Biomechanical characterization of an annulus-sparing spinal disc prosthesis

Abstract

Background Context Current spine arthroplasty devices, require disruption of the annulus fibrosus for implantation. Preliminary studies of a unique annulus sparing intervertebral prosthetic disc (IPD), found that preservation of the annulus resulted in load sharing of the annulus with the prosthesis. Purpose Determine flexibility of the IPD versus fusion constructs in normal and degenerated human spines. Study design/Setting Biomechanical comparison of motion segments in the intact, fusion and mechanical nucleus replacement states for normal and degenerated states. Patient setting Thirty lumbar motion segments. Outcomes Measures Intervertebral height; motion segment range-of-motion (ROM), neutral zone (NZ), stiffness. Methods Motion segments had multi-directional flexibility testing to 7.5 Nm for intact discs, discs reconstructed using the IPD (n=12), or after anterior/posterior fusions (n=18). Interbody height and axial compression stiffness changes were determined for the reconstructed discs by applying axial compression to 1500 N. Analysis included stratifying results to normal mobile vs. rigid degenerated intact motion segments. Results The mean interbody height increase was 1.5 mm for IPD reconstructed discs. vs 3.0 mm for fused segments. Axial compression stiffness was 3.0 ± 0.9 kN/mm for intact compared to 1.2 ± 0.4 kN/mm for IPD reconstructed segments. Reconstructed disc ROM was 9.0° ± 3.7° in flexion-extension, 10.6° ± 3.4° in lateral bending and 2.8° ± 1.4° in axial torsion which was similar to intact values and significantly greater than respective fusion values (p<0.001). Mobile intact segments exhibited significantly greater rotation after fusion vs. their more rigid counterparts (p<0.05), however, intact motion was not related to motion after IPD reconstruction. The NZ and rotational stiffness followed similar trends. Differences in NZ between mobile and rigid intact specimens tended to decrease in the IPD reconstructed state. Conclusion The annulus sparing IPD generally reproduced the intact segment biomechanics in terms of ROM, NZ, and stiffness. Furthermore, the IPD reconstructed discs imparted stability by maintaining a small neutral zone. The IPD reconstructed discs were significantly less rigid than the fusion constructs and may be an attractive alternative for the treatment of DDD.

Non-linear approach in visco-hyperelastic constitutive modelling of polyurethane nanocomposite

“…They did not observe any microscopic changes in the metallic plates; however, bulge of the polyethylene core was visible. Similar compressive tests have been performed recently on prosthesis of another type, namely nucleus-sparing prosthesis (Buttermann and Beaubien 2009). A review of clinical application and some biomechanical aspects of various types of intervertebral disk prostheses is presented in Gamradt and Wang (2005).…”

Controlled Motion with the XL-TDR Lateral-Approach Lumbar Total Disk Replacement: In Vitro Kinematic Investigation

“…2 The long-term clinical results of the prostheses currently available in the market are still unknown, 25 but some of their complications are already described in the literature. 9,26,27 Despite annulus-sparing 28 and posterolateral 29 prostheses in various stages of development, devices in the market are predominantly inserted from anterior approaches to the spine.…”

Critical aspects and challenges for intervertebral disc repair and regeneration—Harnessing advances in tissue engineering

“…Either prolonged detrimental impact or an acute traumatic event can disturb the anabolic‐catabolic balance towards tissue breakdown and loss of function. Current clinical treatments are often not satisfactory in the long‐term and can even trigger a degenerative cascade in adjacent IVDs . It is therefore hypothesized that effective and sustained regeneration may be achieved by therapies that aim to closely mimic the composition and structure of the native tissues.…”