2022, Vol. 26 ›› Issue (36): 5741-5749

Design and finite element analysis of a new type of high adhesion elastic internal fixation alloy plate for anterior cervical spine

Tong Ling1, Xu Yangyang2, Li Zhijun3, 4, Ma Yuan3, Wang Haiyan4, Li Xiaohe3, 4   

Abstract: BACKGROUND: Anterior cervical discectomy and fusion is performed with anterior cervical auxiliary plate. However, due to the large volume of traditional plate, protruding at the anterior edge of vertebral body, and high elastic modulus caused by steel plate material, postoperative patients often have complications, such as swallowing discomfort and adjacent segment degeneration.   
OBJECTIVE: Three-dimensional finite element method was used to compare and analyze the stress distribution characteristics of three new types of self-developed anterior cervical discectomy and elastic internal fixation alloy plates after operation, so as to provide the reference for the improvement and clinical application of implants.
METHODS: Three kinds of inner plants were designed by using Ni-Ti alloy: alloy plate A was ladder type; alloy plate B was arc surface ladder type; and alloy plate C was arc surface type. The thin slice CT images of C5 and C6 segments of a 21-year-old healthy female volunteer were randomly collected and processed by Mimics 21.0, Geomagic Studio 2013, and Abaqus 2020 to construct the finite element models of three new types of anterior cervical alloy plates. The C5 was loaded with 50 N vertical force and 1.5 N·m pure torque load to simulate seven motion states of cervical vertebra: neutrality, flexion, extension, left and right flexion, and left and right rotation. The stress values of six stress concentration areas of three kinds of alloy plates were collected.   
RESULTS AND CONCLUSION: (1) In the neutral position, the stress distributed in each stress concentration area of the three kinds of alloy plates was the smallest relative to the other working conditions. Under the flexion and extension conditions, the average stress of the upper part of the alloy plate A was higher than that of the alloy plate B (P < 0.05). The average stress of the lower part of the alloy plate C was higher than that of the alloy plate B (P < 0.05). Under the lateral flexion condition, the average stress of the flexion side was larger than that of the extension side (P < 0.05). Under the rotating condition, the average stress of the upper part of the rotating opposite side and the lower part of the same side was relatively larger (P < 0.05). During lateral flexion and rotation, the average stress in most areas of alloy plate A was much lower than that of alloy plates B and C (P < 0.05). (2) The average stress of the three kinds of alloy plates was smaller in the neutral position and larger in the rotation, and the maximum stress was almost concentrated around the threaded hole. (3) Alloy plate A was more suitable for patients who need to do a variety of similar lateral flexion and rotation movements. Alloy plate B had little effects on the vertebral body and was suitable for patients with underlying diseases of the vertebral body. Alloy plate C could appropriately increase the lower thickness under the premise of considering related complications. The new alloy plate still needs further experimental and clinical research.
Key words: anterior cervical, discectomy, internal fixator, memory alloy plate, finite element analysis, biomechanics, different operating conditions, stress distribution