Annular Repair

Presented at SMISS Annual Forum 2014
By Roger Haortl MD
With Marjan Alimi MD, Yu Moriguchi MD, PhD, Sara Towne AB,

Disclosures: Roger Haortl MD B; Brainlab, DePuy-Synthes, Ulrich Marjan Alimi MD None., Yu Moriguchi MD, PhD None, Sara Towne AB 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.