• Ashley E Leckie, Margarete K Akens, Kimberly A Woodhouse, Albert J M Yee, and Cari M Whyne.
• Orthopaedic Biomechanics Laboratory, Advanced Regenerative Tissue Engineering Centre, Sunnybrook Research Institute, Toronto, Ontario, Canada.
• Spine. 2012 Sep 15;37(20):E1296-303.

Study DesignAn in vitro biomechanical and imaging study generated from an in vivo porcine model of early stage degenerative disc disease was used to evaluate mechanical property restoration, comparing 2 minimally invasive injection techniques.ObjectiveTo evaluate the ability of an injectable hydrogel to restore the mechanical properties of spinal motion segments with early stage disc degeneration, comparing 2 minimally invasive injection techniques.Summary Of Background DataTreatment of early-stage disc degeneration may benefit from a combination of tissue engineering and minimally invasive therapeutic approaches. A recently developed hydrogel, thiol-modified hyaluronan elastin-like polypeptide (TMHA/EP) composite, has demonstrated potential as an injectable nucleus replacement.MethodsFrom a total of thirteen 35-kg Yorkshire boars, early-stage lumbar disc degeneration was introduced into 10 pigs via injection of chondroitinase ABC. After degeneration, 8 pigs received TMHA/EP augmentation; 1 disc via direct needle injection and a second using a modified kyphoplasty approach. High-resolution magnetic resonance images were acquired of the excised spinal motion segments, followed by biomechanical testing in axial compression, flexion-extension, lateral bending, and torsion.ResultsThe degenerate control motion segments were generally less stiff and more flexible than healthy controls. The injection of TMHA/EP into the degenerated nucleus produced similar mechanical stiffness to healthy controls. The direct-injected discs showed a dispersive pattern of TMHA/EP within the nucleus, whereas the modified kyphoplasty method yielded a bolus of hydrogel. Yet, mechanical behavior was comparable considering the 2 minimally invasive augmentation techniques.ConclusionThe TMHA/EP composite can restore initial mechanical behavior in early-stage disc degeneration. Although both augmentation methods yielded mechanical properties comparable with healthy controls, direct injection represents a simpler technique, uses a smaller-gauge needle, does not introduce air into the disc, and yields a dispersive pattern that may be beneficial for future delivery of cells or growth factors.

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