Oral Posters: Values and Outcomes in Spine Surgery
Presented by: C. Wade - View Audio/Video Presentation (Members Only)
C. Wade(1), A. Deitz(2), G. Malcolmson(2)
(1) Auburn University, Industrial and Systems Engineering, Auburn, AL, United States
(2) Ortho Kinematics, Austin, TX, United States
Several recent studies have examined the influence of lumbar sagittal alignment measurements on the long term clinical outcomes associated with lumbar fusion surgery. In some of these studies, it has been suggested that a sagittal alignment measurement parameter—the interval between the Pelvic Incidence (PI) and Lumbar Lordosis (LL)—be targeted to be 10 degrees or less . Certain lumbar fusion approaches have incorporated intra-operative imaging to help determine if this PI-LL target has been achieved. With pre-operative imaging, images are taken with the patient standing in a neutral posture, whereas intra-operative images are taken with the patient in a lying posture, often the lateral decubitus position. To goal of this study is to assess the appropriateness of using intra-operative to assess PI-LL and reference models drawn from measurements taken from pre-operative images.
Methods: 1,346 patients that were indicated to receive flexion/extension x-rays were imaged in both standing as well as in a lateral decubitus position. Images were evaluated via a vertebral motion analysis system (VMA) (Ortho Kinematics, Austin, TX). The Lumbar Lordosis (LL) angle was calculated for the both the Standing (S) and Lateral Decubitus (LD) images, and for each patient the LL angle was calculated as the angle between the L1 and S1 vertebral bodies.
Results: A comparison of LLS and LLLD was carried out using Student t-test. There was a statistically significant reduction in LLLD (average of 46 degrees) and LLS (average of 41 degrees). The absolute difference in the LLS and the LLLD measurements was calculated for each patient, and the mean absolute difference was 10 degrees, with a standard deviation of 7 degrees. According to this distribution, approximately one third of patients can expect a difference of 17 degrees between the measurements of LLLD in a lateral decubitus position as compared to LLS as measured standing.
Conclusion: The utilization of intra-operative systems to assess LL, and particularly for the assessment of the Pelvic Incidence (PI) minus LL interval, are shown to be significantly underestimating the LL measurement of a patient as compared to values taken pre-operatively with the patient in a standing position. All of the surgical guidelines mentioned in the introduction section pertain to imaging that was done standing up. This raises significant questions regarding the validity of using of an intra-operative LL value in assessing the PI-LL, especially in regard to using PI-LL to help assess whether or not a given level targeted for fusion has enough lordosis. An underestimation of LL would result in an overestimation of the PI-LL interval, which would lead to execessive segmental lordosis being incorporated into a fusion procedure relative to that amount that would be “ideal” based on the goal of achieving a PI-LL measurement of less than 10 degrees.
References:  Rothenfluh, DA, et. al. “Pelvic incidence-lumbar lordosis mismatch predisposes to adjacent segment disease after lumbar spinal fusion.” The Spine Journal. 14 July 2014.