493 - Degree of Mobility at L4-L5 in Preoperative and Intraoperative Images...

General Session: Diagnostic Imaging

Presented by: R. Duculan


R. Duculan(1), C. Mancuso(1), A. Fong(1), M. Rigaud(1), J. Yang(1,2), F. Cammisa(1), A. Sama(1), A. Hughes(1), D. Lebl(1), R. Huang(1), H. Sandhu(1), J. Farmer(1), F. Girardi(1)

(1) Hospital for Special Surgery, New York, NY, United States
(2) Columbia University, Mailman School of Public Health, Department of Epidemiology, New York, NY, United States


Background Context: Flexion and extension images have been used to determine mobility at the level of the disease; however, the degree of mobility in relation to other images, particularly intraop images has not been characterized.

Purpose: The purpose of this analysis is to characterize the degree of mobility in preoperative and intraoperative images in LDS patients undergoing surgery.

Study Design/Setting: Cross-sectional preop and intraop study, tertiary spine center

Patient Sample: 100 consecutive patients undergoing surgery for LDS at L4-5

Outcome Measures: Change in the degree of mobility on preop and intraop images.

Methods: Consecutive patients were enrolled several days preop and completed baseline symptom surveys. CT scans and radiographs (lateral upright, flexion and extension) were obtained preop (4 images) while sagittal fluoroscopic images (supine and prone) were taken intraop (2 images) after anesthesia induction but before incision. Translation and angulation were measured for all 6 images. Mobility is a change in translation and angulation. A change in mobility is the difference between the changes of movement from the minimum. Degree of mobility is defined as an incremental change in mobility on all images from no movement to the maximum degree (range 0 none - 6 most). We used the Pearson's chi square test to assess the overall difference across images and the Poisson regression to identify images that best show an association with degree of mobility. Instability was defined as translation ≥ 3.5 mm or angulation ≥ 11o. All measurements were made according to a set protocol using Sectra IDS7 PACS, and images were calibrated using PACS with the patient's CT images as references.

Results: Mean age was 68, 56% were women, mean BMI was 28, 59% had a smoking history, mean back and leg pain were 6.1 and 5.2 (range 0 none, 10 most), respectively. Of the 100 patients, 54 met criteria for instability: 42% by translation, 4% by angulation, 8% by both; the remaining were classified as stable by these criteria. According to the Poisson regression, the flexion image has a 1.87 (p< 0.001) times higher rate in identifying the degree of mobility in translation while the prone image has a 2.32 (p< 0.001) times higher rate in identifying degree of mobility in angulation compared to the CT image as the reference group. The lateral and supine images combined had the highest rate in identifying the degree of mobility in translation difference (p< 0.001) compared other images. In identifying degree of mobility in angulation difference, the CT and prone images have a rate ratio of 2.32 (p< 0.001) compared to CT and extension images as the reference group. The overall difference across all images is statistically significant (p< 0.001)

Conclusions: Preoperative flexion and extension images are not sensitive enough in identifying the degree of mobility in patients with LDS at L4-L5. Mobility in other images such as prone, lateral upright/supine and CT/prone, gives us the highest rate ratio in identifying mobility in angulation, translation difference and angulation difference, respectively. Furthermore, other variables such as facet morphology, degree of diastasis, and disc height might also help to avoid missing instability in these patients.