Developing a Mechanical and Chemical Model of Degeneration in Young Bovine Lumbar Intervertebral Disks and Reversing Loss in Mechanical Function

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Abstract

Study Design:

A mechanical and chemical model of intervertebral disk (IVD) degeneration was developed by examining the enzymatic degradation of the nucleus pulposus (NP), and a gelatin-based restoration study was performed.

Objective:

It was hypothesized that forced enzymatic degradation of the NP will mimic natural degeneration through the loss of disk height and that an injection of a gelatin solution will restore mechanical function.

Summary of Background Data:

Collagen and proteoglycans are essential for normal NP function. Their chemical destruction, combined with light mechanical loading, will mimic degeneration. Previous studies have determined that collagenase and matrix metalloproteinase-3 are directly implicated in IVD degradation; therefore, these enzymes were used in this model.

Materials and Methods:

On the basis of preliminary testing, 0.5% collagenase, 1% collagenase, and 0.0025% metalloproteinase-3 in phosphate-buffered saline (PBS) were injected directly into the NP of various motion segments from a young bovine lumbar spine and subjected to light cyclic loading. To restore disk height and mechanical function, 20% gelatin in PBS at 70°C was injected into a degraded disk and subjected to the same loading conditions after an allotted hardening time.

Results:

Mechanical testing showed statistically significant changes in disk height between control segments, 1% collagenase, and 0.5% collagenase. 0.5% collagenase had the most accurate appearance and loading pattern of degeneration upon disk transection postloading. A trend in restoration of disk function, given by the lessened loss of disk height upon loading, was observed with injection of gelatin after degradation with 0.5% collagenase.

Conclusions:

This study demonstrated the potential to create a degenerative model using enzymatic degradation of the NP and the possibility to restore function with an injectable therapy. Although gelatin is not a clinically viable option, it provides preliminary data for other injectable IVD therapies.

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