Lumbar endplate microfracture injury induces Modic-like changes, intervertebral disc degeneration and spinal cord sensitization - an in vivo rat model

Abstract

Background context: Endplate (EP) injury plays critical roles in painful IVD degeneration since Modic changes (MCs) are highly associated with pain. Models of EP microfracture that progress to painful conditions are needed to better understand pathophysiological mechanisms and screen therapeutics.

Purpose: Establish in vivo rat lumbar EP microfracture model and assess crosstalk between IVD, vertebra and spinal cord.

Study design/setting: In vivo rat EP microfracture injury model with characterization of IVD degeneration, vertebral remodeling, spinal cord substance P (SubP), and pain-related behaviors.

Methods: EP-injury was induced in 5 month-old male Sprague-Dawley rats L4-5 and L5-6 IVDs by puncturing through the cephalad vertebral body and EP into the NP of the IVDs followed by intradiscal injections of TNFα (n=7) or PBS (n=6), compared with Sham (surgery without EP-injury, n=6). The EP-injury model was assessed for IVD height, histological degeneration, pain-like behaviors (hindpaw von Frey and forepaw grip test), lumbar spine MRI and μCT, and spinal cord SubP.

Results: Surgically-induced EP microfracture with PBS and TNFα injection induced IVD degeneration with decreased IVD height and MRI T2 signal, vertebral remodeling, and secondary damage to cartilage EP adjacent to the injury. Both EP injury groups showed MC-like changes around defects with hypointensity on T1-weighted and hyperintensity on T2-weighted MRI, suggestive of MC type 1. EP injuries caused significantly decreased paw withdrawal threshold, reduced axial grip, and increased spinal cord SubP, suggesting axial spinal discomfort and mechanical hypersensitivity and with spinal cord sensitization.

Conclusions: Surgically-induced EP microfracture can cause crosstalk between IVD, vertebra, and spinal cord with chronic pain-like conditions.

Clinical significance: This rat EP microfracture model was validated to induce broad spinal degenerative changes that may be useful to improve understanding of MC-like changes and for therapeutic screening.

Keywords: Endplate microfracture; In vivo rat model; Intervertebral disc degeneration; Modic changes; Pain; Spinal cord sensitization; Spine.