Oral Posters: Thoraco-lumbar Degenerative

Presented by: A. Richter - View Audio/Video Presentation (Members Only)

Author(s):

A. Richter(1), J. Deckey(1), C. Borges(1), J. Smith(1)

(1) Hoag Orthopaedic Institute, Irvine, CA, United States

Abstract

Introduction: Anterior Lumbar interbody fusion (ALIF) provides the most powerful and accurate opportunity to address sagittal imbalance by restoring lumbar lordosis to match spinopelvic parameters. Modern interbody grafting technology offers a wide array of implant sizes and built in lordosis making it possible to more precisely reconstruct and correct a lumbar lordosis and pelvic incidence mismatch. Preoperatively it is possible to calculate the degree of mismatch and plan surgical correction. Although this calculation predicts a specific alignment, there are inherent variables that produce a result slightly different than the predicted. In this study, we attempt to define this inherent error in order to more accurately predict a sagittal reconstruction. We will assess two methods for calculating the pelvic incidence and lumbar lordosis and preoperative implant selection. One method will use freehand measurements (using PACS) and the other will utilize a measurement software program (Surgimap). We will then evaluate the actual correction obtained compared to our planned correction using the two methods. Our findings will help improve the accuracy of future preoperative planning and surgical outcomes.

Methods: A two-surgeon database was used to identify all patients who underwent anterior lumbar interbody fusion (ALIF) between 2015-2016. Radiographic measurements were obtained on preoperative and postoperative standing lateral lumbar x-rays. Measurements including pelvic incidence (PI), lumbar lordosis (LL), and disc angle at each anterior operative level were used to calculate the degree of correction and compared to the expected correction predicted by preoperative calculations.

Results: Sixty-two patients met the inclusion criteria and had x-rays of sufficient quality that they could be analyzed. Using PACS measurement the average expected correction was 14.6 degrees and average preoperative mismatch was 16.5 degrees. The actual observed correction was 9.1 degrees, which was significantly different (p=0.03) Using Surgimap the average expected correction was 16.5 degrees and the average preoperative mismatch was 14.3 degrees. The actual observed correction was 9.6 degrees, which was significantly different (p=0.009) In order to verify the reliability of our measurement techniques, we also assessed the pre and postoperative measurements obtained for PI. Since the PI is anatomic parameter that is not changed by surgery, any variability in these measurements can be attributed to error in measurement technique. No significant difference was found between pre and postoperative measurements using either measurement technique (p>0.05).

Discussion and Conclusion: In both the freehand and measurement software groups the expected correction was greater than the actual correction, which suggests that the posterior procedure may be responsible for an additional lordotic correction. It is also possible that the anterior/posterior placement of the interbody grafts affects the overall lordosing force that the segment experiences which is supported by the fact that the post surgery segmental lordosis did not always match the lordosis of the specific interbody spacer. Our results suggest that preoperative planning is helpful for the selection of lordotic vs hyperlordotic grafts for correction of lumbar lordosis but there continues to be substantial variability in the actual correction achieved which may be attributable to the exact placement of the interbody grafts or contouring of the posterior instrumentation. Non-the less, it appears that both measurement techniques are accurate tools for assessing PI and LL.