Background. In several previous studies Charlson comorbidity Index (CCI) score was associated with postoperative complications, mortality and re-admission. There are few reports about the influence of CCI score on postoperative clinical outcome. The purpose of this study was to investigate the influence of comorbidities as calculated with CCI on postoperative clinical outcomes after PLIF.Methods. 366 patients who underwent an elective primary single level PLIF were included. Postoperative

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... al outcome was evaluated with the Japanese Orthopaedic Association lumbar score (JOA score). The correlation coefficient between the CCI score and postoperative improvement in JOA score was investigated. Patients were divided into three groups according to their CCI score (0, 1 and 2+). JOA improvement rate, length of stay (LOS) and direct cost were compared between each group. Postoperative complications were also investigated.Results. There was a weak negative relationship between CCI score and JOA improvement rate (r = -0.20). LOS and direct cost had almost no correlation with CCI score. The JOA improvement rate of Group 0 and Group 1 was significantly higher than Group 2+. LOS and direct cost were also significantly different etween Group 0 and Group 2+. There were 14 postoperative complications. Adverse postoperative complications were equivalently distributed in each group, and not associated with the number of comorbidities.Conclusions. A higher CCI score leads to a poor postoperative outcome. The recovery rate of patients with two or more comorbidities was significantly higher than in patients without comorbidities. However, the CCI score did not influence LOS and increased direct costs. The surgeon must take into consideration the patient's comorbidities when planning a surgical intervention in order to achieve a good clinical outcome.