lumbar interbody fusion [15]. Derman et al. [16] reported that a preoperative CCI of 1 or greater was associated with an increased risk of a subsequent emergency department utilization or a hospital readmission after cervical spine arthrodesis. In contrast, another report concluded that CCI is a useful comorbidity index, but was not completely predictive of the incidence of a major complication [17]. Similarly, adverse complications in this study were equivalently distributed between each group, and not associated with the number of comorbidities.
A few reports have been published about the relationship between comorbidities and clinical outcome [18]. Yagi et al. reported in detail about clinical outcomes and CCI after spine surgery, but conceded that the chief limitation of his work is that different instruments were used to measure clinical outcomes [18]. As a result, they could not compare the clinical outcomes directly.
In this study, the clinical outcome of all patients was evaluated using the JOA score. Clinical outcomes were calculated fairly. We also directly compared these scores with CCI.
There was a weak negative correlation between the JOA improvement rate and CCI in this study. Although we could not identify CCI as a predictor of a poor clinical outcome, this study can identify the negative influence of comorbidities on postoperative clinical outcomes after PLIF. Optimal treatment and control of a comorbidity is necessary before surgery, and would be more likely to lead to a satisfactory outcome.
Postoperative rehabilitation is essential to a good clinical and functional outcome. The small frequency or lack of postoperative rehabilitation due to several comorbidities might be related to poor clinical outcomes. In fact, a report in the field of ischemic strokes concluded that a higher modified CCI for stroke score was an independent predictor of poor rehabilitation success, and the authors noted the importance of comorbidities when planning rehabilitation [19]. This conclusion may be similarly applicable to spine. Medical comorbidity was found to be a significant predictor of rehabilitation efficiency in geriatric patients by Patrick [20]. Not only a successful spine surgery but also optimal treatment of comorbidities is necessary for a good clinical outcome. Appropriately treating medical comorbidities may facilitate postoperative rehabilitation and lead to a good recovery after spine surgery.
Every correlation coefficient between CCI score and operative time, intraoperative blood loss, LOS and direct cost was very weak. However, a higher CCI score (Group 2+) was associated with a significantly longer OR time and a more expensive cost of treatment than those in Group 0. In contrast to the present work, previous research studies concluded that a greater comorbidity burden as reflected by a higher CCI did not lead to a prolonged hospital stay or an increased direct cost [15]. The different way in which we divided groups by CCI score vs. previous research methodologies might have influenced these results.
The findings of the present study are useful and beneficial not only for spine surgeon but for patients as well. These results help surgeons to indicate a patient for surgical intervention using a PLIF, and to obtain informed consent from the patients before surgery. Preoperative comorbidities and expected clinical outcomes must be discussed with patients because they can recognize and understand their own status. Furthermore, this information helps them to decide whether they will undergo spinal surgery at all based on if it can render a satisfactory outcome.
This study has several limitations. First, its sample size is small because it is a single center study.
A larger patient sample may achieve a more robust correlation between CCI and postoperative clinical outcome. Secondary, this study did not take into consideration the age of the patients. Several prior works added a 0–4 weighted score depending on the age to the original CCI score [14.15]. Patient age is an important surgical factor and is related to comorbidity. It might influence the CCI score and its correlation with clinical outcomes in this study. Patient age will be considered in further studies for more accurate results. Lastly, the individual cost for a comorbidity is unknown. Direct cost included all hospital charges. It was difficult to isolate the cost of a comorbidity, such as medication or treatment and compare it between comorbidities. Further research must be done to define the influence of CCI on PLIF outcomes more clearly.