BACKGROUND/CONTEXT: Degenerative disc disease (DDD) is associated with longitudinal remodeling of paravertebral tissues. While chronic vertebral changes in advanced stages of DDD are well-studied, very little data exists on acute vertebral bone remodeling at the onset and progression of DDD.
PURPOSE: To longitudinally characterize bony remodeling in a rodent model of disc injury-induced DDD.
STUDY DESIGN/SETTING: In vivo animal study involving a rat annulus fibrosus injury model of DDD.
METHODS: Eight female Lewis rats were assigned to IVD injury (Puncture) or sham surgery (Sham). All rats underwent anterior, transperitoneal approach to the lumbar spine, and Puncture rats underwent annulus fibrosus injury at the L3-L4 and L5-L6 IVDs (n=8 per group). Live µCT imaging (10-μm voxel size) was performed 1 week prior to surgery and postoperatively at 2-week intervals up to a 12-week endpoint. Bone morphology and densitometry of the cranial vertebral body and bony endplate were analyzed and reported with respect to the pre-operative baseline scan. Sagittal Safranin-O/Fast-Green and Toluidine Blue histology evaluated using the Rutges IVD score and a custom vertebral endplate score.
RESULTS: Vertebral trabecular tissue mineral density (TMD), vertebral trabecular spacing (Tb.Sp), endplate TMD and endplate apparent bone mineral density (BMD) were all significantly greater in Puncture compared to Sham at 4 weeks and each subsequent timepoint. Puncture rats exhibited marginally lower endplate total volume (TV). Anterior endplate osteophyte formation and central physeal ossification were observed in Puncture rats. Endpoint histological analysis demonstrated moderate evidence of IVD degeneration, indicating that vertebral bone adaptation occurs in the acute phases of DDD onset and progression.
CONCLUSIONS: Annulus injury-induced DDD leads to acute and progressive changes to the morphology and densitometry of bone in the adjacent vertebral bodies and endplates.
KEYWORDS: Bony remodeling; Degenerative disc disease; Intervertebral disc injury; Modic changes
