[Keel-implants: Activ-L]

Towards biomimetic evolution of artificial intervertebral disc: a review

In lumbar total disc replacement, artificial disc implants are utilized to cure degenerative disc disease and restore natural motion. Human intervertebral discs (IVD) are part of the spine and contribute to delivering six degrees of freedom, elastic deformation, and shock absorption and act differently under different load conditions. Despite advancements in spinal fixation systems and IVD replacement techniques, achieving long-term segmental stability while preserving physiological motion remains a significant challenge. To overcome this issue, the proposed work aims to identify the biomechanics of artificial IVD implants through rigorous analysis. The ultimate goal is to provide the information to explore the design and develop novel implants that seamlessly integrate with the spine, restoring natural spine function and providing long-term, sustainable load-bearing properties, mimicking the resilience and longevity of the natural IVD. To address all these issues, a comprehensive review of the literature was conducted, organizing findings based on body structure, associated diseases, biomechanics, and various IVD development models. The present endeavour involves a critical analysis with the aim of facilitating the input to the design and development of novel IVD implants in the future.

Retrospective study on effectiveness of Activ L total disc replacement

Background

The effectiveness of lumbar total disc replacement (TDR) with different prostheses for sagittal alignment has been reported previously. However, there are only few reports on Activ L TDR and no specific evidence regarding whether sagittal alignment affects the clinical outcomes.

Methods

Eighty-seven patients who underwent mono- or bi-segmental lumbar TDR with Activ L were studied. The films of the upright anteroposterior and lateral spine in neutral, flexion, and extension positions were obtained before surgery and at 1 month and 1 and 3 years after surgery. The radiographic parameters such as lumbar lordosis (LL), index level lordosis (IL), pelvic incidence (PI), pelvic tilt (PT), segmental lordosis (SL), and sacral slope (SS) were measured based on the lateral upright radiographs. Clinical outcomes were evaluated using the Oswestry Disability Index (ODI) and visual analog scale (VAS) pre- and post-operatively.

Results

Eighty-seven patients with complete radiographic data were available for a 3-year follow-up period. Of these, 66 received a single-level TDR, and 21 received a 2-level TDR. At 1 month, the mean LL was similar to the pre-operative data and then was significantly increased to 45.1° at 3 years. On average, the IL tended to significantly increase, while the mean SL at L–5 was increased from 16.5° pre-operatively to 21.0° at 3 years. The mean SL at L1–2, L2–3, L3–4, and L5–S1; PI; PT; and SS showed no obvious difference after 3 years. In contrast, VAS and ODI scores showed significant improvement after surgery.

Conclusions

Activ L TDR showed a favorable effect on sagittal alignment, enhancing the IL while preserving the LL and SS. However, satisfactory clinical results for over a 3-year follow-up were not affected by sagittal alignment.