LAUSR

Study Design. Retrospective investigation using a prospectively collected database. Objective. To examine the appearance and characteristics of vertebral bone marrow edema (BME) in the normal healing of lumbar interbody fusion. Summary of Background Data. Although BME in pathological spinal conditions has been well-documented, the patterns and characteristics of BME in the normal healing process of spinal fusion remains unexplored. Materials and Methods. We reviewed imaging from 225 patients with normal healing following posterior lumbar interbody fusion or transforaminal lumbar interbody fusion. BME was identified on magnetic resonance imaging at the third postoperative week and categorized with respect to its appearance, including assessment of area and extension within the relevant vertebrae. Results. Three hundred eighty-nine of the 450 instrumented vertebrae (86.4%) displayed evidence BME. All instances of BME were associated with the area of contact with the endplate. The average extent of BME was 32.7±1.0%. BME within normal healing following interbody fusion could be categorized into four types: no edema (13.6%), anterior corner (36.6%), around-the-cage focal (48.0%), and diffuse (1.8%). Anterior corner BME was significantly associated with instances of single cage placement than in dual cages (42.6% vs. 24.7%, P=0.0002). Single cages had a significantly higher rate of BME than dual cages (92.0% vs. 75.3%, P<0.0001). The extent of BME was significantly greater in the single cage cohort (36.9% vs. 24.2% in dual cages, P<0.0001). Conclusions. This serves as the first study demonstrating the patterns of BME associated with normal healing following lumbar interbody fusion procedures. Anterior corner BME and around-the-cage focal BME were the most common patterns encountered, with diffuse BME a relatively rare pattern. These findings might contribute to the better differentiation of postoperative pathological events from normal healing following lumbar interbody fusion. Level of Evidence. 4.