39. the Cost and Likelihood of Requiring Additional Surgery Within Two Years after Index Microdiscectomy

BACKGROUND CONTEXT The majority of revision surgeries after instrumented posterior fusion of the thoracolumbar spine are due to implant failures such as screw pull-out, screw loosening, disassembly, and implant breakage, as well as pseudarthrosis, loss of correction, or secondary malalignment. The causes of these construct failures are typically attributable to mechanical misloading or overloading during and immediately after surgery. In this context, proper alignment and tightening of the pedicle screw/rod assembly is crucial to achieve satisfactory clinical results. PURPOSE The objective of this study is to investigate the incidence of postoperative screw/rod mismatch and to analyze the impact of mismatches on clinical outcome in terms of revision surgery, adjacent segment degeneration (ASD) and pain. STUDY DESIGN/SETTING This is a monocentric retrospective observational clinical study. PATIENT SAMPLE A total of 406 patients underwent thoracolumbar fusion surgery with pedicle screw/rod systems for predominantly degenerative pathologies between January 2013 and December 2018. All patients were followed-up clinically and radiologically with a mean follow-up of 5 years. OUTCOME MEASURES Pedicle screw/rod mismatch, revision rate, ASD at the adjacent cranial segment and VAS pain were assessed. METHODS The term revision refers to subsequent procedures in which all or part of the original implants were exchanged or removed. Radiographic parameters were evaluated using a/p and lateral radiographs at final follow-up. The mismatch between pedicle screw and rod was measured as the angle between two parallel lines on either side of each pedicle screw head and a line laterally along the associated rod. Angles other than 90°±0.3° were considered mismatched. Multiple comparisons were counteracted by Bonferroni correction, adjusted significance level was set at p* < 0.01. RESULTS None of the patients were lost to follow-up. Preoperative, postoperative, and follow-up data were available for all included patients. Pedicle screw/rod mismatch was found in 171/406 (42.1%) of patients undergoing fusion surgery, affecting 613/3016 (20.3%) screws. The overall revision incidence was 11.8% (48/406), and a new ASD occurred in 12.1% of all patients (49/406). Mean VAS pain score at final follow-up was 2.0. Comparison of the two groups with and without mismatch revealed statistically significant higher numbers of revision procedures performed (26.9% vs 0.9%), of new ASD (27.5% vs 3.8%), and higher VAS pain scores (2.8/10 vs 1.4/10) for cases with mismatch. When comparing patients who underwent intraoperative correction and/or reduction with those who did not, statistically significant more screw mismatches (63.4% vs 39.7%) and revision surgeries (29.3% vs 9.9%) were noted in patients who had these forceful maneuvers. CONCLUSIONS Pedicle screw/rod mismatch is a relevant occurrence after fusion surgery that negatively affects clinical outcome in terms of revision rate, ASD incidence, and pain intensity. Mismatches indicate that the construct was assembled under mechanical stress. Therefore, uncontrollable correction maneuvers and fixations under constraint should be avoided as far as possible. With the goal of improving patient quality of life and reducing the risk of revision, spinal instrumentation should be applied force-controlled with the lowest possible forces, considering the patient's individual anatomy and sagittal and coronal balance. FDA Device/Drug Status This abstract does not discuss or include any applicable devices or drugs. The majority of revision surgeries after instrumented posterior fusion of the thoracolumbar spine are due to implant failures such as screw pull-out, screw loosening, disassembly, and implant breakage, as well as pseudarthrosis, loss of correction, or secondary malalignment. The causes of these construct failures are typically attributable to mechanical misloading or overloading during and immediately after surgery. In this context, proper alignment and tightening of the pedicle screw/rod assembly is crucial to achieve satisfactory clinical results. The objective of this study is to investigate the incidence of postoperative screw/rod mismatch and to analyze the impact of mismatches on clinical outcome in terms of revision surgery, adjacent segment degeneration (ASD) and pain. This is a monocentric retrospective observational clinical study. A total of 406 patients underwent thoracolumbar fusion surgery with pedicle screw/rod systems for predominantly degenerative pathologies between January 2013 and December 2018. All patients were followed-up clinically and radiologically with a mean follow-up of 5 years. Pedicle screw/rod mismatch, revision rate, ASD at the adjacent cranial segment and VAS pain were assessed. The term revision refers to subsequent procedures in which all or part of the original implants were exchanged or removed. Radiographic parameters were evaluated using a/p and lateral radiographs at final follow-up. The mismatch between pedicle screw and rod was measured as the angle between two parallel lines on either side of each pedicle screw head and a line laterally along the associated rod. Angles other than 90°±0.3° were considered mismatched. Multiple comparisons were counteracted by Bonferroni correction, adjusted significance level was set at p* < 0.01. None of the patients were lost to follow-up. Preoperative, postoperative, and follow-up data were available for all included patients. Pedicle screw/rod mismatch was found in 171/406 (42.1%) of patients undergoing fusion surgery, affecting 613/3016 (20.3%) screws. The overall revision incidence was 11.8% (48/406), and a new ASD occurred in 12.1% of all patients (49/406). Mean VAS pain score at final follow-up was 2.0. Comparison of the two groups with and without mismatch revealed statistically significant higher numbers of revision procedures performed (26.9% vs 0.9%), of new ASD (27.5% vs 3.8%), and higher VAS pain scores (2.8/10 vs 1.4/10) for cases with mismatch. When comparing patients who underwent intraoperative correction and/or reduction with those who did not, statistically significant more screw mismatches (63.4% vs 39.7%) and revision surgeries (29.3% vs 9.9%) were noted in patients who had these forceful maneuvers. Pedicle screw/rod mismatch is a relevant occurrence after fusion surgery that negatively affects clinical outcome in terms of revision rate, ASD incidence, and pain intensity. Mismatches indicate that the construct was assembled under mechanical stress. Therefore, uncontrollable correction maneuvers and fixations under constraint should be avoided as far as possible. With the goal of improving patient quality of life and reducing the risk of revision, spinal instrumentation should be applied force-controlled with the lowest possible forces, considering the patient's individual anatomy and sagittal and coronal balance.