In Vivo Repair Of Rat Annulus Fibrosus Defects Using High Density Collagen Gels

Presented at SMISS Annual Forum 2014
By Yu Moriguchi MD, PhD
With Roger Härtl MD, Marjan Alimi MD, Sara Towne AB, Brandon Borde , Peter Grunert MD, Thamina Khair , Katherine Hudson , Lawrence Bonassar PhD,

Disclosures: Yu Moriguchi MD, PhD None Roger Härtl MD B; Brainlab, DePuy-Synthes, Ulrich, Marjan Alimi MD None., Sara Towne AB None, Brandon Borde None, Peter Grunert MD None, Thamina Khair None, Katherine Hudson None, Lawrence Bonassar PhD None,

Introduction:
Although a discectomy successfully relieves the neurological symptoms of a herniated intervertebral disc (IVD), it does not treat the underlying degenerative process; the annular defect is not repaired. Persistent annular defect is associated with an increased risk of recurrent herniation [1-3] as well as progressive degenerative changes to the IVD [4-6]. It may also be the primary cause of chronic low back pain following discectomy [7]. To date, there is no established method for repairing annular defects in vivo [8].

Aims/Objectives:
To determine whether injectable high-density collagen (HDC) gels can reduce further disc herniation and inhibit degenerative changes in a needle-punctured rat-tail model [10, 11]. To evaluate whether riboflavin (RF) crosslinking of injected collagen influences the repair process

Methods:
31 athymic rats were punctured with an 18-gauge needle at C3/4 in the caudal spine. They were divided into four groups: group 1) punctured and injected with HDC crosslinked with 0.5 mM (n=6) or 0.75mM (n=7) RF; 2) punctured and injected with non-crosslinked collagen (n=6); 3) punctured and untreated (n=8); 4) punctured and injected with FITC-labeled crosslinked collagen (n=4). Degenerative changes to punctured discs as well as NP size and hydration were assessed according to MR imaging and on histological sections [12]. Functionality of repaired AF tissue was measured with mechanical tests - specifically, by comparing the hydraulic permeability of treated discs to that of healthy discs.

Results:
After 5 weeks, untreated discs showed an absence of NP tissue and signs of terminal degenerative changes on MRI and histological sections. In contrast, discs treated with RF crosslinked HDC retained 61% of NP tissue at 18 weeks, maintained the same hydration (T2-intensity) as healthy discs, and showed minimal degenerative changes on histological section. Interestingly, discs treated with crosslinked HDC increased in volume and hydration over time after 5 weeks, while untreated discs and discs treated with non-crosslinked HDC decreased. Injected collagen was seen to form a zipper-like adhesion to the host AF and connective tissue after one week, and by five weeks a fibrous cap had formed that persisted until 18 weeks. Hydraulic permeability of treated discs was similar to that of adjacent healthy discs at 18 weeks.

Conclusions:
Injection of RF-crosslinked HDC gels can repair annular defects, prevent the degenerative cascade, and maintain the functionality of IVDs in a rat-tail spine.