Biomechanical Effects of a Novel Pedicle Screw W-Type Rod Fixation for Lumbar Spondylolysis: A Finite Element Analysis

Direct Repair of Symptomatic Lumbar Spondylolysis Using Rod-Screw-Cable System

OBJECTIVE

To assess the efficacy of a new direct lysis repair technique using internal fixation with rod, screws, and Songer cable in symptomatic lumbar spondylolysis.

METHODS

Between December 2015 and January 2020, patients who were diagnosed with symptomatic lumbar spondylolysis and surgically treated with a rod-screw-cable system were recruited. Pedicle screwing by the Magerl technique was performed in all included patients, followed by direct lysis repair with bone allograft and demineralized bone matrix by stabilizing the posterior lamina and spinous process using a rod-screw-cable system. Clinical outcome was measured using the visual analog scale and Oswestry disability index preoperatively and 6 weeks, 3 months, 6 months, 1 year, and 2 years postoperatively.

RESULTS

Sixteen patients were included in this study-11 men and 5 women (mean age: 47 years; range, 26-67 years). The lytic defects were at L4 and L5 in 6 and 10 patients, respectively. The mean follow-up period was 41 months (24-62 months). The visual analog scale values were 7.3, 6.1, 4.3, 3.3, 2.1, and 1.9 preoperatively and 6 weeks, 3 months, 6 months, 1 year, and 2 years postoperatively, respectively. The Oswestry disability index values were 59.8%, 55.4%, 41.7%, 32.4%, 21.1%, and 16.9% for the same periods, respectively. No patient had an increase in the slip after surgery. There were no significant complications such as implant failure.

CONCLUSIONS

Our technique provides rigid intra-segmental repair of spondylolysis without intersegmental motion interference, even if the patient is older or has disc degeneration.

A novel artificial vertebral implant with Gyroid porous structures for reducing the subsidence and mechanical failure rate after vertebral body replacement

BACKGROUND

Prosthesis subsidence and mechanical failure were considered significant threats after vertebral body replacement during the long-term follow-up. Therefore, improving and optimizing the structure of vertebral substitutes for exceptional performance has become a pivotal challenge in spinal reconstruction.

METHODS

The study aimed to develop a novel artificial vertebral implant (AVI) with triply periodic minimal surface Gyroid porous structures to enhance the safety and stability of prostheses. The biomechanical performance of AVIs under different loading conditions was analyzed using the finite element method. These implants were fabricated using selective laser melting technology and evaluated through static compression and subsidence experiments.

RESULTS

The results demonstrated that the peak stress in the Gyroid porous AVI was consistently lower than that in the traditional porous AVI under all loading conditions, with a maximum reduction of 73.4%. Additionally, it effectively reduced peak stress at the bone-implant interface of the vertebrae. Static compression experiments demonstrated that the Gyroid porous AVI was about 1.63 times to traditional porous AVI in terms of the maximum compression load, indicating that Gyroid porous AVI could meet the safety requirement. Furthermore, static subsidence experiments revealed that the subsidence tendency of Gyroid porous AVI in polyurethane foam (simulated cancellous bone) was approximately 15.7% lower than that of traditional porous AVI.

CONCLUSIONS

The Gyroid porous AVI exhibited higher compressive strength and lower subsidence tendency than the strut-based traditional porous AVI, indicating it may be a promising substitute for spinal reconstruction.