Lightning Podiums: Smorgasboard - Room 802B

Presented by: R. Duculan

Author(s):

C. Mancuso(1), A. Fong(1), M. Rigaud(1), R. Duculan(1), 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

Abstract

Background Context: Translation and angulation measurements on lateral flexion-extension images are traditionally used to diagnosis instability in lumbar degenerative spondylolisthesis (LDS). However, other radiographic features, pain and muscle contractions may impede performance and interpretation of these images and result in under reporting of instability. Other imaging strategies, including while under anesthesia, may reveal instability that flexion-extension images do not.

Purpose: Among patients with LDS whose preop flexion-extension images did not meet criteria for instability, our goal was to compare translation and angulation on preop lateral and CT images, and intraop supine and prone images.

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

Patient Sample: 110 consecutive patients undergoing surgery for LDS at L4-5

Outcome Measures: Within-patient differences in pre- and intraop translation and angulation

Methods: Consecutive patients were enrolled several days preop and completed baseline symptom surveys. CT scans and radiographs were obtained in the lateral upright, flexion, and extension positions. Instability was defined as translation ≥ 3.5 mm or angulation ≥ 11o between flexion and extension. Fluoroscopic images in the sagittal plan were taken intraop after anesthesia induction but before incision, and measurements were made for translation and angulation in supine and prone positions. 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. The following comparisons for translation and angulation were made for patients who were classified as stable by flexion-extension criteria: 1) CT vs upright; 2) upright vs intraop supine; 3) upright vs intraop prone; and 4) intraop supine vs prone. Thresholds for instability for these comparisons similarly were translation ≥ 3.5 mm and angulation ≥ 11o.

Results: Mean age was 67, 56% were women, mean BMI was 29, 54% had a smoking history, mean back and leg pain were 6.3 and 6.7 (range 0 none, 10 most). Of the 110 patients, 10 met criteria for instability by flexion-extension images (6 by translation, 2 by angulation, 2 by both); the remaining 100 were classified as stable by these criteria. However, based on comparison of upright vs CT images, 8 of these 100 were then classified as unstable (8 by translation, 0 by angulation). Among the remaining 92 patients an additional 28 were then classified as unstable on intraop images with the following prevalence: 15 on upright vs supine (12 by translation, 1 by angulation, 2 by both); 20 on upright vs prone (17 by translation, 1 by angulation, 2 by both); and 6 on supine vs prone (6 by translation, 0 by angulation). Thus, overall 36 of the 100 patients classified as stable by flexion-extension images were later found to be unstable by other imaging comparisons. 24 of these 36 patients underwent fusion.

Conclusions: Preop flexion-extension comparisons under reported the prevalence of instability in 36% of patients undergoing surgery for L4-5 LDS. These findings have implications for determining how instability should be defined, preoperative planning, and the need for intraop imaging to correctly identify instability.