William C. Hutton: Disclosure information not submitted.
Purpose of the Study Degenerative changes of the lumbar segments seem an inevitable consequence of aging and are often cited as the chief reason for chronic back pain and neurological complications. Clinical medicine acknowledges several pathologies of intradiscal mass change(s) with respect to disc degeneration and herniation. In general, the degree of degeneration of the disc and the pain vary widely but are correlated. Making the connection important but perhaps more challenging is information regarding degenerative changes linked to genetic, metabolic, and mechanical imbalance. Recent evaluations offer supplemental tissue and cell therapy for disc degeneration and symptomatic relief in therapeutic intervention. The present work evaluated comparative biomechanical properties of motion segments following supplemental allograft injection. Methods Lumbar spines, obtained from 4 different donors, yielded 18 motion segments, of which 13 were injected. Levels were rejected based on annular breaches during specimen preparation. Spines were oriented through radiographs, frozen and then cut mid-vertebral body to attain the greatest number of testable constructs. Nucleus pulposus allograft was reconstituted in saline and cryopreservative, and mixed. A single drop of green food coloring was added to track the injected material. Motion segments were tested using an MTS Mini Bionix (MTS Systems, Eden Prairie, MN, USA) and data evaluated using MultiPurposeTestware Software (MPT). Each disc was tested in axial compression over a displacement of 3000 microns prior to and following injection of the liquid centrally into the disc. Disc injections were made with a 22-gauge needle and a standard 5-cc syringe. Injection volumes averaged 0.60ml with range from 0.2-1.0ml. Load displacement curves were used to evaluate stiffness, and displacement variations needed to attain similar forces of loading. Summary of Findings Supplemental allograft injection bolstered mechanical support for intervertebral disc. Differences in load-displacement were calculated between motion segments prior to and after injection. Motion segments demonstrated a difference in stiffness that was not correlated with the volume of material injected. Following cut section of the discs, photographs of the injected material demonstrated that the allograft was retained centrally within the disc and not avulsed from the annular margins (Figure 1). Load-displacement curve depict two hysteresis curves – in each track, the lower curve represents the load, and the upper tracing the recovery. A comparison of before and after disc injection depicts the “normal” in the left tracing, and the same disc following 0.7 ml allograft supplementation, indicating that the same force can be reached with a lesser excursion (Figure 2). Conclusions Viable allograft material is clinically available as an HCTP tissue, with numerous studies supporting the benefit of supplemental biologic intervention to reduce disc pain, and enhance quality of life. Tissue supplementation strategy has been ongoing in orthopedic clinical practice for hundreds of years. Viable allograft supplementation offers a cost-effective intervention that might buffer nerve compression, and at the same a potential to bolster biologic metabolism in the disc with cells and matrix. This is the first study to demonstrate evidence of supplemental tissue offering mechanical support.