P122. Early outcomes of multilevel ACDF with segmental plate fixation

BACKGROUND CONTEXT Multilevel anterior cervical discectomy and fusion (ACDF) constructs with a single contiguous plate have higher rates of pseudoarthrosis, dysphagia, and mechanical failure compared to single level fusions. Optimal placement of long plates may also present a technical challenge, requiring multiple X-rays and prolonged retraction of the soft tissue. The use of segmental plating in multilevel ACDF has been proposed as a means of making anterior fixation more facile, while avoiding the biomechanical limitations of “zero profile” ACDF constructs with integrated fixation. Preclinical cadaveric studies have demonstrated the potential biomechanical benefit of segmental plate fixation in multilevel surgeries. PURPOSE To study the clinical and radiographic outcomes of segmental plate fixation in multilevel ACDF. METHODS We prospectively followed patients undergoing multilevel ACDF with segmental plating at our institution from 2018-2021. Pre- and postoperative demographic/radiographic characteristics and patient reported outcome measures (PROMs) were recorded. Patients were followed for at least 1-year postoperatively (mean 18 months; range 12-47 months). Fusion was assessed using evaluation of bridging bone and interspinous movement (ISM, <2mm) on flexion/extension X-rays. CT imaging was not obtained as part of the standard of care, but was assessed for fusion when available. RESULTS A total of 92 patients with 1-year followup data were analyzed. Significant improvements in arm pain, neck pain, and disability were observed. NDI scores improved from an average of 34.9 (17.9) preop to 16.6 (12.7) at 1 year (p<0.001). Average change in C2-C7 lordosis from preop to immediate postop was 7.3º (p<0.001), and from postop to 1yr was -2.6º (p<0.001). Segmental lordosis at instrumented levels (N=187) increased by an average of 4.4º from preop to postop (p<0.001) and reduced by -1.7º from postop to 1yr (p<0.001). The overall rate of fusion at 1 year was 92.7% by bony bridging and 71.9% by ISM (2mm and no instances of pseudoarthrosis were seen on CT. There were no postoperative alignment measures that predicted fusion rates with significance. Of note, no significant differences in fusion rates were observed based on number of levels treated (2 to 4 levels, p>0.35). Three patients (3.3%) required additional surgery for persistent myeloradiculopathy and two patients (2.2%) developed adjacent segment disease requiring treatment. No patients required reoperation for pseudoarthrosis or instrumentation failure. CONCLUSIONS Segmental plating in multilevel ACDF appears safe and led to a significant improvement in pain, disability, and radiographic alignment in this cohort. There was an excellent rate of fusion for multilevel ACDF based on bone bridging. However, a greater than expected amount of interspinous movement (28%, >2mm) was observed in asymptomatic patients. Importantly, in all cases of ISM>2mm in which CT imaging was available (35.2%) fusion was observed, reinforcing recent studies demonstrating the low positive predictive value of dynamic X-rays in identifying pseudoarthrosis. This appears to be particularly true in the context of multilevel ACDF with segmental plating, where CT imaging is likely to be more accurate in assessing fusion. Unlike traditional ACDF, the number of levels treated did not appear to influence rates of subsidence and fusion in segmental ACDF. Further research is needed to evaluate the long-term clinical impact of segmental plating, particularly as it applies to adjacent segment degeneration. FDA Device/Drug Status This abstract does not discuss or include any applicable devices or drugs. Multilevel anterior cervical discectomy and fusion (ACDF) constructs with a single contiguous plate have higher rates of pseudoarthrosis, dysphagia, and mechanical failure compared to single level fusions. Optimal placement of long plates may also present a technical challenge, requiring multiple X-rays and prolonged retraction of the soft tissue. The use of segmental plating in multilevel ACDF has been proposed as a means of making anterior fixation more facile, while avoiding the biomechanical limitations of “zero profile” ACDF constructs with integrated fixation. Preclinical cadaveric studies have demonstrated the potential biomechanical benefit of segmental plate fixation in multilevel surgeries. To study the clinical and radiographic outcomes of segmental plate fixation in multilevel ACDF. We prospectively followed patients undergoing multilevel ACDF with segmental plating at our institution from 2018-2021. Pre- and postoperative demographic/radiographic characteristics and patient reported outcome measures (PROMs) were recorded. Patients were followed for at least 1-year postoperatively (mean 18 months; range 12-47 months). Fusion was assessed using evaluation of bridging bone and interspinous movement (ISM, <2mm) on flexion/extension X-rays. CT imaging was not obtained as part of the standard of care, but was assessed for fusion when available. A total of 92 patients with 1-year followup data were analyzed. Significant improvements in arm pain, neck pain, and disability were observed. NDI scores improved from an average of 34.9 (17.9) preop to 16.6 (12.7) at 1 year (p<0.001). Average change in C2-C7 lordosis from preop to immediate postop was 7.3º (p<0.001), and from postop to 1yr was -2.6º (p<0.001). Segmental lordosis at instrumented levels (N=187) increased by an average of 4.4º from preop to postop (p<0.001) and reduced by -1.7º from postop to 1yr (p<0.001). The overall rate of fusion at 1 year was 92.7% by bony bridging and 71.9% by ISM (2mm and no instances of pseudoarthrosis were seen on CT. There were no postoperative alignment measures that predicted fusion rates with significance. Of note, no significant differences in fusion rates were observed based on number of levels treated (2 to 4 levels, p>0.35). Three patients (3.3%) required additional surgery for persistent myeloradiculopathy and two patients (2.2%) developed adjacent segment disease requiring treatment. No patients required reoperation for pseudoarthrosis or instrumentation failure. Segmental plating in multilevel ACDF appears safe and led to a significant improvement in pain, disability, and radiographic alignment in this cohort. There was an excellent rate of fusion for multilevel ACDF based on bone bridging. However, a greater than expected amount of interspinous movement (28%, >2mm) was observed in asymptomatic patients. Importantly, in all cases of ISM>2mm in which CT imaging was available (35.2%) fusion was observed, reinforcing recent studies demonstrating the low positive predictive value of dynamic X-rays in identifying pseudoarthrosis. This appears to be particularly true in the context of multilevel ACDF with segmental plating, where CT imaging is likely to be more accurate in assessing fusion. Unlike traditional ACDF, the number of levels treated did not appear to influence rates of subsidence and fusion in segmental ACDF. Further research is needed to evaluate the long-term clinical impact of segmental plating, particularly as it applies to adjacent segment degeneration.